java - 如何将 Jackson 与嵌套泛型一起使用？

Question

我用的是 Retrofit 和 Jackson。有一个 POJO 是这样的:

public class QuotationHttpResult<T> {
    private int code;
    private Result result;

    public T getData(){
        return result == null ? null : result.getData();
    }

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public Result getResult() {
        return result;
    }

    public void setResult(Result result) {
        this.result = result;
    }

    class Result{
        private T data;

        public T getData() {
            return data;
        }
    }
} 

归档的数据就是我需要的，有时是一个POJO，有时是一个List。当它是一个列表时，即使我使用 TypeReference，jackson 也只是将数据转换为 LinkedHashMap:Json 字符串是:

 {"code": 0,
     "result": {
         "data": [
            {
            "id": "1000",
            "name": "tecent"
            }, 
            {
            "id": "1001",
            "name": "alibaba"
            }
         ]
       }
    }

转换代码:

ObjectMapper mapper = new ObjectMapper();
QuotationHttpResult<List<MyClass>> result = mapper.readValue(json,new TypeReference<QuotationHttpResult<List<MyClass>>>() {});

MyClass 很简单:

class MyClass{
    String id;
    String name;
}

我看到这个问题，How to use Jackson with Generics , 当我不嵌套泛型时一切顺利，但是当嵌套泛型时我该怎么办？

Answer 1

首先你应该制作Result静态 ( more info ) 或将其移出 QuotationHttpResult ，所以 jackson 可以看到它 data类型。因此，您必须将其设为通用 Result<T> .您还必须将 getter 和 setter 添加到您的 MyClass POJO 或为 jackson 添加注解。

这是演示:

public class QuotationHttpResult<T> {
    private int code;

    private Result<T> result;

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public Result<T> getResult() {
        return result;
    }

    public void setResult(Result<T> result) {
        this.result = result;
    }

    public static class Result<T>{
        private T data;

        public T getData() {
            return data;
        }

        public void setData(T data) {
            this.data = data;
        }
    }
}

public class MyClass {
    private String id;
    private String name;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

public static void main(String[] args) throws IOException {
    String json = " {\"code\": 0,\n" +
            "     \"result\": {\n" +
            "         \"data\": [\n" +
            "            {\n" +
            "            \"id\": \"1000\",\n" +
            "            \"name\": \"tecent\"\n" +
            "            }, \n" +
            "            {\n" +
            "            \"id\": \"1001\",\n" +
            "            \"name\": \"alibaba\"\n" +
            "            }\n" +
            "         ]\n" +
            "       }\n" +
            "    }";
    ObjectMapper mapper = new ObjectMapper();
    QuotationHttpResult<MyClass> result = mapper.readValue(json,new TypeReference<QuotationHttpResult<List<MyClass>>>() {});
    System.out.println(result);
}