How to Merge Java Objects Dynamically

Question

public class MyClass{
   public String elem1;
   public int elem2;
   public MyType elem3;
.................
}

MyClass object1=new MyClass();
MyClass object2=new MyClass();
object1.elem1=...
object1.elem2=...
...
object2.elem1=...
object2.elem2=null
.....

What I want is something like

object1.merge(object2);

where it will dynamically traverse all members on MyClass and run this on every member

if(object1.elem != object2.elem && object2.elem!=null)
 object1.elem=object2.elem;

Is such a mechanism exist in Java?

Answer 1

use reflection. go over fields of class. Psuedo:

Field[] fields = aClass.getFields();
for (Field field : fields) {
     // get value
     Object value = field.get(objectInstance);
     // check the values are different, then update 
     field.set(objetInstance, value);    
}

and match the values. if they differ, then update the value.

Answer 2

An option that is more efficient than Reflection would be to store the fields in a map:

Map<String, Object> fields;

void merge(MyClass other){
    for (String fieldName : fields.keys()){
        Object thisValue = this.fields.get(key);
        Object otherValue = other.fields.get(key);
        if (thisValue != otherValue && otherValue != null){

                this.fields.put(fieldName, otherValue);
        }
    }
}

This would make the merge more efficient but would make general field access less efficient.

Answer 3

您可以使用反射自己编写这样的方法（从Class.getFields()开始），但是没有工具在标准API中执行此操作。

Answer 4

是的，它是可能的，它被称为反射 。

Answer 5

There is nothing built in. However you might want to have a look at Dozer . Maybe with some tweaking it will be capable of doing this.

You can also do this using reflection (which is what Dozer does).