How to Deploy a Java Applet Using JNLP: A Step-by-Step Guide

What is the process to deploy a Java applet using JNLP?

Example of a JNLP file: 
<application-desc main-class="com.example.Main">
    <update check="always"/>
</application-desc>

Deploying a Java applet using Java Network Launch Protocol (JNLP) allows users to run Java applications directly from the web browser without needing to install them locally. This method leverages the Java Web Start technology to manage the deployment and execution of Java applications.

<jnlp spec="1.0+" codebase="http://example.com/" href="myapplet.jnlp">
    <information>
        <title>My Java Applet</title>
        <vendor>Example Corp</vendor>
        <description>My first applet using JNLP</description>
    </information>
    <security>
        <all-permissions/>
    </security>
    <resources>
        <j2se version="1.8+"/>
        <jar href="myapplet.jar"/>
    </resources>
    <application-desc main-class="com.example.Main"/>
</jnlp>

Causes

• Lack of proper security settings in the JNLP file.
• Incomplete or incorrect MIME type configurations on the server.
• User's Java Runtime Environment (JRE) settings may block the applet from running.

Solutions

• Ensure the JNLP file includes correct security policies and permissions.
• Configure the server to serve JNLP files with MIME type `application/x-java-jnlp-file`.
• Instruct users to enable Java content in their browser settings.
• Test with the latest version of JRE to ensure compatibility.

Mistake: Not specifying a correct MIME type on the server for JNLP files.

Solution: Configure your server to use 'application/x-java-jnlp-file' as the MIME type for JNLP files.

Mistake: Ignoring security restrictions that may prevent applet execution.

Solution: Include <security><all-permissions/></security> in your JNLP file to stop most security issues.

Mistake: Failing to test the deployment across different browsers and environments.

Solution: Ensure comprehensive testing on various Java versions and browsers to catch compatibility issues.