16 Applets and Java Web Start Applications

If your application does not run, perform the following checks:

The following are troubleshooting techniques for common configuration problems:

The Java Control Panel can be launched from the bin directory of the JRE installation folder. On Windows operating systems, you can also access it from Control Panel > Java.

Use the Java Control Panel if you need to:

• See which versions of the JRE are installed and active

• Temporarily enable or disable the use of a particular version of the JRE

• Set "global" parameters to be passed to the JVM when an applet or Web Start application is launched

• Enable or disable the use of the Java Plugin in a particular browser

• Tune behavior of the Plugin or Web Start application by specifying configuration parameters such as the ___location of cache of temporary files or enable tracing, as shown in Figure 16-1.

Figure 16-1 The Java Runtime Environment Settings Window

Description of "Figure 16-1 The Java Runtime Environment Settings Window"

Open the Java Control Panel, and click View on the Java tab. Select the Runtime Parameters cell for the JRE that you want to change, and enter parameters into this cell.

To pass parameters to a specific JVM used with Java Web Start or an applet, use one of the following techniques:

To get access to trace information:

The trace file is saved into the log directory in the Java deployment home folder. See Java Deployment Home. The file name has the prefix javaws or plugin, depending on what you are running. One trace file is produced per process, but one application can be launched using several processes.

To get the maximum level of detail in the trace file, edit the deployment.properties file (which is located in the Java deployment home directory) and add the following line:

deployment.trace.level=all

By default, a maximum of five trace files are created. The oldest trace files are automatically deleted. To change the limit of the maximum number of trace files, add the following line to the deployment.properties file:

deployment.max.output.files=max_number_of_trace_files

You can use the Java console to view the trace log at runtime. By default, the Java console is hidden. Enable it in the Java Control Panel.

Application jars and resources are cached on the disk to avoid loading them the next time they are needed.

The default ___location of the cache depends on the operating system and can be overridden in the Java Control Panel.

Settings and controls for the cache are available in the General tab of the Java Control Panel, in the Temporary Internet Files section. Click Settings to change the ___location and size of the cache. Click View to see what files are in the cache.

You can clean the cache by running javaws -uninstall, or open the Java Control Panel's General tab, click View, and delete the files manually. You can also use the Java Control Panel to uninstall individual applications and extensions.

In general, Java Web Start applications use the system network configuration by default, and applets use the browser network settings. You can set network proxies explicitly using the Java Control Panel.

In particular, the Java technology networking layer automatically detects which networking stack to use. However, sometimes autodetection does not work, and you may see Permission Denied exceptions trying to open a socket to download your application or applet, even while the same URL is accessible using the same proxy settings with other tools. This problem was seen on some Windows 7 systems when VPN software was used. This can be resolved by explicitly passing a parameter to the JVM:

-Djava.net.preferIPv4Stack=true

See Pass Parameters to the JRE.

If your applet does not start, ensure that you enable tracing and the Java console as explained previously. Then, use the following hints to find the reason why the applet does not work.

Do you get a trace file generated or see the Java console?

• • No, I don't get a trace file.

    Check if the Java technology is detected. See Validation.

    • Yes

      Look at the JVM browser issues from Browser or Java Process Crash.

    • No

      It is likely to be a configuration issue. See Common Configuration Problems, and if it does not help, look at the JVM browser issues from Browser or Java Process Crash.

  • Yes, I have a trace file.

    It is unlikely to be a configuration issue (unless you have the new generation plugin disabled). The problem is likely to be specific to this applet. Try to launch some other applets to confirm. Look at JVM client issues from Browser or Java Process Crash.

A crash could be caused by a platform or application issue.

Typically, if a crash happens in the JVM, then there should be an hs_err_*log file created in the current working directory. On Windows, it is often placed on the desktop. It is the same crash report file as for standalone applications. See Fatal Error Log.

If you can see native libraries loaded from the deployment cache directory, especially if you see code from these libraries in the crash stack, then it is very likely to be a bug in the application.

Otherwise, it is a JRE bug and needs to be reported to Bug Database.

The following are two scenarios to consider for a crash by platform or application issue.

• JVM browser issues: Get more details about a JVM running in the browser process. Set the following two environment variables before starting the browser:

  JPI_PLUGIN2_DEBUG=1
  JPI_PLUGIN2_VERBOSE=1
  

  On Windows, there should be a command window associated with the browser process. All browser VM debug output goes into the command window. Check to see if any exceptions are visible there. A Java thread dump can be obtained by using the Control+Break key sequence on the command window.

  On the Oracle Solaris or Linux platforms, after setting these variables, start the browser from the same session. All browser VM debug output goes into the terminal window. To get a Java thread dump, on a separate terminal, use kill -3 pid or kill -SIGQUIT pid, where pid is the process ID of the browser process.

  There are heartbeat messages sent between the client VM and browser VM. The heartbeat messages can be turned off by setting the JPI_PLUGIN2_NO_HEARTBEAT environment variable to 1. This will help isolate whether the problem is related to the heartbeat.

  If the log is not opening and environment variables are set in the browser process, then it is likely that the JRE is not installed correctly or Java is disabled. Check for configuration errors, and try to reinstall the JRE if nothing else helps.

• JVM client issues: Check the latest trace file for ideas.

  Note: The same client JVM may be shared between multiple applets. Sometimes intermittent failures happen because the shared JVM does not have enough resources available (for example, heap size). In that case, a page reload often helps to resolve the problem.

  If an application fails with an Out of memory error, then the heap size needs to be increased. This can be done in the application deployment descriptor (JNLP file) or in the Java Control Panel using runtime parameters for JRE in use.

  If an application is signed and the user declined a security dialog box, then this may cause the application fail. The decision made by the user is remembered until the JVM is restarted. To see the security dialog box again, the user may need to restart the browser.

If a Java applet or Web Start application is signed, a certificate security warning dialog box will pop up and the user must click Run to give all permissions to the code of the application.

To avoid seeing this dialog box, you can do one of the following:

• User accepts the certificate used to sign the application and selects the Always trust content from this publisher check box. Then, next time permissions will be granted to this application automatically (until the certificate expires or is removed from the trusted key store).

• The certificate can be manually imported into the JRE trusted certificate store. To import the certificate using the Java Control Panel, on the Security tab, click Certificates and then Trusted Certificates. To import a certificate into the certificate store from the command line, use the keytool utility (in the JRE's bin folder).

• Grant AllPermissions in the Java policy file located at ${user.home}/.java.policy, or point to any Java policy file which has AllPermissions in the $(JRE_HOME)/lib/security/java.security file. Permissions can be granted to all applications or restricted to a particular URL. See Default Policy Implementation and Policy File Syntax for more details on .java.policy.