Week5 Intro Server Side i

8/11/2019 Week5 Intro Server Side i

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Introduction toServer-Side Web Development

Introduction to Server-Side Web

Development

Server-Side Web Development with Servlets and JSP; basic concepts and syntax

16 th February 2006

Bogdan L. [email protected]


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16 th February 2006 Bogdan L. Vrusias 2006 2

Introduction Most web sites want to display dynamic content based on

users requests and expectations.

Most contents, such as images, text, and banner ads, areeasiest to build with HTML editors.

We need to mix the "static" content of HTML files with"directives" for accessing or generating dynamic content.

Introducing:


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Contents History of JavaServer Pages (JSP)

Fundamentals of server-side programming.

Comparison to other server-side languages

Fundamentals of JavaServer Pages / Servlets.

Servlets

JavaServer Pages

Tomcat


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History: The Beginning 1991 beginning of WWW beginning of HTML

No dynamic pages the Webmaster

Too many static HTML pages had to be created for each

website. Need for change


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History: First approach - CGI Solution C ommon G ateway Interface ( CGI ) technology

created.

Dynamic pagesusing Perl and C

Problem these languages are not the simplest Need for change

Java had the answer Servlets


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History: Servlets and JSP Servlets are pure Java objects that generate HTML by writing it to a

stream .

The files do not contain any HTML tags; they simply contain Javacode which write out HTML (as strings) to produce the page that issent to the user's browser.

but it was quite painful to develop any large scale application with a bunch of servlets running around doing println() statements.

This is why Sun invented JSPs in the first place: to compete with theease-of-development of Microsoft's ASP files, which could combine

HTML tags and code in a single file.


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A dynamic Web Page Static web page is a page whose content consists of some HTML that

was predetermined and was typed directly into a text editor and savedas " .htm" or " .html " file.

Dynamic web page is a page whose content is generated at runtimedynamically.

6. Browser processes HTMLand displays page.

2. Client request web page

1. Author writesinstructions

3. Web serverlocates instructions

file4. Web server

processesinstructions tocreate HTML

5. HTML stream returned to browser


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Requests and Responses


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Other Server-Side programming languages CGI

Perl, C, C++

ColdFusion Tags with encapsulated functionality

ASP (Active Server Pages) and ASP .NET VBasic, JavaScript, C# ADO

PHP (Personal Home Pages) Syntax similar to C and Perl Open-source, cross-platform


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JSP vs .NET and ASP Similarities

Create interactive pages with web-based applications Separates programming logic from page design through the use of

component technology Faster and Easier alternative to older, more cryptic technologies

such as CGI

Differences (?) JSP: Platform and server Independent

JSP can run on any web server

Supported by large number of tools ASP: Relies on Microsoft platforms and servers

Restricted to MS Windows based platforms because of ActiveXControls ( that is to change now? )

Can be ported to different platforms using third party products, butActiveX must be present on the platform.


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Why Use JSPs? Write once, run anywhere ( JAVA ).

JSPs are entirely platform independent, both in dynamic Web pages and underlying server components.

Emphasize components. JSPs encourage the use of reusable, cross-platform server

components called JavaBeans. Therefore saves development time,while giving you the power and flexibility of the Java

programming language.

Provide a front door to the Enterprises Java platform. JSPs are an integral part of the Java Platform for the Enterprise,

which brings Java technology to enterprise computing. You candevelop enterprise-wide or middle-tier server applications, using aJSP web site as a front end.


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Advantages of Java According to java.sun.com:

More mature, powerful, and scalable than Basic-based scriptinglanguages

Java helps developers protect against system crashes, ASP and NT

systems are susceptible to crashing Java helps with memory management by providing protection

against memory leaks

Well supported, large collection of APIs


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JSP Model Architectures

Model 1 Model 2

BROWSER

SERVLET(CONTROLLER)

JSP(VIEW)

JAVABEAN

requestresponse

JSP / Servlet Container

DATADATA

Data Tier

BROWSER

JSP PAGE

JAVABEAN

requestresponse

JSP / Servlet Container

DATADATA

Data Tier


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What are Servlets? Servlets are objects that reside on a Java enabled web

server, that work on the request-response principle.

Servlets are to the server-side what applets are to the clientside

Servlets do not have a GUI associated with them

Servlets are faster and cleaner than CGI scripts

Servlets use a standard API

Servlets provide all the advantages of Java


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Servlet Code Sampleimport javax.servlet.*;import java.io.*;

import java.util.*;

public class SimpleServlet extends GenericServlet {

public void service(ServletRequest request, ServletResponse response)

throws ServletException, IOException {response.setContentType("text/html");

printWriter pw = response.getWriter();

pw.println("\n");

for(int counter = 1; counter


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Servlet Lifecycle1. When a server loads a servlet, it runs the servlet's init() method.

Even though most servlets are run in multi-threaded servers, there areno concurrency issues during servlet initialization.

2. After the server loads and initializes the servlet, the servlet is able tohandle client requests. It processes them in its service() method.

3. Servlets run until they are removed from the service, by calling theservlet's destroy() method.

NOTE: Servlets can run multiple service methods at a time. It isimportant, therefore, that service methods be written in a thread-safemanner. If, for some reason, a server should not run multiple servicemethods concurrently, the servlet should implement theSingleThreadModel interface.


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Servlet Lifecycle Diagram

Uninstantiated

Instantiated

Initialised

ServicingRequests

ProcessRequests

ProcessRequests

GarbageCollectionservice() destroy()

init()

doGet() doPost()


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Servlet Architecture Overview The central abstraction in the Servlet API is the Servlet interface.

All servlets implement this interface, either directly or, morecommonly, by extending a class that implements it such asHttpServlet .

When a servlet accepts a call from a client, it receives two objects: oneis a ServletRequest and the other is a ServletResponse . The ServletRequest class encapsulates the communication from the

client to the server The ServletResponse class encapsulates the communication from the

servlet back to the client.


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ServletRequest The ServletRequest interface allows the servlet access to

information such as: the names of the parameters passed in by the client the protocol (scheme) being used by the client the names of the remote host that made the request and the server that

received it.

It also provides the servlet with access to the input stream,ServletInputStream , through which the servlet gets data fromclients that are using application protocols such as the http POST method.

CLIENT SERVER


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ServletResponse

The ServletResponse interface gives the servlet methods forreplying to the client. It allows the servlet to: set the content length and mime type of the reply provides an output stream, ServletOutputStream , and a "writer"

through which the servlet can send the reply data.

Subclasses of ServletResponse give the servlet more protocol-specific capabilities. For example, HttpServletResponse contains methods that allow the servlet to manipulate HTTP-specificheader information.

CLIENT SERVER


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Interacting with Clients I Servlet writers who are developing HTTP servlets that

specialize the HttpServlet class should override themethod or methods designed to handle the HTTPinteractions that their servlet will handle.

The candidate methods include: doGet , for handling GET, conditional GET and HEAD requests doPost , for handling POST requests doPut , for handling PUT requests doDelete , for handling DELETE requests


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I d i


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Reading Form Data Example - GET

When submitted, the browser would execute the following URL:

http://www.somewhere.com/servlet/aservlet?key1=x&key2=y

Alternatively

LINK

I d i


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Reading Form Data Example - POSTThe HTML

...

Please Enter your name

...

Example continues next page...


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Introd ction to


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How Servlets relate to JSPs JSPs and servlets are two different ways to accomplish the

same goal: generating dynamic HTML pages using Javacode. One puts Java code in your HTML, and one putsHTML in your Java code .

Functionally, they are equivalent. In fact, under the covers,the web server takes a JSP and converts it to thecorresponding servlet and dynamically compiles it.

BUT servlets have the following deficiencies: It is hard to write and maintain the HTML You cannot use standard HTML tools The HTML is inaccessible to non-Java developers


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Introduction to


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Scriptlets

e.g.


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ExpressionsAn expression prints out a string value on the page's bufferoutput:

Using scriplets this would look like:

Introduction to


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Declarations 0 );

}

%>

Introduction to


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CommentsThe comments are not printed on page's buffer, therefore are not viewed by theclient.

Introduction to


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Directives Here is what directives look like in a general form:

There are three directives: specifies information that affects the page

e.g.

includes a file at the location of the include directive(parsed)e.g.

allows the use of custom tags in the pagee.g.

Introduction to


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Page Directive

Introduction to


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Include Directive

Use the include directive to include a file in the main JSPdocument at the time the document is translated into aservlet.

What is included is the actual content of the respective file.


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Introduction to


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Include Action Element The jsp:include action lets you include the output (not the actual code )

of a page at request time:

NOTE : Is it similar to ???


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Introduction to


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Server-Side Web Development


Implicit Objects and the JSP Environment The scriptlets and expressions written in a JSP page do not stand alone

as a complete program they need an environment in which tooperate.

The JSP container provides this environment and makes it accessibleto the page author through what are called implicit objects :

request (HttpServletRequest ) response (HttpServletResponce ) application (ServletContext ) session (HttpSession ) out (JspWriter ) pageContext config page exception

Introduction to


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Basic request Methods String getParameter (String name) Enumeration getParameterNames ()

String getMethod () (e.g "POST", "GET")

Cookie[] getCookies ()

String getHeader(String name)

Enumeration getHeaderNames()

HttpSession getSession(boolean create)

...

Introduction to


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Basic response Methods void sendRedirect () void addCookie (Cookie cookie)

void setHeader(String name)

void addHeader(String name)

void sendError(int sc [, String msg])

Introduction to


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Basic session Methods Object getAttribute (String name) void setAttribute (String name, Object value)

Enumeration getAttributeNames ()

int setMaxInactiveInterval ()

int getMaxInactiveInterval()

void invalidate()

void isNew()

void logout()

String getId()

Introduction to


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Basic application Methods String getRealPath (String path) Object getAttribute (String name)

void setAttribute (String name , Object value)

void removeAttribute (String name)

Enumeration getAttributeNames ()

void log(String msg)

URL getResource(String path)

Introduction to


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Basic out Methods void print (String value) void println (String value)

void newLine ()

void clear()

Introduction to


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Tomcat

Tomcat is the official JavaServer Pages Web server. Tomcat is the official reference implementation of the Java

Servlet and JavaServer Pages technologies. Developedunder the Apache license in an open and participatory

environment. Other popular Web servers are:

Apache Java Application Server Macromedia JRun Jetty Internet Information Server (IIS) Jigsaw

http://jakarta.apache.org/tomcat/
http://java.sun.com/products/jsp/tomcat/


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Introduction to


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Closing

Questions???

Remarks???

Comments!!! Evaluation!

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