反序列化列表<Interface>与杰克逊

Question

I want to deserialize json to class Foo:

class Foo {
   List<IBar> bars;
}

interface IBar {
   ...
}

class Bar implements IBar {
   ...
}

IBar has two implementations, but when deserializing I always want to use the first implementation. (This should ideally make the problem easier, because there is no runtime type checking required)

I am sure I can write custom deserializers, but felt there must be something easier.

I found this annotation, which works perfectly when there is no list.

@JsonDeserialize(as=Bar.class)
IBar bar;

List<IBar> bars; // Don't know how to use the annotation here.

Answer 1

@JsonDeserialize(contentAs=Bar.class)
List<IBar> bars;

Answer 2

Why don't you just use a TypeReference ?

For instance...

Json file test.json in /your/path/ :

[{"s":"blah"},{"s":"baz"}]

Main class in package test :

public class Main {
    public static void main(String[] args) {
        ObjectMapper mapper = new ObjectMapper();
        try {
            List<IBar> actuallyFoos = mapper.readValue(
                    new File("/your/path/test.json"), new TypeReference<List<Foo>>() {
                    });
            for (IBar ibar : actuallyFoos) {
                System.out.println(ibar.getClass());
            }
        }
        catch (Throwable t) {
            t.printStackTrace();
        }
    }

    static interface IBar {
        public String getS();

        public void setS(String s);
    }

    static class Foo implements IBar {
        protected String s;

        public String getS() {
            return s;
        }

        public void setS(String s) {
            this.s = s;
        }
    }

    static class Bar implements IBar {
        protected String s;

        public String getS() {
            return s;
        }

        public void setS(String s) {
            this.s = s;
        }
    }
}

Output of the main method:

class test.Main$Foo
class test.Main$Foo

Answer 3

Put the annotation on the IBar interface declaration rather than the field, ie:

@JsonDeserialize(as=Bar.class)
interface IBar {
   ...
}