Java Plug-in Home Page


Java Plug-in was formerly known as Project Java Activator during its early access phases.



         Java Plug-in Basics
         Pricing and Availability
         Features and Benefits
         How Does it Work?
         HTML Converter
         Miscellaneous Questions

Java Plug-in Basics   back to top

Q: What is the Java Plug-in?

A: Java Plug-in is a software product from Sun Microsystems, Inc. that allows enterprise web managers to direct Java applets and JavaBeans components on their intranet web pages to run using Sun's Java Runtime Environment (JRE).

Q: Which web browsers and platforms are supported by Java Plug-in?

A: Sun supports the following configurations:

  Internet Explorer 3.02 Internet Explorer 4.0 Navigator 3.0 Navigator 4.0
Windows 95 X X X X
Windows 98   X X X
Windows NT X X X X
Solaris/SPARC     X X
Solaris/x86     X  

Q: Does the Java Plug-in work on platforms other than Windows or Solaris (for example, Mac OS, AIX, Linux, HP-UX, etc.) versions of IE or Navigator?

A: For information about support for Java Plug-in on other operating systems, please contact the operating system provider.

Q: For whom is the Java Plug-in intended?

A: The Java Plug-in was designed for enterprise customers who wish to deploy JDK 1.1-based applets on their intranet web pages, and support Windows- and Solaris-based browsers in their enterprise.

Q: Is there documentation available for Java Plug-in?

A: To assist in your deployment of Java Plug-in, Sun has made available a variety of technical documentation. Documentation regarding the HTML specifications, using Java Plug-in in intranet environments, how proxy configuration works, how to script applets, and much more are available from the Java Plug-in documentation page.

Q: What information should I provide when reporting a bug? 

A: When reporting bugs against Java Plug-in, always include the following information:

  1. Operating system, including version number
  2. Web browser, including version number
  3. Complete output of the Java Console window
  4. Network configuration information--proxy, special intranet environment, etc.
  5. Complete description of the failure/problem encountered. Please delineate the steps taken to reproduce the problem one-by-one.

Pricing and Availability back to top

Q: When will the Java Plug-in be available? 

A: The 1.1.1 release which provides support for the complete JDK 1.1 feature set is now available.

Q: What does the Java Plug-in cost? 

A: Nothing. The Java Plug-in and the Java Plug-in HTML Converter are provided free of charge, and are freely redistributable. Please see the license agreement provided with the Java Plug-in and the Java Plug-in HTML Converter for the complete set of terms and conditions for each.

Q: Does Sun intend to charge for future releases of the Java Plug-in? 

A: We have no such plans at this time.

Q: Will there be future releases of the Java Plug-in?

A: Yes. The Java Plug-in is future-ready, which means that new versions will be able to ship when new technologies are incorporated into the Java Platform (for example, the JDK 1.2, Java HotSpot, etc.). Sun plans to provide an early access release of the next version of the Java Plug-in, with bundled support for JDK 1.2, later this summer.

Q: What is the planned schedule for availability of the Java Plug-in 1.1.1 for the Macintosh? 

A: Java Plug-in for the Macintosh is currently under development by Apple, and is slated to be available this summer. Please contact Apple directly for specifics.

Features and Benefits   back to top  

Q: What features does the Java Plug-in offer?

A: The Java Plug-in delivers several key capabilities to enterprises using Internet Explorer or Netscape's Navigator on Win32 and Solaris desktops:


         Full JDK 1.1 support
         Full Java Compatible support
         Future-ready architecture
         Free public download and easy install
         Free Java Plug-in HTML Converter

A complete list of the features of the Java Plug-in and Java Plug-in HTML Converter are also available from the Java Plug-in documentation page.

Q: What is the advantage of downloading and using the Java Plug-in rather than the browser's default Java virtual machine?

A: Using the Java Plug-in allows enterprises to:

  1. Take full advantage of JDK 1.1 functionality such as JavaBeans, JNI, and RMI today.
  2. Develop and deploy 100% Pure Java applets on Internet Explorer and Netscape Navigator browsers, and be assured that they will run reliably and consistently in both browsers.
  3. Be assured that they will receive support for the latest releases of Sun's JDK--including JDK 1.2 and the high-performance Java HotSpot virtual machine--in Internet Explorer and Navigator as soon as Sun releases them.

Q: Can I set up the Java Plug-in software to download from an intranet web server (behind a firewall), rather than downloading it from Sun's web site? 

A: Yes. For more information, see the Guide to Using Java Plug-in in Intranet Environments and the Java Plug-in documentation page.

Q: Does the Java Plug-in provide support for Netscape Navigator? 

A: Yes. The java Plug-in supports Netscape Navigator 3.0 and later on Windows 95 and 98, Windows NT 4.0, and Solaris 2.5 and 2.6-based systems.

Q: Does Java Plug-in support scripting? 

A: Java Plug-in supports scripting of applets in Internet Explorer. However, such scripting is not available when using Java Plug-in in Navigator. Because of limitations in Netscape's plug-in API, scripting cannot be supported directly (through LiveConnect) in Navigator. We are working closely with Netscape to address this issue in a future release of Navigator.

Q: Does the Java Plug-in include a just-in-time (JIT) compiler?

A: Yes. The Win32 edition of Java Plug-in includes the latest Symantec JIT 3.0 compiler.

Q: What version of the JDK does the Java Plug-in support? 

A: The Java Plug-in features a future-ready architecture that makes it easy for Sun to bring the latest JDK features and functionality to Windows and Solaris desktops. The 1.1.1 release of the Java Plug-in incorporates JRE 1.1.6, the most recently completed version of the JRE available.

Q: Does the Java Plug-in offer support for all the features in JDK 1.1?

A: Yes. The Java Plug-in uses the same JRE that users can download from Sun's web site today (see here) .

Q: Will the Java Plug-in work with the next release of the JDK?

A: Yes. With this release developers can configure the Java Plug-in to use the Java runtime in the current beta release of JDK 1.2, enabling developers to begin testing their JDK 1.2-based Java applets in Navigator and Internet Explorer immediately. We expect to issue an early access release of the Java Plug-in with bundled support for JDK 1.2 later this summer.

Q: Is the Java Plug-in fully compliant with the JCK (Java Compatibility Kit) test suite for JDK 1.1?

A: The 1.1.1 release of the Java Plug-in is fully compliant with the JCK test suite for JDK 1.1, including the RMI and JNI tests.

Q: Netscape recently announced JDK 1.1 support for Communicator 4.0.4 -- is the Java Plug-in still necessary?

A: Yes. While Netscape recently increased the number of JDK 1.1 features it supports in Communicator 4.0.4, it is still not feature complete nor fully compliant with the JCK. The Java Plug-in is the only way to guarantee full support of the latest JDK and full JCK compliance.

Q: Which JDK 1.1 features does Netscape not support?

A: There are several, including support for multiple JAR files and not all thread methods are implemented. Netscape has provided further information on known incompatibilities in their JDK 1.1 patch for Communicator at http://developer.netscape.com/.

Q: Does Java Plug-in support signed applets?

A: Yes, Java Plug-in supports standard JDK 1.1 signed JARs. See Using Signed Applets for more details.

Q: Does Java Plug-in support JNI?

A: Yes, Java Plug-in supports the Java Native Method Interface (JNI). See JNI and Java Plug-in for more details.

Q: Does the Java Plug-in automatically recognize and use the proxy server configuration that the browser was using?

A: Yes, Java Plug-in automatically recognizes the Internet settings in your browser when it starts. It means that it can go over the firewalls/proxies as long as the settings in your browser are correct.

Q: What protocol does Java Plug-in support over the proxy?

A: Currently, only HTTP, FTP, and Gopher are supported in the 1.1.1 release of Java Plug-in. HTTPS (SSL) and SOCKS are planned for a future release.

Q: Does Java Plug-in support proxy-bypass list?

A: Yes, the 1.1.1 release of the Java Plug-in supports the proxy-bypass list.

Q: Does Java Plug-in support auto-proxy-configuration in the browser?

A: Yes, the 1.1.1 release of the Java Plug-in supports auto-proxy-configuration for both Internet Explorer and Navigator.

Q: Does Java Plug-in support SSL?

A: No. We are evaluating the feature for a future release of Java Plug-in.

How Does it Work?   back to top  

Q: Does the Java Plug-in replace Microsoft's or Netscape's Java runtime with Sun's JRE?

A: No. The Java Plug-in does not replace the browser's underlying virtual machine. Rather, the Java Plug-in simply enables web page authors to specify that Sun's JRE is used instead of the default Java runtime.

Q: Do developers need to modify their applets in order to support the Java Plug-in?

A: No. Any JDK 1.1-based, 100% Pure Java applets should run unmodified using the Java Plug-in.

Q: What happens on browsers other than IE or Navigator, or on non-supported platforms?

A: The default conversion template provided with the Java Plug-in HTML Converter (used on the demonstration page), is designed such that the applet will not be rendered in browsers other than Internet Explorer and Netscape Navigator on platforms other than Windows 95, Windows 98, Windows NT 4.0, and Solaris 2.5 and 2.6. However the Java Plug-in HTML Converter provides additional templates allowing web page authors to specify that on non-supported platforms applets will be rendered using the original <APPLET> tag using the browser's default Java runtime. See this related question for more information.

Q: As a web page author, how do I use the Java Plug-in?

A: To utilize all of the features and capabilities of JDK 1.1 in IE or Navigator, web page authors must modify the page's HTML to specify the use of Sun's JRE via the Java Plug-in. Sun is providing a written specification, to guide web page authors how to make these changes. In addition, Sun provides the Java Plug-in HTML Converter, free of charge, that will automatically make the changes to the HTML of a selected web page (or set of web pages).

Q: How long does it take to download and install the Java Plug-in the first time?

A: The Java Plug-in installer is approximately 5 MB in size. Download and install times will vary depending on the type of network connection and overall system performance. We expect typical total download and installation times (over a local area network) will vary from three to ten minutes. In subsequent encounters of web pages that specify the use of the Java Plug-in, it is invoked instantaneously from the user's hard drive and the applet is rendered.

Q: Why is the download and installation experience different in Netscape Navigator than in Internet Explorer?

A: The releases of Netscape Navigator supported by the Java Plug-in do not provide mechanisms that allow for the automatic download and installation of the Java Plug-in software, as in Internet Explorer. The first time Netscape Navigator comes across a web page that is enabled for the Java Plug-in (the "activated page"), it redirects the user to another web page to download and install the Java Plug-in software on the user's system. The user must then return to the "activated page" to render the applet using the Java Plug-in. From that point forward, the browser automatically invokes the Java Plug-in software each time it comes across web pages that supports the technology--completely transparent to the end user.

Q: How can I open the Java Plug-in Console on Windows 95, Windows 98 or Windows NT? 

A: On the Start menu, choose Start-->Programs-->Java Plug-in Control Panel, then select "Enable Console." After restarting the browser, you should see the Console window.

HTML Converter   back to top  

Q: How will web page authors get the the Java Plug-in HTML Converter?

A: Sun is distributing the Java Plug-in HTML Converter royalty-free through the Java Plug-in HTML Converter download page.

Q: How significant or complex are the HTML changes required to invoke the Java Plug-in?

A: The Java Plug-in requires that web page authors make changes to their existing HTML code if they wish to have their JDK 1.1-based applets run using the Java Plug-in, rather than the browser's default Java runtime. While the changes are not trivial, they are not overly complex either.

To make this process easy for web page authors, Sun provides the Java Plug-in HTML Converter, free of charge, to automate this process. In addition, Sun has provided a detailed specification outlining the HTML changes required to use the Java Plug-in, and how web page authors can implement them "by hand". The Java Plug-in HTML Converter can be downloaded from the HTML Converter download page. For the HTML specification, see the Java Plug-in HTML Specification.

Q: What capabilities do the supplementary templates provided with the Java Plug-in HTML Converter provide? 

A: The Java Plug-in HTML Converter provides both a default template (default.tpl), and three supplementary templates. These supplementary templates allow web page authors to more explicitly target the browsers and platforms used in their environment when modifying their pages using the Java Plug-in HTML Converter:

  1. default.tpl:  The default template used by the Java Plug-in HTML Converter. The converted page can be used in Internet Explorer and Navigator to invoke the Java Plug-in on the supported platforms.
  2. extend.tpl:  The converted page can be used in any browser on any platform. If the browser is Internet Explorer or Navigator on Windows 95, Windows NT, or Solaris, Java Plug-in will be invoked. Otherwise, the browser's default Java runtime is used.
  3. ieonly.tpl:  The converted page can be used to invoke Java Plug-in in Internet Explorer on the supported platforms.
  4. nsonly.tpl:  The converted page can be used to invoke Java Plug-in in Navigator on the supported platforms. 

Q: How can I install the Java (.zip) version of the Java Plug-in HTML Converter? 

A: Set the CLASSPATH to the xxx.ZIP file that you just downloaded, and type "java install".

Q: How can I run the Java (.zip) version of the Java Plug-in HTML Converter after the installation?

A: The instructions are provided in the converter directory.

Q. Why don't my signed applets work with the Java Plug-in? 

A: Signed applets using the JDK javakey mechanism are supported in Java Plug-in.

The most common problem is that the identitydb.obj file is not in the expected home directory. To check where Java Plug-in expects to find the user's home directory, you can use the Java Control Panel to enable the Java Console. Then when Java Plug-in starts up it will print out the user's home directory as the third line on the console.

Make sure that your identitydb.obj file is in that directory.

Q. The JIT doesn't seem to be enabled. Why not? 

A: Normally the JIT is enabled by default. However there is a known bug that can sometimes affect the JIT. To make sure the JIT is enabled you can set the Windows environment variable JAVA_COMPILER=symcjit.

Troubleshooting   back to top  

Q: My Netscape browser exits after reporting a divide-by-zero error. Why is this happening?

A: There is a known conflict when using JRE 1.1.8 and the Full Circle feature in Netscape Navigator 4.6 that causes unstable behavior of Java Plug-in 1.1.3. This conflict results in the browser exiting after the user clicks "OK" in an error dialog box reporting a divide-by- zero error has occurred.

If this occurs, please disable the Full Circle software while using Java Plug-in . To disable Full Circle, do the following:

  1. From the Start menu, select Programs -> Netscape Communicator 4.6 -> Utilities -> Netscape Quality Feedback Agent
  2. On the Settings menu of the Feedback Agent select "Turn Agent Off"

Q: I successfully installed Java Plug-in, but I cannot get any of the examples or the control panel to work. What is the problem?

A: In order to use the examples or the control panel you must first enable JavaScript.

Q: My signed applet is working fine in JDK/JRE AppletViewer. However, after I start using Java Plug-in in Internet Explorer or Netscape Navigator, it stops working. What's going on? 

A: AppletViewer and Java Plug-in look for the identitydb.obj file in different locations. Please make sure the identitydb.obj file is in the right location when running Java Plug-in.

Q: When I tried to deploy Java Plug-in in the intranet and put the binaries in the internal web server, IE doesn't download and install Java Plug-in when it encounters the converted page. What's going on? 

A: You may want to check that the CODEBASE in the OBJECT tag actually has the correct URL for the Java Plug-in. Also, turning off execute privileges on the directory in which you put the Java Plug-in executable may help.

Q: My applet contains an AWT dialog window. When it is displayed in the Java Plug-in, everything seems to hang. It used to work in Java Plug-in Early Access and JDK 1.1.5. What's going on? My applet is created using Symantec Visual Cafe. 

A: It turns out that a change in the JDK 1.1.6 is causing this problem. If the show() method in your Dialog class is synchronized, the Java Plug-in will hang. To resolve this issue, you can simply remove the synchronized keyword from the show() method.

Q: I am trying to install the Java Plug-in in a network drive. However, it doesn't install. Why? 

A: If your network drive is protected or read-only, you will not be able to install the Java Plug-in. Please contact your system administrator for more details.

Q: I am trying to install Java Plug-in. However, whenever the install program tries to install the Java Plug-in for Netscape Navigator, it displays an error. My Navigator is on a network drive. Is there a way to fix this? 

A: If your Navigator is installed on a network drive, you may not have the permission to install the plugin DLL into the Navigator Plugins directory. Please contact your system administrator for more details.

Q: I am trying to call AppletContext.getDocumentBase, but all I get is a URL without the filename of the document in both IE and NS. Why? 

A: This is a known issue in Java Plug-in 1.1.1. Because of the limitation of the Netscape Plug-in API, we were not able to obtain the filename of the document. Thus, calling AppletContext.getDocumentBase returns only the URL without the filename.

Q: I'm having trouble installing the Java Plug-in on my Win32 machine. I see the error: "An application error has occurred and an application error log is being generated. Exception: access violation ..." What might be the problem? 

A: The Win32 installation (using Installshield's installer) may not work if you have Quarterdeck's Cleansweep product running in the background.

Q: I am experiencing problems getting an applet to render using Java Plug-in. What is the cause of this?

A: While this may be due to a variety of circumstances unique to your operating environment, two frequent causes of this problem and the requisite workarounds are provided below:

Scenario 1: Security Exception

I am using the Java Plug-in and each time I try to load an applet on a web page that specifies the Java Plug-in, when the applet is loaded, a SecurityException is triggered.

Problem: Your network does not support DNS (Domain Name Service). In order to perform certain security checks, the Applet SecurityManager needs to be able to find the IP address from which your applet was downloaded. If DNS is not available, these security checks may fail.

Workaround: When visiting the target web page, specify an IP address rather than a hostname in the URL. For example, use "".

Scenario 2: Applet does not start using IE 3.02 and NT 4.0

I am using the Java Plug-in to run the demos on Sun's web site, using Internet Explorer 3.02 on Windows NT 4.0. Instead of rendering the applet, the browser displays a message that says "Your browser understands the <APPLET> tag but is not running the applet for some reason"

Problem: This is caused by an installation bug in Internet Explorer 3.02. When you install Internet Explorer 3.02 on Windows NT 4.0, some of the settings are stored in the HKEY_CURRENT_USER in the Windows registry. However, when you login to Windows NT using another user account, these settings in the registry can no longer be accessed because they are in a different user account.

Workaround: Either reinstall Internet Explorer 3.02 in the current user account, or install Internet Explorer 4.

Q: I changed my browser setting when Java Plug-in is running, but it still uses the old settings after the change?

A: The browser settings are read in by Java Plug-in when it is started. These settings are valid throughout the lifetime of the browser session. To make Java Plug-in read in the new settings, simply restart your browser. If you running Active Desktop with Java Plug-in, you need to restart the machine.

Q: Why does Java Plug-in not work when my server is protected?

A: Most mechanisms in enabling protected directories in the web server use cookies. However, Java Plug-in does not currently provide support for cookies. Although you may login to your web server and generate a cookie with your browser, it is not accessible by Java Plug-in.

Q: Using Navigator, when I print a web page that contains an applet using Java Plug-in, the applet does not show up in the printout. Why?

A: This is caused by a bug in the plug-in API in Navigator 4.0 and later. There is currently no workaround to this problem. This problem does not appear when using Java Plug-in with Navigator 3.0.

Q: When I loaded my applet, it said "noninit" or "applet not initialized" in the browser's status bar. How can I identify the cause of the problem?

A: Follow these steps:

  1. Select Java Console from the Java Plug-in Control Panel and run the applet again.
  2. Look at the error message in the Java Console.
  3. If you are accessing the applet through the network, make sure the proxy info shown in the Java Console is correct.
  4. Make sure all the class/JAR files are in the right directory.
  5. Make sure the converted HTML page is correct.
  6. Try the unconverted page with AppletViewer on the same machine. If it works, please recheck 3, 4, and 5 again.

Q: After I install Java Plug-in, why won't the Win32 plug-in load in Navigator?

A: It may be that installation of Java Plug-in didn't complete successfully. Make sure the file NPJava32.dll is in the Plugin directory. Otherwise, just copy it from the Plug-in/bin directory, and it should work.

Q: After I installed the Netscape JDK 1.1 patch to Navigator 4.04, the Java Plug-in becomes unstable in Navigator. After I uninstalled the patch, the Java Plug-in works fine again. What's going on? Would Navigator 4.05 work better?

A: It is a known problem that applying the Netscape JDK 1.1 patch to Navigator 4.04 can make the browser unstable even without using Java Plug-in. For further information on known problems with the JDK 1.1 patch for Navigator, please check http://developer.netscape.com. Currently, the Netscape JDK 1.1 patch for Navigator 4.05 is also available, but it is still in preview release. If you have experienced stability problems using Project Java Activator for Navigator with the JDK 1.1 patch, we strongly recommend that you uninstall the patch.

Miscellaneous Questions   back to top  

Q: How do I specify a JAR file as part of an OBJECT or EMBED tag? 

A: You can specify one or more JAR files by defining an ARCHIVE parameter to the OBJECT or EMBED tag.

With the OBJECT tag this looks like:

   <PARAM NAME=archive VALUE=demo.jar,fred.jar>

With the  
             EMBED tag this looks like:


              Q: Does Java Plug-in support multiple JAR files in the                 ARCHIVE attribute in the                  APPLET tag? If so, why can't I get this to work?              

              A: Java Plug-in supports the  
             ARCHIVE attribute
in both the  
             EMBED and  
             OBJECT tags.  The most common mistake
is to put the JAR files in the wrong order. For example, if you use the Swing
set in Java Plug-in and specify  
Java Plug-in will fail to load the applet because by the time
              Myjar.jar is loaded and Java Plug-in tries to initialize
the applet,  
             swing.jar is not yet loaded. The JAR files in the
              ARCHIVE should be in the order of dependency. Since  
depends on everything else, it should be put at the end of the list. The
other common mistake is to put spaces or paths with the JAR file lists.

              Q: When I uninstall Java Plug-in, the Win32 plugin seems to stay in the machine. How can I remove that?   

              A: Delete the  
             NPJava32.dll from the Plugin directory.

              Q: Can I print from a Java Plug-in applet?  

              A: The Java Security Manager in JDK 1.1 does not allow applets
to create print jobs. This restriction may be relaxed in a future release.

              Q: Why do I get a yellow banner across my applet frame when using Java Plug-in? 

              A: When an applet creates a free-standing Frame, Java Plug-in
adds a yellow warning banner so users will realize they are dealing
with an untrusted applet window.

              Q: Can I disable the yellow warning banner on frames?  

              A: The yellow warning banner is an important security feature.
It cannot be disabled by untrusted applets.

If you use a signed applet, where the signing key is trusted by the
end user, then the warning banner will not be shown.

              Q: How do I prevent the warning banner covering my GUI state?  

              A: You should use the  
             getInsets() method to find
the size of your frame's decorative border. This includes the warning
banner. For example, if you create a  
             Frame with size 100x100, you
might find it has  
             insets [top=42,left=5,bottom=5,right=6] giving
you a drawable area of 89x53. You need to position your work within
the drawable area.

If you need to create a drawable area of a particular size, first 
create and show the  
             Frame, then use  
             getInsets to find 
the insets' sizes, then figure out the desired frame size by adding your 
desired size to the insets, then use  
             frame.setSize() to set your 
frame to that size.

              Q: Why does InetAddress.getLocalHost().getHostName() return "localhost"? 

This is a deliberate security feature in the JDK.  Untrusted applets
will not be given the real host name.

Trusted applets (such as signed applets) will be given the real host name.

              Q: Are the MIME types "application/x-java-vm/java-applet" and "application/x-java-vm/java-bean" still recognized by Java  Plug-in? 

              A: These two MIME types were used by the Java Plug-in 
EA1 release. In EA2, we introduced four new MIME types:

<td>    </td>
<td> </td>
<td>    </td>
<td> </td>
<td>    </td>
<td> </td>
<td>    </td>
<td> </td>

Java Plug-in 1.1.1 supports the following MIME types:
<td>    </td>
<td> </td>
<td>    </td>
<td> </td>

In addition, Java Plug-in 1.1.1 supports the following MIME types:
<td>    </td>
<td> </td>
<td>    </td>
<td> </td>

For more information about these MIME types, please check the Java Plug-in
HTML Specification. The old MIME types were still supported in EA2 and EA3 for
backward compatibility. However, these two old MIME types are not supported
in the FCS release. Please update your HTML pages accordingly.








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