Used for grabbing a value associated with a key from a manifest in your classpath.

Manifests.java

import java.io.IOException;
import java.net.URL;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.jar.Manifest;
import java.util.stream.Stream;

/**
 * Created by kylestev
 */
public class Manifests {
    private static final String MANIFEST_FILE = "META-INF/MANIFEST.MF";

    private static List<URL> manifestUrls() {
        try {
            final ClassLoader current = Thread.currentThread().getContextClassLoader();

            return Collections.list(current.getResources(MANIFEST_FILE));
        } catch (IOException e) {
            return Collections.emptyList();
        }
    }

    private static Manifest loadManifest(final URL url) {
        try {
            return new Manifest(url.openStream());
        } catch (IOException e) {
            return null;
        }
    }

    private static Stream<Manifest> load() {
        return manifestUrls()
                .stream()
                .map(Manifests::loadManifest)
                .filter(m -> m != null);
    }

    public static Optional<String> get(final String key) {
        return load()
                .map(m -> m.getMainAttributes().getValue(key))
                .filter(v -> v != null)
                .findFirst();
    }
}