06_Creating the Web Tier Using Java Server Pages

6Copyright © 2007, Oracle. All rights reserved.

Creating the Web Tier Using JavaServer Pages

6-2 Copyright © 2007, Oracle. All rights reserved.

Objectives

After completing this lesson, you should be able to do the following:

• Describe the relationship between JavaServer Pages (JSP) and servlets

• List implicit objects on JSP pages

• Describe the semantics of JSP tags

• Create a JSP segment

• Explain the use of JSP tag files

• Run and debug a JSP-based application


JavaServer Pages

Generates

Dynamic content

JSP

Connects to

EJB

Client

Request

Database

Response


Comparing Servlets and JSPs

Servlets:

• Are Java programs with embedded HTML code

• Generate dynamic content

• Do not separate static and dynamic content

JavaServer Pages:

• Are HTML pages with embedded Java code or pure XML

• Generate dynamic content

• Separate static and dynamic content


Invoking JSPs

HTML

JSP

Invoke

Servlet

JSP


Date JSP

<%@ page contentType="text/html;charset=WINDOWS-1252"%><html> <head><meta http-equiv="Content-Type" content="text/html; charset=WINDOWS-1252"><title> Show Date </title></head><body><h2> The current time is: </h2><p> <%= new java.util.Date() %> </p></body></html>


Date Servlet

...public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType(CONTENT_TYPE); PrintWriter out = response.getWriter(); out.println("<html>"); out.println("<head><title>Show Date </title></head><body><h2>The current time is:</h2><p>"); out.println(new java.util.Date()); out.println("</body></html>"); out.close(); }...


Automated JSP Features

• A JSP is automatically converted into a servlet the first time it is invoked:– Java source files are generated.– Java class files are generated.– The Java Just-In-Time compiler can be used.

• A JSP can contain extensible components:– Tags: Libraries such as OC4J JSP (OJSP) or

custom-developed tags– JavaBeans (Beans are reused and their properties

are automatically introspected.)


JSP Life Cycle

http://host/date.jsp

Java EE container

Create servletdate.java

Compile servletdate.class

1

Servlet life cycle

Firsttime

Yes

2

3

No

OC4J


Basic JSP Elements

A JSP contains three main elements:

• Text elements

• Directives

• Scripting elements– Declarations– Expressions – Scriptlets


Declarations

• Are used to define methods or variables

• Begin with the sequence <%!• End with the sequence %>• Are inserted into the body of the servlet class, not

within a method, during translation

• Are used in conjunction with expressions or scriptlets

<%! private int i=3; %><%! private String a="Hello", b=" World"; %>


Expressions

• Begin with the sequence <%=• Contain Java expressions that are evaluated and

inserted into the servlet’s output

• End with the sequence %>• Do not end with a semicolon

<%= i+1 %><%= a + b %><%= new java.util.Date() %>

1

2


Scriptlets

• Begin with the sequence <%• Contain a block of Java code that is executed

every time a request is made

• End with the sequence %>

<% if (i<3) out.print("i<3"); if (i==3) out.print("i==3"); else out.print("i>3");%>


Implicit Objects

There are eight implicit objects, also known as predefined variables, in JSP:• request• response• session• out

• application• config• pageContext• page

These objects are created in the generated servlet.


Example


Directives

• Are used to set global values such as class declarations and method implementations

• Begin with the sequence <%@• End with the sequence %>• Are of the following types:

– page– include– taglib


include: Example


page Directive

You can define the following attributes by using the page directive:

• import• contentType• isThreadSafe• session• buffer• autoFlush

• extends• info• errorPage• isErrorPage• language


JSP and JavaBeans

package lesson04;import java.lang.*;import java.util.*;public class LuckyNumberBean { private int luckyNum; public LuckyNumberBean() { luckyNum = (int) (1000 * Math.random()); } public int getLuckyNum() { return luckyNum; } public void setLuckyNum(int luckyNum) { this.luckyNum = luckyNum; }}


Using JavaBeans with JSP

Accessing JavaBeans with the <jsp:useBean> tag:

<jsp:useBean id="myBean" scope="session" class="lesson04.LuckyNumberBean" />


page scope

scope Attribute of <jsp:useBean> Tag

Client

Page 1 Page 2 Page 3

Request

Forward

Response

Request

Response

page scope page scope

request scope request scope

session scope


Accessing and Setting Bean Property

• Accessing bean property:

• Setting bean property:

<jsp:getProperty name="myBean" property=“luckyNum" />

<jsp:setProperty name="myBean" property=“luckyNum" value="10" />


JSP XML Document

• Contains <jsp:root> as its root element

• Includes only XML syntax and does not include the traditional JSP tags

• Can be processed directly by the JSP container

• Can be used with XML development tools


Traditional Syntax Versus XML Syntax

Traditional: XML:• It has no root element.

• page directive<%@ page %>

• Declaration tag<%! %>

• Expression tag<%= expression %>

• Scriptlet<% %>

• <jsp:root> is the root element.

• <jsp:directive.page/>

• <jsp:declaration></jsp:declaration>

• <jsp:expression></jsp:expression>

• <jsp:scriptlet></jsp:scriptlet>


JSP Segments

• Use a JSP segment for creating a partial JSP page.

• Include one or more segments in a JSP using <jsp:include>.

JSP segment – footer.jspf:

JSP:

Copyright 2005, <a href="http://www.oracle.com"> Oracle</a>

<%@ include file="/footer.jspf"%>


JDeveloper and JSPs

• The JSP Wizard in JDeveloper is used to create JSPs containing skeleton code.

• Structure Pane helps to ensure that the JSP and HTML tags are properly formatted.

• Tag Insight automatically inserts end tags after starting a scriptlet.

• The JSP code is automatically created and recompiled.

• JDeveloper increases productivity while debugging JSPs:– Automatically includes source Java files such as

your JavaBean source– Enables you to set breakpoints and watch

expressions in JSPs


Summary

In this lesson, you should have learned how to:

• Identify the differences and similarities between JSPs and servlets

• Use declarations, expressions, scriptlets, and implicit objects on JSP pages

• Use JavaBeans with JSPs

• Create a JSP segment

• Explain the use of JSP tag files

• Run and debug a JSP-based application


Practice Overview: Developing JSPs

This practice covers the following topics:

• Building a basic JSP

• Developing a JSP that uses the request and session objects

• Building a JSP to display the results

06_Creating the Web Tier Using Java Server Pages

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