Java 具有泛型的命令对象

我有一个控制器，它有一个

命令对象

，它使用以下泛型：

@Controller
@RequestMapping(value = "/first")
public class MyFirstController {

    @RequestMapping(value = "/something", method = RequestMethod.POST)
    @ResponseBody
    public ADifferentDTO doSomething(RequestDTO<MyStringObject> requestDTO, HttpServletRequest request,
            HttpServletResponse response) {

            requestDTO.getSomeObject(); // ERROR HERE


            //.. do something
    }
}

---

有什么方法可以做到这一点吗？

你是对的，这是因为类型擦除

可能最简单的解决方案是创建一个RequestDTO子类，用每个My*对象参数化，并将其用作命令对象类

举个例子：

@SpringBootApplication
public class So44423504Application {

    public static void main(String[] args) {
        SpringApplication.run(So44423504Application.class, args);
    }

    @RestController
    @RequestMapping(value = "/first")
    public static class MyFirstController {

        public static class MyStringRequestDTO extends RequestDTO<MyStringObject> {}

        public static class MyIntegerRequestDTO extends RequestDTO<MyIntegerObject> {}

        @PostMapping(value = "/something")
        public String doSomething(@ModelAttribute MyStringRequestDTO/*MyIntegerRequestDTO*/ requestDTO) throws JsonProcessingException {
            return new ObjectMapper().writeValueAsString(requestDTO);
        }
    }

    public static class RequestDTO<T> {
        private T someObject;
        // getter and setter
    }

    public static class MyStringObject {
        private String someString;

        public MyStringObject() { } // required since another non-default ctor is present.

        public MyStringObject(String someString){
            this.someString = someString;
        }

        // getter and setter
    }

    public static class MyIntegerObject {
        private Integer someInteger;
        private Integer anotherInteger;

        public MyIntegerObject() { } // required since another non-default ctor is present.

        public MyIntegerObject(Integer someInteger, Integer anotherInteger){
            this.someInteger = someInteger;
            this.anotherInteger = anotherInteger;
        }
        // getters and setters
    }
}

---

您的控制器如何知道如何根据从客户端传递的内容构造RequestDTO？如果您看到的是编译器错误，则不涉及类型擦除。@LewBloch这是一个运行时error@MinhKieu它不知道如何构造它，因为传入的不是

MyStringObject

。哇，我有点惊讶，竟然这么容易！非常感谢。快速提问，我不明白的是扩展参数化类的类如何修复类型擦除问题。因此，

MyStringRequestDTO

被认为是一个MyStringObject，即使“extends RequestDTO”在运行时不会被解析为MyStringObject？很快，这是编译器在

.class

文件中存储类型信息的一种方式，因为我们声明T=MyStringObject，所以它在运行时可用。尝试运行以下代码段

System.out.println（MyStringRequestDTO.class.getGenericSuperclass（）.getTypeName（））；System.out.println（新RequestDTO（）.getClass（）.getGenericSuperclass（）.getTypeName（））公共类com.stackoverflow.so44423504.MyStringRequestDTO扩展com.stackoverflow.so44423504.RequestDTO

保留所有类型信息。

public class RequestDTO {

    private MyStringObject someObject;
    // some other objects here as well that are from a submitted form (not listed)


    public void setSomeObject(MyStringObject someObject){
        this.someObject = someObject;
    }

    public MyStringObject getSomeObject(){
        return someObject;
    }
}

@SpringBootApplication
public class So44423504Application {

    public static void main(String[] args) {
        SpringApplication.run(So44423504Application.class, args);
    }

    @RestController
    @RequestMapping(value = "/first")
    public static class MyFirstController {

        public static class MyStringRequestDTO extends RequestDTO<MyStringObject> {}

        public static class MyIntegerRequestDTO extends RequestDTO<MyIntegerObject> {}

        @PostMapping(value = "/something")
        public String doSomething(@ModelAttribute MyStringRequestDTO/*MyIntegerRequestDTO*/ requestDTO) throws JsonProcessingException {
            return new ObjectMapper().writeValueAsString(requestDTO);
        }
    }

    public static class RequestDTO<T> {
        private T someObject;
        // getter and setter
    }

    public static class MyStringObject {
        private String someString;

        public MyStringObject() { } // required since another non-default ctor is present.

        public MyStringObject(String someString){
            this.someString = someString;
        }

        // getter and setter
    }

    public static class MyIntegerObject {
        private Integer someInteger;
        private Integer anotherInteger;

        public MyIntegerObject() { } // required since another non-default ctor is present.

        public MyIntegerObject(Integer someInteger, Integer anotherInteger){
            this.someInteger = someInteger;
            this.anotherInteger = anotherInteger;
        }
        // getters and setters
    }
}

$ curl -XPOST 'localhost:8080/first/something?someObject.someInteger=23&someObject.anotherInteger=42'
{"someObject":{"someInteger":23,"anotherInteger":42}}%

$ curl -XPOST 'localhost:8080/first/something?someObject.someString=test'                            
{"someObject":{"someString":"test"}}%