Comparing POJO classes

[Wagner Danda Da Silva Filho]

Hi there!

I need to compare two POJO classes and find out which properties are different. I've tried BeanComparator (from BeanUtils) but it doesn't shows me the different properties...

For example, I have the following class:

public class Person {
    private String name;
    private Integer age;
    public String getName() { ... }
    public Integer getAge() { ... }
    public void setName() { ... }
    public void setAge() { ... }
}

And now I have two instances with different values, and I want to compare them:

Person p1 = new Person();
p1.setName("Wagner");
p1.setAge(new Integer(26));
 
Person p2 = new Person();
p2.setName("John");
p2.setAge(new Integer(26));
 
...
 
ArrayList changedFiels = new ArrayList();
 
// I don't wanna do this:
if( ! p1.getName().equals(p2.getName()) ) { 
  changedFiels.add("name");
}
if( ! p1.getAge().equals(p2.getAge()) ) {
  changedFiels.add("age");
}

Now imagine that my POJO classe have lot's of properties, I don't want to add a "if" for each property... Is there an API that could do this dirty work?

PS: I've considered creating my own utility class using reflection, but first I'm searching for a ready solution. I don't like to reinvent the wheel.

[Steve Morrow]

Have a look at Jakarta Commons BeanUtils, which has a method to return a bean's properties as a Map. You can then iterate through the elements, comparing as needed.

Out of curiosity, I'm assuming you're wanting to compare fields on an individual basis, and not simply comparing objects (in which case you'd look to override equals/hashCode and/or implement Comparable).

Hope this helps...

[Wagner Danda Da Silva Filho]

Hey Steve, thanks for you help, your assumption is correct.

So, now I'm using "BeanUtils.describe(...)" to get the properties of my POJO as a map. Then I iterate over it and compare the properties of the two POJO classes using "PropertyUtils.getProperty(...)". Here is code I wrote and its working:

public ArrayList compareBeans(Object newBean, Object oldBean) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
if( newBean.getClass() != oldBean.getClass()  ) {
throw new IllegalArgumentException("The beans must be from the same Class!");
}
ArrayList changesArr = new ArrayList();
Iterator keysIt = BeanUtils.describe(newBean).keySet().iterator();
while (keysIt.hasNext()) {
String key = (String) keysIt.next();
Object oldValue = PropertyUtils.getProperty(oldBean, key);
Object newValue = PropertyUtils.getProperty(newBean, key);
if( oldValue != newValue ) {// Ignores when both are "null"
if( ( (oldValue != null) && !oldValue.equals(newValue) )
 || ( (newValue != null) && !newValue.equals(oldValue) ) ) {
changesArr.add(key);
} 
}
}
return changesArr;
}

Thanks again for your help Steve.
[ November 17, 2005: Message edited by: Wagner Danda ]