find out the differences between two java beans for version tracking

Question

say i have a java bean/an entity with 100 fields (inherited or not it is not relevant in this case). After update operations - in a transaction, i want to determine which fields are modified to track updates like a CVS. What is the easiest way to do this? Any Framework suggestion? Should i make two instances of this object and iterate over all fields and match the values of fields ? How would the best equals method seem in such situations ? The following equals() seems very awkward :

return (field1.equals(o.field1)) &&  (field2.equals(o.field2)) &&   (field3.equals(o.field3)) &&   ... (field100.equals(o.field100)); 

Answer 1

You could use Apache Commons Beanutils. Here's a simple example:

package at.percom.temp.zztests;  import java.lang.reflect.InvocationTargetException; import org.apache.commons.beanutils.BeanMap; import org.apache.commons.beanutils.PropertyUtilsBean; import java.util.Arrays; import java.util.HashSet; import java.util.Objects; import java.util.Set;  public class Main {      public static void main(String[] args) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {         Main main = new Main();         main.start();     }      public void start() throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {         SampleBean oldSample = new SampleBean("John", "Doe", 1971);         SampleBean newSample = new SampleBean("John X.", "Doe", 1971);          SampleBean diffSample = (SampleBean) compareObjects(oldSample, newSample, new HashSet<>(Arrays.asList("lastName")), 10L);     }  public Object compareObjects(Object oldObject, Object newObject, Set<String> propertyNamesToAvoid, Long deep) {     return compareObjects(oldObject, newObject, propertyNamesToAvoid, deep, null); }  private Object compareObjects(Object oldObject, Object newObject, Set<String> propertyNamesToAvoid, Long deep,         String parentPropertyPath) {     propertyNamesToAvoid = propertyNamesToAvoid != null ? propertyNamesToAvoid : new HashSet<>();     parentPropertyPath = parentPropertyPath != null ? parentPropertyPath : "";      Object diffObject = null;     try {         diffObject = oldObject.getClass().newInstance();     } catch (Exception e) {         return diffObject;     }      BeanMap map = new BeanMap(oldObject);      PropertyUtilsBean propUtils = new PropertyUtilsBean();      for (Object propNameObject : map.keySet()) {         String propertyName = (String) propNameObject;         String propertyPath = parentPropertyPath + propertyName;          if (!propUtils.isWriteable(diffObject, propertyName) || !propUtils.isReadable(newObject, propertyName)                 || propertyNamesToAvoid.contains(propertyPath)) {             continue;         }          Object property1 = null;         try {             property1 = propUtils.getProperty(oldObject, propertyName);         } catch (Exception e) {         }         Object property2 = null;         try {             property2 = propUtils.getProperty(newObject, propertyName);         } catch (Exception e) {         }         try {             if (property1 != null && property2 != null && property1.getClass().getName().startsWith("com.racing.company")                     && (deep == null || deep > 0)) {                 Object diffProperty = compareObjects(property1, property2, propertyNamesToAvoid,                         deep != null ? deep - 1 : null, propertyPath + ".");                 propUtils.setProperty(diffObject, propertyName, diffProperty);             } else {                 if (!Objects.deepEquals(property1, property2)) {                     propUtils.setProperty(diffObject, propertyName, property2);                     System.out.println("> " + propertyPath + " is different (oldValue=\"" + property1 + "\", newValue=\""                             + property2 + "\")");                 } else {                     System.out.println("  " + propertyPath + " is equal");                 }             }         } catch (Exception e) {         }     }      return diffObject; }      public class SampleBean {          public String firstName;         public String lastName;         public int yearOfBirth;          public SampleBean(String firstName, String lastName, int yearOfBirth) {             this.firstName = firstName;             this.lastName = lastName;             this.yearOfBirth = yearOfBirth;         }          public String getFirstName() {             return firstName;         }          public String getLastName() {             return lastName;         }          public int getYearOfBirth() {             return yearOfBirth;         }     } } 

Answer 2

Hey look at Javers it's exactly what you need - objects auditing and diff framework . With Javers you can persist changes done on your domain objects with a single javers.commit() call after every update. When you persist some changes you can easily read them by javers.getChangeHistory, e.g.

public static void main(String... args) {     //get Javers instance     Javers javers = JaversBuilder.javers().build();      //create java bean     User user = new User(1, "John");      //commit current state     javers.commit("author", user);      //update operation     user.setUserName("David");      //commit change     javers.commit("author", user);      //read 100 last changes     List<Change> changes = javers.getChangeHistory(instanceId(1, User.class), 100);      //print change log     System.out.printf(javers.processChangeList(changes, new SimpleTextChangeLog())); } 

and the output is:

commit 2.0, author:author, 2015-01-07 23:00:10   changed object: org.javers.demo.User/1     value changed on 'userName' property: 'John' -> 'David' commit 1.0, author:author, 2015-01-07 23:00:10     new object: 'org.javers.demo.User/1