Taking Advantage of Sun’s Java Plug-in

Although Sun encourages the use of the <applet> tag for all applets, an experienced developer will recognize that this does not always give you the recommended behavior. For example, in some browsers, <applet> does not give you the full functionality of Sun’s Java Plug-in while the <object> tag, which is mapped to the mime type application/x-java-applet., does. Table 2-1 shows the effect of the <applet> tag in comparison to the <object> or <embed> tags. You can see that the suggested <applet> tag will only have the desired results in the Mozilla/Netscape. To work around the different usage of the <applet> tag, you have two options. You can just use the tag listed in Table 2-1 that invokes the Java Plug-in or you can use Sun’s HTML converter to get HTML that will work in any browser. This is available at http://java.sun.com/products/plugin/1.3/docs/htmlconv.html

Table 2-1 Interpretation of HTML tags in common Mac OS X browsers

Note: Internet Explorer in Mac OS X version 10.2 may not interperet tags as documented in Table 2-1. The Mac OS X version 10.2 Java Release Notes have more information on this topic.

Although your applets should continue to function in Mac OS X version 10.2, you might want to modify the HTML that calls them so that they take full advantage of the underlying Java Plug-in as illustrated in “Effect of HTML tags in Mac OS X 10.2”.

Figure 2-1 Effect of HTML tags in Mac OS X 10.2

What will this modification give you? Primarily, it will provide for a better experience for people that use your applets. Changes have been made in the following areas which are discussed below:

• Jar file caching


• Signed jar files


• The Java Console


• Ability to fine tune the applet through the Java Plugin Settings application.

This section covers:

Jar Caching
Signed Jar Files
The Java Console
Java Plugin Settings

Jar Caching

You can now designate that you want to store certain jar files for repeated use. If you developed for Mac OS 9, you will notice that this is similar to jar caching on MRJ 2.2.x. The cache is stored in the users home folder in Library/Caches/Java. To take advantage of jar file caching, you may need to modify your HTML with the following tags:

<PARAM NAME = "cache_option" VALUE="plugin">

Turns on caching

<PARAM NAME = "cache_archive" VALUE="a.jar, b.jar, c.jar ">

This is an optional tag used to specify the list of jar files you want to cache

Jar files in cache_archive are searched first, then the jar files designated with the ARCHIVE tag are used

<PARAM NAME = "cache_version" VALUE="1.2.0.1, 2.1.1.2, 1.1.2.7">

This is an optional tag used to specify the version number of the jar files designated with cache_archive. Each value corresponds to the respective jar files designated with cache_archive. If the version value is newer than what is cached, the jar file in the cache will be updated. If this tag is omitted, the plugin will check the server to see if their is a newer version available, and cache that version.

Jar file caching in Mac OS X version 10.2 conforms to the Java 1.3.1_03 standard. It does not conform to the Java 1.4 standard. This means that there are certain things you should keep in mind:

• Jar files in the ARCHIVE parameter are not cached.


• The <cache_version_ex> parameter is not supported.


• There is no Jar file indexing support.


• For better compatibility with the future it is suggested that you use the <cache_archive> and <cache_version> parameters.

Signed Jar Files

Signed jar files work the same as they did in Mac OS X version 10.1. If a user decides to always trust your jar file, a certificate will be stored in the user’s home folder in Preferences/Java Plugin certificates 1.3.1

What has changed is that users may now view their jar file certificates in the Java Plugin Setting application.

The Java Console

The Java Console provides a way to view what is happening with you applet while it is running. It can give you interactive thread information and allow you to force garbage collection. The Java Console is now the display medium for System.out System.err which were displayed in the Console applications in previous versions of Mac OS X. Overall, the Java Console provides you a simple way to log and trace the behavior of your Java applet.

Java Plugin Settings

This is a user application that allows users to fine tune how applets behave in Mac OS X. It behaves on Mac OS X such as it does on other platforms. Now that users can adjust settings like the virtual machine size, it important to recognize that settings you set while testing may not be the default settings that users have on their computer. These settings are stored per user in ~/Library/Preferences/com.apple.java.plugin.properties131.