The JFC Swing Tutorial: A Guide to Constructing GUIs (2nd Edition)

This section discusses problems that you might encounter while using Java Web Start technology. If you don't find the answer to your question or problem here, you might find it in the Java Web Start documentation online at:

http://java.sun.com/products/javawebstart/index.html

You should also refer to the Java Web Start FAQ. In addition to addressing general questions about installation, licensing, security, and how it works, there's also a troubleshooting section:

http://java.sun.com/products/javawebstart/faq.html

For the most up-to-date version of The Java Tutorial's Java Web Start troubleshooting section, see:

http://java.sun.com/docs/books/tutorial/information/javawebstart.html

Problem: My browser seems to find the JNLP file, but Java Web Start says it can't find it.

Solution: This situation usually happens when your browser and your copy of Java Web Start have different proxy settings. To fix this problem:

1. Launch the Java Web Start Application Manager. ^[1]

   ^[1] You can launch the Application Manager either directly by double-clicking the Java Web Start icon on your computer's desktop or by using your browser to visit a special JNLP file such as the one at: http://java.sun.com/docs/books/tutorial/information/player.jnlp.

2. Choose the File > Preferences menu item.

3. Choose the General tab from the window that appears.

4. Set the proxy to a better value. For example, if you're behind a firewall and Use Browser is selected, try selecting Manual and entering an HTTP proxy server and port (often 8080). If you aren't behind a firewall, try selecting None . Or, if Use Browser is initially deselected, try selecting it.

Problem: What should I do when Java Web Start reports that the installation is bad?

Solution: The installation is faulty when Java Web Start can't find or launch the Java runtime environment (JRE). The simplest way to fix this problem is to reinstall Java Web Start.

Problem: When I start Java Web Start nothing happens except for a splash screen.

Solution 1: The likely cause of this problem is that you're using a Beta release of JRE 1.3.0 with Java Web Start. You can check what JRE you are using by selecting the Java tab on the Preference panel (select File > Preferences to open from the Application Manager.) In this case, your best solution is to reinstall a current version.

Solution 2: The cache may be corrupted. You can clear the cache from the Preferences panel. Choose the Advanced tab and click the Clear Folder button.

Problem: Why does my browser show the JNLP file as plain text?

Solution: Most likely your Web server is unaware of the proper MIME type for JNLP files. You must create an association between the file extension, jnlp , and the mime type, application/x-java-jnlp-file , on your server. The steps for doing this depend on which Web server you're using; you should contact your system administrator for help. In addition, if your network uses proxy servers, ensure that up-to-date versions of files are being returned.

Problem: What does the "Warning: Failed to verify the authenticity of this certificate. No assertions can be made of the origin or validity of the code." mean?

Solution: A certificate can only be trusted if you trust the certificate authority (CA) that created it. Java Web Start ships with a set of trusted root certificates from the most common CAs. If you sign your application with a certificate that is authorized by someone and is not in the set of trusted root certificates, you will see this warning message; for example this will happen if you use a self-signed certificate. You can see the list of trusted root certificates by choosing the Root Certificates tab on the Preferences panel. (In the Application Manager, select File > Preferences to open the Preferences panel.)

Problem: I cannot seem to access my local system as "localhost" to download resources.

Solution: If you are running in an environment with a proxy server, your system will fail to load the resource. To work around this problem you can either:

• Remove your proxy settings. In the Application Manager, select File > Preferences and choose the General tab. Select the Manual proxy and clear both the HTTP proxy and HTTP port settings.

• Use the exact IP address or name of the host: instead of "localhost," for example, 64.124.140.199 .

Problem: How do I trace System.out and System.err to debug my application?

Solution: In the Application Manager, select File > Preferences and choose the Advanced tab. Select the S how Java Console option to display all application output to System.out and System.err . You can also select the Log Output option and specify a log file to record the messages.