Chapter 9 Continued: Win32 Platform

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On Win32 platforms, Java Plug-In software is bundled with the Java 2 Runtime Environment. Java Plug-In lets web browsers use the Java 2 Runtime Environment to run 1.2-based applets and JavaBeans components instead of the web browser's default virtual machine. The Java Plug-In works with Netscape Communicator and Microsoft Internet Explorer.

• Get Downloads
• Install JRE with Java Plug-In
• Install HTML Converter
• Install the Security Policy File
  • Types of Policy Files
  • Installing the Policy File
  • Changing the Name or Location
• Run the Administration Applet
• How Does it Work?

Get Downloads

To install and use the Java Runtime Environment with Java Plug-In, you need the following downloads. Put the downloads in a temporary directory.

• Java Runtime Environment with Java Plug-In for Win32 Platforms.
• Java Plug-In HTML Converter

Install JRE with Java Plug-In

An optionally installable version of the Java 2 Runtime Environment with Java Plug-In is included with the Java 2 SDK download. You can also download and install Java 2 Runtime Environment with Java Plug-In separately.

Either way, install the Java 2 Runtime Environment with Java Plug-In by double-clicking its icon and following the installation instructions. When the installation completes, you will see the Java Plug-In control panel on your Windows Start menu under Programs.

Install the HTML Converter

Your browser will not automatically use the Java Plug-In when you load an HTML file with an applet. You have to download and run the Java Plug-In HTML Converter on the HTML page that invokes the applet to direct the applet ro run using the plug-in instead of the browser's default runtime.

Unzip the Java Plug-In HTML Converter download:

  unzip htmlconv12.zip

Add the HTMLConverter.java program or its directory to your CLASSPATH.

Security Policy File

The auction application uses an applet running in a browser for administrative operations. In the Java 2 platform, applets are restricted to a sandbox-like environment and need permission to access system resources outside their restricted environment. Applets are restricted to read operations within their local directory. All other access operations require permission.

Types of Policy Files

You need a policy file to grant access permissions to the Administration applet. If the applet runs on a disk other than the disk where the browser is running, the applet will also need to be signed. See Signed Applets for information on signing and deploying applets.

There are three kinds of policy files: system, user, and program. The system policy file is located in jdk1.2\jre\lib\security\java.policy or jre1.2\lib\security/java.policy and contains permissions for everyone on the system.

The user policy file is located in the user's home directory. The user policy file provides a way to give certain users additional permissions over those granted to everyone on the system. The permissions in the system file are combined with the permissions in the user file.

A program policy file can be located anywhere. It is specifically named when an application is invoked with the java command or when an applet is invoked with applet viewer. When an application or applet is invoked with a specific policy file, the permissions in that policy file take the place of (are not combined with) permissions specified in the system or user policy file. Program policy files are used for program testing or intranet deployment of applets and applications.

Install the Security Policy File

Place the security policy file in your home directory and name it java.policy. When the applet tries to perform an action that requires a policy file with a permission, the policy file is loaded from this directory and remains in effect until you exit and restart the browser.

If an applet tries to perform an access operation without the right permission, it quietly quits without raising either an applet or a browser error.

Changing the Name or Location

You can change the name and/or location of the default system or user policy file. Edit the jdk1.2\jre\lib\security\java.security or jre1.2\lib\security\java.security file and add a third entry specifying the name and location of an alternative policy file.

  policy.url.1=file:${java.home}\lib\security\java.policy
  policy.url.2=file:${user.home}\java.policy
  policy.url.3=file:\<mypolicyfile path and name>

Note: On Windows/NT machines, you might place the policy file in the C:\Winnt\Profiles\<userid>\java.policy directory.

Run the Administration Applet

Copy the Java Archive (JAR) file with the Administration applet and policy file to its final location. In this example, that location is the \home\zelda\public_html directory. Next, extract the applet class file and policy file from the JAR file:

  cp admin.jar \home\zelda\public_html
  jar xf applet.jar

The extraction places the policy file under public_html and creates an admin directory under the public_html directory with the applet class file in it. Rename the policy file in the public_html directory to java.policy and copy it to your home directory.

In the public_html directory, create an HTML file that invokes the Administration applet class. Be sure to include the admin directory when you specify the applet class to the CODE option. Note that when using Java Plug-In, you cannot have the browser load the class file from the Java Archive (JAR) file.

<HTML>
<BODY>
<APPLET CODE=admin/AdminApplet.class
  WIDTH=550
  HEIGHT=150>
</APPLET>
</BODY>
</HTML>

Start the HTML Converter.

  java HTMLConverter

In the HTML Converter graphical user interface, select One File:, specify the path to the admin.html file, and click the Convert button.

How Does It Work?

On Windows machines, the Java Plug-In finds the Java Runtime Environment (JRE) by running the OLE custom control file beans.ocx installed by default in the \Program Files\JavaSoft\1.2\bin web browser directory. The OLE control examines the Windows registry to find the Java Plug-In key and uses the value associated with that key to find the installed JRE.

If you find that the wrong JRE is being loaded, use regedit to check the Java Plug-In registry values for the current user. If no JRE is installed, the control checks the Java Plug-in values for HKEY_LOCAL_MACHINE. You should see a value for Java Runtime Environment under Software\JavaSoft.

After the conversion completes, load the admin.html file in your browser.

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