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

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

	@Testpublic 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

    @Testpublic 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

@Datastatic 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

    @Testpublic 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

    @Testpublic 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

    @Testpublic 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

    @Testpublic 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

    @Testpublic 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

    @Testpublic 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