토비의 봄 TV 2회 - 수퍼 타입 토큰

(시청일 : 20170924)

- https://www.youtube.com/watch?v=01sdXvZSjcI : 스프링에서 사용되는 ParameterizedTypeReference의 작동 원리인 Super Type Token의 동작 원리와 활용법을 알아봅니다.

■ Type Token : 타입 정보를 key로 넘겨서 value를 리턴

■ Type Safe Token 예제 코드

public class TypeToken {

    static Class TypeSafeMap {

        Map<Class<?>, Object> map = new HashMap<>();

        <T> void put(Class<T> clazz, T value) {

            map.put(clazz, value);

        }

        <T> T get(Class<T> clazz) {

            return clazz.cast(map.get(clazz));

        }

    }

    public static void main(String[] args) throws Exception {

        TypeSafeMap m = new TypeSafeMap();

        m.put(Integer.class, 1);

        m.put(String.class, "String");

        m.put(List.class, Arrays.asList(1,2,3));

        System.out.println(m.get(Integer.class));

        System.out.println(m.get(String.class));

        System.out.println(m.get(List.class));

    }

}

■ Super Type Token 예제 코드   => 메모리 누수를 야기하는 등 좋지 않은 코드라서, 2.5회에서 개선 됨.

public class SuperTypeToken {

    static Class TypeSafeMap {

        Map<TypeReference<?>, Object> map = new HashMap<>();

    <T> void put(TypeReference<T> tr, T value) {

        map.put(tr, value);

    }

    <T> T get(TypeReference<T> tr) {

        if (tr.type instanceof Class<?>)

            return ((Class<T>)tr.type).cast(map.get(tr));

        else

            return ((Class<T>)((ParameterizedType)tr.type).getRawType()).cast(map.get(tr)); // TR<List<String>>

    }

}

    static class TypeReference<T> {

        Type type;

        public TypeReference() {

            Type stype = getClass().getGenericSuperclass();

            if (stype instanceof ParameterizedType) {

                this.type = ((ParameterizedType) stype).getActualTypeArguments()[0];

            } else throw new RuntimeException();

        }

        @Override

        public boolean equals(Object o) {

            if (this == o) return true;

            if (o == null || getClass().getGenericSuperclass() != o.getClass().getGenericSuperclass()) return false;

            TypeReference that = (TypeReference) o;

            return type.equals(that.type);

        }

        @Override

        public int hashCode() {

            return type.hashCode();

        }

    }

   public static void main(String[] args) throws Exception {

        TypeReference m = new TypeSafeMap();

        m.put(new TypeReference<Integer>() {}, 1);

        m.put(new TypeReference<String>() {}, "String");

        m.put(new TypeReference<List<Integer>>() {}, Arrays.asList(1,2,3)); // List<Integer>

        m.put(new TypeReference<List<String>>() {}, Arrays.asList("a","b","c")); // List<String>

        m.put(new TypeReference<List<List<String>>>() {}, Arrays.asList(Arrays.asList("a"),Arrays.asList("b"),Arrays.asList("c"))); // List<String>

        System.out.println(m.get(new TypeReference<Integer>() {}));

        System.out.println(m.get(new TypeReference<String>() {}));

        System.out.println(m.get(new TypeReference<List<Integer>>() {}));

        System.out.println(m.get(new TypeReference<List<String>>() {}));

        System.out.println(m.get(new TypeReference<List<List<String>>>() {}));

}

}

■ 위의 코드와 유사한 Spring 3.2 버전 이상에서 지원하는

ParameterizedTypeReference의 사용 예제

public class SpringTypeReference {

    public static void main(String[] args) {

        ParameterizedTypeReference<?> typeRef = new ParameterizedTypeReference<List<Map<Set<Integer>, String>>>() {};

        System.out.println(typeRef.getType());

    }

}

 

■ ParameterizedTypeReference의 사용 사례

@SpringBootApplication

public class TobyTv002liveApplication {

    public static void main(String[] args) {

        SpringApplication.run(TobyTv002liveApplication.class, args);

    }

    @RestController

    public static class MyController {

        @RequestMapping("/")

        public List<User> users() {

            return Arrays.asList(new User("A"), new User("B"), new User("C"));

        }

    }

    public static class User {

        String name;

        public User(String name) {

            this.name = name;

        }

        public User() {

        }

        public String getName() {

            return name;

        }

        @Override

        public String toString() {

            return "User[" +

                    "name='" + name + '\'' +

                    ']';

        }

    }

}

public class SpringTypeReference {

    public static void main(String[] args) {

        RestTemplate rt = new RestTemplate();

        // 타입 safe하지 않음

//        List<Map> users = rt.getForObject("http://localhost:8080";, List.class);

//        System.out.println(users.get(0).getName("name"));

        List<User> users = rt.exchange("http://localhost:8080";,

                HttpMethod.Get, null, new ParameterizedTypeReference<List<User>>() {}).getBody();

        users.forEach(System.out::println );

    }

}