如何在嵌套参数parameter中获取批注?

问题描述

如果我有这样的功能，

public void park( List< @myNote("list") List< @myNote("integer") Integer>> l){ System.out.println("park"); }

如果我使用Parameter.getAnnotations()和Paramter.getDeclaredAnnotation，则只能获取@myNote("list").有什么方法可以获取批注@myNote("integer")?

If I use Parameter.getAnnotations() and Paramter.getDeclaredAnnotation, I can only get @myNote("list"). Are any ways to get the annotation @myNote("integer")?

这可能与

推荐答案

以下是用于打印注释的代码，因此您可以看到在反射API中可以找到它们的位置.

Here is code to print the annotations, so you can see where in the reflection API they can be found.

基本上，您调用 param.getAnnotatedType() ，检查 AnnotatedType 是 AnnotatedParameterizedType ，然后调用 getAnnotatedActualTypeArguments() 来获取泛型类型参数，然后递归执行.

Basically, you call param.getAnnotatedType(), check if the AnnotatedType is an AnnotatedParameterizedType, and call getAnnotatedActualTypeArguments() to get the generic type arguments, and do that recursively.

对于每个AnnotatedType(顶级或嵌套)，您调用 getDeclaredAnnotations() 或 getAnnotations() 以获得该类型的注释.

For each AnnotatedType, top-level or nested, you call getDeclaredAnnotations() or getAnnotations() to get the annotations on that type.

我添加了其他内容，以便您可以了解其工作原理.

I added extra stuff, just so you can see how it works.

public class Test {
    public static void main(String[] args) {
        Method method = Test.class.getDeclaredMethod("park", List.class, Map.class);
        for (Parameter param : method.getParameters()) {
            System.out.println("Parameter: " + param);
            printAnnotatedType(1, param.getAnnotatedType());
        }
    }
    static void printAnnotatedType(int indent, AnnotatedType type) {
        System.out.println("  ".repeat(indent) + "AnnotatedType: " + type);
        System.out.println("  ".repeat(indent + 2) + "Type: " + type.getType());
        for (Annotation annotation : type.getDeclaredAnnotations()) {
            System.out.println("  ".repeat(indent + 2) + "Annotation: " + annotation);
        }
        if (type instanceof AnnotatedParameterizedType) {
            AnnotatedParameterizedType pt = (AnnotatedParameterizedType) type;
            for (AnnotatedType typeArg : pt.getAnnotatedActualTypeArguments()) {
                printAnnotatedType(indent + 1, typeArg);
            }
        }
    }
    public void park(@myNote("p0") List< @myNote("list") List< @myNote("integer") @myOther Integer>> l,
                     @myNote("p1") Map< @myNote("key") Long, @myNote("value") String> m) {
        System.out.println("park");
    }
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE_USE)
@interface myNote {
    String value();
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE_USE)
@interface myOther {
}

输出

Parameter: java.util.List<java.util.List<java.lang.Integer>> arg0
  AnnotatedType: @myNote(value="p0") java.util.List<@myNote(value="list") java.util.List<@myNote(value="integer") @myOther() java.lang.Integer>>
      Type: java.util.List<java.util.List<java.lang.Integer>>
      Annotation: @myNote(value="p0")
    AnnotatedType: @myNote(value="list") java.util.List<@myNote(value="integer") @myOther() java.lang.Integer>
        Type: java.util.List<java.lang.Integer>
        Annotation: @myNote(value="list")
      AnnotatedType: @myNote(value="integer") @myOther() java.lang.Integer
          Type: class java.lang.Integer
          Annotation: @myNote(value="integer")
          Annotation: @myOther()
Parameter: java.util.Map<java.lang.Long, java.lang.String> arg1
  AnnotatedType: @myNote(value="p1") java.util.Map<@myNote(value="key") java.lang.Long, @myNote(value="value") java.lang.String>
      Type: java.util.Map<java.lang.Long, java.lang.String>
      Annotation: @myNote(value="p1")
    AnnotatedType: @myNote(value="key") java.lang.Long
        Type: class java.lang.Long
        Annotation: @myNote(value="key")
    AnnotatedType: @myNote(value="value") java.lang.String
        Type: class java.lang.String
        Annotation: @myNote(value="value")

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