First JSP Example

We begin our introduction to JavaServer Pages with a simple example, clock.jsp (Fig. 27.1), in which the current date and time are inserted into a Web page using a JSP expression.

Figure 27.1. JSP expression inserting the date and time into a Web page.

(This item is displayed on pages 1283 - 1284 in the print version)

"http://www.w3.org/1999/xhtml"> 8 9 "refresh" content = "60" /> 10

 1  "1.0"?>
 2 -//W3C//DTD XHTML 1.0 Strict//EN"
 3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
 4
 5 
 6
 7 
A Simple JSP Example 11 16 17 18

"big">Simple JSP Example

19 "border: 6px outset;"> 20 21 27 28
"background-color: black;"> 22

"big" style = "color: cyan;"> 23 24 <%= new java.util.Date() %> 25

26
29 30

As you can see, most of clock.jsp consists of XHTML markup. [Note: We assume that the reader already knows XHTML and Cascading Style Sheets (CSS). For those who are not familiar with XHTML and CSS, we have included three chapters from our book Internet & World Wide Web How to Program, Third Edition as PDF documents on the CD that accompanies this bookIntroduction to XHTML: Part 1, Introduction to XHTML: Part 2 and Cascading Style Sheets (CSS).] In cases like this, JSPs are easier to implement than servlets. In a servlet that performs the same task as this JSP, each line of XHTML markup typically is a separate Java statement that outputs the string representing the markup as part of the response to the client. Writing code to output markup can often lead to errors. Most JSP editors provide syntax coloring to help programmers check that their markup follows proper syntax.

Software Engineering Observation 27.2

JavaServer Pages are easier to implement than servlets when the response to a client request consists primarily of markup that remains constant between requests.

 

The JSP in Fig. 27.1 generates an XHTML document that displays the current date and time. The key line in this JSP (line 24) is the expression

 <%= new java.util.Date() %>

 

JSP expressions are delimited by <%= and %>. The preceding expression creates a new instance of class Date (package java.util). By default, a Date object is initialized with the current date and time. When the client requests this JSP, the preceding expression inserts the String representation of the date and time in the response to the client. [Note: Because the client of a JSP could be anywhere in the world, the JSP should return the date in the client locale's format. However, the JSP executes on the server, so the server's locale determines the String representation of the Date. In Fig. 27.10, clock2.jsp determines the client's locale, then uses a DateFormat (package java.text) object to format the date using that locale.]

Software Engineering Observation 27.3

The JSP container converts the result of every JSP expression into a string that is output as part of the response to the client.

 

We use the XHTML meta element in line 9 to set a refresh interval of 60 seconds for the document. This causes the browser to request clock.jsp every 60 seconds. For each request to clock.jsp, the JSP container reevaluates the expression in line 24, creating a new Date object with the server's current date and time.

As in Chapter 26, we use Apache Tomcat to test our JSPs in the jhtp6 Web application we created previously. For details on creating and configuring the jhtp6 Web application, review Section 26.3 and Section 26.4.1. To test clock.jsp, create a new directory called jsp in the jhtp6 subdirectory of Tomcat's webapps directory. Next, copy clock.jsp into the jsp directory. Open your Web browser and enter the following URL to test clock.jsp:

 http://localhost:8080/jhtp6/jsp/clock.jsp

 

When you first invoke the JSP, you may notice a brief delay as Tomcat translates the JSP into a servlet and invokes the servlet to respond to your request. [Note: It is not necessary to create a directory named jsp in a Web application. We use this directory to separate the examples in this chapter from the servlet examples in Chapter 26.]

Introduction to Computers, the Internet and the World Wide Web

Introduction to Java Applications

Introduction to Classes and Objects

Control Statements: Part I

Control Statements: Part 2

Methods: A Deeper Look

Arrays

Classes and Objects: A Deeper Look

Object-Oriented Programming: Inheritance

Object-Oriented Programming: Polymorphism

GUI Components: Part 1

Graphics and Java 2D™

Exception Handling

Files and Streams

Recursion

Searching and Sorting

Data Structures

Generics

Collections

Introduction to Java Applets

Multimedia: Applets and Applications

GUI Components: Part 2

Multithreading

Networking

Accessing Databases with JDBC

Servlets

JavaServer Pages (JSP)

Formatted Output

Strings, Characters and Regular Expressions

Appendix A. Operator Precedence Chart

Appendix B. ASCII Character Set

Appendix C. Keywords and Reserved Words

Appendix D. Primitive Types

Appendix E. (On CD) Number Systems

Appendix F. (On CD) Unicode®

Appendix G. Using the Java API Documentation

Appendix H. (On CD) Creating Documentation with javadoc

Appendix I. (On CD) Bit Manipulation

Appendix J. (On CD) ATM Case Study Code

Appendix K. (On CD) Labeled break and continue Statements

Appendix L. (On CD) UML 2: Additional Diagram Types

Appendix M. (On CD) Design Patterns

Appendix N. Using the Debugger

Inside Back Cover

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Java(c) How to Program
Java How to Program (6th Edition) (How to Program (Deitel))
ISBN: 0131483986
EAN: 2147483647
Year: 2003
Pages: 615
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