How to override properties if exist otherwise keep them in java objects spring boot-CodePudding

if we have two obejcts a and b of two classes A and B,

    public class A{
    String prop1;
    String prop2;
    String prop3;
    String prop4;
    
   public A(String prop1, String prop2, String prop3, String prop4) {
        this.prop1 = prop1;
        this.prop2 = prop2;
        this.prop3 = prop3;
        this.prop4 = prop4;
    }

    public A() {
    }
   //... setters and getters
    }




    public class B{
    String prop2;
    String prop3;

public B(String prop2, String prop3) {
        this.prop1 = prop1;
        this.prop2 = prop2;
        this.prop3 = prop3;
        this.prop4 = prop4;
    }

    public B() {
    }

    }

A a = new A("prop1","prop2","prop3","prop4");
B b = new B();
b.setProp3("p");

How can we copy not null properties from b to a ? in the example above, how we can copy prop3 which is not null and ignore prop2 which is null.

CodePudding user response：

You can use MapStruct.
It's a library that is very easy to use and you can copy all the properties from a class to another.

@Mapper
public interface AToBMapper {
    A toB(A a);
    B toA(B b);
}

A a = new A("prop1","prop2","prop3","prop4");
B = mapper.toB(a);

This is very useful when you need to copy the properties from a DTO to an Entity.

If you don't want to create a new object but update an existing one, it's also possible as you can see here : MapStruct: How to map to existing target?

More exemple here : https://www.baeldung.com/mapstruct

CodePudding user response：

It would be possible to accomplish this with reflection or a library like BeanUtils but maybe consider using the KISS principle and just write a simple method for it:

public void copyToA(A a, B b) {
  if (b.getProp2() != null) a.setProp2(b.getProp2());
  if (b.getProp3() != null) a.setProp3(b.getProp3());
}

With BeanUtils you could extend BeanUtilsBean to overwrite copyProperty and check if the value is null and then just use it like this:

var beanUtilsBean = new YourBeanUtilsBean();
beanUtilsBean.copyProperties(a, b);

For more information check out this answer https://stackoverflow.com/a/3521314/11480721: