How to Read the Manifest File of Your Own Jar When Running From an Applet or Webstart?

How to Read the Manifest File of Your Own Jar

Reading the Manifest file of your own Jar is essential for understanding the structure and dependencies of your code. However, accessing the Manifest file can be challenging, especially when running the application from an applet or webstart.

To overcome this challenge, you have two primary options:

1. Iterate Through URLs

This method involves iterating through all the resources loaded into the Java Runtime and examining their URLs. The goal is to identify the URL that contains the META-INF/MANIFEST.MF file and read it as a Manifest object. The following code snippet demonstrates this approach:

Enumeration<URL> resources = getClass().getClassLoader().getResources("META-INF/MANIFEST.MF");
while (resources.hasMoreElements()) {
    try {
        Manifest manifest = new Manifest(resources.nextElement().openStream());
        // Check if this is your manifest and process it accordingly
    } catch (IOException e) {
        // Handle the exception
    }
}

2. Check Loader Type and Use findResource()

If the getClassloader() returns an instance of java.net.URLClassLoader (like AppletClassLoader), you can cast it and call the findResource() method. This method has been known to retrieve the desired manifest directly, particularly for applets. Here's an example:

URLClassLoader cl = (URLClassLoader) getClass().getClassLoader();
try {
    URL url = cl.findResource("META-INF/MANIFEST.MF");
    Manifest manifest = new Manifest(url.openStream());
    // Process the manifest
} catch (IOException e) {
    // Handle the exception
}

By utilizing one of these approaches, you can effectively read the Manifest file associated with your own Jar, even when running from a restricted environment like an applet or webstart.

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