How to compare two objects and get the changed fields

Question

In here im logging the changes that has been done to a particular Object record. So im comparing the old record and the updated record to log the updated fields as a String. Any idea how can I do this?

Dinger

Compare field by field and log the changed ones? – Snooperscope

Seems your are not happy with comparing each attributes. In this case JAVERS can be an option. – Ballot

Is your old record stored in an object and you set the new record to it, or you use 2 record object to store this 2 records? – Crackleware

Answer 1

Well i found a solution as below :

  private static List<String> getDifference(Object s1, Object s2) throws IllegalAccessException {
    List<String> values = new ArrayList<>();
    for (Field field : s1.getClass().getDeclaredFields()) {
        field.setAccessible(true);
        Object value1 = field.get(s1);
        Object value2 = field.get(s2);
        if (value1 != null && value2 != null) {
            if (!Objects.equals(value1, value2)) {
                values.add(String.valueOf(field.getName()+": "+value1+" -> "+value2));
            }
        }
    }
    return values;
}

Dinger

Answer 2

You may use javers library for this.

  <groupId>org.javers</groupId>
  <artifactId>javers-core</artifactId>

POJO:

    public class Person {
    private Integer id;
    private String name;

    // standard getters/constructors
}

Usage:

    @Test
public void givenPersonObject_whenApplyModificationOnIt_thenShouldDetectChange() {
    // given
    Javers javers = JaversBuilder.javers().build();

    Person person = new Person(1, "Michael Program");
    Person personAfterModification = new Person(1, "Michael Java");

    // when
    Diff diff = javers.compare(person, personAfterModification);

    // then
    ValueChange change = diff.getChangesByType(ValueChange.class).get(0);

    assertThat(diff.getChanges()).hasSize(1);
    assertThat(change.getPropertyName()).isEqualTo("name");
    assertThat(change.getLeft()).isEqualTo("Michael Program");
    assertThat(change.getRight()).isEqualTo("Michael Java");
}

Plus other use cases are supported as well.

Ellsworthellwood

It does not answer to question. javers only shows difference, but does not provide information about field. – Masha

Answer 3

Kotlin generic function with reflection

It's not a perfect answer to this question, but maybe someone could use it.

data class Difference(val old: Any?, val new: Any?)

fun findDifferencesInObjects(
    old: Any,
    new: Any,
    propertyPath: String? = null
): MutableMap<String, Difference> {
    val differences = mutableMapOf<String, Difference>()
    if (old::class != new::class) return differences

    @Suppress("UNCHECKED_CAST")
    old::class.memberProperties.map { property -> property as KProperty1<Any, *>
        val newPropertyPath = propertyPath?.plus('.')?.plus(property.name) ?: property.name
        property.isAccessible = true
        val oldValue = property.get(old)
        val newValue = property.get(new)

        if (oldValue == null && newValue == null) return@map
        if (oldValue == null || newValue == null) {
            differences[newPropertyPath] = Difference(oldValue, newValue)
            return@map
        }

        if (oldValue::class.isData || newValue::class.isData) {
            differences.putAll(findDifferencesInObject(oldValue, newValue, newPropertyPath))
        } else if (!Objects.equals(oldValue, newValue)) {
            differences[newPropertyPath] = Difference(oldValue, newValue)
        }
    }
    return differences
}

Result

{
  "some.nested.and.changed.field": {
    "old": "this value is old",
    "new": "this value is new"
  },
  ...
}

Rod

Answer 4

1. maybe this method can help you to solve you problem

     /**
     * get o1 and o2 different value of field name
     * @param o1 source
     * @param o2 target
     * @return
     * @throws IllegalAccessException
     */
    public static List<String> getDiffName(Object o1,Object o2) throws IllegalAccessException {
        //require o1 and o2 is not null
        if (o1==null&&o2==null){
            return Collections.emptyList();
        }
        //if only one has null
        if (o1 == null){
            return getAllFiledName(o2);
        }
        if (o2 == null){
            return getAllFiledName(o1);
        }
        //source field
        Field[] fields=o1.getClass().getDeclaredFields();
        List<String> fieldList=new ArrayList<>(fields.length);
        //if class is same using this to call
        if (o1.getClass().equals(o2.getClass())){
            //loop field to equals the field
            for (Field field : fields) {
                //to set the field access
                field.setAccessible(true);
                Object source = field.get(o1);
                Object target = field.get(o2);
                //using jdk8 equals to compare two objects
                if (!Objects.equals(source, target)){
                    fieldList.add(field.getName());
                }
            }
        }else {
            //maybe o1 class is not same as o2 class
            Field[] targetFields=o2.getClass().getDeclaredFields();
            List<String> sameFieldNameList=new ArrayList<>();
            //loop o1 field
            for (Field field : fields) {
                String name = field.getName();
                //loop target field to get same field
                for (Field targetField : targetFields) {
                    //if name is equal to compare
                    if (targetField.getName().equals(name)){
                        //add same field to list
                        sameFieldNameList.add(name);
                        //set access
                        field.setAccessible(true);
                        Object source = field.get(o1);
                        //set target access
                        targetField.setAccessible(true);
                        Object target = targetField.get(o2);
                        //equals
                        if (!Objects.equals(source, target)){
                            fieldList.add(field.getName());
                        }
                    }
                }
            }
            //after loop add different source
            for (Field targetField : targetFields) {
                //add not same field
                if (!sameFieldNameList.contains(targetField.getName())){
                    fieldList.add(targetField.getName());
                }
            }
        }
        return fieldList;
    }

    /**
     * getAllFiledName
     * @param obj
     * @return
     */
    private static List<String> getAllFiledName(Object obj) {
        Field[] declaredFields = obj.getClass().getDeclaredFields();
        List<String> list=new ArrayList<>(declaredFields.length);
        for (Field field : declaredFields) {
            list.add(field.getName());
        }
        return list;
    }

2. this method can compare two object which have the same name field ,if they don't have same field,return all field Name

Pyrimidine