Instanceof returns false for same class after serialization

Question

Instanceof returns false for same class after org.springframework.security.oauth2.common.util.SerializationUtils fasterxml deserialization in Spring boot application

new ObjectMapper().readValue(serialized, User.class);

Class

public class User implements Serializable {//...
}

Because new object getClass().getClassloader() returns different classloader, how to fix this and casting issue?

Answer 1

In this case you should compare the class names rather then using instanceof. Even if the classes are loaded by different class loaders the canonical names will be the same:

public boolean haveSameCanonicalName(Object object, Class<?> clazz) {
     String actualClassName = object.getClass().getCanonicalName();
     String expectedClassName = clazz.getCanonicalName();
     return actualClassName.equals(expectedClassName);
}

And then you can use it like this:

if (haveSameCanonicalName(user, User.class)) {
    // Do something here
}

UPDATE:

If you still need to cast the object there is a workaround:

 public class CrossCastUtils {

    private final ObjectOutputStream oos;
    private final ObjectInputStream ois;

    public CrossCastUtils() throws IOException {
        final PipedOutputStream pos = new PipedOutputStream();
        final PipedInputStream pis = new PipedInputStream(pos);
        oos = new ObjectOutputStream(pos);
        ois = new ObjectInputStream(pis);
    }

    public <T> T cast(Object object) throws IOException, ClassNotFoundException {
        oos.writeObject(object);
        oos.flush();
        return (T) ois.readObject();
    }

Try to run this test:

@Test
public void testCrossCast(){
    Object initial = ... // retrieve it as you did before
    User result = CrossCastUtils.cast(initial);

    assertFalse(initial instanceof User);
    assertTrue(result instanceof User);
}