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Exploring the Solutions
Typically there are three ways to run a Java graphic application without an X11 window server
installation.
#1: Using Sun JDK 1.4 Headless Mode
The Sun JDK 1.4 implementation provides a new Headless graphics operation mode. The headless feature is activated by setting the Sun JDK 1.4 -specific java.awt.headless system property to "true." For example, with an appropriate Java virtual machine command line option:
java -Djava.awt.headless=true
Unfortunately, Sun JDK 1.4 versions up to at least 1.4.1.1 have certain problems that limit the usefulness of this feature. In particular, you still need the X11 runtime libraries. This means that an X11 environment must be installed on the system, but you don't need to start the X11 server itself.
This project attempted to set the java.awt.headless system property value to "true," with surprising results—the following exception was thrown and when I requested the registration page (with the embedded, dynamic visual image), it was not generated properly:
[21/04/06 11:33:00:388 EDT] 456af8da WebGroup E SRVE0026E: [Servlet Error]-[Captcha]: java.awt.HeadlessException
at sun.java2d.HeadlessGraphicsEnvironment.getDefaultScreenDevice(HeadlessGraphicsEnvironment.java:98)
at nl.captcha.text.imp.DefaultWordRenderer.renderWord(DefaultWordRenderer.java:59)
at nl.captcha.servlet.DefaultCaptchaIml.createImage(DefaultCaptchaIml.java:103)
at nl.captcha.servlet.CaptchaServlet.doGet(CaptchaServlet.java:44)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at com.ibm.ws.webcontainer.servlet.StrictServletInstance.doService(StrictServletInstance.java:110)
at com.ibm.ws.webcontainer.servlet.StrictLifecycleServlet._service(StrictLifecycleServlet.java:174)
at com.ibm.ws.webcontainer.servlet.IdleServletState.service(StrictLifecycleServlet.java:313)
at com.ibm.ws.webcontainer.servlet.StrictLifecycleServlet.service(StrictLifecycleServlet.java:116)
at com.ibm.ws.webcontainer.servlet.ServletInstance.service(ServletInstance.java:283)
at com.ibm.ws.webcontainer.servlet.ValidServletReferenceState.dispatch(ValidServletReferenceState.java:42)
at com.ibm.ws.webcontainer.servlet.ServletInstanceReference.dispatch(ServletInstanceReference.java:40)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.handleWebAppDispatch(WebAppRequestDispatcher.java:974)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.dispatch(WebAppRequestDispatcher.java:555)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java:200)
at com.ibm.ws.webcontainer.srt.WebAppInvoker.doForward(WebAppInvoker.java:119)
at com.ibm.ws.webcontainer.srt.WebAppInvoker.handleInvocationHook(WebAppInvoker.java:276)
at com.ibm.ws.webcontainer.cache.invocation.CachedInvocation.handleInvocation(CachedInvocation.java:71)
at com.ibm.ws.webcontainer.srp.ServletRequestProcessor.dispatchByURI(ServletRequestProcessor.java:182)
at com.ibm.ws.webcontainer.oselistener.OSEListenerDispatcher.service(OSEListener.java:334)
at com.ibm.ws.webcontainer.http.HttpConnection.handleRequest(HttpConnection.java:56)
at com.ibm.ws.http.HttpConnection.readAndHandleRequest(HttpConnection.java:618)
at com.ibm.ws.http.HttpConnection.run(HttpConnection.java:443)
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:593)
Research revealed that that the Sun JDK 1.4.2 has one bug reported for handling the Headless mode (bug_id=5004298: Running in Headless mode still produces Headless exception with GTK UI). Click here for more information aabout this bug.
As you can see, the exception was thrown at the line 59 from the method of renderWord (String word, int width, int height) inside the nl.captcha.text.imp.DefaultWordRenderer.java class in SimpleCaptcha library:
Line 58 ………………GraphicsEnvironment ge =
GraphicsEnvironment.getLocalGraphicsEnvironment();
Line 59 ………………GraphicsDevice gd = ge.getDefaultScreenDevice();
Line 59 ………………GraphicsConfiguration gc = gd.getDefaultConfiguration();
In fact, the above three lines of code, inside the nl.captcha.text.imp.DefaultWordRenderer.java class, are a defect of the SimpleCaptcha library's 0.03 release. The object references GraphicsEnvironment, GraphicsDevice, and GraphicsConfiguration have been created, but never be used anywhere inside the library. You'll need to remove them from the DefaultWordRenderer class' source if your application is running in headless mode.
The corresponding code change, along with the recompiled SimpleCaptcha source code, can be found in the source code: lsimplecaptcha-20060421.jar under the $PROJECT_ROOT$/dist ("$PROJECT_ROOT$ = C:\aolWebRegAdmin\SimpleCaptchaWeb, which is the SimpleCaptcha open source project root. Please see the details in Figures 1 and 2. The SimpleCaptcha project source code can be downloaded here.
Figure 1: The SimpleCaptcha project directory structure within the IBM WSAD5.1 IDE.
Figure 2: Recompiling the SimpleCaptcha source code and generating the .jar file.
Note: In order to use the Ant build.xml file for the auto build, you'll need to modify the builld.properties file to your corresponding J2EE .jar file path:
j2ee.jar=C:/Program Files/IBM/WebSphere Studio/
Application Developer/v5.1.1/runtimes/aes_v4_jar/lib/j2ee.jar
build.xml and builld.properties are located in the project root directory. Even though you comment out the above source code and recompile and package the SimpleCaptcha .jar with the Ant build file, the embedded image will still not show due to JDK1.4.2's bug id#:5004298:
Figure 3: The Random text image does not show up on the test page.
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