http://javers.org is library that does exacly what you need: has methods like compare(Object leftGraph, Object rightGraph) returning the Diff object. Diff contains a list of changes (ReferenceChange, ValueChange, PropertyChange) e.g.

given:
DummyUser user =  dummyUser("id").withSex(FEMALE).build();
DummyUser user2 = dummyUser("id").withSex(MALE).build();
Javers javers = JaversTestBuilder.newInstance()

when:
Diff diff = javers.compare(user, user2)

then:
diff.changes.size() == 1
ValueChange change = diff.changes[0]
change.leftValue == FEMALE
change.rightValue == MALE

It can handle cycles in graphs.

In addition you can get Snapshot of any graph object. Javers has JSON serializers and deserializers to snapshot, and changes so you can easily save them in database. With this library you can easily implement a module for auditing.

You can use java Reflection to compare two same type beans those have getter for all comparing properties.

public static void compareBeans(Object bean1, Object bean2, String... propertyNames)
          throws IntrospectionException,
          IllegalAccessException, InvocationTargetException {
        Set<String> names = new HashSet<String>(Arrays
            .asList(propertyNames));
        BeanInfo beanInfo = Introspector.getBeanInfo(bean1
            .getClass());
        for (PropertyDescriptor prop : beanInfo
            .getPropertyDescriptors()) {
          if (names.remove(prop.getName())) {
            Method getter = prop.getReadMethod();
            Object value1 = getter.invoke(bean1);
            Object value2 = getter.invoke(bean2);
            if (value1 == value2
                || (value1 != null && value1.equals(value2))) {
              continue;
            }

            System.out.println("Property = "+prop.getName() +" Value of been1 ="+value1 +" : Value of bean2 ="+value2);
          }
        }
      }

Usage:

If i compare two beans of Student class which has two properties name and age like

BeanComparator.compareBeans(new Student("Amita", 21), new Student("Amit", 23) , props);

Output:

Property = age Value of been1 =21 : Value of bean2 =23
Property = name Value of been1 =Amita : Value of bean2 =Amit