Spring ResolvableType满足你对Java泛型的任何操作和幻想

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背景

我们是否经常在写一些工具类或者SDK的时候需要获取类上面的泛型
比如父类的泛型,这样的

	static class Person<T, V> {

    }

    static class Student extends Person<String, Integer> {

    }

比如接口上的泛型

	interface StudentServiceImpl<T, V> {
    }

    static class StudentService implements StudentServiceImpl<String, Student> {
    }

等等一系列需要获取泛型的操作，但是Java的原生SDK还是比较难用和冗余的，所以Spring在
此背景下又扩展了Java 反射对泛型的操作，及ResolvableType类。下面我们一起来学习下吧

ResolvableType 的使用

获取父类的泛型

	static class Person<T, V> {}
    static class Student extends Person<String, Integer> {}

• 获取方式

	@Test
    public void getPersonGenericBySpring() {
        ResolvableType resolvableType = ResolvableType.forClass(Student.class);
        for (ResolvableType generic : resolvableType.getSuperType().getGenerics()) {
            System.out.println(generic.resolve());
        }
    }

• 运行结果

获取接口上的泛型

	interface StudentServiceImpl<T, V> { }
    static class StudentService implements StudentServiceImpl<String, Student> { }

• 获取方式

    @Test
    public void getInterfaceBySpring() {
        ResolvableType resolvableType = ResolvableType.forClass(StudentService.class);
        for (ResolvableType anInterface : resolvableType.getInterfaces()) {
            for (ResolvableType generic : anInterface.getGenerics()) {
                System.out.println(generic.resolve());
            }
        }
    }

• 运行结果

获取属性上的泛型

测试类

@Data
    static class GenericClass {
        private List<String> listString;

        private List<List<String>> listLists;

        private Map<String, Long> maps;

        private Person<String, Integer> person;

        private HashMap<String, List<String>> method() {
            return null;
        }

        public GenericClass(List<List<String>> list, Map<String, Map<String, Integer>> map) {
        }
    }

获取属性对象的泛型

• 获取方式

    @Test
    public void getPropertyGeneric() {
        ResolvableType resolvableType = ResolvableType.forField(ReflectionUtils.findField(GenericClass.class, "person"));
        for (ResolvableType generic : resolvableType.getGenerics()) {
            System.out.println(generic.resolve());
        }
    }

• 运行结果
  

获取属性List上的泛型

• 获取方式

    @Test
    public void getPropertyListsGeneric() {
        ResolvableType resolvableType = ResolvableType.forField(ReflectionUtils.findField(GenericClass.class, "listString"));
        for (ResolvableType generic : resolvableType.getGenerics()) {
            System.out.println(generic.resolve());
        }
    }

• 获取结果
  

获取属性List嵌套List的泛型

• 获取方式

    @Test
    public void getPropertyListAndListGeneric() {
        ResolvableType resolvableType = ResolvableType.forField(ReflectionUtils.findField(GenericClass.class, "listLists"));
        ResolvableType generic1 = resolvableType.getGeneric(0);
        // 第一层
        System.out.println("第一层泛型: " + generic1.resolve());
        // 第二层
        ResolvableType generic = generic1.getGeneric(0);
        System.out.println("第二层泛型: " + generic.resolve());
        Class<?> resolve = resolvableType.getGeneric(0, 0).resolve();
        // 也可以使用如下方式获取
        System.out.println("第二层泛型: " + resolve);
    }

• 结果
  

获取属性Map上的泛型

• 获取方式

    @Test
    public void getPropertyMapGeneric() {
        ResolvableType resolvableType = ResolvableType
                .forField(ReflectionUtils.findField(GenericClass.class, "maps"));
        for (ResolvableType generic : resolvableType.getGenerics()) {
            System.out.println(generic.resolve());
        }
    }

• 获取结果
  

获取方法返回值的泛型

• 获取方式

    @Test
    public void getMethodGeneric() {
        ResolvableType resolvableType =
                ResolvableType.forMethodReturnType(ReflectionUtils.findMethod(GenericClass.class, "method"));
        // 第一层
        for (ResolvableType generic : resolvableType.getGenerics()) {
            System.out.println("Map中的泛型: " + generic.resolve());
        }
        // 获取第二层的
        System.out.println("Map中List的泛型: " + resolvableType.getGeneric(1, 0).resolve());

    }

• 获取结果
  

获取构造方法参数的泛型

• 获取方式

    @Test
    public void getConstructorGeneric() {
        ResolvableType resolvableType =
                ResolvableType.forConstructorParameter(ClassUtils.getConstructorIfAvailable(GenericClass.class, List.class, Map.class), 1);
        for (ResolvableType generic : resolvableType.getGenerics()) {
            System.out.println("构造方法参数泛型: " + generic.resolve());
        }
        System.out.println("Map中的泛型: " + resolvableType.getGeneric(1, 0).resolve());
    }

• 获取结果
  

参考

博客