How to dynamically load a class, de-serialize an object that was serialized using the loaded class, and ignore serialVersionUID in a unit test.

DynamicClassLoadingExample.java

  private URLClassLoader childClassLoader;
  private Class<?> clazz;

  @Before
  public void init() throws Exception {
    // put class file in same package together with this source file
    URL url = getClass().getResource("MyClass.class").toURI().toURL();
    childClassLoader = new URLClassLoader(new URL[] { url },
      getClass().getClassLoader());
    clazz = childClassLoader.loadClass("com.bpd.old.MyClass");
  }

  @After
  public void cleanup() throws Exception {
    childClassLoader.close();
  }

  @Test
  public void test() throws Exception {
    InputStream is = getClass().getResourceAsStream("MyClass.old");
    CustomObjectInputStream ois = new CustomObjectInputStream(is);
    System.out.println(ois.readObject());
  }

  private class CustomObjectInputStream extends ObjectInputStream {

    public CustomObjectInputStream(InputStream in) throws IOException {
      super(in);
    }

    @Override
    protected Class<?> resolveClass(ObjectStreamClass desc) throws IOException,
        ClassNotFoundException {
      if (!desc.getName().contains("com.bpd.old.MyClass")) {
        return super.resolveClass(desc);
      }
      return clazz;
    }

    @Override
    protected ObjectStreamClass readClassDescriptor() throws IOException,
        ClassNotFoundException {
      ObjectStreamClass resultClassDescriptor = super.readClassDescriptor();
      if (resultClassDescriptor.getSerialVersionUID() == 0) {
        // if serialVersionUID is zero, object is an enum
        return resultClassDescriptor;
      }
      ObjectStreamClass localClassDescriptor = ObjectStreamClass.lookup(clazz);
      if (localClassDescriptor != null) {
        final long localSUID = localClassDescriptor.getSerialVersionUID();
        final long streamSUID = resultClassDescriptor.getSerialVersionUID();
        if (streamSUID != localSUID) {
          resultClassDescriptor = localClassDescriptor;
        }
      }
      return resultClassDescriptor;
    }

  }