09 JSTL Tutorial

8/2/2019 09 JSTL Tutorial

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2009 Marty Hall

The JSP Standard TaLibrary (JSTL)

-

in MVC-Based JSP PagesCustomized Java EE Training: http://courses.coreservlets.com/

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2009 Marty Hall

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Agenda

Obtaining JSTL documentation and code

The JSTL Expression Language

Looping TagsLooping a certain number of times

Looping over data structures

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Conditional Evaluation Tags

Multiple choices

Database Access Tags Other Tags

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Installation




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JSTL Overview

Full JSTLContains many common and useful JSP custom tags

Particularly useful when you are using MVC, but the

Based on the Struts looping and logic tags

ot art of the JSP 1.2 2.0 or 2.1 s ecs It is a separate specification that requires a separate

download

The JSP expression language came from JSTL, but is now

art of JSP 2.0, JSP 2.1, and JSF

The JSTL Specification is available in PDFhttp://jcp.org/en/jsr/detail?id=52

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Downloading JSTL

JSTL 1.1 ome page

http://jakarta.apache.org/taglibs/doc/standard-doc/intro.html

own oa http://jakarta.apache.org/site/downloads/

downloads_taglibs-standard.cgi

ocumen a on ava oc http://java.sun.com/products/jsp/jstl/1.1/docs/tlddocs/

Note Many server packages (e.g., MyFaces) and IDEs (e.g.,

MyEclipse) alreadyhave JSTL 1.1 bundled

JSTL 1.2As of 10/2008, only available as part of Java EE 5

Not as a separate download for use in other servers10


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Enabling JSTL with Eclipse or

EclipseDownload from

Apache site .

standard.jaronto WEB-INF/lib

They also

show up here.

ey a so ge s e n Web App Libraries

I usually rename JAR

You drop

them here.

es o s ow exac vers on

MyEclipse ,

FileNewWeb Project,select JSTL 1.1 option

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Enabling JSTL Manually

Put in Web AppDrop JAR files in the WEB-INF/lib folder

of your Web app

Add the JAR files to the CLASSPATH used by your

development environmentDo notadd to the CLASSPATH used by the server

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The JSTL Expression Language

Accessed via ${expression}

Similar to JavaScript and XPath

Provides shorthand notation to access:Attributes of standard servlet objects

Bean properties

, ,

Is standard part of JSP 2.0 and 2.1 ,

In JSP 2.0, the EL can be used anywhere

web.xmlelement and page directive attribute let yousa e e or ac war compa y

EL covered in separate lecture13

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Iteration Tags




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Constructs for Handling-

Simplest

Bean ${cust.withdrawals}

for Page

Author

Custom tag (non-looping)

Custom tag (looping) ee examp es n A vance ustom ags

lecture

JSTL looMost

JSP scripting loop

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for Page

Author

Looping Tags: Summary

Looping with explicit numeric values

Blah, blah ${name}

Looping over data structures , , ,

Blah, blah ${name}

forTokens

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Looping Tags: Motivation

JSP without JSTL


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Looping with a Designated Step

.

Timeout exceeded.

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Looping Down Arrays (Servlet)public class ArrayServlet extends HttpServlet {

,

HttpServletResponse response)

throws ServletException, IOException {

= " " " " " "

request.setAttribute("words", words);

String address = "/WEB-INF/results/array-loop.jsp";

=

request.getRequestDispatcher(address);

dispatcher.forward(request, response);

}

Note url-pattern in web.xml is /test-array

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Looping Down Arrays

${word}

Values of the test Parameter:< H2>

${val}

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Note for Older Servers

Examples in this lecture assume JSP 2.0+ a so runs n o er servers, ut you ave to rep ace

direct output of ${foo} with

Previous exam le JSP 2.0+

${word}

Previous exam le JSP 1.2

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${foo} vs.

c:out runs on older serversOracle 9i, BEA WebLogic 8.x, IBM WebSphere 5.x

c:out escapes HTML (XML) characters outputs

Very important if value being output comes from end user.

=" " =" "

c:out lets you supply a default value or

The default is output when ${foo} evaluates to null

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Looping Down Collections: Notes

Can loop down collections other than arrays items can refer to an array, collection (List, Map, Set,

etc.), comma-separated String, Iterator, or Enumeration

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${bean.property}


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Looping Down Arrays:

public class ArrayServlet2 extends HttpServlet {

public void doGet(HttpServletRequest request,



Name[] names ={ new Name("Bill", "Gates"),

new ame arry , son ,

new Name("Sam", "Palmisano"),

new Name("Scott", "McNealy"),

new Name("Eric", "Schmidt"),

" " " ",

request.setAttribute("names", names);

String[][] sales =

{ {"2005", "12,459", "15,622"},

"2006" "18 123" "17 789"

{"2007", "21,444", "23,555"} };

request.setAttribute("sales", sales);

String address = "/WEB-INF/results/array-loop2.jsp";RequestDispatcher dispatcher =

request.getRequestDispatcher(address);

dispatcher.forward(request, response);

}

}27

Note: url-pattern is /test-array2


public class Name {

private String firstName;

private String lastName;

public Name(String firstName, String lastName) {

setFirstName(firstName);

setLastName(lastName);

}

public String getFirstName() { return(firstName); }

public void setFirstName(String firstName) {

this.firstName = firstName;

}

public String getLastName() { return(lastName); }

public void setLastName(String lastName) {

this.lastName = lastName;

}

}28


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Attendees at the coreservlets.com Party

${name.firstName} ${name.lastName}

Comparing Apples and Oranges

Year

Apples Sold

Oranges Sold

${col}

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Loop Status

You can assign varStatus.

Usually using c:if (covered later in this lecture)

index (int: the current index)

first (boolean: is this the first entry?)

last (boolean: is this the first entry?)

begin (Integer: value of 'begin' attribute)en nteger: va ue o en attr ute

step (Integer: value of 'step' attribute)31

Loop Status: Example

Names:

${name},

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Looping Down Comma-

${country}

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Looping Down Arbitrarily-

${color}

Point:forTokensbuilt on forEach:you can build your

based on JSTL tags

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HTML Code

...

Getting XML Data from Server...

City Type:

>37

Servlet Codepublic class ShowCities extends HttpServlet {

public void doGet(HttpServletRequest request,



response.setHeader("Cache-Control", "no-cache");

response.se ea er ragma , no-cac e ;

String cityType = request.getParameter("cityType");

List cities = findCities(cityType);

request.setAttribute("cities", cities);String format = request.getParameter("format");

String outputPage;

if ("xml".equals(format)) {

" ".

outputPage = "/WEB-INF/results/cities-xml.jsp";

} ...

RequestDispatcher dispatcher =

request.getRequestDispatcher(outputPage);

dispatcher.include(request, response);

}38


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Original JSP Code- - .

CityTime

ea ng opu a on ea ng

${cities[0].name}

${cities[0].shortTime}

${cities[0].population}

... , , --

${cities[4].name}

${cities[4].shortTime}

${cities[4].population}

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Problems with JSP Code

RepetitiveAlmost-identical city entries repeated five times

If the city format changes, all five entries need to change

resumes exac y ve c esWill not work with a different number of cities

Even thou h both the servlet code and the client-sideJavaScript code can handle any number of cities

Solution se

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Updated JSP Code- .

City

Population

=" "

uri="http://java.sun.com/jsp/jstl/core" %>

${city.name}

${city.shortTime}

< o ulation>${cit . o ulation}

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Alternative Version- .

" ". .

City

Population

=" " =" "

${city.name}

cit .shortTime < time>

${city.population}

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XML Data: Results

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JSON Version: Original- - .

{ headings: ["City", "Time", "Population"],

. , . ,

"${cities[0].population}"],

["${cities[1].name}", "${cities[1].shortTime}",

c es .popu a on ,



" c t es .name ", " c t es .s ortT me ",



"${c t es[4].populat on}"]]

}

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JSON Version: Updated- .


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Delimited String Version: Original- - .

City#Time#Population

. . .

${cities[1].name}#${cities[1].shortTime}#${cities[1].population}


. . .


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Delimited String Version: Updated- .


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String Version: Results

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2009 Marty Hall

Logic Tags




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Conditional Evaluation Tags

One choice: if

Content

Lots of choices: choose

Content1

Content2

...

ContentN

Default Content

Caution: resist use of business logic!51

The "if" Tag

(greater than 7)

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The "choose" Tag

${i}

:

(small)

(medium)

(large)

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2009 Marty Hall

Pages




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Output Pages vs. Direct-Access

Output pages n pages t at are t e resu t o a nav gat on ru e .e., ste

under to-view-id), you can use JSTL as shown onprevious slides nce ean s a rea y n reques , sess on, or app ca on

Direct access pages JSTL does not know about faces-confi .xml so ou

cannot refer to beans that are listed there but not yetinstantiated

Usin direct-access a es is rare in real life but is veruseful for testing when learning JSTL

Solution: use h:outputText to refer to bean once first Declare bean containing array of numbers in faces-config.xml

First num: ...

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JSF Does Not Know About JSTL

JSTL puts data in page scope s wor s

$ name

Example assumes this is an output page and "names" set

earlier b JSF This fails

" ":ou pu ex va ue= name

Supposedly fixed in JSTL 1.2But there are no standalone releases of JSTL 1.2Use facelets instead

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2009 Marty Hall

Database Access Tags



Database Access Tags

pec es a a source can a so e se y con g se ngs

ueries database and stores ResultSet in variableWarning: this usage violates rule of keeping business

logic out of presentation layer. Instead, do database

access in servlet and ass results to JSP via MVC.

actions as a single transaction

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Aside: The Microsoft Access

Database that comes preinstalled withMicrosoft Office

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Using Microsoft Access via

Click Start, Settings, Control Panel,Administrative Tools, Data Sources, SystemDSN, and select Add

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Select Microsoft Access Driver, Finish, typea name under Data Source Name, and hit

Select

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Navigate to the Samples directory of MSOffice, select Northwind.mdb, hit OK, thenhit OK in following two windows

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Driver sun.jdbc.odbc.JdbcOdbcDriver

Comes bundled with JDK

jdbc:odbc:Northwind Local access only; for testing. Not for serious applications.

UsernameEmpty string

Password

Empty string

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sql:setDataSource

You can set a data source globally viaconfiguration settings or application-scopedvariables.

Or, you can set it on a specific page


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sql:query

Form 1: use the sql attribute

Form 2: put the query in the body of the tagsq :query var= resu s

SELECT * FROM

OptionsdataSource

maxRows

startRow au on

Embedding SQL directly in JSP may be hard to maintain.65

Simple Example

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Simple Example (Continued)

${row.firstname}

${row.lastname}

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Simple Example: Results

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2009 Marty Hall

Other Tags



URL-Handling Tags

Read content from arbitrary URLs

Insert into page

Store in variable

Or make accessible via a reader

Unlike , not restricted to own system Redirects response to specified URL

Encodes a request parameter and adds it to a URL

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Formatting Tags

Formats a numeric value as a number, currency value, or

percent, in a locale-specific manner

Reads string representations of number, currency value,or percent

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Internationalization (I18N) Tags

Sets Locale

< m : un e>

etr eves oca ze message rom a resource un e

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XML Manipulation Tags

Core

XPath

XSLT

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Summary

JSTL overview JSTL s s m ar to t e o Struts oop ng an og c tags, ut etter

JSTL is standardized, but not a standard part of JSP You have to add JAR files to WEB-INF/lib

t s suppose to e nc u e w t a mp ementat ons

Supports a concise expression language

Lets you access bean properties and implicit objects EL is standard part of JSP 2.0, JSP 2.1, and JSF

Looping tags

Arrays, collections, maps, strings, etc.

Conditional evaluation tags Single options

Multiple options

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Summary (Continued)

Database Access TagsAlways a bad idea when using MVC approach

With or without a framework like JSF or Struts

sql:query to perform query

Loop down results using iteration tags

Other tagsHandling URLS

Internationalizing pages

Formatting strings

Bad idea when using MVC

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2009 Marty Hall

Questions?

09 JSTL Tutorial

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