Map a list of object to another list using Dozer's custom converters

问题

What I am trying to do is to map a List of entities to a list of their String ids (more or less) using Dozer.

Obviously, it implies Custom Converter. My first idea was to make a converter from MyEntity to a String, and then say to Dozer something like "Map every object of this collection using this converter". But I couldn't figure out how to do so.

So my second idea was to make a converter form a list of entities to a list of string, directly. My problem on this idea is that I was strugling on something ridiculous which is to get the type of my list in the constructor, as below (which doesn't work at all):

public MyEntityListConverter() {
    super(List<MyEntity>.class, List<String>.class);
}

I don't know how to pass an instantiated list's class in a single row wihout declaring anything.

So if someone know either :

How to specify to dozer an object convertor to use in collection mapping
How to get instantiated list type
A third/better solution to try

回答1:

The way you tried is not possible due to generic types. And if it was, Dozer cannot detect types at runtime.

1st solution with List<>

Your converter :

public class MyEntityToStringConverter extends DozerConverter<MyEntity, String> {
    // TODO constructor + impl
}

Your mapping :

mapping(MyEntityA.class, MyEntityB.class)
.fields("myEntityList", "myStringList",
    hintA(MyEntity.class),
    hintB(String.class));

mapping(MyEntity.class, String.class)
.fields(this_(), this_(), customConverter(MyEntityToStringConverter.class));

2nd solution with list wrappers

You can try to create your custom classes extending a list impl.

public class MyEntityList extends ArrayList<MyEntity> {

}

public class MyStringList extends ArrayList<String> {

}

Change your field in the parent classes you want to map.

Your converter :

public class MyEntityToStringConverter extends DozerConverter<MyEntityList, MyStringList> {
    // TODO constructor + impl
}

Your mapping :

mapping(MyEntityA.class, MyEntityB.class)
.fields("myEntityList", "myStringList", customConverter(MyEntityToStringConverter.class));

回答2:

Another option would be

super((Class<List<MyEntity>>) (Class<?>) List.class,(Class<List<String>>) (Class<?>) List.class);

回答3:

I very much inclined to @Ludovic solution, but there might be a catch as mentioned in my comment up there.

But a slight tweak works for me though - register the custom converter in "configuration" rather than field level. I'm using XML config but it should work with coding config:

<configuration>
  <custom-converters>
    <converter type="f.q.c.n.MyEntityToStringConverter">
      <class-a>java.lang.String</class-a>
      <class-b>f.q.c.n.MyEntity</class-b>
    </converter>
  </custom-converters>
</configuration>

来源：https://stackoverflow.com/questions/29033756/map-a-list-of-object-to-another-list-using-dozers-custom-converters

标签

java

Spring

arraylist

orm

dozer