Modelmapper：如何在源对象为空时应用自定义映射？(Modelmapper: How to apply custom mapping when source object is null?)

 让我们假设我有班MySource ： 
 
public class MySource {
    public String fieldA;
    public String fieldB;

    public MySource(String A, String B) {
       this.fieldA = A;
       this.fieldB = B;
    }
}
 
 我想将它翻译成MyTarget对象： 
 
public class MyTarget {
    public String fieldA;
    public String fieldB;
}
 
 使用默认的ModelMapper设置我可以通过以下方式实现它： 
 
ModelMapper modelMapper = new ModelMapper();
MySource src = new MySource("A field", "B field");
MyTarget trg = modelMapper.map(src, MyTarget.class); //success! fields are copied
 
 但是，它可能会发生， MySource对象将为null 。 在这种情况下，MyTarget也将为null ： 
 
    ModelMapper modelMapper = new ModelMapper();
    MySource src = null;
    MyTarget trg = modelMapper.map(src, MyTarget.class); //trg = null
 
 我想用这种方式指定自定义映射，即（伪代码）： 
 
 MySource src != null ? [perform default mapping] : [return new MyTarget()] 
 
 有没有人有想法如何写一个合适的转换器来实现？ 

Lets assume I have class MySource:
 
public class MySource {
    public String fieldA;
    public String fieldB;

    public MySource(String A, String B) {
       this.fieldA = A;
       this.fieldB = B;
    }
}
 
and I would like to translate it to object MyTarget:
 
public class MyTarget {
    public String fieldA;
    public String fieldB;
}
 
using default ModelMapper settings I can achieve it in the following way: 
 
ModelMapper modelMapper = new ModelMapper();
MySource src = new MySource("A field", "B field");
MyTarget trg = modelMapper.map(src, MyTarget.class); //success! fields are copied
 
It can happen however, that MySource object will be null. In this case, MyTarget will be also null:
 
    ModelMapper modelMapper = new ModelMapper();
    MySource src = null;
    MyTarget trg = modelMapper.map(src, MyTarget.class); //trg = null
 
I would like to specify custom mapping in such a way, that (pseudo code): 
 
MySource src != null ? [perform default mapping] : [return new MyTarget()]
 
Does anybody have idea how to write an appropriate converter to achieve that?

原文：https://stackoverflow.com/questions/37971193