Deep reflective compare equals

Question

I am trying to validate serialize and de-serialize routines by comparing the resulting object with the original object. The routines can serialize arbitrary and deeply nested classes and consequently I want a comparison routine which can be given the original and final instance and reflectively walk through each value type and compare the values and iteratively dive into reference types to compare values.

I have tried the Apache Commons Lang EqualsBuilder.reflectionEquals(inst1, inst2) but this does not appear to do a very deep comparison, it simply compares reference types for equality rather than diving deeper into them:

The following code illustrates my issue. The first call to reflectionEquals returns true but the second returns false.

Is there a library routine anyone could recommend?

class dummy {
    dummy2 nestedClass;
}

class dummy2 {
    int intVal;
}

@Test
public void testRefEqu() {

    dummy inst1 = new dummy();
    inst1.nestedClass = new dummy2();
    inst1.nestedClass.intVal = 2;
    dummy inst2 = new dummy();
    inst2.nestedClass = new dummy2();
    inst2.nestedClass.intVal = 2;
    boolean isEqual = EqualsBuilder.reflectionEquals(inst1.nestedClass, inst2.nestedClass);
    isEqual = EqualsBuilder.reflectionEquals(inst1, inst2);
}

Answer 1

From the answer to this question https://stackoverflow.com/a/1449051/116509 and from some preliminary testing, it looks like Unitils' ReflectionAssert.assertReflectionEquals does what you're expecting. (Edit: but may be abandoned, so you could try AssertJ https://assertj.github.io/doc/#assertj-core-recursive-comparison)

2021 edit: EqualsBuilder now has a testRecursive option. However the unit test libraries mentioned will give you a better failure message to help debug, so depending on context, they're still the best option.

Answer 2

One method would be to compare objects using reflection - but this is tricky. Another strategy would be to compare byte arrays of serialized objects:

class dummy implements Serializable {
    dummy2 nestedClass;
}

class dummy2  implements Serializable {
    int intVal;
}

@Test
public void testRefEqu() throws IOException {

    dummy inst1 = new dummy();
    inst1.nestedClass = new dummy2();
    inst1.nestedClass.intVal = 2;

    dummy inst2 = new dummy();
    inst2.nestedClass = new dummy2();
    inst2.nestedClass.intVal = 2;

    boolean isEqual1 = EqualsBuilder.reflectionEquals(inst1.nestedClass, inst2.nestedClass);
    boolean isEqual2 = EqualsBuilder.reflectionEquals(inst1, inst2);

    System.out.println(isEqual1);
    System.out. println(isEqual2);

    ByteArrayOutputStream baos1 =new ByteArrayOutputStream();
    ObjectOutputStream oos1 = new ObjectOutputStream(baos1);
    oos1.writeObject(inst1);
    oos1.close();

    ByteArrayOutputStream baos2 =new ByteArrayOutputStream();
    ObjectOutputStream oos2 = new ObjectOutputStream(baos2);
    oos2.writeObject(inst1);
    oos2.close();

    byte[] arr1 = baos1.toByteArray();
    byte[] arr2 = baos2.toByteArray();

    boolean isEqual3 = Arrays.equals(arr1, arr2);

    System.out.println(isEqual3);

}

Your application serializes and deserializes objects so this approach seems to be the fastest solution (in terms of CPU operations) for your problem.

Answer 3

You can use AssertJ's field by field recursive comparison feature, for example:

import static org.assertj.core.api.BDDAssertions.then;

then(actualObject).usingRecursiveComparison().isEqualTo(expectedObject);

Answer 4

I understand that this is a late reply, but this might be useful to someone in need. So in my project I was in need to compare the entire set of deserialzied values to see if they matched properly and the dep I used is Javers. It integrates well with SpringBoot and the usage is very straight forward.

Here is the sample impl:

@RunWith(SpringRunner.class)
public class DeserializerTest {

    private HubMessage message;
    private static final String EXPECTED_INVALID_MSG = "testInvalidMessage";
    private PlatformEventHeader msgHeaders;
    private ObjectMapper objectMapper = new ObjectMapper();
    private final DeserializerClass testDeserializerClass = new DeserializerClass();
    private String TOPIC_TEST = "testTopic";
    private static final String ACTUAL_HUBMESSAGE = "XXXStringValueofmessage";
    @Before
    public void stubSetup() throws IOException {
        // setup the message
       message = new HubMessage ();

        //setup the headers
       msgHeaders = new PlatformEventHeader();
        ...
        ...

        DomainEvent event= new DomainEvent();
        Map<String, String> msgEventObjMap = new HashMap<>();
        ...
        event.setMessage(msgEventObjMap);
        message.setEvent(event);
        message.setHeader(msgHeaders);

    }

    @Test
   public void test_deserialize_validMessage() throws JsonProcessingException {
          // My actual deserialzierClass
          HubMessage messageReceived = testDeserializerClass.deserialize(TOPIC_TEST,  
             new RecordHeaders(),ACTUAL_HUBMESSAGE .getBytes());

        Javers javers = JaversBuilder.javers().build();
        Diff diff = javers.compare((Object)objectMapper.convertValue(messageReceived, Object.class),
                (Object)objectMapper.readValue(ACTUAL_HUBMESSAGE, Object.class));
        Assert.assertEquals(diff.getChanges().size() , 0);
    }

I used the Diff to identify if any changes are there in the objects. Now overriding/using toString() is not efficient as it expects the properties tobe in the same order for the expected and actual value in Matchers. Unitils solve this might impose a lot of headache with a lot of third party jars that are downloaded transitively. So a better bet is to use Javers.io

Answer 5

Implement the equals() method on the classes in question. The equals of each call will compare the equality of the nested classes (or, if you like, will compare the equality of the data members). A correctly written equals method will always result in a deep compare.

In your example, the dummy class equals would be something like this:

public boolean equals(Object other)
{
    if (other == this) return true;
    if (other instanceOf dummy)
    {
        dummy dummyOther = (dummy)other;
        if (nestedClass == dummyOther.nestedClass)
        {
           return true;
        }
        else if (nestedClass != null)
        {
           return nestedClass.equals(dummyOther);
        }
        else // nestedClass == null and dummyOther.nestedClass != null.
        {
           return false;
        }
    }
    else
    {
      return false;
    }
}