8/8/2019 Struts FAQ

1/40

http://dev.fyicenter.com/Interview-

Questions/Struts/Do_we_need_to_pay_the_Struts_if_being_used_in_co.html

***************************************************************************************************

*****

1. What is Struts?

1.Struts is a web page development framework and an open source software that

helps developers build web applications quickly and easily. Struts combines Java

Servlets, Java Server Pages, custom tags, and message resources into a unifiedframework. It is a cooperative, synergistic platform, suitable for development

teams, independent developers, and everyone between.

2.The core of the Struts framework is a flexible control layer based on standard

technologies like Java Servlets, JavaBeans, ResourceBundles, and XML, as well as

various Jakarta Commons packages. Struts encourages application architectures

based on the Model 2 approach, a variation of the classic Model-View-Controller

(MVC) design paradigm. Struts provides its own Controller component and

integrates with other technologies to provide the Model and the View. For the

Model, Struts can interact with standard data access technologies, like JDBC and

EJB, as well as most any third-party packages, like Hibernate, iBATIS, or ObjectRelational Bridge. For the View, Struts works well with JavaServer Pages, including

JSTL and JSF, as well as Velocity Templates, XSLT, and other presentation systems.

The Struts framework provides the invisible underpinnings every professional web

application needs to survive. Struts helps you create an extensible development

environment for your application, based on published standards and proven design

patterns.

3. Struts Frame work is the implementation of Model-View-Controller (MVC) design

pattern for the JSP. Struts is maintained as a part of Apache Jakarta project and is

open source. Struts Framework is suited for the application of any size. Latest

version of struts can be downloaded from http://jakarta.apache.org/. We are using

jakarta-struts-1.1 and jakarta-tomcat-5.0.4 for this tutorial.

*************************************************************************************

2. How is the MVC design pattern used in Struts framework?

In the MVC design pattern, application flow is mediated by a central Controller. The

Controller delegates requests to an appropriate handler. The handlers are tied to a

Model, and each handler acts as an adapter between the request and the Model.

The Model represents, or encapsulates, an application's business logic or state.

Control is usually then forwarded back through the Controller to the appropriateView. The forwarding can be determined by consulting a set of mappings, usually

loaded from a database or configuration file. This provides a loose coupling between

the View and Model, which can make an application significantly easier to create

and maintain.

Controller--Servlet controller which supplied by Struts itself; View --- what you can

see on the screen, a JSP page and presentation components; Model --- System state

and a business logic JavaBeans.

*************************************************************************************

http://dev.fyicenter.com/Interview-%20Questions/Struts/Do_we_need_to_pay_the_Struts_if_being_used_in_co.htmlhttp://dev.fyicenter.com/Interview-%20Questions/Struts/Do_we_need_to_pay_the_Struts_if_being_used_in_co.htmlhttp://dev.fyicenter.com/Interview-%20Questions/Struts/Do_we_need_to_pay_the_Struts_if_being_used_in_co.htmlhttp://dev.fyicenter.com/Interview-%20Questions/Struts/Do_we_need_to_pay_the_Struts_if_being_used_in_co.html

8/8/2019 Struts FAQ

2/40

3. Who makes the Struts?

Struts is hosted by the Apache Software Foundation(ASF) as part of its Jakarta

project, like Tomcat, Ant and Velocity.

*************************************************************************************

4. Why it called Struts?

Because the designers want to remind us of the invisible underpinnings that hold up

our houses, buildings, bridges, and ourselves when we are on stilts. This excellent

description of Struts reflect the role the Struts plays in developing web applications.

*************************************************************************************

5. Do we need to pay the Struts if being used in commercial purpose?

No. Struts is available for commercial use at no charge under the Apache Software

License. You can also integrate the Struts components into your own framework just

as if they were writtern in house without any red tape, fees, or other hassles.

*************************************************************************************

6. What are the core classes of Struts?

Action, ActionForm, ActionServlet, ActionMapping, ActionForward are basic classes

of Structs.

*************************************************************************************

7. What is the design role played by Struts?

The role played by Structs is controller in Model/View/Controller(MVC) style. The

View is played by JSP and Model is played by JDBC or generic data source classes.The Struts controller is a set of programmable components that allow developers to

define exactly how the application interacts with the user.

*************************************************************************************

8. How Struts control data flow?

Struts implements the MVC/Layers pattern through the use of ActionForwards and

ActionMappings to keep control-flow decisions out of presentation layer.

*************************************************************************************

9. What configuration files are used in Struts?

ApplicationResources.properties

struts-config.xml

*************************************************************************************

10. What helpers in the form of JSP pages are provided in Struts framework?

--struts-html.tld

--struts-bean.tld

8/8/2019 Struts FAQ

3/40

--struts-logic.tld

*************************************************************************************

11. Is Struts efficient?

The Struts is not only thread-safe but thread-dependent(instantiates each

Action once and allows other requests to be threaded through the original object.

ActionForm beans minimize subclass code and shorten subclass hierarchies

The Struts tag libraries provide general-purpose functionality

The Struts components are reusable by the application

The Struts localization strategies reduce the need for redundant JSPs

The Struts is designed with an open architecture--subclass available

The Struts is lightweight (5 core packages, 5 tag libraries)

The Struts is open source and well documented (code to be examined easily)

The Struts is model neutral

*************************************************************************************

12. How you will enable front-end validation based on the xml in validation.xml?

The < html:javascript > tag to allow front-end validation based on the xml in

validation.xml. For example the code: < html:javascript formName=logonForm

dynamicJavascript=true staticJavascript=true / > generates the client side java

script for the form logonForm as defined in the validation.xml file. The when added in the jsp file generates the client site validation

script.

*************************************************************************************

13. What is ActionServlet?

The class org.apache.struts.action.ActionServlet is the called the ActionServlet. In

the the Jakarta Struts Framework this class plays the role of controller. All the

requests to the server goes through the controller. Controller is responsible for

handling all the requests.

*************************************************************************************

14. How you will make available any Message Resources Definitions file to the

Struts Framework Environment?

Message Resources Definitions file are simple .properties files and these files

contains the messages that can be used in the struts project. Message Resources

Definitions files can be added to the struts-config.xml file through < message-

resources / > tag. Example: < message-resources parameter= MessageResources /

>

15. What is Action Class?

8/8/2019 Struts FAQ

4/40

The Action Class is part of the Model and is a wrapper around the business logic.

The purpose of Action Class is to translate the HttpServletRequest to the business

logic. To use the Action, we need to Subclass and overwrite the execute() method.

In the Action Class all the database/business processing are done. It is advisable to

perform all the database related stuffs in the Action Class. The ActionServlet

(commad) passes the parameterized class to Action Form using the execute()

method. The return type of the execute method is ActionForward which is used by

the Struts Framework to forward the request to the file as per the value of the

returned ActionForward object.

***************************************************************************************************

*****

16. Write code of any Action Class?

Here is the code of Action Class that returns the ActionForward object.

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.Action;

import org.apache.struts.action.ActionForm;

import org.apache.struts.action.ActionForward;

import org.apache.struts.action.ActionMapping;

public class TestAction extends Action

{

public ActionForward execute(

ActionMapping mapping,

ActionForm form,

HttpServletRequest request,

HttpServletResponse response) throws Exception

{

return mapping.findForward(\"testAction\");

}

}

***************************************************************************************************

*****

17. What is ActionForm?

8/8/2019 Struts FAQ

5/40

An ActionForm is a JavaBean that extends org.apache.struts.action.ActionForm.

ActionForm maintains the session state for web application and the ActionForm

object is automatically populated on the server side with data entered from a form

on the client side.

18. What is Struts Validator Framework?

Struts Framework provides the functionality to validate the form data. It can be use

to validate the data on the users browser as well as on the server side. Struts

Framework emits the java scripts and it can be used validate the form data on theclient browser. Server side validation of form can be accomplished by sub classing

your From Bean with DynaValidatorForm class. The Validator framework was

developed by David Winterfeldt as third-party add-on to Struts. Now the Validator

framework is a part of Jakarta Commons project and it can be used with or without

Struts. The Validator framework comes integrated with the Struts Framework and

can be used without doing any extra settings.

19. Give the Details of XML files used in Validator Framework?

The Validator Framework uses two XML configuration files validator-rules.xml and

validation.xml. The validator-rules.xml defines the standard validation routines,these are reusable and used in validation.xml. to define the form specific

validations. The validation.xml defines the validations applied to a form bean.

***************************************************************************************************

*****

20. How you will display validation fail errors on jsp page?

The following tag displays all the errors:

< html:errors/ >

20. Why do we need Struts?

Java technologies give developers a serious boost when creating and maintaining

applications to meet the demands of today's public Web sites and enterprise

intranets. Struts combines Java Servlets, Java ServerPages, custom tags, and

message resources into a unified framework. The end result is a cooperative,

synergistic platform, suitable for development teams, independent developers, and

everyone in between.

***************************************************************************************************

*****

21. How does Struts work?

Java Servlets are designed to handle requests made by Web browsers. Java

ServerPages are designed to create dynamic Web pages that can turn billboard

sites into live applications. Struts uses a special Servlet as a switchboard to route

requests from Web browsers to the appropriate ServerPage. This makes Web

applications much easier to design, create, and maintain.

***************************************************************************************************

*****

22. Is Struts compatible with other Java technologies?

8/8/2019 Struts FAQ

6/40

Yes. Struts is committed to supporting industry standards. Struts acts as an

integrator of Java technologies so that they can be used in the "real world".

***************************************************************************************************

*****

23. Who wrote Struts?

There are several active committers to the Struts project, working cooperatively

from around the globe. Dozens of individual developers and committers contributed

to the Struts 1.x codebase. All interested Java developers are invited to contributeto the project. Struts is a Apache Software Foundation project, with the mission to

"provide secure, enterprise-grade server solutions based on the Java Platform that

are developed in an open and cooperative fashion".

Struts was created by Craig R. McClanahan and donated to The Apache Software

Foundation in May 2000. Craig was the primary developer of both Struts 1.x and

Tomcat 4. Tomcat 4 was the basis for the official reference implementation for a

servlet 2.3 and JSP 1.2 container.

Craig's current focus is as architect of the Sun Java Studio Creator (formerly Project

Rave). Craig also serves as the Specification Lead for JavaServer Faces (JSR-127),and is the Web Layer Architect for the Java2 Enterprise Edition (J2EE) platform as a

whole.

***************************************************************************************************

*****

24. Why is it called Struts?

It's a reference to struts in the architectural sense, a reminder of the nearly invisible

pieces that hold up buildings, houses, and bridges.

********************************************************************************************************

25. Do I have to credit Struts on my own website?

You need to credit Struts if you redistribute your own framework based on Struts for

other people to use. (See the Apache License for details.) But you do not need to

credit Struts just because your web application utilizes the framework. It's the same

situation as using the Apache HTTPD server or Tomcat. Not required if its just

running your web site.

***************************************************************************************************

*****

26. Where can I get a copy of Struts?

The best place to download Struts is at struts.apache.org. The nightly builds are

very stable, and recommended as the best place to start today.

***************************************************************************************************

*****

27. How do I install Struts?

8/8/2019 Struts FAQ

7/40

To develop applications with Struts, you can usually just add the Struts JAR file to

your Java development environment. You can then start using the Struts classes as

part of your own application. A blank Struts application (in the webapps directory,

open struts-blank.war) is provided, which you can just copy to get a quick-start on

your own brainchild.

Since the full source code for Struts is available, we also provide complete

instructions for compiling your own Struts JAR from scratch. (This is actually easier

than it looks!)

Your Struts application can usually be deployed using a standard WAR file. In most

cases, you simply deposit the WAR file on your application server, and it is installed

automatically. If not, step-by-step installation instructions for various servlet

containers are available.

***************************************************************************************************

*****

28. When do I need "struts.jar" on my classpath?

When you are compiling an application that uses the Struts classes, you must have

the "struts.jar" on the classpath your compiler sees -- it does not have to be on yourCLASSPATH environment variable.

Why is that an important distinction? Because if you are using a servlet container on

your development machine to test your application, the "struts.jar" must not be on

your CLASSPATH environment variable when running the container. (This is because

each Web application must also have their own copy of the Struts classes, and the

container will become confused if it is on the environment path as well.)

There are several general approaches to this issue:

* Use ANT for building your projects -- it can easily assemble classpaths for thecompiler. (This is how Struts itself is built, along with Tomcat and most other Java-

based projects).

* Use an IDE where you can configure the "class path" used for compilation

independent of the CLASSPATH environment variable.

* Use a shell script that temporarily adds struts.jar to the classpath just for

compilation, for example javac -classpath /path/to/struts.jar:$CLASSPATH $@

***************************************************************************************************

*****

29. Does Struts include its own unit tests?

Struts currently has two testing environments, to reflect the fact that some things

can be tested statically, and some really need to be done in the environment of a

running servlet container.

For static unit tests, we use the JUnit framework. The sources for these tests are in

the "src/test" hierarchy in the source repository, and are executed via the

"test.junit" target in the top-level build.xml file. Such tests are focused on the low-

level functionality of individual methods, are particularly suitable for the static

methods in the org.apache.struts.util utility classes. In the test hierarchy, there are

8/8/2019 Struts FAQ

8/40

also some "mock object" classes (in the org.apache.struts.mock package) so that

you can package up things that look like servlet API and Struts API objects to pass in

as arguments to such tests.

Another valuable tool is Struts TestCase which provides a useful harness for Action

classes that can be used with JUnit or Cactus.

***************************************************************************************************

*****

30. If the framework doesn't do what I want, can I request that a feature be added?

First, it's important to remember that Struts is an all-volunteer project. We don't

charge anyone anything to use Struts. Committers and other developers work on

Struts because they need to use it with their own applications. If others can use it

too, that's "icing on the cake". If you submit a patch for a feature that a Committer

finds useful, then that Committer may choose to volunteer his or her time to apply

the patch. If you just submit an idea without a patch, it is much less likely to be

added (since first someone else has to volunteer their time to write the patch).

We are grateful for any patches, and we welcome new ideas, but the best way to

see that something gets added to the framework is to do as much of the work asyou can, rather than rely on the "kindness of strangers". Worst case, you can apply

the patch to your copy of Struts and still use the feature in your own application.

(Which is what open source is ~really~ all about.)

***************************************************************************************************

*****

31. Where can I get help with Struts?

The Struts package comes complete with a Users Guide to introduce people to the

framework and its underlying technologies. Various components also have their own

in-depth Developers Guide, to cover more advanced topics. Comprehensive

Javadocs are included along with the full source code. For your convenience, these

are bundled together as a self-installing application. The struts-documentation.war

is the same bundle that is deployed as the Struts Web site.

The Strut's mailing list is also very active, and welcomes posts from new users.

Before posting a new question, be sure to consult the MAILING LIST ARCHIVE and

the very excellent How To Ask Questions The Smart Way by Eric Raymond. Please

do be sure to turn off HTML in your email client before posting.

***************************************************************************************************

*****

32. What's the difference between Struts and Turbine? What's the difference

between Struts and Expresso?

If you are starting from scratch, packages like Turbine and Expresso can be very

helpful since they try to provide all of the basic services that your team is likely to

need. Such services include things like data persistence and logging.

If you are not starting from scratch, and need to hook up your web application to an

existing infrastructure, then "plain vanilla" Struts can be a better choice. The core

8/8/2019 Struts FAQ

9/40

Struts framework does not presuppose that you are using a given set of data

persistence, presentation, or logging tools. Anything goes =:0)

Compared to other offerings, Struts endeavors to be a minimalist framework. We try

leverage existing technologies whenever we can and provide only the missing

pieces you need to combine disparate technologies into a coherent application. This

is great when you want to select your own tools to use with Struts. But, if you prefer

a more integrated infrastructure, then packages like Turbine or Expresso (which

uses Struts) are perfectly good ways to go.

See also

* < http://www.mail-archive.com/struts-user@jakarta.apache.org/msg03206.html >

* < http://www.mail-archive.com/general@jakarta.apache.org/msg00495.html >

* < http://jakarta.apache.org/velocity/ymtd/ymtd.html >

***************************************************************************************************

*****

33. Why aren't the Struts tags maintained as part of the Jakarta Taglibs project?

Development of both products began about the same time. Leading up to the

release of 1.0, it was thought better to continue to develop the taglibs alongside the

controller. Now that 1.0 is out, the JavaServer Pages Standard Taglib is in active

development. Once work on JSTL stabilizes, the Struts taglibs will be revisited. Tags

which are not linked directly to the framework may be hosted at Jakarta Taglibs

instead.

***************************************************************************************************

*****

34. Are the Struts tags XHTML compliant?

If you use an

8/8/2019 Struts FAQ

10/40

JSTL, the JavaServer Standard Tag Library, is a set of JSP tags that are designed to

make it easier to develop Web applications. JavaServer Faces (JSF) is a specification

for a new technology that promises to make it easier to write MVC applications,

both for the Web and for the desktop.

The inventor of Struts, Craig McClanahan, is the specification co-lead for JavaServer

Faces (JSR 127), and architect of the reference implemenation as well as Java Studio

Creator. Both JSTL and JSF are complementary to Struts.

The mainstay of the Struts framework is the controller components, which can beused with any Java presentation technology. As new technologies become available,

it is certain that new "glue" components will also appear to help these technologies

work as well with Struts.

Struts originally came bundled with a set of custom JSP tags. Today, several

extensions are available to help you use Struts with other popular presentation

technologies, like XSLT and Velocity. Likewise, extensions for JSTL and JSF are now

available as well.

The JSTL reference implementation is available through the Jakarta Taglibs site. A

JSTL taglibs for Struts, Struts-El , is available and distributed with Struts beginningwith the 1.1 release.

The JSF specification and reference implementation is available through Sun's The

JSF specification and reference implementation is available through Sun's Java

ServerFaces page. An early-release JavaServer Faces taglib for Struts, Struts-Faces,

is also in early release and available through the nightly build. The Struts Faces

taglib is expected to work with any compliant JSF implementation, including

MyFaces.

***************************************************************************************************

*****

37. Is there a particularly good IDE to use with Struts

Struts should work well with any development environment that you would like to

use, as well as with any programmers editor. The members of the Struts

development team each use their own tools such as Emacs, IDEA, Eclipse, and

NetBeans.

38. Why was reload removed from Struts (since 1.1)?

The problem with ReloadAction was that Struts was trying to act like a container,

but it couldn't do a proper job of it. For example, you can't reload classes that havebeen modified, or (portably) add new classes to a running web application (even if

the container supported it).

Meanwhile, as Struts 1.1 was being developed, work progressed on things like

Tomcat's reload command via the Manager webapp. This feature allows you to

quickly reload-on-demand, complete with saving and restoring your session). It

started to make even less sense for Struts to half-implement a feature that

containers are implementing fully.

A more minor point is that freezing the configuration information at application

startup time allows Struts to safely access the mapping information without

8/8/2019 Struts FAQ

11/40

bothering with synchronization. The "startup-only" strategy creates a modest but

real improvement in performance for all users.

So, ReloadAction is not supported since Struts 1.1 for two reasons:

* It never did let you reload everything that you would really want to -- particularly

changed classes -- so many people ended up having to reload the webapp anyway.

* Containers are starting to offer reload-on-demand features which does the same

thing as the Struts ReloadAction, only better.

* Not supporting ReloadAction lets Struts avoid doing synchronization locks around

all the lookups (like figuring out which action to use, or the destination of an

ActionForward) so applications can run a little faster.

Of course, if someone came up with an implementation that solved these problems

without creating any others, we would not be opposed to including a new

ReloadAction.

***************************************************************************************************

*****

39. What is a modular application? What does module-relative mean?

Since Struts 1.1, the framework supports multiple application modules. All

applications have at least one root, or default, module. Like the root directory in a

file system, the default application has no name. (Or is named with an empty string,

depending your viewpoint.) Developing an application with only a default module is

no different from how applications were developed under Struts 1.0. Since Struts

1.1, you can add additional modules to your application, each of which can have

their own configuration files, messages resources, and so forth. Each module is

developed in the same way as the default module. Applications that were

developed as a single module can added to a multiple module application, andmodules can promoted to a standalone application without change. For more about

configuring your application to support multiple modules, see Configuring

Applications in the User Guide.

But to answer the question =:0), a modular application is a Struts application that

uses more than one module. Module-relative means that the URI starts at the

module level, rather than at the context level, or the absolute-URL level.

* Absolute URL: http://localhost/myApplication/myModule/myAction.do

* context-relative: /myModule/myAction.do

* module-relative: /myAction.do

The Struts Examples application is a modular application that was assembled from

several applications that were created independently.

***************************************************************************************************

*****

40. Why are some of the class and element names counter-intuitive?

The framework grew in the telling and, as it evolved, some of the names drifted.

8/8/2019 Struts FAQ

12/40

The good thing about a nightly build, is that everything becomes available to the

community as soon as it is written. The bad thing about a nightly build is that things

like class names get locked down early and then become difficult to change.

***************************************************************************************************

*****

41. Why is ActionForm a base class rather than an interface?

The MVC design pattern is very simple to understand but much more difficult to live

with. You just need this little bit of Business Logic in the View logic or you need justthat little bit of View logic in the Business tier and pretty soon you have a real mess.

Making ActionForm a class takes advantage of the single inheritance restriction of

Java to it makes it more difficult for people to do things that they should not do.

ActionForms implemented as interfaces encourage making the property types

match the underlying business tier instead of Strings, which violates one of the

primary purposes for ActionForms in the first place (the ability to reproduce invalid

input, which is a fundamental user expectation). ActionForms as an interface would

also encourage using existing DAO objects as ActionForms by adding

implements ActionForm to the class. This violates the MVC design patterngoal of separation of the view and business logic.

Since the goal of struts is to enforce this separation, it just makes more sense for

Struts to own the ActionForm.

DynaActionForms relieve developers of maintaining simple ActionForms. For near

zero maintenance, try Niall Pemberton's LazyActionForm

***************************************************************************************************

*****

42. Do ActionForms have to be true JavaBeans?

The utilities that Struts uses (Commons-BeanUtils since 1.1) require that ActionForm

properties follow the JavaBean patterns for mutators and accessors (get*,set*,is*).

Since Struts uses the Introspection API with the ActionForms, some containers may

require that all the JavaBean patterns be followed, including declaring "implements

Serializable" for each subclass. The safest thing is to review the JavaBean

specification and follow all the prescribed patterns.

Since Struts 1.1, you can also use DynaActionForms and mapped-backed forms,

which are not true JavaBeans. For more see ActionForm classes in the User Guide

and Using Hashmaps with ActionForms in this FAQ.

***************************************************************************************************

*****

43. Can I use multiple HTML form elements with the same name?

Yes. Define the element as an array and Struts will autopopulate it like any other.

private String[] id= {};

public String[] getId() { return this.id; }

public void setItem(String id[]) {this.id = id;}

8/8/2019 Struts FAQ

13/40

And so forth

***************************************************************************************************

*****

44. Can I use multiple HTML form elements with the same name?

Yes. The issue is that only one action class can be associated with a single form. So

the real issue is how do I decode multiple submit types to a single Action class.

There is more than one way to achieve this functionality.

The way that is suggested by struts is right out of the javadoc for

LookupDispatchAction . Basically, LookupDispatchAction is using the keys from

ApplicationProperties.resources as keys to a map of actions available to your Action

class. It uses reflection to decode the request and invoke the proper action. It also

takes advantage of the struts tags and is straight forward to

implement.

You can roll your own with JavaScript events and javascript:void

(document.forms["myform"].submit) on any html element. This gives you control of

how you want your page to look. Again you will have to decode the expected action

in the execute method of your action form if you choose this route.

***************************************************************************************************

*****

45. Why doesn't the focus feature on the tag work in every

circumstance?

Unfortunately, there is some disagreement between the various browsers, and

different versions of the same browser, as to how the focus can be set. The

tag provides a quick and easy JavaScript that will set the focus on a

form for most versions of most browsers. If this feature doesn't work for you, then

you should set the focus using your own JavaScript. The focus feature is a

convenient "value-add" -- not a core requirement of the tag. If you do come up with

a JavaScript that provides the final solution to this project, please post your patch to

this Bugzilla ticket.

***************************************************************************************************

*****

46. Why are my checkboxes not being set from ON to OFF?

A problem with a checkbox is that the browser will only include it in the request

when it is checked. If it is not checked, the HTML specification suggests that it notbe sent (i.e. omitted from the request). If the value of the checkbox is being

persisted, either in a session bean or in the model, a checked box can never

unchecked by a HTML form -- because the form can never send a signal to uncheck

the box. The application must somehow ascertain that since the element was not

sent that the corresponding value is unchecked.

The recommended approach for Struts applications is to use the reset method in

the ActionForm to set all properties represented by checkboxes to null or false. The

checked boxes submitted by the form will then set those properties to true. The

omitted properties will remain false. Another solution is to use radio buttons

instead, which always submit a value.

8/8/2019 Struts FAQ

14/40

It is important to note that the HTML specification recommends this same behavior

whenever a control is not "successful". Any blank element in a HTML form is not

guaranteed to submitted. It is therefor very important to set the default values for

an ActionForm correctly, and to implement the reset method when the ActionForm

might kept in session scope.

***************************************************************************************************

*****

47. Can I use JavaScript to submit a form?

You can submit a form with a link as below. BTW, the examples below assume you

are in an block and 'myForm' is picked up from the struts-config.xml name field of

the action.

8/8/2019 Struts FAQ

15/40

// ... delete action ...

}

}

}

}

This is just one of many ways to achieve submitting a form and decoding theintended action. Once you get used to the framework you will find other ways that

make more sense for your coding style and requirements. Just remember this

example is completely non-functional without JavaScript.

Here is a link which utilizes the LookupDispatch action to submit forms with multiple

actions without javascript: http://husted.com/struts/tips/003.html

***************************************************************************************************

*****

48. How do I use JavaScript to ...

Struts is mainly a server-side technology. We bundled in some JSP tags to expose

the framework components to your presentation page, but past that, the usual

development process applies.

Interactive pages require the use of JavaScript. (That's why it was invented.) If you

want things popping up or doing this when they click that, you are outside the

scope of Struts and back into the web development mainstream.

You use JavaScript with Struts the same way you use with any presentation page.

Since JavaScript is a client-side technology, you can use simple relative references

to your scripts. If you need to fire a JavaScript from a HTML control, the Struts HTMLtags have properties for the JavaScript events.

A very good JavaScript resource is Matt Kruse's site at

http://www.mattkruse.com/javascript/ Do I need to implement reset and set all my

form properties to their initial values?

No. You need to set checkbox properties to false if the ActionForm is being retained

in session scope. This is because an unchecked box does not submit an attribute.

Only checked boxes submit attributes. If the form is in session scope, and the

checkbox was checked, there is no way to turn it back off without the reset method.

Resetting the properties for other controls, or for a request scope form, is pointless.If the form is in request scope, everything already just started at the initial value.

***************************************************************************************************

*****

49. Can't I just create some of my JavaBeans in the JSP using a scriptlet?

Struts is designed to encourage a Model 2/MVC architecture. But there is nothing

that prevents you from using Model 1 techniques in your JavaServer Pages, so the

answer to the question is "Yes, you can".

8/8/2019 Struts FAQ

16/40

Though, using Model 1 techniques in a Struts application does go against the grain.

The approach recommended by most Struts developers is to create and populate

whatever objects the view may need in the Action, and then forward these through

the request. Some objects may also be created and stored in the session or context,

depending on how they are used.

Likewise, there is nothing to prevent you from using scriptlets along with JSP tags in

your pages. Though, many Struts developers report writing very complex scriplet-

free applications and recommend the JSP tag approach to others.

For help with Model 1 techniques and scriptlets, you might consider joining the

Javasoft JSP-interest mailing list, where there are more people still using these

approaches.

***************************************************************************************************

*****

50. Can I use other beans or hashmaps with ActionForms?

Yes. There are several ways that you can use other beans or hashmaps with

ActionForms.

* ActionForms can have other beansor hashmaps as properties

* "Value Beans" or "Data Transfer Objects" (DTOs) can be used independently of

ActionForms to transfer data to the view

* ActionForms can use Maps to support "dynamic" properties (since Struts 1.1)

ActionForms (a.k.a. "form beans") are really just Java beans (with a few special

methods) that Struts creates and puts into session or request scope for you. There

is nothing preventing you from using other beans, or including them in your form

beans. Here are some examples:

Collections as properties Suppose that you need to display a pulldown list of

available colors on an input form in your application. You can include a string-valued

colorSelected property in your ActionForm to represent the user's selection and a

colorOptions property implemented as a Collection (of strings) to store the available

color choices. Assuming that you have defined the getters and setters for the

colorSelected and colorOptions properties in your orderEntryForm form bean, you

can render the pulldown list using:

The list will be populated using the strings in the colorOptions collection of the

orderEntryForm and the value that the user selects will go into the colorSelected

property that gets posted to the subsequent Action. Note that we are assuming

here that the colorOptions property of the orderEntryForm has already been set.

See How can I prepopulate a form? for instructions on how to set form bean

properties before rendering edit forms that expect properties to be pre-set.

8/8/2019 Struts FAQ

17/40

Independent DTO An Action that retrieves a list of open orders (as an ArrayList of

Order objects) can use a DTO independently of any form bean to transfer search

results to the view. First, the Action's execute method performs the search and puts

the DTO into the request:

ArrayList results = businessObject.executeSearch(searchParameters);

request.setAttribute("searchResults",results);

Then the view can iterate through the results using the "searchResults" request keyto reference the DTO:

`

..other properties...

***************************************************************************************************

*****

51. Why do the Struts tags provide for so little formatting?

The Struts tags seem to provide only the most rudimentary functionality. Why is

there not better support for date formatting and advanced string handling?

Three reasons:

First, work started on the JSTL and we didn't want to duplicate the effort.

Second, work started on Java Server Faces, and we didn't want to duplicate that

effort either.

Third, in a Model 2 application, most of the formatting can be handled in the

ActionForms (or in the business tier), so all the tag has to do is spit out a string. This

leads to better reuse since the same "how to format" code does not need to be

repeated in every instance. You can "say it once" in a JavaBean and be done with it.

Why don't the Struts taglibs offer more layout options?

Since the Struts tags are open source, you can extend them to provide whatever

additional formatting you may need. If you are interested in a pre-written taglib that

offers more layout options, see the struts-layout taglib.

In the same arena, there is a well regarded contributor taglib that can help youcreate Menus for your Struts applications.

***************************************************************************************************

*****

52. Why does the tag URL-encode javascript and mailto links?

The tag is not intended for use with client-side references like those

used to launch Javascripts or email clients. The purpose of link tag is to interject the

context (or module) path into the URI so that your server-side links are not

dependent on your context (or module) name. It also encodes the link, as needed,

to maintain the client's session on the server. Neither feature applies to client-side

8/8/2019 Struts FAQ

18/40

links, so there is no reason to use the tag. Simply markup the client-

side links using the standard tag.

***************************************************************************************************

*****

53. How can I scroll through list of pages like the search results in google?

Many Struts developers use the Pager from the JSPTags site.

http://jsptags.com/tags/navigation/pager/

***************************************************************************************************

*****

54. Why does the option tag render selected=selected instead of just selected?

Attribute minimization (that is, specifying an attribute with no value) is a place

where HTML violates standard XML syntax rules. This matters a lot for people

writing to browsers that support XHTML, where doing so makes the page invalid.It's

much better for Struts to use the expanded syntax, which works the same on

existing browsers interpreting HTML, and newer browsers that expect XHTML-

compliant syntax. Struts is following the behavior recommended by the XHTML

specification

***************************************************************************************************

*****

55. Do I have to use JSPs with my application?

The short answer to this question is: No, you are not limited to JavaServer Pages.

The longer answer is that you can use any type of presentation technology which

can be returned by a web server or Java container. The list includes but is not

limited to:

* JavaServer Pages,

* HTML pages,

* WML files,

* Java servlets,

* Velocity templates, and

* XML/XLST

Some people even mix and match apparently unrelated technologies, like PHP, into

the same web application.

***************************************************************************************************

*****

56. Do ActionForms have to be true JavaBeans?

ActionForms are added to a servlet scope (session or request) as beans. What this

means is that, for certain functionality to be available, your ActionForms will have to

follow a few simple rules.

http://jsptags.com/tags/navigation/pager/http://jsptags.com/tags/navigation/pager/

8/8/2019 Struts FAQ

19/40

First, your ActionForm bean must have a zero-arguments constructor. This is

required because Struts must be able to dynamically create new instances of your

form bean class, while knowing only the class name. This is not an onerous

restriction, however, because Struts will also populate your form bean's properties

(from the request parameters) for you.

Second, the fields of your form bean are made available to the framework by

supplying public getter and setter methods that follow the naming design patterns

described in the JavaBeans Specification. For most users, that means using the

following idiom for each of your form bean's properties:

private {type} fieldName;

public {type} getFieldName() {

return (this.fieldName);

}

public void setFieldName({type} fieldName) {

this.fieldName = fieldName;

}

NOTE - you MUST obey the capitalization conventions shown above for your

ActionForm properties to be recognized. The property name in this example is

"fieldName", and that must also be the name of the input field that corresponds to

this property. A bean property may have a "getter" method and a "setter" method

(in a form bean, it is typical to have both) whose name starts with "get" or "set",

followed by the property name with the first character capitalized. (For boolean

properties, it is also legal to use "is" instead of "get" as the prefix for the getter

method.)

Advanced JavaBeans users will know that you can tell the system you want to use

different names for the getter and setter methods, by using a java.beans.BeanInfo

class associated with your form bean. Normally, however, it is much more

convenient to follow the standard conventions.

WARNING - developers might be tempted to use one of the following techniques,

but any of them will cause your property not to be recognized by the JavaBeans

introspection facilities, and therefore cause your applications to misbehave:

* Using getter and setter method names that do not match - if you have a getFoo()

method for your getter, but a setBar() method for your setter, Java will not

recognize these methods as referring to the same property. Instead, the language

will think you have a read-only property named "foo" and a write-only property

named "bar".

* Using more than one setter method with the same name - The Java language lets

you "overload" methods, as long as the argument types are different. For example,

you could have a setStartDate(java.util.Date date) method and a

setStartDate(String date) method in the same class, and the compiled code would

know which method to call based on the parameter type being passed. However,

8/8/2019 Struts FAQ

20/40

doing this for form bean properties will prevent Java from recognizing that you have

a "startDate" property at all.

There are other rules to follow if you want other features of your form beans to be

exposed. These include indexed attributes and mapped attributes. They are

covered in detail in other areas of the Struts documentation, in particular:

indexedprops.html

For a complete explanation of what a JavaBean is, and everything it can do, see the

JavaBeans Specification (version 1.01) at:

http://java.sun.com/products/javabeans/docs/beans.101.pdf

***************************************************************************************************

*****

57. Do I have to have a separate ActionForm bean for every HTML form?

This is an interesting question. As a newbie, it is a good practice to create a new

ActionForm for each action sequence. You can use DynaActionForms to help reduce

the effort required, or use the code generation facilities of your IDE.

Some issues to keep in mind regarding reuse of form beans are as follows:

* Validation - You might need to use different validation rules depending upon the

action that is currently being executed.

* Persistence - Be careful that a form populated in one action is not unexpectedly

reused in a different action. Multiple entries in struts-config.xml for the same

ActionForm subclass can help (especially if you store your form beans in session

scope). Alternatively, storing form beans in request scope can avoid unexpected

interactions (as well as reduce the memory footprint of your application, because no

server-side objects will need to be saved in between requests.

* Checkboxes - If you do as recommended and reset your boolean properties (for

fields presented as checkboxes), and the page you are currently displaying does not

have a checkbox for every boolean property on the form bean, the undisplayed

boolean properties will always appear to have a false value.

* Workflow - The most common need for form bean reuse is workflow. Out of the

box, Struts has limited support for workflow, but a common pattern is to use a

single form bean with all of the properties for all of the pages of a workflow. You will

need a good understanding of the environment (ActionForms, Actions, etc.) prior to

being able to put together a smooth workflow environment using a single form

bean.

As you get more comfortable, there are a few shortcuts you can take in order to

reuse your ActionForm beans. Most of these shortcuts depend on how you have

chosen to implement your Action / ActionForm combinations.

How can I prepopulate a form?

The simplest way to prepopulate a form is to have an Action whose sole purpose is

to populate an ActionForm and forward to the servlet or JSP to render that form

back to the client. A separate Action would then be use to process the submitted

form fields, by declaring an instance of the same form bean name.

http://java.sun.com/products/javabeans/docs/beans.101.pdfhttp://java.sun.com/products/javabeans/docs/beans.101.pdf

8/8/2019 Struts FAQ

21/40

The struts-example example application that is shipped with Struts illustrates this

design pattern nicely. Note the following definitions from the struts-config.xml file:

...

...

...

...

...

...

...

Note the following features of this approach:

* Both the /editRegistration and /saveRegistration actions use the same form bean.

8/8/2019 Struts FAQ

22/40

* When the /editRegistration action is entered, Struts will have pre-created an

empty form bean instance, and passed it to the execute() method. The setup action

is free to preconfigure the values that will be displayed when the form is rendered,

simply by setting the corresponding form bean properties.

* When the setup action completes configuring the properties of the form bean, it

should return an ActionForm that points at the page which will display this form. If

you are using the Struts JSP tag library, the action attribute on your

tag will be set to /saveRegistration in order for the form to be submitted to the

processing action.

* Note that the setup action (/editRegistration) turns off validation on the form that

is being set up. You will normally want to include this attribute in the configuration

of your setup actions, because you are not planning to actually process the results

-- you simply want to take advantage of the fact that Struts will precreate a form

bean instance of the correct class for you.

* The processing action (/saveRegistration), on the other hand, leaves out the

validate attribute, which defaults to true. This tells Struts to perform the validations

associated with this form bean before invoking the processing action at all. If any

validation errors have occurred, Struts will forward back to your input page(technically, it forwards back to an ActionForward named "registration" in this case,

because the example webapp uses the inputForward attribute in the element -- see

the documentation describing struts-config.xml for more information) instead of

calling your processing action.

***************************************************************************************************

*****

58. Can I have an Action without a form?

Yes. If your Action does not need any data and it does

not need to make any data available to the view or

controller component that it forwards to, it doesn't need

a form. A good example of an Action with no ActionForm is

the LogoffAction in the struts example application:

This action needs no data other than the user's session, which

it can get from the Request, and it doesn't need to prepare any

view elements for display, so it does not need a form.

However, you cannot use the tag without

8/8/2019 Struts FAQ

23/40

an ActionForm. Even if you want to use the

tag with a simple Action that does not require input,

the tag will expect you to use some type of ActionForm,

even if it is an empty subclass without any properties.

***************************************************************************************************

*****

59. Can you give me a simple example of using the requiredif Validator rule?

First off, there's an even newer Validator rule called

validwhen, which is almost certainly what you want to use,

since it is much easier and more powerful.

It will be available in the first release after 1.1 ships.

The example shown below could be coded with validwhen as:

test

((((sex == 'm') OR (sex == 'M'))

AND (*this* == null)) OR (*this* != null))

Let's assume you have a medical information form

with three fields, sex, pregnancyTest, and testResult.

If sex is 'f' or 'F',

pregnancyTest is required. If pregnancyTest is not blank,

testResult is required. The entry in your validation.xml

file would look like this:

8/8/2019 Struts FAQ

24/40

field[0]

sex

fieldTest[0]

EQUAL

fieldValue[0]

F

field[1]

sex

fieldTest[1]

EQUAL

fieldValue[1]

f

fieldJoin

OR

8/8/2019 Struts FAQ

25/40

property="testResult" depends="requiredif">

field[0]

pregnancyTest

fieldTest[0]

NOTNULL

***************************************************************************************************

*****

60. When is the best time to validate input?

This is an excellent question. Let's step back a second and think about a typical mid

to large size application. If we start from the back end and work toward the view we

have:

1) Database: Most modern databases are going to validate for required fields,

duplicate records, security constraints, etc.

2) Business Logic: Here you are going to check for valid data relationships and

things that make sense for the particular problem you are triing to solve.

... This is where struts comes into the picture, by now the system should be pretty

well bulletproof. What we are going to do is make validation friendlier and

informative. Rember it is OK to have duplicate validations...

3) ActionErrors validate(ActionMapping map, HttpServletRequest req) is where you

can do your validation and feed back to the view, information required to correct

any errors. validate is run after the form has been reset and after the ActionForm

properties have been set from corresponding view based input. Also remember youcan turn validation off with validate="false" in the action mapping in the struts-

config.xml. This is done by returning an ActionErrors collection with messages from

your ApplicationResources.properties file.

Here you have access to the request so you can see what kinds of action is being

requested to fine tune your validations. The tag allows you to dump

all errors on your page or a particular error associated with a particular property.

The input attribute of the struts-config.xml action allows you to send validation

errors to a particular jsp / html / tile page.

8/8/2019 Struts FAQ

26/40

4) You can have the system perform low level validations and client side feedback

using a ValidatorForm or its derivatives. This will generate javascript and give

instant feedback to the user for simple data entry errors. You code your validations

in the validator-rules.xml file. A working knowledge of regular expressions is

necessary to use this feature effectively.

***************************************************************************************************

*****

61. How can I avoid validating a form before data is entered?

The simplest way is to have two actions. The first one has the job of setting the form

data, i.e. a blank registration screen. The second action in our writes the

registration data to the database. Struts would take care of invoking the validation

and returning the user to the correct screen if validation was not complete.

The EditRegistration action in the struts example application illustrates this:

< action path="/editRegistration">

type="org.apache.struts.webapp.example.EditRegistrationAction"

attribute="registrationForm"

scope="request"

validate="false">

8/8/2019 Struts FAQ

27/40

8/8/2019 Struts FAQ

28/40

type="actions.MyWizard"

name="MyWizard"

validate="true"

input="/WEB-INF/jsp/mywizard3.jsp">

The pieces of the wizard are as follows:

forms.MyWizard.java - the form bean holding the information required

actions.MyWizard.java - the actions of the wizard, note the use of

LookupDispatchAction allows for one action class with several methods. All the real

work will be done in the 'finish' method.

mywizard[x].jsp - the data collection jsp's

mywizarddone.jsp - the 'success' page

mywizardcancel.jsp - the 'cancel' page

63. How can I 'chain' Actions?

Chaining actions can be done by simply using the

proper mapping in your forward entries

in the struts-config.xml file.

Assume you had the following two classes:

/* com/AAction.java */

...

public class AAction extends Action

{

public ActionForward

execute(ActionMapping mapping,

ActionForm form,

8/8/2019 Struts FAQ

29/40

HttpServletRequest request,

HttpServletResponse response) throws

Exception

{

// Do something

return mapping.findForward("success");

}

}

/* com/BAction.java */

...

public class BAction extends Action

{

public ActionForward

execute(ActionMapping mapping,

ActionForm form,

HttpServletRequest request,

HttpServletResponse response) throws

Exception

{

// Do something else

return mapping.findForward("success");

}

}

Then you can chain together these two actions with

the Struts configuration as shown

in the following excerpt:

...

8/8/2019 Struts FAQ

30/40

type="com.AAction"

validate="false">

...

Here we are assuming you are using a suffix-based (.do) servlet mapping, whichis recommended since module support requires it. When you send your browser to

the web application and name the action A.do (i.e. http://localhost:8080/app/A.do) it

will execute AAction.execute(), which will then forward to the "success" mapping.

This causes the execution of BAction.execute() since the entry for "success" in the

configuration file uses the .do suffix.

Of course it is also possible to chain actions programmatically, but the power and

ease of being able to "reroute" your web application's structure using the XML

configuration file is much easier to maintain.

As a rule, chaining Actions is not recommended. If your business classes are

properly factored, you should be able to call whatever methods you need from any

Action, without splicing them together into a cybernetic Rube Goldberg device.

If you must chain Actions, be aware of the following: calling the second Action from

the first Action has the same effect as calling the second Action from scratch. If

both of your Actions change the properties of a formbean, the changes made by the

first Action will be lost because Struts calls the reset() method on the formbean

when the second Action is called.

64. Struts GenericDataSource Just a general question

Struts GenericDataSource Just a general question - I'm building an application that

will run stand-alone, not in an application server. I need to manage some database

connections. Is the struts GenericDataSource a good candidate to do this for me? I

basicly just need a connection pool from where I can get connections and then

return them to optimize performance.

If this struts class is not a good candidate, can someone recommend a similar pool-

manager that is lean and mean and easy to use?

Answer 1

8/8/2019 Struts FAQ

31/40

The Struts 1.0 GenericDataSource is not a good candidate for a production server.

In Struts 1.1, the Commons DBCP is used istead, which is a good candidate for a

production server. (You can also use the DBCP in Struts 1.0 by specifying the type

and including the Commons JARs.)

Another popular choice is Poolman. It's not under active development, but I believe

you can still download it from SourceForge. Poolman is also very easy to use outside

of Struts.

Many containers also offer support for connection pools. The one that ships withResin is quite good. The later versions of Tomcat bundle the Commons DBCP.

Regardless of what pool you use, a good practice is to hide it behind some type of

adaptor class of your own (often a singleton), to make it easy to change later. So

your classes call your adaptor, and your adaptor calls whichever pool you are using.

A neat and often-overlooked aspect of the Struts DataSource manager is that it

supports loading multiple connection pools and giving each a name. So you might

have one pool for internal use and another for public use. This way, the public

connections can't swap your administrative access to the application. Each pool

could also have its own login, and therefore different rights to the underlyingdatabase.

Answer 2

int i=1;

with Struts 1.0 and jdbc,use GenericDataSource

not in struts-xml, but in Client.properties

my Client.properties

instanceBd=oraID

userPasswd=xxx/yyyy

maxCount=20

minCount=19

port=1521

driver=oracle.jdbc.driver.OracleDriver

url=jdbc:oracle:thin:@serverName:port:instanceBd

on the code init (struts 1.0 or struts 1.1):

GenericDataSource ng = new GenericDataSource ();

ng.setUser (mprop.getUserBd());

ng.setPassword (mprop.getPasswdBd());

ng.setUrl (mprop.getUrl());

ng.setDriverClass(mprop.getDriverClass());

8/8/2019 Struts FAQ

32/40

ng.setMaxCount(mprop.getMaxCount());

ng.setMinCount (mprop.getMinCount());

ng.setDescription("jdbc OracleDriver");

ng.setAutoCommit(true);

try { ng.open(); } catch (java.sql.SQLException e) {

}

in business logic (or pool) :

Connect cn = ng.getConnection();

it's work.

with struts 1.1 , struts-legacy.jar

is necessy for this codes.

65. Dynamic pages using struts

Is it possible to create the elements of a page(jsp) dynamically based on the results

of a data base query, when using struts framework?

If you are talking about rendering a report, then sure. The Action iteracts with the

business layer/data access objects to acquire the data, and then passes it to the

presentation page bundled up as a JavaBean or a collection of JavaBeans. The JSP

tags (and other systems) all use reflection, so you can use whatever JavaBean youlike.

If you are talking about creating a dynamic data-entry form, then "not so much".

Struts 1.1 supports map-backed ActionForms, but the page still needs to know what

input fields are going to be needed. For a truly dynamic input form, I guess the key

would be some type of tag that took a map and then generated a column of input

fields. (Wouldn't work for everyone, since a lot of forms must be designed just so.)

For extra credit, the entry names could (optionally) be resource keys that were used

to find the label text.

Text fields would be easy. Others would need some type of JavaBean with

properties to tell the tag what to output. A bit of work, but obviously doable.

Of course, you'd probably want to validate the form before passing it back to the

database. I imagine it's possible to use the validator in a non-declarative way, but I

don't know anyone whose doing that. If you can do a db query to get the

information about the form, I imagine you could also do a query to get the

information about validations for the form. It would probably be easier to write your

own engine than adopt the validator. (It's not really that complicated to do.)

8/8/2019 Struts FAQ

33/40

People often ask about "dynamic input forms", but most of us just can't get our

head around the use case. It's hard to understand what you do with the dynamic

data when it comes back. Most application don't allow you to input or update an

arbitrary (e.g. dynamic) set of fields.

66. What's the best way to deal with migrating a large application from Struts to

JSF? Is there any tool support that can help?

Answer: This is a complicated task depending on your Struts application. Because

the two frameworks have different goals, there are some challenges. Migrate yourresponse pages first. Keep the Struts controller and place and forward to JSF pages.

Then you can configure Struts forwards to go through the Faces servlet. Consider

looking at the Struts-Faces framework from Apache. See the framework chapter in

JSF in Action.

67. Declarative Exception Handling

If you have developed web applications long enough, you will realize a recurring

pattern emerges: when the backend (e.g. the EJB tier) throws you an exception, you

nearly always need to display an error page corresponding to the type of that

exception. Sooner or later, you will come up with a mechanism to use a lookup table(e.g. an HashMap) to lookup an error page from the exception class.

Struts 1.1 now provides a similar but more powerful mechanism to declare

exception handling. In Struts 1.1, you can declare in the struts-config.xml the

associations between an exception class and an exception handler. Using the

default exception handler included in Struts, you can also specify the path of the

error pages. With this information, Struts will automatically forward to the specified

pages when an uncaught exception is thrown from an Action.

Like other facilities in Struts, the exception handlers are pluggable. You can write

and define your own handler classes if needed.

68. Can you compare the advantages and disadvantages of JSF vs. Struts ?

This is a very popular question these days. In general, JSF is still fairly new and will

take time to fully mature. However, I see JSF being able to accomplish everything

Struts can, plus more. Struts evolved out of necessity. It was created by developers

who were tired of coding the same logic again and again. JSF emerged both from

necessity and competition.

Struts has several benefits:

* Struts is a mature and proven framework. It has been around for a few years anddeployed successfully on many projects. The WebSphere Application Server admin

console is a Struts application.

* Struts uses the Front Controller and Command patterns and can handle

sophisticated controller logic.

* In addition to the core controller function, it has many add-on benefits such as

layouts with Tiles, declarative exception handling, and internationalization.

There are disadvantages:

8/8/2019 Struts FAQ

34/40

* Struts is very JSP-centric and takes other frameworks to adapt to other view

technologies.

* Although Struts has a rich tag library, it is still geared towards helping the

controller aspect of development and does not give a sense that you are dealing

with components on a page. Therefore, it is not as toolable from a view perspective.

* Struts requires knowledge of Java. Its goal was to aid Java developers, but not to

hide Java. It does not hide details of the Java language to Web developers that well.

* ActionForms are linked programmatically to the Struts framework. Therefore, to

decouple the model, you need to write transfer code or use utilities to move data

from Action Forms to the Model on input.

JSF is an evolution of a few frameworks, including Struts. The creator of Struts, Craig

McClanahan, is one of the JSF specification leads. Therefore, it is not by accident to

see some overlap between Struts and JSF. However, one of JSF's major goals is to

help J2EE Web applications to be easily developed using RAD tools. As such, it

introduces a rich component model. JSF has several advantages:

* JSF is a specification from Sun and will be included in future versions of the J2EE

specification. All major vendors are pledging strong support for JSF.

* JSF uses the Page Controller Pattern and therefore aids in Page rich applications.

Components can respond to event from components on a page.

* JSF has a well-defined request lifecycle allowing for plugability at different levels.

* One powerful example of plugability is building your own render toolkit. The ability

to separate the rendering portion from the controller portion of the framework

allows for wonderful opportunities of extensibility. Component providers can writetheir own toolkits to render different markup languages, such as XML or WML. In

addition, the render toolkit is not tied to JSP.

* Because JSF has a rich component model, it favors a RAD style of development. I

can now build my Web pages using drag and drop technology. In addition, JSF gives

me a way to link visual components to back model components without breaking

the layering.

JSF has disadvantages:

* JSF is still quite new and evolving. It will take some time to see successful

deployments and wide usage. In addition, as vendors write components, they may

not do everything you want them to.

* JSF by hand is not easier than Struts. Its goal was more oriented to RAD. Those

who prefer to do things by hand (for example, the vi type guy who does not like

IDEs) may find Struts easier to develop.

* Struts navigation may be a bit more flexible and adhere to more complex

controller logic.

69. Both JSF and Struts will continue to exist for a while ?

8/8/2019 Struts FAQ

35/40

Both JSF and Struts will continue to exist for a while. The Struts community is aware

of JSF and is positioning itself to have strong support for JSF. See What about JSTL

and JavaServer faces?

From a tools perspective, if you look at the support for JSF versus Struts in

WebSphere Studio, the Struts tools are focused around the controller aspects. The

Web Diagram editor helps build your Struts configuration and the wizards/editors

build Struts artifacts. The JSF tools are geared towards building pages, and in

essence, hide the JSF framework from you. Expect WebSphere Studio to support

both frameworks for a while. As JSF matures, expect to see some of the controlleraspects in JSF to become toolable.

70. Multiple Sub-applications

One of the shortcomings in Struts 1.0 is manageability of the configuration file

(commonly known as struts-config.xml) when the development of the application

involves a sizable team. This problem arises because a Struts-based application

must run under one controller servlet, the ActionServlet, and the ActionServlet can

use only one struts-config.xml. It is not an issue when the project is relatively small

and the team consists of a couple of developers; however, when the project size

becomes significant and the project involves a large number of developers,maintaining all the mapping information in a single file becomes increasingly

problematic.

Struts 1.1 solves this problem nicely by introducing multiple sub-applications. In

Struts 1.1, each sub-application has its own struts-config.xml file. A large Struts-

based application can thus be easily partitioned into largely independent modules,

i.e. sub-applications, and each sub-team can maintain their struts-config.xml

independently.

The sub-application scheme is a natural extension of the servlet context mapping

scheme of the URI paths used by servlet containers. According to the Servletstandard, when the servlet container receives a request with a URL, the servlet

container will try to match the prefix of the URI path to a deployed web-application

in the container. What Struts 1.1 does is it maps the second prefix of the path to a

sub-application. In effect, this prefix mapping scheme creates another level of

namespace for each sub-application. For example, for the URI,

http://some-host.com/myApp/module2/editSubscription.do

/myApp is the context path for a web-application called "myApp" and /module2 is

the sub-app prefix for a Struts sub-application called "module2".

71. DynaBean and BeanUtils

Another major complaint usually heard amongst Struts 1.0 users is the extensive

effort involved in writing the FormBean (a.k.a. ActionForm) classes.

Struts provides two-way automatic population between HTML forms and Java

objects, the FormBeans. To take advantage of this however, you have to write one

FormBean per HTML form. (In some use cases, a FormBean can actually be shared

between multiple HTML forms. But those are specific cases.) Struts' FormBean

standard follows faithfully the verbose JavaBean standard to define and access

properties. Besides, to encourage a maintainable architecture, Struts enforces a

8/8/2019 Struts FAQ

36/40

pattern such that it is very difficult to 'reuse' a model-layer object (e.g. a

ValueObject from the EJB tier) as a FormBean. Combining all these factors, a

developer has to spend a significant amount of time to write tedious getters/setters

for all the FormBean classes.

Struts 1.1 offers an alternative, Dynamic ActionForms, which are based on

DynaBeans. Simply put, DynaBeans are type-safe name-value pairs (think

HashMaps) but behave like normal JavaBeans with the help of the BeanUtils library.

(Both the DynaBeans and the BeanUtils library were found to be useful and generic

enough that they have been 'promoted' into Jakarta's Commons project.) WithDynamic ActionForms, instead of coding the tedious setters/getters, developers can

declare the required properties in the struts-config.xml files. Struts will instantiate

and initialize Dynamic ActionForm objects with the appropriate metadata. From

then onwards, The Dynamic ActionForm instance is treated as if it is an ordinary

JavaBean by Struts and the BeanUtils library.

72. Validator

The Validator is not exactly a new feature. The Validator has been in the contrib

package in the distribution since Struts 1.0.1. Since then, part of it has now been

refactored and moved into the Jakarta-Commons subproject and renamed theCommons-Validator and the Struts specific portion is now called the Struts-

Validator. However, since it is in the contrib package, people may overlook it and it

is worthwhile to mention it here.

The Validator provides an extensible framework to define validation rules to validate

user inputs in forms. What is appealing in the Validator is that it generates both the

server-side validation code and the client-side validation code (i.e. Javascript) from

the same set of validation rules defined in an XML configuration file. The Validator

performs the validation based on regular-expression pattern matching. While a

handful of commonly used validators are shipped with the framework (e.g. date

validator, range validator), you can always define your own ones to suit your need.

73. Default Sub-application

To maintain backward compatibility, Struts 1.1 allows one default sub-application

per application. The URI of the resources (i.e. JSPs, HTMLs, etc) in the default sub-

application will have an empty sub-app prefix. This means when an existing 1.0

application is "dropped" into Struts 1.1, theoretically, it will automatically become

the default sub-application.

74. Direct Requests to JSPs

To take the full advantage of sub-application support, Struts 1.1 stipulates the

requirement that all requests must flow through the controller servlet, i.e. the

ActionServlet. Effectively, this means all JSPs must be fronted by Actions. Instead of

allowing direct requests to any of the JSPs, all requests must go through an Action

and let the Action forward to the appropriate JSP.

This is perhaps the biggest impact of migration to Struts 1.1 if you have not

followed this idiom in your applications. This restriction is required because without

going through the ActionServlet, Struts navigation taglibs (e.g. and

) used in the JSPs will not have the correct sub-app context to work with.

8/8/2019 Struts FAQ

37/40

75. ActionServlet Configurations

With the introduction of sub-applications, a more flexible way is introduced to

configure each sub-application independently. Many of the configuration entries

(e.g. resource bundle location, maximum upload file size, etc) that used to be

defined in web.xml have now been moved to struts-config.xml. The original entries

in web.xml are deprecated but will still be effective.

76. Action.execute() and Action.getResources()

In Struts 1.0, request handling logic is coded in Action.perform(); however,

Action.perform() throws only IOException and SevletException. To facilitate the new

declarative exception handling , the request handling method needs to throw

Exception, the superclass of all the checked exceptions. Therefore, to both maintain

backward compatibility and facilitate declarative exception handling,

Action.perform() is now deprecated in favour of Action.execute().

You also have to be careful if you use DispatchAction in your existing applications.

At the time of writing, the DispatchAction in Struts 1.1 beta has not yet been

updated to use execute(). (A bug report has been filed in Struts' bug database.)

Therefore, without modifying the DispatchAction class yourself, declarativeexception handling will not work with DispatchAction subclasses.

In addition, Action.getResources() is now deprecated. Instead, you should call

Action.getResources(HttpServletRequest) instead. This allows Struts to return to you

the sub-application specific message resources. Otherwise, the message resources

for the default sub-app will be used.

77. Library Dependency

Struts 1.1 now depends on a handful of libraries from other Jakarta subprojects (e.g.

Commons-Logging, Commons-Collections, etc.). Some of these libraries may cause

classloading conflicts in some servlet containers. So far, people have reported in the

mailing list the classloading problem of commons-digester/jaxp1.1, and commons-

logging causing deployment difficulties in Struts 1.1 applications running on

Weblogic 6.0. (The problems have been corrected in Weblogic 6.1 and 7.0.)

78. Resources under WEB-INF

According to the Servlet specification, resources (e.g. JSP files) stored under WEB-

INF are protected and cannot be accessed directly by the browsers. One design

idiom for Struts 1.0 is to put all the JSP files under WEB-INF and front them by

Actions so that clients cannot illegally access the JSPs.

With the introduction of sub-application prefixes in Struts 1.1, mapping resources

under WEB-INF gets complicated. Extra configuration steps utilizing the pagePattern

and forwardPattern attributes of the element in struts-config.xml is required to

inform Struts to construct the paths correctly. More specifically, you need to set

these attributes to the pattern "/WEB-INF/$A$P".

79. What is the Jakarta Struts Framework?

Jakarta Struts is an open source implementation of MVC

(Model-View-Controller) pattern for the development of web based applications.

8/8/2019 Struts FAQ

38/40

Jakarta Struts is a robust architecture and can be used for the development of

applications of any size.

The Struts framework makes it easier to design scalable, reliable Web

applications.

80. What is an ActionServlet?

The class org.apache.struts.action.ActionServlet is called the ActionServlet.

In the Jakarta Struts Framework this class plays the role of controller.

All the requests to the server go through the Controller.

The Controller is responsible for handling all the requests.

81. How can one make any Message Resources definitions file available to the

Struts Framework environment?

Answer: Message Resources definitions file are simple .properties files and

these files contain the messages that can be used in the struts project.

Message Resources definition files can be added to the struts-config.xml file

through tag. Example:

82. What is an Action Class?

The Action Class is part of the Model and is a wrapper around the business

logic.

The purpose of the Action Class is to translate the HttpServletRequest to thebusiness logic.

To use the Action, we need to subclass and overwrite the execute() method.

All the database and business processing is done in the Action class.

It is advisable to perform all the database related work in the Action class.

The ActionServlet (command) passes the parameterized class to ActionForm using

the execute() method.

The return type of the execute method is ActionForward which is used by the StrutsFramework to forward the request to the file according to the value of the returned

ActionForward object.

83. Write code of any Action Class?

Here is the code of Action Class that returns the ActionForward object.

package j2eeonline.jdj.com;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

8/8/2019 Struts FAQ

39/40

import org.apache.struts.action.Action;

import org.apache.struts.action.ActionForm;

import org.apache.struts.action.ActionForward;

import org.apache.struts.action.ActionMapping;

public class TestAction extends Action{

public ActionForward execute(ActionMapping mapping, ActionForm form,HttpServletRequest request,

HttpServletResponse response) throws Exception{

return mapping.findForward("testAction");

}

}

84. What is an ActionForm?

An ActionForm is a JavaBean that extends org.apache.struts.action.ActionForm.

ActionForm maintains the session state for web application and the ActionForm

object is automatically populated on the server side with data entered from a form

on the client side.

85. What is Struts Validator Framework?

The Struts Framework provides the functionality to validate the form data.

It can be used to validate the data in the users browser as well as on the server

side.

Struts Framework checks the JavaScript code and it can be used to validate the

form data on the client browser.

Server side validation of form data can be accomplished by subclassing yo