附录 - ResolvableType 泛型操作类

Spring强化泛型操作的工具。Class，Field，Method 都有获取 Type 的需求,但是他们获取类型的方式又不统一，回顾下JDK获取Type的方法：

public class TypeTest {
  static class Animal<T> {
    public String name;
    public List<Pair<String, String>> propList;
  }
  static class Dog extends Animal<TypeTest> implements Serializable {
    private static final long serialVersionUID = 8833550896791988000L;
    public Dog() {
    }
    public Dog(String name) {
    }
    public Dog(List<Pair<String, String>> propList) {
    }
    public String say(List<Pair<String, String>> propList) {
      return "OK";
    }
  }
  /**
     * Class获取Type
     */
  @Test
  public void test1() {
    Dog dog = new Dog();
    System.out.println(dog.getClass().getSuperclass());
    System.out.println(dog.getClass().getGenericSuperclass());
    System.out.println(Arrays.toString(dog.getClass().getGenericInterfaces()));
    // class cn.lichenghao.TypeTest$Animal
    // cn.lichenghao.TypeTest$Animal<cn.lichenghao.TypeTest>
    // [interface java.io.Serializable]
  }
  /**
     * Field获取Type
     */
  @Test
  public void test2() {
    Dog dog = new Dog();
    Field[] fields = dog.getClass().getFields();
    for (Field field : fields) {
      System.out.println(field.getType() + "--" + field.getGenericType());
    }
    // class java.lang.String--class java.lang.String
    // interface java.util.List--java.util.List<javafx.util.Pair<java.lang.String, java.lang.String>>
  }
  /**
     * Method获取Type
     */
  @Test
  public void test3() throws NoSuchMethodException {
    Dog dog = new Dog();
    Method methodSay = dog.getClass().getMethod("say", List.class);
    System.out.println(Arrays.toString(methodSay.getParameterTypes()));
    System.out.println(Arrays.toString(methodSay.getGenericParameterTypes()));
    // [interface java.util.List]
    // [java.util.List<javafx.util.Pair<java.lang.String, java.lang.String>>]
    for (Constructor<?> constructor : dog.getClass().getConstructors()) {
      System.out.println(Arrays.toString(constructor.getGenericParameterTypes()));
    }
    // []
    // [java.util.List<javafx.util.Pair<java.lang.String, java.lang.String>>]
    // [class java.lang.String]
  }
}

Class、Field、Method 等都有可能获取 Type，但是每个获取的方式又不一样。Spring 中的 ResolvableType 是一个适配器，通过统一的方法规范调用来获取Type，如下演示代码所示：

@Test
public void test10() throws NoSuchFieldException, NoSuchMethodException {
  Dog dog = new Dog();
  // 根据实例创建 ResolvableType
  ResolvableType resolvableTypeDog = ResolvableType.forInstance(dog);
  System.out.println(resolvableTypeDog.getType());
  System.out.println(Arrays.toString(resolvableTypeDog.getGenerics()));
  // class cn.lichenghao.TypeTest$Dog
  // []
  // 根据原始类型 Class 创建 ResolvableType
  ResolvableType resolvableTypeClass = ResolvableType.forClass(dog.getClass());
  System.out.println(resolvableTypeClass.getType());
  System.out.println(Arrays.toString(resolvableTypeClass.getGenerics()));
  // class cn.lichenghao.TypeTest$Dog
  // []
  // 根据成员变量创建 ResolvableType
  ResolvableType resolvableTypeProp = ResolvableType.forField(dog.getClass().getField("propList"));
  System.out.println(resolvableTypeProp.getType());
  System.out.println(Arrays.toString(resolvableTypeProp.getGenerics()));
  // java.util.List<javafx.util.Pair<java.lang.String, java.lang.String>>
  // [javafx.util.Pair<java.lang.String, java.lang.String>]
  // 根据Method创建 ResolvableType
  System.out.println("根据Method创建 ResolvableType ==");
  MethodParameter methodParameter = MethodParameter
      .forParameter(dog.getClass().getMethod("say2", List.class, Map.class).getParameters()[1]);
  ResolvableType resolvableTypeSay =
    ResolvableType.forMethodParameter(methodParameter);
  System.out.println(resolvableTypeSay.getType());
  System.out.println(Arrays.toString(resolvableTypeSay.getGenerics()));
  // java.util.Map<java.lang.String, org.springframework.core.Ordered>
  // [java.lang.String, org.springframework.core.Ordered]
}