Need to read own Jar's manifest, and not root-classloaders' manifest

Question

Hi,

i need to read the Manifest file, which delivered my class. but it seems that when i use

 getClass().getClassLoader().getResources(...)

i end up getting the MANIFEST from the first Jar loaded into the Java Runtime. My app will be running from applet or webstart, so i will not have access to my own .jar file i guess

i actually want to read the 'Export-package' attribute from the jar which started the Felix OSGi, so that i can expose those packages to Felix.

does anybody have an idea? Thanks

Answer 1

You can do one of two things:

1) Call getResources() and iterate through the returned collection of URLs, reading them as manifests until you find yours:

Enumeration<URL> resources = getClass().getClassLoader()
  .getResources("META-INF/MANIFEST.MF");
while (resources.hasMoreElements()) {
    try {
      Manifest manifest = new Manifest(resources.nextElement().openStream());
      // check that this is your manifest and do what you need or get the next one
      ...
    } catch (IOException E) {
      // handle
    }
}

2) You can try checking whether getClass().getClassLoader() is an instance of java.net.URLClassLoader. Majority of Sun classloaders are, including AppletClassLoader. You can then cast it and call findResource() which has been known - for applets, at least - to return the needed manifest directly:

URLClassLoader cl = (URLClassLoader) getClass().getClassLoader();
try {
  URL url = cl.findResource("META-INF/MANIFEST.MF");
  Manifest manifest = new Manifest(url.openStream());
  // do stuff with it
  ...
} catch (IOException E) {
  // handle
}

Answer 2

Why are you including the getClassLoader step? If you say "this.getClass().getResource()" you should be getting resources relative to the calling class. I've never used ClassLoader.getResource(), though from a quick look at the Java Docs it sounds like that will get you the first resource of that name found in any current classpath.

Answer 3

You can find the URL for your class first. If it's a JAR, then you load the manifest from there. For example,

Class clazz = MyClass.class;
String className = clazz.getSimpleName() + ".class";
String classPath = clazz.getResource(className).toString();
if (!classPath.startWith("jar")) {
  // Class not from JAR
  return;
}
String manifestPath = classPath.substring(0, classPath.lastIndexOf("!") + 1) + 
    "/META-INF/MANIFEST.MF";
Manifest manifest = new Manifest(new URL(manifestPath).openStream());
Attributes attr = manifest.getMainAttributes();
String value = attr.get(name);