How to read manifest.mf from POJO class (not a servlet) instantiated by spring?

Question

I have a simple service called BuildNumberService which would be instantiated by spring.

I'm trying to find the cleanest code for the class to find out the MANIFEST.MF file from the jar file it has been packaged into.

The code has to run inside a servlet container.

@Service
public class BuildNumberService {

    private static final String IMPLEMENTATION_BUILD = "Implementation-Build";

    private String version = null;

    public BuildNumberService() {

      // find correct manifest.mf
      // ?????


      // then read IMPLEMENTATION_BUILD attributes and caches it.
       Attributes mainAttributes = mf.getMainAttributes();
       version = mainAttributes.getValue(IMPLEMENTATION_BUILD);
    }

    public String getVersion() {
        return this.version;
    }
}

How would you do that ?

Edit: Actually, what I'm trying to do, is, find a resource by name which sits in the same package as the actual class.

Answer 1

I guess you can see the answer to that question.

Answer 2

Well if you know the jar is on the file system (e.g. not inside a war) and you also know that the security manager gives you the permission to access a class' protection domain, you can do it like this:

public static InputStream findManifest(final Class<?> clazz) throws IOException,
    URISyntaxException{
    final URL jarUrl =
        clazz.getProtectionDomain().getCodeSource().getLocation();
    final JarFile jf = new JarFile(new File(jarUrl.toURI()));
    final ZipEntry entry = jf.getEntry("META-INF/MANIFEST.MF");
    return entry == null ? null : jf.getInputStream(entry);
}