用示例在Java中封装 getAnnotationsByType() 方法
Java.lang.Package 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/Package.html#getAnnotationsByType-java.lang.Class-