Troubleshooting CODEBASE

Contents

The CODEBASE attribute

The CODE attribute

Troubleshooting applets

Applet doesn't run in browser

ClassFormatError

Testing in your local environment

Moving from your local development environment

Speeding up applets with the ARCHIVE parameter

Useful documents

The Java Tutorial on the <APPLET> tag

The CODEBASE attribute.

You can use the CODEBASE attribute in an <APPLET> tag to specify a URL where the browser should look for the applet's Java class files. Without the CODEBASE tag, a web browser will look for the required classes under the same directory as the HTML file containing the <APPLET> tag. Using CODEBASE is convenient, since it allows you to organize your class files under a single directory, separate from the HTML content of your site.

Applets writen to work with the WebLogic Server often require WebLogic classes, so it is good practice to use the CODEBASE attribute to allow the browser to load the required classes out of the WebLogic installation. WebLogic provides a special servlet, called the ClasspathServlet, that will serve classes from the WebLogic Server's classpath. The ClasspathServlet is registered by default in the weblogic.properties file under the virtual servlet name "classes". When you set CODEBASE to a URL such as:

  CODEBASE="http://www.weblogic.com/classes/"

  CODEBASE="/classes/"

When you start the WebLogic Server, the weblogic.class.path property given on the command line should include the classes/ directory, and the myserver/serverclasses/ directory, located under the root WebLogic installation. (For more details on starting the WebLogic Server, see Setting up and starting the WebLogic Server.)

You should place your applet classes under the myserver/serverclasses/ directory, so they may be served by the ClasspathServlet. This directory is pointed to by the %SERVER_CLASSES% environment variable if you have run the setEnv script to set up your development environment.

Configuring the ClasspathServlet is described in detail in the WebLogic Administrator's Guide, Setting up WebLogic as an HTTP Server.

The CODE attribute

Your <APPLET> tag must contain the CODE attribute, which specifies the full package name of the main applet classfile. The extension ".class" at the end of the CODE is optional. For example, the phonebook1 applet is declared under the package examples.applets, so would be requested in an <APPLET> tag with:

  <APPLET CODE="examples.applets.phonebook1"
          CODEBASE="/classes/" >

Here is a quick summary of how you would set up your WebLogic Server to serve the applet "c:/weblogic/classes/examples/applets/phonebook1.class" from an HTML file called "phonebook1.html". This example is taken from the examples/applets directory under the WebLogic installation.

1. Open a command prompt and set up your environment using the setEnv script, as described in Setting up your development environment. Change to the directory containing the PhoneBook1.java source file, and compile it using:

    $  javac -d %SERVER_CLASSES% PhoneBook1.java

   This will place the compiled applet class under the myserver/serverclasses directory, where it can be served by the ClasspathServlet.

2. Register the ClasspathServlet in the weblogic.properties file with:

   weblogic.httpd.register.classes=weblogic.servlet.ClasspathServlet
   

   This is already registered by default, but you should check that the property is not commented out.

3. Create an HTML file that includes the applet and call it "phonebook1.html". Place this HTML file under the document root of the server. In the HTML file, add the <APPLET> tag:

     <applet code="examples.applets.PhoneBook1"
   	codebase="/classes/"
           width=500 height=800> 
       <param name=weblogic_url value="t3://localhost:7001">
       <param name=poolname value="demoPool">
     </applet>

   The <param> tags provide configuration information for this specific applet.

4. Start (or restart) the WebLogic Server.

5. In your browser, open the URL:

   http://WebLogicURL:Port/classes/phonebook1.html

   where WebLogicURL:Port is the URL and listen port of your WebLogic Server.

For more information on the APPLET tag and CODEBASE, see JavaSoft's Overview of Applets document, part of their Java Tutorial.

For more information on serving files with your WebLogic Server, read the WebLogic Administrators Guide document, Setting up WebLogic as an HTTP server.

Troubleshooting applets

Here are some scenarios you may run into using applets:

Applet doesn't run in browser

I'm using WebLogic JDBC in an applet to retrieve data from a DBMS. If I run the class using the Sun Appletviewer on my local machine, I have no problems. But when I try to run the applet in a Netscape browser, it will not connect.

If your applet works in Appletviewer but not in a browser, it is an indication that you are violating a Netscape security restriction; in this case, the violation is that an applet cannot open a socket to a machine other than the one from which it loaded the applet. To solve this problem, you will have to serve your applet code from the same machine that hosts the DBMS.

Note: The IP naming format you use in the applet CODEBASE and the URL you use to make a connection to the WebLogic Server must match exactly. You can't use dot-notation format in one place and domain name format in the other.

ClassFormatError

If you are getting a ClassFormatError, it probably indicates that there is a problem with your HTTP server configuration. It could be that you haven't put the WebLogic or applet classes in the correct directory on the HTTP server, or that you are specifying the CODEBASE or the CODE incorrectly in your APPLET tag. Here are some examples.

I downloaded your distribution and copied the classes to my HTTP server. I created an applet and placed it on the server in the directory /webz/ns-home/classes/applets/myapp.class. I am calling the applet with the following APPLET tag:

  <APPLET
    CODEBASE=http://myserver.com/webz/ns-home/classes
    CODE=applets.myapp
    WIDTH=500 HEIGHT=600>

This didn't work.

Your CODEBASE should point to the document root of the server. In the scenario above, the directory path you have referenced in the CODEBASE tag is an absolute directory path on the HTTP server.

Your CODEBASE should always be the URL of the server, plus the path that originates from the HTTP document root.

Solution: Place the applet in the document root of your HTTP server. If the document root is webz/ns-home/, then your APPLET tag will be:

  <APPLET
    CODEBASE="http://myserver.com/classes"
    CODE=applets.myapp
    WIDTH=500 HEIGHT=600>

If you are using the WebLogic Server as an HTTP server, there are other considerations in setting up your APPLET tag. For more information, read Setting up WebLogic as an HTTP server.

Testing in your local environment

You will still need to set a CLASSPATH in the shell in which you start WebLogic. WebLogic recommends that you never set CLASSPATH in your environment, but rather set CLASSPATH appropriately in the shell from which you run WebLogic.

Moving from your local development environment

If you are running the applet on the same machine that you installed the WebLogic distribution, this may obscure problems you are having with CODEBASE. The applet will first look for the WebLogic classes in your local CLASSPATH. If you haven't properly installed the classes for serving applets from the HTTP server, the applet will default to your local CLASSPATH and work, obscuring the problem. To test your HTTP configuration properly, you need to temporarily rename the WebLogic classes in your local CLASSPATH or try your applet from another machine.

Speeding up applets with the ARCHIVE parameter

Note: The procedure when using Appletviewer, Netscape Navigator (3.0 and later only), and the HotJava browser differs from that used for Microsoft Internet Explorer (4.0 and later only). For complete compatibility, both methods may be combined.

Procedure for Netscape, Appletviewer, and HotJava

  <APPLET 
    CODEBASE="http://myserver.com/classes"
    CODE=myFile.class 
    ARCHIVE="myArchive.jar,jarfiles/myArchive2.jar"
    WIDTH=500 HEIGHT=600> 
    </APPLET>

will specify that the browser look first in the same directory as the HTML page for myArchive.jar and then in the "jarfiles" directory below the current directory for myArchive2.jar. If the browser cannot locate the required files in the .jar file, it will look in the location specified by the CODEBASE parameter.

Procedure for Microsoft Internet Explorer

<APPLET 
  CODEBASE="http://myserver.com/classes"
  CODE="myfile.class"
  WIDTH=500
  HEIGHT=600>

 <PARAM NAME=cabbase VALUE="myArchive.cab">

 </APPLET>

Combining both .cab and .jar files

<APPLET 
  CODEBASE="http://myserver.com/classes"
  CODE="myfile.class"
  ARCHIVE="myArchive.jar,jarfiles/myArchive2.jar"
  WIDTH=500
  HEIGHT=600>

 <PARAM NAME=cabbase VALUE="myArchive.cab">

 </APPLET>

Copyright © 2000 BEA Systems, Inc. All rights reserved.
Required browser: Netscape 4.0 or higher, or Microsoft Internet Explorer 4.0 or higher.
Last updated 01/14/1999