annotation 例子-优快云博客

本文介绍了一个使用Java注解的例子，展示了如何定义自定义注解、如何应用这些注解到类和字段上，以及如何通过反射读取注解信息。

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@Retention ： RetentionPolicy. SOURCE,CLASS,RUNTIME
@Target ：ElementType.TYPE,FIELD,METHOD,PARAMETER,CONSTRUCTOR,LOCAL_VARIABLE,ANNOTATION_TYPE,PACKAGE

@Retention(RetentionPolicy.RUNTIME)
@Target(value = ElementType.FIELD)
public @interface In {

    /**
     * 范围
     * 
     * @return
     */
    String scope();

    /**
     * 值
     * 
     * @return
     */
    String value();
}

@Retention(RetentionPolicy.RUNTIME)
@Target(value = ElementType.TYPE)
public @interface UserInfo {

    String name();

    String age();
}

@UserInfo(name = "sefer", age = "27")
public class User {

    @In(scope = "request", value = "hangzhou")
    String address;

    public String getAddress() {
	return address;
    }

    public void setAddress(String address) {
	this.address = address;
    }
}

public class GetUser {

    public static void main(String[] args) {
	AnnotatedElement an = User.class;
	boolean isUserInfo = an.isAnnotationPresent(UserInfo.class);

	if (isUserInfo) {
	    UserInfo userInfo = an.getAnnotation(UserInfo.class);
	    String name = userInfo.name();
	    String age = userInfo.age();
	    System.out.println("name: " + name);
	    System.out.println("age: " + age);
	}

	User user = new User();

	Field[] fields = user.getClass().getDeclaredFields();

	for (Field field : fields) {
	    // 重要:避免java虚拟机检查对私有成员的访问权限
	    field.setAccessible(true);
	    boolean isIn = field.isAnnotationPresent(In.class);
	    if (isIn) {
		In in = field.getAnnotation(In.class);
		System.out.println(field.getName() + "value: " + in.value());
		System.out.println(field.getName() + " save scope: "
			+ in.scope());

	    }
	}
    }
}