Java中的 AnnotatedElement getDeclaredAnnotationsByType() 方法及示例

Java.lang.AnnotatedElement 类的getDeclaredAnnotations()方法用于获取实现该接口的类中存在的指定声明注解类型的声明注解。该方法返回指定的声明注释类型的声明注释数组。

句法：

public A[] getDeclaredAnnotationsByType(Class declared annotationClass)

参数：此方法接受一个参数声明的annotationClass ，它是要获取的声明注释的类型。

返回值：此方法返回指定声明注释类型的声明注释数组。

异常：此方法抛出：

• NullPointerException：如果给定的声明注释类为空。

下面的程序演示了 getDeclaredAnnotationsByType() 方法。

示例 1：

// Java program to demonstrate
// getDeclaredAnnotationsByType() method
  
import java.util.*;
import java.lang.reflect.*;
import java.lang.annotation.*;
  
// create a custom DeclaredAnnotation
@Retention(RetentionPolicy.RUNTIME)
@interface DeclaredAnnotation {
  
    // This declared annotation has two attributes.
    public String key();
  
    public String value();
}
  
// call DeclaredAnnotation for method
// and pass values for declared annotation
@DeclaredAnnotation(key = "GFG", value = "GeeksForGeeks")
public class Test {
  
    public Object obj;
  
    public static void main(String[] args)
        throws ClassNotFoundException
    {
  
        // returns the Class object
        // for this myAnnotatedElement
        AnnotatedElement myAnnotatedElement
            = Test.class;
  
        System.out.println(
            "AnnotatedElement represented"
            + " by myAnnotatedElement: "
            + myAnnotatedElement.toString());
  
        // Get the declared annotation
        // using getDeclaredAnnotationsByType() method
        System.out.println(
            "DeclaredAnnotation of myAnnotatedElement"
            + " of type DeclaredAnnotation: "
            + Arrays.toString(
                  myAnnotatedElement
                      .getDeclaredAnnotationsByType(
                          DeclaredAnnotation.class)));
    }
}

输出：

AnnotatedElement represented by myAnnotatedElement: class Test
DeclaredAnnotation of myAnnotatedElement of type DeclaredAnnotation: [@DeclaredAnnotation(key=GFG, value=GeeksForGeeks)]

示例 2：

// Java program to demonstrate
// getDeclaredAnnotationsByType() method
  
import java.util.*;
import java.lang.reflect.*;
import java.lang.annotation.*;
  
@Deprecated
public class Test {
  
    public Object obj;
  
    public static void main(String[] args)
        throws ClassNotFoundException
    {
        try {
  
            // returns the Class object
            // for this myAnnotatedElement
            AnnotatedElement myAnnotatedElement
                = Test.class;
  
            System.out.println(
                "AnnotatedElement represented"
                + " by myAnnotatedElement: "
                + myAnnotatedElement.toString());
  
            // Get the declared annotation
            // using getDeclaredAnnotationsByType() method
            System.out.println(
                "DeclaredAnnotation of myAnnotatedElement"
                + " of type Deprecated: "
                + Arrays.toString(
                      myAnnotatedElement
                          .getDeclaredAnnotationsByType(
                              Deprecated.class)));
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

输出：

AnnotatedElement represented by myAnnotatedElement: class Test
DeclaredAnnotation of myAnnotatedElement of type Deprecated: [@java.lang.Deprecated()]

参考： https://docs.oracle.com/javase/9/docs/api/ Java/lang/reflect/AnnotatedElement.html#getAnnotationsByType-java.lang.Class-