1 Java Server Pages (JSP) - Sharad Ballepu. 2 Servlets & JSPs Agenda Introduction JSP Elements...
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Java Server Pages (JSP) - Sharad Ballepu
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Servlets & JSPsAgenda
• Introduction • JSP Elements• Implicit Objects• Tag Libraries• JSP Actions• Error Handling• Demo
Java Server Pages (JSP)
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Introduction – What is JSP
• JSP Stands for Java Server Pages
• Presents dynamic content to users
• Handles the presentation logic in an MVC architecture
Co
ntain
er
servlet
JSP
request
response
HelperObjects
(business logic)
(presentation logic)
Bu
siness
Tier
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Introduction – JSP v/s Servlet
Servlets JSP
Handles dynamic data
Handles business logic Handles presentation logic
Lifecylce methods init() : can be overridden service() : can be overridden destroy() : can be overridden
Lifecylce methods jspInit() : can be overridden _jspService() : cannot be overridden jspDestroy() : can be overridden
Html within javaout.println(“<htrml><body>”);out.println(“Time is” + new Date());out.println(“</body></html>”);
Java within html<html><body>Time is <%=new Date()%></body></html>
Runs within a Web Container
How is JSP different / similar to Servlet?
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Introduction – JSP is a Servlet
• In the end, a JSP is just a Servlet
0010 00011100 10010001 0011
Import javax.servlet.
HttpServlet.*JSP Servlet
MyJsp.jsp MyJsp_jsp.java MyJsp_jsp.class MyJsp_jsp Servlet
writes
Is translated to Compiles to Is loaded andInitialized as
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Introduction – Comments
• JSP Comments <%-- {CODE HERE} --%> Does not show the comments on the page Does not show the comments in page source Can only be used outside JSP Elements
• HTML Comments <!– {CODE HERE} --> Does not show the comments on the page Shows the comments in page source Can only be used outside JSP Elements
• Single line Comments // {CODE HERE} When put outside JSP Elements, shows comments on the page & source When put inside Scriptlets/Declarations, does not show on page & source Can be used inside scriptlets/declarations and outside JSP Elements
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JSP Elements – Intro
JSP Declarations :: Code that goes outside the service method
JSP Scriptlets :: Code that goes within the service method
JSP Expressions :: Code inside expressions is evaluated
JSP Directives :: Commands given to the JSP engine
• Need to write some Java in your HTML?
• Want to make your HTML more dynamic?
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JSP Elements - Declarations
• What are declarations?– Whatever goes inside the “<%!{JAVA_HERE}%>” tags is called a
declaration– Everything you write in a declarations goes outside the service method– Treat them as instance methods and instance variables
• What do you declare in declarations?– You can declare methods and variables in declarations
• Why do you need declarations?– You have any variable that needs to be shared across different
requests.– You have repeated common code in you jsp, declare it in a method.
• Example<%! int instanceVar = 10; %>
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JSP Elements - Declarations
Request 2
Request 3
Request 1
Service1 Service2 Service3
Declarations
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JSP Elements - Scriptlets
• What are declarations?– Whatever goes inside the “<%{JAVA_HERE}%>” tags is called
a scriptlet– Everything you write in a scriptlets goes in the service method– Treat variables in scriptlets as method/local variables
• What do you put in scriptlets?– Business logic in JSPs are put in scriptlets. Set of java
statements
• Why do you need scriptlets?– Need to perform some small business logic (if logic is complex,
do in java)– Need to perform some basic validations
• Example<% int localVar = 10; %>
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JSP Elements - Expressions
• What are expressions?– Whatever goes inside the “<%={JAVA_HERE}%>” tags is called
an expression– Code inside expressions is evaluated, and output is displayed– Whatever is put inside expressions should evaluate to a value
• What do you put in scriptlets?– Variables or methods that return some values
• Why do you need scriptlets?– Need to print some text onto the page
• Example<%= localVar %>
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JSP Elements - Example
<html><head><title>JSP Elements Example</title> </head> <body> <%! int userCnt = 0; %>
<% String name = "Sharad"; userCnt++; %> <table> <tr><td> Welcome <%=name%>. You are user number <%=userCnt%> </td></tr> </table> </body></html>
Expressions
Declarations
Scriptlets
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JSP Elements - Directives
• What are directives?– Whatever goes inside the “<%@{DIRECTIVES}%>” tags is
called a directive– Directives gives pre-processing commands to the JSP Engine.– Everything in directives are processed before JSP is translated
to Servlet
• What do you put in directives?– Processing commands to the JSP Engine.
• Why do you need directives?– To incorporate certain additional features into the JSP– Modifying the Servlet behaviour generated from the JSP– Include other html/jsp files in the JSP.– Provide tag libraries
Example<%@ page import=“java.util.ArrayList” %>
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Directives – page directive
• Any number of the pre-defined attributes can be added to the page directive
<%@ page import = “{IMPORTED_CLASSES}” contentType = “{CONTENT_TYPE}” isThreadSafe = “{true/false} session = “{true/false}” buffer = “{BUFFER_SIZE}” autoflush = “{true/false}” extends = “{EXTENDS_FROM_PAGE}” info = “{PAGE_INFO”} errorPage = “{ERROR_PAGE_NAME}” isErrorPage = “{true/false}” language = “{LANGUAGE}”
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Directives – include directive
• Including other page content into your JSP
<%@ include file = {PAGE_URL_TO_INCLUDE} %>• Includes files at translation time
• If included file is modified, the main jsp needs to be recompiled
Main page
<%@ include file =“header.jsp"/>
<%@ include file =“footer.jsp"/><table><tr> <td>Contact Details</td><tr></table>
Hello <%=userName%>
header.jsp
footer.jspmain.jsp
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Directives – taglib directive
• Providing output based on common custom logic
<%@ taglib uri=“{TLD_FILE}" prefix=“{PREFIX}" %>
• Components involved in tag libraries
Tag handler class Common custom logic and HTML generation
Descriptor configuration file Directive’s properties mapping information
taglib directive Used in JSPs to use the tag handler functionality
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taglib directive – high-level overview
<%@ taglib uri=“sharmanjTags” prefix=“sharmanj” %>…..< sharmanj:txtBox length=“10“ name=“userName”/>….. test.jsp
<web-app> <taglib> <taglib-uri>sharmanjTags</taglib-uri> <taglib-location> sharmanj-taglib.tld </taglib-location> </taglib></web-app>
web.xml
<tag> <name>txtBox</name> <tagclass>TxtBoxTag</tagclass> <bodycontent>EMPTY</bodycontent> <attribute> <name>name</name> <required>true</required> …. </attribute>…</tag>
public class TxtBoxTag extends TagSupport { public int doStartTag() { …. }}
TxtBoxTag.java
sharmanj-taglib.tld
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Implicit Objects - Introduction
• Set of predefined objects readily available for use.
– out: JspWriter
– request: HttpRequest
– response: HttpResponse
– session: HttpSession
– config: ServletConfig
– application: ServletContex
– page: JSP page
– pageContext: Special object
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Implicit Objects - Example
<html> <head> <title>JSP Implicit objects Example</title> </head> <body> <% if (“YES”.equals(request.getAttribute(“SCOPE”))) { out.println(“REQUEST”); } else { if (“YES”.equals(session.getAttribute(“SCOPE”))) { out.println(“SESSION”);
} else { out.println(“NONE”);
} } %> </body></html>
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Implicit Objects – out
• An instance of JspWriter
• Writes statements to the page
• The java way to display text on the webpage
• Displaying dynamic data
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Implicit Objects – request
• Instance of HttpServletRequest
• Use the attributes stored in request object for display /basic validations in JSP
Servlet JSP
Helper Object
(a = 10)
Uses helper object
Forwards request to JSP
a = 10
request.setAttribute(“a”, “10”)Servlet JSP
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Implicit Objects – response
• Instance of HttpServletResponse
• Send the response back to the client (HTML in most of the cases)
JSP1
Send response to client
JSP1Redirect to JSP2 JSP2
Send response to client
response.sendRedirect(“url”);
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Implicit Objects – session
• Instance of HttpSession
• Retrieve and set the session attributes in JSP
• Remember the client across multiple requests
Web App CLIENT
Request 1
Request 1
Response1
Response2
SESSION
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Implicit Objects – config and application
• config - Instance of ServletConfig• Application – instance of ServletContext
JSP 1
Servlet Context
Servlet Config Servlet ConfigServlet Config Servlet Config
JSP 1JSP 1JSP 1
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Implicit Objects – page
Main page<table><tr> <td>Contact Details</td><tr></table>
Hello <%=userName%><jsp:include page=“/header.jsp"/>
<jsp:include page=“/footer.jsp"/>
header.jsp
footer.jspmain.jsp
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Implicit Objects – pageContext
request
page
application
session
Lea
st v
isib
le t
o m
ost
vis
ible
pageContext
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JSP Actions
<jsp:include>
<jsp:forward>
<jsp:param>
<jsp:useBean>
<jsp:getProperty>
<jsp:setProperty>
• Special tags which provides special features
• The container handles these tags in a special way
• Addresses certain common functionalities
• Achieve functionality with less code, and more standard way
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JSP Actions - <jsp:include>
<jsp:include page="{PAGE_TO_INCLUDE}" flush="true" />
Definition:Includes a page at the given location in the main page
Syntax:
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JSP Actions – Include Action v/s Include Directive
Include Directive Include Action
Translation time Run time
Copies the included file References to the included file
For static content For dynamic content
Cannot pass parameters Can pass parameters
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JSP Actions - <jsp:forward>
<jsp:forward page=“{PAGE_TO_FORWARD}" />
Definition:Forwards the request to the given page
Syntax:
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JSP Actions - <jsp:param>
<jsp:include page="{PAGE_TO_INCLUDE}" flush="true" > <jsp:param name=“{parameterName}” value="{paramValue}" /></jsp:include>
Definition:Pass parameters to the included/forwarded page
Syntax:
<jsp:forward page="{PAGE_TO_FORWARD}" flush="true" > <jsp:param name=“{parameterName}” value="{paramValue}" /></jsp:forward>
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JSP Actions - <jsp:useBean>
Servlet JSP
bean
How can I use that bean?
getId();setId(..)getName()setName(…)
request.setAttribute(“userBean”, userBean”) <jsp:useBean …./>
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JSP Actions - <jsp:useBean>
<jsp:useBean id=“{beanInstanceName}" scope="page|request|session|application" class=“{package.class}" type=“{package.class}" beanName=" {package.beanName}”></ jsp:useBean>
Definition:Instantiate a bean class, use bean properties, and set property values
Syntax:
UserBean ub = new UserBean();
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JSP Actions - <jsp:getProperty>
<jsp:getProperty name=“{beanInstanceName}" property= “{propertyName}">
Definition:Gets property values of a Bean
Syntax:
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JSP Actions - <jsp:setProperty>
<jsp:setProperty name=“{beanInstanceName}" property= "*" | property="propertyName" param=“{parameterName}" value="{paramValue}" } />
Definition:Sets property values in a Bean
Syntax:
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JSP Actions – useBean
<jsp:useBean id=“userBean" scope="session“ class=“com.sharmanj.UserBean" >
<jsp:setProperty name=“userBean” property=“userName” value=“Sharad”/> </ jsp:useBean>
<jsp:getProperty name=“userBean" property=“userName" />
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Error Handling – Types of errors
• Errors in java code in scriptlets
handle errors in try/catch block
may occur at runtime
• Errors in HTML
adhere to the HTML rules
can be caught during testing
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Error Handling
Why is error handling important in JSPs?
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Error Handling – Error page
• Error pages come to the rescue
<%@page isErrorPage="true" %> <html> <head> <title>My Error Page</title> </head> <body> We are sorry, the page you are trying to access is currently not available. Please try after some time </body></html>
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Error Handling
• Specify error page in your main page
<%@page errorPage=“errPage.jsp" %><html> <head> <title>This is the main page</title> </head> <body> ………………….. …………………..
…………………… ……………………
// ERROR CODE GOES HERE
…………………. …………………. </body></html>
• Specify error page in web.xml
<web-app>…………….……………
<error-page> <exception-type>com.a.myExp</exception-type> <location>/error.jsp</location> </error-page>
<error-page> <error-code>404</error-code> <location>/errorServlet</location> </error-page>
………………..……………….</web-app>
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Thanks
