How to Access the Manifest File of the Originating JAR in Applet or Webstart Environments?

Retrieving the Manifest File of the Originating JAR

To access the Manifest file of the JAR that initiated your application, conventional methods like getClass().getClassLoader().getResources(...) may not suffice, especially in environments like applets or webstart applications. Here are two alternative approaches to consider:

Iterating through Retrieved URLs:

1. Use getResources() to retrieve a collection of URLs representing potential Manifest files.
2. Iterate through these URLs, reading each one as a Manifest until you locate the one you need.

Example Code:

Enumeration<URL> resources = getClass().getClassLoader().getResources("META-INF/MANIFEST.MF");
while (resources.hasMoreElements()) {
    try {
        URL url = resources.nextElement();
        Manifest manifest = new Manifest(url.openStream());
        // If manifest is null, try using JarInputStream instead: manifest = url.openStream().getManifest();

        // Verify and process the manifest as needed
        ...
    } catch (IOException e) {
        // Handle the exception
    }
}

Checking ClassLoader Type and Using findResource():

1. Determine if getClass().getClassLoader() is an instance of java.net.URLClassLoader, typically the case for Sun classloaders, including AppletClassLoader.
2. If so, cast it and use findResource() to retrieve the Manifest.

Example Code:

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

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