Java中的类 getAnnotationsByType() 方法和示例

Java.lang.Class 类的getAnnotationsByType()方法用于获取该类中存在的指定注解类型的注解。该方法返回指定注释类型的注释数组。

句法：

public A[] getAnnotationsByType(Class annotationClass)

参数：这个方法接受一个参数annotationClass ，它是要获取的注解的类型。

返回值：此方法返回指定注释类型的注释数组。

异常：此方法抛出：

• NullPointerException：如果给定的注释类为空。

下面的程序演示了 getAnnotationsByType() 方法。

示例 1：

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

输出：

Class represented by myClass: class Test
Annotation of myClass of type Annotation: [@Annotation(key=GFG, value=GeeksForGeeks)]

示例 2：

// Java program to demonstrate
// getAnnotationsByType() method
  
import java.util.*;
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 class
            Class myClass = Test.class;
  
            System.out.println(
                "Class represented by myClass: "
                + myClass.toString());
  
            // Get the annotation
            // using getAnnotationsByType() method
            System.out.println(
                "Annotation of myClass of type Deprecated: "
                + Arrays.toString(
                      myClass
                          .getAnnotationsByType(
                              Deprecated.class)));
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

输出：

Class represented by myClass: class Test
Annotation of myClass of type Deprecated: [@java.lang.Deprecated()]

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