Reading my own Jar's Manifest

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.startsWith("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.getValue("Manifest-Version");

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
   }
   

You can use Manifests from jcabi-manifests and read any attribute from any of available MANIFEST.MF files with just one line:

String value = Manifests.read("My-Attribute");

The only dependency you need is:

<dependency>
  <groupId>com.jcabi</groupId>
  <artifactId>jcabi-manifests</artifactId>
  <version>0.7.5</version>
</dependency>

Also, see this blog post for more details: http://www.yegor256.com/2014/07/03/how-to-read-manifest-mf.html