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170

Chapter 7 Generating the Server Response: HTTP Response Headers

sage in the designated face and size, with a gray, oblique shadowed version of

the message shown behind the main string. This operation makes use of sev 

eral facilities available only in the Java 2 platform. First, it makes use of any

font that is installed on the server system, rather than limiting itself to the

standard names (

Serif

, 

SansSerif

, 

Monospaced

, 

Dialog

, and 

DialogIn 

put

) available to JDK 1.1 programs. 

Second, it uses the 

translate

, 

scale

, and 

shear

 transformations to cre 

ate the shadowed version of the main message. Consequently, the servlet will

run only in servlet engines running on the Java 2 platform. You would expect

this to be the case with engines supporting the servlet 2.2 specification, since

that is the servlet version stipulated in J2EE. 

Even if you are using a server that supports only version 2.1, you should

still use the Java 2 platform if you can, since it tends to be significantly more

efficient for server side tasks. However, many servlet 2.1 engines come pre 

configured to use JDK 1.1, and changing the Java version is not always sim 

ple. So, for example, Tomcat and the JSWDK automatically make use of

whichever version of Java is first in your 

PATH

, but the Java Web Server uses a

bundled version of JDK 1.1.

Listing 7.10 shows an HTML form used as a front end to the servlet. Fig 

ures 7 5 through 7 8 show some possible results. Just to simplify experimen 

tation, Listing 7.11 presents an interactive application that lets you specify

the message, font name, and font size on the command line, popping up a

JFrame

 that shows the same image as the servlet would return. Figure 7 9

shows one typical result. 

Listing 7.8  ShadowedText.java 

package coreservlets;

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

import java.awt.*;

/** Servlet that generates GIF images representing

 *  a designated message with an oblique shadowed

 *  version behind it.

 *  

 *  Only runs on servers that support Java 2, since

 */

public class ShadowedText extends HttpServlet {

  public void doGet(HttpServletRequest request,

                    HttpServletResponse response)

      throws ServletException, IOException {

    String message = request.getParameter("message");

    if ((message == null) || (message.length() == 0)) {

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.