1. the Java Server Pages (JSP) Technology Model

ADV. JAVA With SCWCD/ OCWCD Material

173

By Mr. Durga

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By Mr. Durga

JSP's 2.1v 1) 2) 3) 4) 5)

The Java Server pages (JSP) Technology model Building JSP Pages Using Standard Actions Building JSP Pages Using the Expression Language(EL) Building JSP Pages using Tag Libraries(JSTL) Building a Custom Tag Library

JSP Technology Model

1) JSP API and life cycle Translation Phase JSP-API javax.servlet.jsp.JspPage( javax.servlet.jsp.JspPage(I) I) javax.servlet.jsp.HttpJspPage( javax.servlet.jsp.HttpJspPage(I) I) Internal implementation of HttpJspBase class ? LifeCycle of JSP PreCompilation PreCompilation of JSP       

2) JSP ELEMENTS : Template Text JSP Directives : 1) page directive  import session  isELIgnored  isThreadSafe  contentType  language  buffer  autoFlush  extends  info  isErrorPage  errorPage  pageEncoding   
















By Mr. Durga

3) taglib directive 3) Scripting Elements  Traditional Scripting elements Scriptlets Declarations Expressions Comments Jsp comments  Html comments  Java comments  VISIBILITY of comments  Comparision of Scripting Elements   Modern Scripting elements EL JSTL    

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4) JSP Actions 5) JSP Implicit Objects/elements :  request  response  config  application  session  out : How to write write response in Jsp ? What is the difference between PrintWriter and JspWriter ? What is the difference between out.write(100) out.write(100) and out.print(100) out.print(100) ?  page  pageContext To get all other Jsp implicit objects : To perform RequestDispatcher Mechanism : To perform Attribute Management in any scope (Jsp scopes)  exception Declarative Approach Programmatic Approach Which approach is best approach to configure error pages ?   

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6) JSP Scopes request scope session scope  
















By Mr. Durga

JSP API and life cycle Describes the purpose and event sequence of JSP page life cycle. 1. 2. 3. 4. 5. 6. 7.

Translation phase Jsp page compilation Load the class Create an Instance (Instantiation) Call jspInit( ) Call _jspService( ) Call jspDestroy( )

Translation Phase : 1. The process of translating t ranslating Jsp page (.jsp file) into corresponding Servlet (.java file) is called translation phase. 2. This can be done by Jsp container(engine) , In tomcat t omcat this engine is called "JASPER" 3. The generated .java file is available in the following location(Tomcat6.0\work\catalina location(Tomcat6.0\work\catalina\contextrootnam \contextrootnamejsp1\org\apache ejsp1\org\apache\jsp) \jsp) In weblogic : user-projects\domain\mydomain user-projects\domain\mydomain\myserver\.. \myserver\............... ............. JSP-API : 1. Every class which is generated for the jsp , must implementsjavax.servlet.jsp. implementsjavax.servlet.jsp.JspPage(I JspPage(I)) Or javax.servlet.jsp.HttpJspPage javax.servlet.jsp.HttpJspPage either directly or indirectly 2. Tomcat people provided a base class org.apache.jasper.runtime.HttpJspBase org.apache.jasper.runtime.HttpJspBase for implementing the above 2 interfaces. Hence any Servlet which is generated by tomcat is extending this HttpJspBase class.
















By Mr. Durga

HttpJspBase class name will will be valid from f rom vendor to vendor (server to server) javax.servlet.jsp.JspPage( javax.servlet. jsp.JspPage(I) I) : This interface defines the following 2 methods 1. jspInit( ) 2. jspDestroy( ) jspInit( ) : public void jspInit( ) 1. This method will be executed only once to perform initialization activities , whenever we are sending first request to the JSP 2. Web-container always calls init(ServletConfig sc) presents in HttpJspBase class , which intern calls jspInit( ) 3. If we have any initialization activities we have to override jspInit( ) in our Jsp public class HttpJspBase --- { public final void init(ServletConfig config)throws ServletException ServletException { jspInit(); } } Various possibilities possibilities of overriding jspInit( ) in our JSP
















By Mr. Durga

//our own initialization } %> The server time is : <%=new java.util.Date()%> This method will be executed at the time of first request. We can't override init(ServletConfig sc) in jsp, because it it is declared declared as final in HttpJspBase class jspDestroy( ) public void jspDestroy() 1. This method will be executed only once to perform cleanup activities just before taking jsp from out of service. public void jspDestroy( ) 2. Web-container always calls destroy( ) available in HttpJspBase which intern calls jspDestroy()

class HttpJspBase { final destroy() { jspDestroy() ; } jspDestroy() {} } If we have any cleanUp activity we should override jspDestroy( ) & we can't o verride destroy( ) , because it is declared as final in HttpJspBase class. javax.servlet.jsp.HttpJspPage( javax.servlet. jsp.HttpJspPage(I) I) : 1. It is the child interface of JspPage(I),it contains only one method i.e., _jspservice( _jspservice( ) public void _jspService(HttpServletReques _jspService(HttpServletRequestt req , HttpServletResponse res) throws ServletException, IOException 2. This method will be executed for every request. 3. Web-container always calls service(HSR,HSR) of HttpJspBase class, class, which intern calls our _jspService(HSR,HSR) _jspService(HSR,HSR) 4. _jspService( ) should be generated automatically automatically by the the web-container at at translation phase and we can't override. 5. If we write _jspService( ) in the jsp explicitly then generated Servlet class contains two _jspService( ) , which causes compile time error.(with in the same class 2 methods methods with same same signature is not possible)


















By Mr. Durga

public final void init(ServletConfig config) throws ServletException ServletException { super.init(config); jspInit(); } public final void destroy() { jspDestroy(); jspDestroy(); } public void jspInit() {} public void jspDestroy() {} public final void service(HttpServletRequest req, HttpServletResponse res) throws ServletException,IOException ServletException,IOException { _ jspService(req, jspService(req, res); } public abstract void _jspService(HttpServletRequest _jspService(HttpServletRequest req, HttpServletResponse res) throws ServletException,IOException; public String getServletInfo() { return "Jsp information"; } }

What is the signature of Underscore Underscore in _jspService( ) ? We can't write this method explicitly and it should be generated automatically by the web-container. In our Jsp , which of the following methods we can write explicitly ? 1. 2. 3. 4. 5. 6.

init(ServletConfig sc) //X-- final so wrong jspInit( ) //right destroy() //wrong jspDestroy() //right service() //wrong _jspService() //wrong


















By Mr. Durga

2. If any problem occurs at the time of translation Or at the time of compilation we will get 500 status code response. 3. JspPage will be participated into translated in the following cases : 1. At the time of 1st request 2. When compared with earlier request , Source code of the jsp got modified . For this web-container will use ARAXIS tool to compare time stamps of .jsp and .class file date.jsp (date_jsp.java) <%! static { System.out.println("class System.out.println("class is loading"); } public date_jsp() { System.out.println("The System.out.println("The generated java class object is created"); } public void jspInit() { System.out.println("jspInit() System.out.println("jspInit() will be called"); } public void jspDestroy() { System.out.println("jspDestroy() System.out.println("jspDestroy() will b e called"); } %> The server time is : <%= new java.util.Date() java.util.Date() %> PreCompilation PreCompila tion of JSP : 1. We can initiate translation phase explicitly by using pre-compilation process( upto jspInit() ). 2. Jsp specification provides a special request parameter "jsp-precompile" to perform precompilation . We can use this parameter to hit the jsp for compilation without processing any request. 3. We can invoke pre-compilation pre-compilation as follows : http://localhost:8080/jsp1/da http://localhost:8080/jsp1/date.jsp?jsp_prec te.jsp?jsp_precompile=true ompile=true [ [ upto jspInit( j spInit( ) will be executed ] 4. The main advantages of pre-compilation are


















Objective : Identify , describe describe and write Jsp code for the following elements 1. Template Text

By Mr. Durga


















By Mr. Durga

public final class date_jsp extends HttpJspBase { public void _jspService(-,-)-- { out.write("The server time is:"); out.print(new java.util.Date()); java.util.Date()); } } The Template text will become argument to write() where as Expression value will become argument to print() , what is the reason. write( ) can take only character data as argument and template text is always character data. Hence template text will become argument to out.write( ). Expression value can be any data type , hence we can't use write( ) , compulsory we should go for print( ) which can take any type of argument. JSP Directives : A directive is a translation time instruction to the jsp engine by using directives. we can specify whether current jsp error page or not, not , whether the current jsp participating into session traffic or not. Syntax: <%@directive-name <%@directive-name attribute-name=attribute-value1,.... attribute-name=attribute-value1,.... %> There are 3 types of directives 1) Page directive : ● It can be used to specify overall properties of jsp page to the jsp engine ● <%@ page isErrorPage="true" %> ● This directive specifies that the current jsp is error page and hence jsp engine makes exception implicit object available to the jsp page. 2) Include directive : We can use this directive to include the t he content of some other page into current page at


















By Mr. Durga

JSP Actions : Actions are commands to Jsp engine , They direct jsp engine to perform certain task at execution time(Runtime). The following are various standard actions available in jsp 1) 2) 3) 4) 5) 6) 7) 8) 9)

< jsp:useBean > < jsp:getProperty > < jsp:setProperty > < jsp:include > < jsp:forward > < jsp:param > < jsp:plugIn > < jsp:fallBack > < jsp:params >

Ex: It includes the response of header.jsp in the current page response at runtime.(Dynamic include). Scripting Elements : There are 2 types of Scripting elements 1. Traditional Scripting elements 1. Expressions 2. Scriptlets 3. Declarative 4. Comments 2. Modern Scripting elements




















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By Mr. Durga

Inside expressions we can take method calls also but void return type method calls are not allowed. <%= math.random( math.random( ) %> //valid <%=(new AL( ) ).clear( ).clear( ) %> // invalid because void return type methods methods are not allowed Inside expression space is not allowed between % and = , ot herwise it will be treated as scriptlet which causes compile time error . <% =20 %> _jspService() { =20 ; // invalid invalid statememt }

Declarations are not allowed in expressions i.e., declaring variables,methods variables,methods etc., <%= String s="durga" s="durga" %> OR out.println(String s="durga"); s="durga"); //invalid Which of the following Expressions are valid ? 1. <%= 2*3 %> //valid 2. <%= 2<3 %> //valid 3. <%= math.sqrt(4) %> //valid


















By Mr. Durga

This Jsp is invalid and generates '1' as response every time, here count variable is local. <%! int count = 0 ; %> <% count++; out.println(count); %> <% /* any java code; it will be placed in generated servlet _jspService() */ %> <% System.out.println("hello"); // valid %> <%


















It is the local variable present inside _jspService()

By Mr. Durga

It is the instance variable present in generated Servlet , out side of _jspService()

Note : It's never recommended to write scriptlets in t he jsp. Declarations : (<%! %>) 1. We can use declaration tag to declare instance variables , instance methods, static variables , static methods , instance and static blocks , constructors, inner classes etc., <%! // any java declarations %> 2. These declarations will be placed directly in the generated Servlet but outside of _jspService( ) <%! int x = 10 ; static int y = 20; public void m1() { System.out.println("allowed"); } %>


















By Mr. Durga

1. Jsp comments <%-- Jsp comments --%> 2. Html comments 3. Java comments 1. Single line 2. Multi line Jsp Comments : <%-- Jsp comment --%> 1. Also known as hidden comments , because these are not visible in i n the remaining phases of jsp execution (like .java, .class, and response). 2. This comments are highly recommended recommended to use in the Jsp Html Comments : 1. Also known as template text comments 2. These are visible to the end-user as the part of generated response source code, hence these


















Java

// visible visible /* ..... */

By Mr. Durga

not visible

Translator can perform only one level translation , hence among declaration,scriptlet,expressions declaration,scriptlet,expressions and comments we can't take another i.e., nesting of scripting elements are not allowed otherwise we will get compiletime error. <%! <%-- Jsp comments --%> // invalid int a=10; %> <% <% out.println("hello") o ut.println("hello");; %>//invalid %>// invalid %> <% out.print(<%= 10+2+3 %>);//invalid %> <%-<% out.print("It is valid because i'm in comments"); %> --%> Comparision of Scripting Elements :




















page : This page directive specifies overall properties of Jsp page to Jsp engine, we can use this directive no.of times and any where. Syntax: <%@ page attribute-name=attribute-value attribute-name=attribute-value %> The following are list of possible attributes of the page directive (13): (13): 1. 2. 3. 4. 5.

import session isELIgnored isThreadSafe contentType

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Q : Which of the following are valid ? <%@ page import="java.util.*" import="java.util.*" import="java.io.*" import="java.io.*" %> //valid <%@ page session="true" session="true" session="false" %> //invalid <%@ page isELIgnored="true" isELIgnored="true" isELIgnored="false" %> <%@ page session="true" session="true" %> //valid <%@ page language=java %> //invalid The following packages are not required to import bydefault available in every Jsp.

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ADV. JAVA With SCWCD/ OCWCD Material 

By Mr. Durga

If we are taking other than true or false , then we will ger translation time error.

<%@ page session="ashok" %> //invalid Which of the folowing make session object is available to Jsp ? <%@ page session="true" %> //valid <%@ page session="false" %> //invalid // invalid <%@ page session=true %> //invalid <%@ page contentType="text/html" %> //valid

isELIgnored Expression Language introduced in jsp 1.2v


















By Mr. Durga

isThreadSafe="false" The current Jsp is not Thread Safe hence to provide thread safety generated servlet should implement SingleThreadModel SingleThreadModel interface, In this case the jsp can process only one request at a time. t ime. The default value for isThreadSafe isThreadSafe value is "true". Which of the following to provide Thread Safety to the Jsp ?    

<%@ page isThreadSafe="true" %> // not provide <%@ page isThreadSafe="false" isThreadSafe="false" %> // provide <%@ page isThreadSafe="true" isThreadSafe="false" isThreadSafe="false" %> // not provide No special arrangement is required because jsp is Thread Safe by def ault. ault.

contentType


















By Mr. Durga

info Defines a string that gets put in to the translated page just show that we can get it using the generated servlet inherited getServletInfo()) . isErrorPage It is defined in exception implicit object. errorPage It is defined in exception implicit object.




















By Mr. Durga

No, by default Sevlet is not ThreadSafe and we van provide Thread Safety by implementing implementing SingleThreadModel SingleThreadModel interface. Is Jsp is ThreadSafe by default ?


















<%@ include file="header.jsp" %> welcome to learners , it is enough

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main.jsp <%@ include file="header.jsp" %> The result of x is : <%= x*100 %> //1000

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ADV. JAVA With SCWCD/ OCWCD Material 

By Mr. Durga

All the methods present in HttpServletRequest and HttpServletResponse can be applicable on this request and response implicit objects.

index.html


















web.xml MyJsp

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1. the Java Server Pages (JSP) Technology Model

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