How to use

getDelegate

method

in

co.cask.cdap.common.lang.Delegators

/**
 * Finds the {@link MapReduceClassLoader} from the {@link ClassLoader} inside the given {@link Configuration}.
 *
 * @throws IllegalArgumentException if no {@link MapReduceClassLoader} can be found from the {@link Configuration}.
 */
public static MapReduceClassLoader getFromConfiguration(Configuration configuration) {
 return Delegators.getDelegate(configuration.getClassLoader(), MapReduceClassLoader.class);
}

/**
 * Finds the {@link MapReduceClassLoader} from the {@link ClassLoader} inside the given {@link Configuration}.
 *
 * @throws IllegalArgumentException if no {@link MapReduceClassLoader} can be found from the {@link Configuration}.
 */
public static MapReduceClassLoader getFromConfiguration(Configuration configuration) {
 return Delegators.getDelegate(configuration.getClassLoader(), MapReduceClassLoader.class);
}

@Test
public void testWeakReferenceClassLoader() throws Exception {
 // Creates a jar that has Application class in it.
 Location jar = AppJarHelper.createDeploymentJar(new LocalLocationFactory(TMP_FOLDER.newFolder()),
                         ClassLoaderTest.class);
 // Create a class loader that load from that jar.
 File unpackDir = TMP_FOLDER.newFolder();
 BundleJarUtil.unJar(jar, unpackDir);
 ClassLoader cl = new DirectoryClassLoader(unpackDir, null, "lib");
 // Wrap it with the WeakReference ClassLoader
 ClassLoader classLoader = new WeakReferenceDelegatorClassLoader(cl);
 // Load class from the wrapped ClassLoader, should succeed and should be loaded by the delegating ClassLoader.
 Class<?> cls = classLoader.loadClass(ClassLoaderTest.class.getName());
 Assert.assertSame(cl, cls.getClassLoader());
 Assert.assertSame(cl, Delegators.getDelegate(classLoader, ClassLoader.class));
 // There is no good way to test the GC of the weak reference referent since it depends on GC.
}