apr 3, 2013 jsp java server pages. 2 a “hello world” servlet (from the tomcat installation...
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Apr 3, 2013
JSP
Java Server Pages
2
A “Hello World” servlet(from the Tomcat installation documentation)
public class HelloServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); String docType = "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " + "Transitional//EN\">\n"; out.println(docType + "<HTML>\n" + "<HEAD><TITLE>Hello</TITLE></HEAD>\n" + "<BODY BGCOLOR=\"#FDF5E6\">\n" + "<H1>Hello World</H1>\n" + "</BODY></HTML>"); }} This is mostly Java with a little HTML mixed in
HelloWorld import java.io.*;import javax.servlet.*;import javax.servlet.http.*;
public class HelloWorld extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("<html>"); out.println("<body>"); out.println("<head>"); out.println("<title>Hello CS764!</title>"); out.println("</head>"); out.println("<body>"); out.println("<h1>Hello CS764!</h1>"); out.println("</body>"); out.println("</html>");
out.close(); }}
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Servlets
The purpose of a servlet is to create a Web page in response to a client request
Servlets are written in Java, with a little HTML mixed in The HTML is enclosed in out.println( ) statements
JSP (Java Server Pages) is an alternate way of creating servlets JSP is written as ordinary HTML, with a little Java mixed in The Java is enclosed in special tags, such as <% ... %> The HTML is known as the template text
JSP files must have the extension .jsp JSP is translated into a Java servlet, which is then compiled Servlets are run in the usual way The browser or other client sees only the resultant HTML, as usual
Tomcat knows how to handle servlets and JSP pages
JSP Introduction
• JavaServer Pages (JSP) is a server-side programming technology that enables the creation of dynamic, platform-independent method for building Web-based applications.
• JSP have access to the entire family of Java APIs, including the JDBC API to access enterprise databases.
• JavaServer Pages (JSP) is a technology for developing web pages that support dynamic content which helps developers insert java code in HTML pages by making use of special JSP tags, most of which start with <% and end with %>.
Why Use JSP?• Performance is significantly better because JSP allows
embedding Dynamic Elements in HTML Pages itself instead of having a separate CGI files.
• JSP are always compiled before it's processed by the server (unlike CGI/Perl which requires the server to load an interpreter and the target script each time the page is requested.)
• JavaServer Pages are built on top of the Java Servlets API, so like Servlets, JSP also has access to all the powerful Enterprise Java APIs, including JDBC, JNDI, EJB, JAXP etc.
• JSP pages can be used in combination with servlets that handle the business logic
JSP - Architecture
JSP Processing
JSP life cycle
JSP life cycle JSP Initialization: When a container loads a JSP it invokes
the jspInit() method before servicing any requests.
public void jspInit(){ // Initialization code... }
JSP Execution: This phase of the JSP life cycle represents all interactions with requests until the JSP is destroyed.
void _jspService(HttpServletRequest request,
HttpServletResponse response) { // Service handling code... }
JSP Cleanup: The destruction phase of the JSP life cycle represents when a JSP is being removed from use by a container.
public void jspDestroy() { // Your cleanup code goes here. }
The Scriptlet
A scriptlet can contain any number of JAVA language statements, variable or method declarations, or expressions that are valid in the page scripting language.
Syntax of Scriptlet:
<% code fragment %>
<jsp:scriptlet> code fragment </jsp:scriptlet>
Example:
<html> <head><title>Hello World</title></head>
<body> Hello World!<br/>
<% out.println(“Welcome to JSP”) %> </body> </html>
JSP Declarations:
A declaration declares one or more variables or methods that you can use in Java code later in the JSP file.
You must declare the variable or method before you use it in the JSP file.
Syntax of JSP Declarations:
<%! declaration; [ declaration; ]+ ... %>
<jsp:declaration> code fragment </jsp:declaration>
<%! int i = 0; %>
<%! int a, b, c; %>
<%! Circle a = new Circle(2.0); %>
JSP Expression:
A JSP expression element contains a scripting language expression that is evaluated, converted to a String, and inserted where the expression appears in the JSP file.
<%= expression %>
<jsp:expression> expression </jsp:expression>
Example:
<html> <head><title>A Comment Test</title></head> <body> <p> Today's date: <%= (new java.util.Date()).toLocaleString()%> </p> </body> </html> Result:
Today's date: 11-Sep-2010 21:24:25
JSP Comments:
JSP comment marks text or statements that the JSP container should ignore.
Syntax:
<%-- This is JSP comment --%>
Example:
<html> <head><title>A Comment Test</title></head> <body> <h2>A Test of Comments</h2> <%-- This comment will not be visible in the page source --%> </body> </html>
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JSP scripting elements
<%= expression %> The expression is evaluated and the result is inserted into the HTML page
<% code %> The code is inserted into the servlet's service method This construction is called a scriptlet
<%! declarations %> The declarations are inserted into the servlet class, not into a method
JSP Tags Examples
Comments <%-- …...text…... --%>
Declaration <%! int i; %>
<%! int numOfStudents(arg1,..) {} %>
Expression <%= 1+1 %>
Scriptlets <% … java code … %>
include file <%@ include file=“*.jsp” %>
…...
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Example JSP
<HTML><BODY>Hello! The time is now <%= new java.util.Date() %></BODY></HTML>
Notes: The <%= ... %> tag is used, because we are computing a
value and inserting it into the HTML The fully qualified name (java.util.Date) is used, instead
of the short name (Date), because we haven’t yet talked about how to do import declarations
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Variables
You can declare your own variables, as usual JSP provides several predefined variables
request : The HttpServletRequest parameter response : The HttpServletResponse parameter session : The HttpSession associated with the request, or
null if there is none out : A JspWriter (like a PrintWriter) used to send output
to the client Example:
Your hostname: <%= request.getRemoteHost() %>
A First JSP
<html>
<head></head>
<body>
<p>Enter two numbers and click the
‘calculate’ button.</p>
<form action=“calculator.jsp” method=“get”>
<input type=text name=value1><br>
<input type=text name=value2 ><br>
<input type=submit name=calculate value=calculate>
</form>
</body>
</html>
Calculator.html
<html><head><title>A simple calculator: results</title></head><body><%-- A simpler example 1+1=2 --%>1+1 = <%= 1+1 %><%-- A simple calculator --%><h2>The sum of your two numbers is:</h2><%= Integer.parseInt(request.getParameter("value1")) + Integer.parseInt(request.getParameter("value2")) %></body></html>
Calculator.jsp
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Scriptlets
Scriptlets are enclosed in <% ... %> tags Scriptlets do not produce a value that is inserted directly into the
HTML (as is done with <%= ... %>) Scriptlets are Java code that may write into the HTML Example:
<% String queryData = request.getQueryString(); out.println("Attached GET data: " + queryData); %>
Scriptlets are inserted into the servlet exactly as written, and are not compiled until the entire servlet is compiled
Example:<% if (Math.random() < 0.5) { %> Have a <B>nice</B> day!<% } else { %> Have a <B>lousy</B> day!<% } %>
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Declarations
Use <%! ... %> for declarations to be added to your servlet class, not to any particular method Caution: Servlets are multithreaded, so nonlocal variables
must be handled with extreme care If declared with <% ... %>, variables are local and OK Data can also safely be put in the request or session
objects Example:
<%! private int accessCount = 0; %> Accesses to page since server reboot: <%= ++accessCount %>
You can use <%! ... %> to declare methods as easily as to declare variables
Exception handling in JSP
• These are nothing but the abnormal conditions which interrupts the normal flow of execution.
• Mostly they occur because of the wrong data entered by user.
• It is must to handle exceptions in order to give meaningful message to the user
• So that user would be able to understand the issue and take appropriate action.
Exception handling using exception implicit object
Index.jsp
<%@ page errorPage="errorpage.jsp" %>
<html> <head>
<title>JSP exception handling example</title> </head> <body> <% //Declared and initialized two integers int num1 = 122;
int num2 = 0;
//It should throw Arithmetic Exception
int div = num1/num2; %>
</body> </html>
Errorpage.jsp
<%@ page isErrorPage="true" %> <html>
<head> <title>Display the Exception Message here</title> </head>
<body> <h2>errorpage.jsp</h2>
<i>An exception has occurred in the index.jsp Page. Please fix the errors. Below is the error message:</i> <b>
<%= exception %></b>
</body>
</html>
Exception handling using try catch blocks within scriptlets
Error.jsp
<html> <head> <title>Exception handling using try catch blocks</title>
</head> <body> <% try
{ //I have defined an array of length 5 int arr[]={1,2,3,4,5};
int num=arr[6];
out.println("7th element of arr"+num); }
catch (Exception exp){ out.println("There is something wrong: " + exp); } %>
</body> </html>
JSP Directives
• JSP directives provide directions and instructions to the container, telling it how to handle certain aspects of JSP processing.
• A JSP directive affects the overall structure of the servlet class. It usually has the following form:
• <%@ directive attribute="value" %>
Directive Types
DirectiveDescription
<%@ page ... %>Defines page-dependent attributes, such as scripting language, error page, and buffering requirements.
<%@ include ... %>Includes a file during the translation phase.
<%@ taglib ... %>Declares a tag library, containing custom actions, used in the page
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Directives
Directives affect the servlet class itself A directive has the form:
<%@ directive attribute="value" %>or <%@ directive attribute1="value1" attribute2="value2" ... attributeN="valueN" %>
The most useful directive is page, which lets you import packages Example: <%@ page import="java.util.*" %>
The page Directive
• The page directive is used to provide instructions to the container that pertain to the current JSP page.
• Code page directives anywhere in your JSP page.
• By convention, page directives are coded at the top of the JSP page.
Syntax of page directive:
<%@ page attribute="value" %>
<jsp:directive.page attribute="value" />
Page Directive Attribute• import
• session
• isErrorPage
• errorPage
• ContentType
• isThreadSafe
• extends
• info
• language
• autoflush
• buffer
Page Directive Example
<%@ page import="java.util.*" %>
<HTML> <BODY>
<% System.out.println( "Evaluating date now" );
Date date = new Date(); %>
Hello! The time is now <%= date %>
</BODY>
</HTML>
The taglib Directive
• The JavaServer Pages API allows you to define custom JSP tags that look like HTML or XML tags
• A tag library is a set of user-defined tags that implement custom behavior.
The taglib directive declares that your JSP page uses a set of custom tags, identifies the location of the library, and provides a means for identifying the custom tags in your JSP page.
Syntax:
<%@ taglib uri="uri" prefix="prefixOfTag" >
<jsp:directive.taglib uri="uri" prefix="prefixOfTag" />
JSP Taglib Example
The custlib tag library contains a tag called hello.
If you wanted to use the hello tag with a prefix of mytag, your tag would be<mytag:hello>
Code:
<%@ taglib uri="http://www.example.com/custlib" prefix="mytag" %> <html> <body>
<mytag:hello/> </body>
</html>
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The include directive
The include directive inserts another file into the file being parsed The included file is treated as just more JSP, hence it can
include static HTML, scripting elements, actions, and directives
Syntax: <%@ include file="URL " %> The URL is treated as relative to the JSP page If the URL begins with a slash, it is treated as relative to the
home directory of the Web server The include directive is especially useful for inserting
things like navigation bars
JSP Include Directive Example
Index.jsp
<html> <head> <title>Passing Parameters to Include directive</title>
</head> <body>
<%@ include file="file1.jsp" %>
<%! String country="India";
String state="UP";
String city="Agra"; %>
<% session.setAttribute("co", country); session.setAttribute("st", state); session.setAttribute("ci", city); %> </body> </html>
Output
File1.jsp
<%=session.getAttribute("co") %> <%=session.getAttribute("st") %> <%=session.getAttribute("ci") %>
Output:
India UP Agra
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Actions
Actions are XML-syntax tags used to control the servlet engine
<jsp:include page="URL " flush="true" /> Inserts the indicated relative URL at execution time (not at
compile time, like the include directive does) This is great for rapidly changing data
<jsp:forward page="URL" /><jsp:forward page="<%= JavaExpression %>" /> Jump to the (static) URL or the (dynamically computed) JavaExpression resulting in a URL
Directives vs Actions
• Directives are used during translation phase while actions are used during request processing phase.
• Unlike Directives Actions are re-evaluated each time the page is accessed.
JSP Forward Example 1 – without passing parameters
Index.jsp Contains
<html> <head> <title>JSP forward action tag example</title> </head> <body> <p align="center">My main JSP page</p>
<jsp:forward page="display.jsp" /> </body> </html>
display.jsp
<html> <head> <title>Display Page</title>
</head> <body> Hello this is a display.jsp Page
</body> </html>
JSP Forward Example 2 – with parameters
Index.jsp
<html> <head>
<title>JSP forward example with parameters</title> </head> <body>
<jsp:forward page="display.jsp">
<jsp:param name="name" value="Chaitanya" />
<jsp:param name="site" value="BeginnersBook.com" />
<jsp:param name="tutorialname" value="jsp forward action" />
<jsp:param name="reqcamefrom" value="index.jsp" /> </jsp:forward> </body> </html>
Display.jsp
<html> <head> <title>Display Page</title> </head> <body>
<h2>Hello this is a display.jsp Page</h2>
My name is: <%=request.getParameter("name") %><br> Website: <%=request.getParameter("site") %><br>
Topic: <%=request.getParameter("tutorialname") %><br> Forward Request came from the page: <%=request.getParameter("reqcamefrom") %>
</body>
</html>
<jsp:include> Action
• include page directive this action is also used to insert a JSP file in another file.
Syntax of <jsp:include> :
<jsp:include page="page URL" flush="Boolean Value" />
Example:
<html> <head>
<title>Demo of JSP include Action Tag</title> </head> <body> <h3>JSP page: Demo Include</h3> <jsp:include page="sample.jsp" flush="false" /> </body> </html>
<jsp:forward> Action
• <jsp:forward> is used for redirecting the request.
• When this action is encountered on a JSP page the control gets transferred to the page mentioned in this action.
Syntax of <jsp:forward> :
<jsp:forward page="URL of the another static, JSP OR Servlet page" />
Example
<html> <head>
<title>Demo of JSP Forward Action Tag</title> </head> <body> <h3>JSP page: Demo forward</h3> <jsp:forward page="second.jsp" />
</body>
</html>
<jsp:param> Action
• This action is useful for passing the parameters to Other JSP action tags such as JSP include & JSP forward tag.
• This way new JSP pages can have access to those parameters using request object itself.
• Syntax of <jsp:param>:
<jsp: param name="param_name_here" value="value_of_parameter_here" />
First.jsp<html> <head> <title>Demo of JSP Param Action
Tag</title> </head> <body> <h3>JSP page: Demo Param along with forward</h3>
<jsp:forward page="second.jsp">
<jsp:param name ="date" value="20-05-2012" /> <jsp:param name ="time" value="10:15AM" /> <jsp:param name ="data" value="ABC" /> </jsp:forward>
</body> </html>
Second File:
Date:<%= request.getParameter("date") %>
Time:<%= request.getParameter("time") %> My Data:<%= request.getParameter("data") %>
<jsp:useBean> Action
This action is useful when you want to use Beans in a JSP page, through this tag you can easily invoke a bean.
Syntax of <jsp:useBean>:
<jsp: useBean id="unique_name_to_identify_bean" class="package_name.class_name>
EmployeeTest.jsp
<html> <head> <title>JSP Page to show use of useBean action</title> </head>
<body> <h1>Demo: Action</h1>
<jsp:useBean id="student" class="javabeansample.StuBean"/>
<jsp:setProperty name="student" property="*"/>
<h1> name:<jsp:getProperty name="student" property="name"/>
<br> empno:<jsp:getProperty name="student" property="rollno"/><br> </h1>
</body> </html>
StudentBean.java
package javabeansample;
public class StuBean {
public StuBean() { }
private String name;
private int rollno;
public void setName(String name) {
this.name=name; }
public String getName() { return name; }
public void setRollno(int rollno) {
this.rollno=rollno; }
public int getRollno() { return rollno; } }
<jsp:plugin> Action
• This tag is used when there is a need of a plugin to run a Bean class or an Applet.
JSP - Database Access
• Understanding on how JDBC application works.
• Before starting with database access through a JSP, make sure that you have proper JDBC environment setup along with a database.
Steps to creatd JDBC
Tables creationLoad the driver managerConnection establishmentStatement creationsProcess the result setExecute the statementClose the connection and statementStop the program
Creating a Database Table
String table ;
table= "CREATE TABLE Employee11(Emp_code integer, Emp_name varchar(10))";
st.executeUpdate(table);
Connection Establishment
Is an interface in java.sql package Specifies connection with specific database like: MySQL, Ms-Access, Oracle etc and java files.The SQL statements are executed within the context of the Connection interface.
Class.forName(String driver):
Connection Establishment
Syntax
Connection conn; Class.forname(“com.mysql.jdbc.Driver”).newInstance();
DriverManagerIt is a class of java.sql package that controls a set of JDBC drivers. Each driver has to be register with this class.getConnection(String url, String userName, String password): url: - Database url where stored or created your database userName: - User name of MySQL password: -Password of MySQL
Load the JDBC Driver into the database
Syntax
String userName = "root";
String password = "mysql";
String url = "jdbc:mysql://localhost/programs";
conn = DriverManager.getConnection(url,userName,password);
Create the statements and update the values in the table structure
Statement st=conn.createStatement(); st.execute("create table stud10(rollno
int,name text,m1 int,m2 int)"); st.executeUpdate("insert into stud10
values(2,'rani',50,90)");
Process the Query result set
rs=st.executeQuery("select * from stud10");
while(rs.next())
{
System.out.println(rs.getInt(1));
System.out.println(rs.getString(2));
System.out.println(rs.getInt(3));
System.out.println(rs.getInt(4));
}
Close the connection
con.close():This method is used for disconnecting the connection. It frees all the resources occupied by the database.
Close the statement and connection
st.close(); conn.close();
Final Steps
To import Syntax
export CLASSPATH=$CLASSPATH:/usr/share/java/mysql-connector-java-5.1.6.jar
To Compile
Javac Filename.java To Run
java Filename
Error Report
printStackTrace():The method is used to show error messages. If the connection is not established then exception is thrown and print the message.
Create Tablemysql> use TEST;
mysql> create table Employees ( id int not null, age int not null, first varchar (255), last varchar (255) );
Query OK, 0 rows affected (0.08 sec)
mysql>
Create Data Records
mysql> INSERT INTO Employees VALUES (100, 18, 'Zara', 'Ali');
Query OK, 1 row affected (0.05 sec)
mysql> INSERT INTO Employees VALUES (101, 25, 'Mahnaz', 'Fatma');
Query OK, 1 row affected (0.00 sec)
Connecting JSP To Mysql Database
Login.html
<body><form action="login.jsp" method="post">
User name :<input type="text" name="usr" />password :<input type="password" name="pwd" /><input type="submit" /></form></body>
Reg.html
<form action="reg.jsp" method="post“>Email :<input type="text" name="email" />First name :<input type="text" name="fname" />Last name :<input type="text" name="lname" />User name :<input type="text" name="userid" />password :<input type="password" name="pwd" /><input type="submit" /></form>
Login.jsp<%@ page import ="java.sql.*" %>
<%@ page import ="javax.sql.*" %><% String userid=request.getParameter("user"); session.putValue("userid",userid); String pwd=request.getParameter("pwd"); Class.forName("com.mysql.jdbc.Driver"); java.sql.Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","root"); Statement st= con.createStatement(); ResultSet rs=st.executeQuery("select * from users where user_id='"+userid+"'"); if(rs.next()) { if(rs.getString(2).equals(pwd)) { out.println("welcome"+userid); } else { out.println("Invalid password try again"); } } else %>
Reg.jsp<%@ page import ="java.sql.*" %>
<%@ page import ="javax.sql.*" %><%String user=request.getParameter("userid"); session.putValue("userid",user); String pwd=request.getParameter("pwd"); String fname=request.getParameter("fname"); String lname=request.getParameter("lname"); String email=request.getParameter("email"); Class.forName("com.mysql.jdbc.Driver"); java.sql.Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","root"); Statement st= con.createStatement(); ResultSet rs; int i=st.executeUpdate("insert into users values ('"+user+"','"+pwd+"','"+fname+"','"+lname+"','"+email+"')");
%>
Index.html
<HTML> <HEAD>
<TITLE>Database Lookup</TITLE> </HEAD> <BODY> <H1>Database Lookup</H1>
<FORM ACTION="basic.jsp" METHOD="POST"> Please enter the ID of the publisher you want to find: <BR>
<INPUT TYPE="TEXT" NAME="id"> <BR>
<INPUT TYPE="SUBMIT" value="Submit"> </FORM> </BODY>
<HTML>
Basic.jsp
<%@ page import="java.sql.*" %>
<% Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); %><HTML> <HEAD> <TITLE>Fetching Data From a Database</TITLE> </HEAD>
<BODY> <H1>Fetching Data From a Database</H1>
<% Connection connection = DriverManager.getConnection( "jdbc:odbc:data", "YourName", "password");
Statement statement = connection.createStatement(); String id = request.getParameter("id");
ResultSet resultset = statement.executeQuery("select * from Publishers where pub_id = '" + id + "'") ;
if(!resultset.next()) { out.println("Sorry, could not find that publisher. "); } else { %>
Basic.jsp
<TABLE BORDER="1"> <TR> <TH>ID</TH> <TH>Name</TH> <TH>City</TH> <TH>State</TH> <TH>Country</TH> </TR> <TR> <TD>
<%= resultset.getString(1) %> </TD> <TD>
<%= resultset.getString(2) %> </TD> <TD>
<%= resultset.getString(3) %> </TD> <TD>
<%= resultset.getString(4) %> </TD> <TD>
<%= resultset.getString(5) %> </TD> </TR>
</TABLE> <BR> <% } %>
</BODY> </HTML>
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JSP in XML
JSP can be embedded in XML as well as in HTML Due to XML’s syntax rules, the tags must be different
(but they do the same things) HTML: <%= expression %>
XML: <jsp:expression>expression</jsp:expression>
HTML: <% code %>XML: <jsp:scriptlet>code</jsp:scriptlet>
HTML: <%! declarations %>XML: <jsp:declaration>declarations</jsp:declaration>
HTML: <%@ include file=URL %>XML: <jsp:directive.include file="URL"/>
Sending XML from a JSP
<%@ page contentType="text/xml" %>
File Content:
<%@ page contentType="text/xml" %> <books>
<book> <name>Padam History</name> <author>ZARA</author>
<price>100</price> </book>
</books>
Processing XML in JSP
Books.xml
<books> <book> <name>Padam History</name> <author>ZARA</author> <price>100</price> </book> <book> <name>Great Mistry</name> <author>NUHA</author> <price>2000</price> </book>
</books>
Formatting XML with JSP
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl= "http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:output method="html" indent="yes"/>
<xsl:template match="/">
<html> <body> <xsl:apply-templates/> </body> </html> </xsl:template> <xsl:template match="books">
<table border="1" width="100%">
<xsl:for-each select="book"> <tr>
<td> <i><xsl:value-of select="name"/></i> </td>
<td> <xsl:value-of select="author"/> </td>
<td> <xsl:value-of select="price"/> </td> </tr>
</xsl:for-each> </table> </xsl:template> </xsl:stylesheet>
JSP Session tracking
• Server may be responding to several clients at a time
• So session tracking is a way by which a server can identify the client.
Session Tracking Techniques
a) Cookies
b) Hidden Fields
c) URL Rewriting
d) Session Object
Cookie
• Cookie is a key value pair of information, sent by the server to the browser
• The browser sends back this identifier to the server with every request there on.
Types of cookies:
· Session cookies - are temporary cookies and are deleted as soon as user closes the browser. The next time user visits the same website, server will treat it as a new client as cookies are already deleted.
· Persistent cookies - remains on hard drive until we delete them or they expire.
Cookie Creation
Cookie cookie = new Cookie(“sessionID”, “some unique value”);
response.addCookie(cookie);
Hidden Field• Hidden fields are similar to other input fields with the only
difference is that these fields are not displayed on the page
• But its value is sent as other input fields. For example
<input type=”hidden” name=”sessionId” value=”unique value”/>
• Is a hidden form field which will not displayed to the user
• But its value will be send to the server and can be retrieved using request.getParameter(“sessionId”) .
URL Rewriting
URL Rewriting is the approach in which a session (unique) identifier gets appended with each request URL so server can identify the user session.
For example if we apply URL rewriting on http://localhost:8080/jsp-tutorial/home.jsp , it will become something like
?jSessionId=XYZ where
jSessionId=XYZ is the attached session identifier and value XYZ will be used by server to identify the user session.
Session Object
• Session object is representation of a user session.
• User Session starts when a user opens a browser and sends the first request to server.
• Session object is available in all the request (in entire user session)
• So attributes stored in Http session in will be available in any servlet or in a jsp
Session Object
How to get a Session Object – By calling getSession() API on HttpServletRequest object
a) HttpSession session = request.getSession()
b) HttpSession session = request.getSession(Boolean)
Destroy or Invalidate Session –
To invalidate the session use -
session.invalidate();
Important methods
· Object getAttribute(String attributeName) – this method is used to get the attribute stored in a session scope by attribute name. Remember the return type is Object.
· void setAttribute(String attributeName, Object value)- this method is used to store an attribute in session scope. This method takes two arguments- one is attribute name and another is value.
· void removeAttribute(String attributeName)- this method is used to remove the attribute from session.
· public boolean isNew()- This method returns true if server does not found any state of the client.
JSP Session Tracking Examples<html> <head> <title> Display Session Information </title> </head>
%@page import="java.util.Date" % <body> <%
long creationTime = session.getCreationTime();
String sessionId = session.getId();
long lastAccessedTime = session.getLastAccessedTime();
Date createDate= new Date(creationTime);
Date lastAccessedDate= new Date(lastAccessedTime);
StringBuffer buffer = new StringBuffer();
if(session.isNew()) { buffer.append("<h3>Welcome </h3>"); }
else { buffer.append("<h3>Welcome Back!! </h3>"); }
buffer.append("<STRONG> Session ID : </STRONG>" + sessionId); buffer.append(" <BR/> ");
buffer.append("<STRONG> Session Creation Time </STRONG>: " + createDate);
buffer.append(" <BR/> "); buffer.append("<STRONG> Last Accessed Time : </STRONG>" + lastAccessedDate);
buffer.append(" <BR/> ");
%>
<%= buffer.toString() %> </body> </html>
Output
88
The End