Java自定义Annotation学习1

本次学习的目标是为了获取如下Java类成员中ID的值:

package com.perficient.annotation;

public class WebPage {
	
	@Identifier(id= "A")
	public String buttonA;
	
	@Identifier(id= "B")
	public String buttonB;

}

创建自定义的Annotation:

package com.perficient.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


@Target(ElementType.FIELD) 
@Retention(RetentionPolicy.RUNTIME)    
public @interface Identifier {
	
	public String id();
	
}

注意:Target一定要给予正确的值,如果是类成员的话用Field,是方法要用Method

编写测试类

package com.perficient.annotation;

import java.lang.reflect.Field;

public class AnnotationTest {
	public static void main(String[] args) throws ClassNotFoundException {
		String className = "com.perficient.annotation.WebPage";
		Class<?> test = Class.forName(className);
		Field[] fields = test.getFields();
		for (Field field : fields){
			System.out.println("The field Name is:" + field);
			boolean flag = field.isAnnotationPresent(Identifier.class);
			if (flag) {
				Identifier idt = (Identifier) field
						.getAnnotation(Identifier.class);
				System.out.println("Id is:" + idt.id());
			} else {
				System.out.println("The annotation can't be found");
			}						
		}		
	}
}

注意:如果是Method,需要使用getDeclaredMethods(),如果用getMethods()不会返回我们所需要的结果

输出结果:

The field Name is:public java.lang.String com.perficient.annotation.WebPage.buttonA
Id is:A
The field Name is:public java.lang.String com.perficient.annotation.WebPage.buttonB
Id is:B