JAVA - 如何将对象的属性复制到具有相同属性的另一个对象？

Question

Let's say we have an Object A defined like this:

public class ObjectA {
    private Attribute a1;
    private Attribute a2;
    private Attribute a3;
}

For some reason, I need to create a second object B with only the first two attriutes of the Object A :

public class ObjectB {
    private Attribute a1;
    private Attribute a2;
}

So my question is: what is the best approach to copy an Object A to an Object B ? I've been copying the attributes by getters and setters one by one but something tells me there must be a better way to do this ! Especially when the object will have a lot of attributes, I have to write lines and lines of code just to copy all of them to the second Object B ...

Thanks a lot :)

EDIT: I've been being alerted by a "possible duplicate of another question" : How do I copy an object in Java?

My question is slightly different in a way that I'm dealing with 2 different objects who just share the same attributes but not totally !

Answer 1

尝试使用Dozer或BeanUtils等库

Answer 2

To expand on my comment:

Using Dozer it can be as easy as:

Mapper mapper = new DozerBeanMapper();
ObjectA source = new ObjectA();
ObjectB target = mapper.map(source , ObjectB.class);

or if your target class doesn't have a no-arg constructor:

ObjectA source = new ObjectA();
ObjectB target = new ObjectB(/*args*/);
mapper.map(source, target );

From the Documentation (emphasis by me):

After performing the Dozer mapping, the result will be a new instance of the destination object that contains values for all fields that have the same field name as the source object . If any of the mapped attributes are of different data types, the Dozer mapping engine will automatically perform data type conversion.

Answer 3

What you need is Object mappers. Try Orika or Dozer . The objects need not be of the same type. While mapping if it finds the attributes of the same name and type, it automatically maps it.

MapperFacade mapper = mapperFactory.getMapperFacade();
UserDTO userDTO = new UserDTO();
userDTO.setName("xyz");
..
User user = mapper.map(userDTO, User.class);

You can also customize if you have to map different attribute names.

MapperFactory mapperFactory = new DefaultMapperFactory.Builder().build();
mapperFactory.classMap(UserDTO.class, User.class)
            .field("name", "username")
            .byDefault().register();
mapper = mapperFactory.getMapperFacade();
...
User user = mapper.map(userDTO, User.class);