Java自定义运行时注解

Java注解–自定义注解–运行时注解

@Retention(RetentionPolicy.RUNTIME)表示运行时保留的注解。我们可以在运行时，通过java反射机制，获取到注解信息。

运行时注解处理器类库(java.lang.reflect.AnnotatedElement)

接口AnnotatedElement表示程序中的注解元素，可以使用反射读取。接口中返回的所有注解都是不可变和可序列化的，接口方法返回的数组可以被修改，但不会影响原有的注解。接口的getAnnotationsByType(Class)和getDeclaredAnnotationsByType(Class)方法支持重复注解。

自定义运行期注解例子

项目地址

目标为class的注解

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

/**
 * Created by victor on 2017/5/30.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface ClassInfo {

    String name() default "";

    String description() default "";
}

目标为方法的注解

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

/**
 * Created by victor on 2017/5/30.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface MethodInfo {

    String name() default "";

    String description() default "";
}

目标为属性的注解

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

/**
 * Created by victor on 2017/5/30.
 */

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface FieldInfo {

    String name() default "";

    String description() default "";
}

注解处理工具

import java.lang.reflect.Field;
import java.lang.reflect.Method;

/**
 * Created by victor on 2017/5/30.
 */
public class InfoUtil {
    public static void HandleInfo(Class clazz){
        if(clazz.isAnnotationPresent(ClassInfo.class)) {
            ClassInfo classInfo = clazz.getAnnotation(ClassInfo.class);
            System.out.println("classInfo:\n"+classInfo.name()+"::"+classInfo.description());
        }

        Method[] methods = clazz.getDeclaredMethods();
        for(Method item: methods){
            if(item.isAnnotationPresent(MethodInfo.class)){
                MethodInfo methodInfo = item.getAnnotation(MethodInfo.class);
                System.out.println("methodInfo:\n"+methodInfo.name()+"::"+methodInfo.description());
            }
        }

        Field[] fields = clazz.getDeclaredFields();
        for(Field item: fields){
            if(item.isAnnotationPresent(FieldInfo.class)){
                FieldInfo fieldInfo = item.getAnnotation(FieldInfo.class);
                System.out.println("methodInfo:\n"+fieldInfo.name()+"::"+fieldInfo.description());
            }
        }
    }
}

实体类demo

/**
 * Created by victor on 2017/5/30.
 */
@ClassInfo(name = "DemoClass",description = "A demo class for annotation")
public class Demo {

    @FieldInfo(name = "DemoField",description = "A demo field for annotation")
    private String name;

    @MethodInfo(name = "DemoMethod", description = "A demo method for annotation")
    public String getName() {
        return name;
    }
}

测试类

/**
 * Created by victor on 2017/5/30.
 */
public class Test {
    public static void main(String[] args){
        InfoUtil.HandleInfo(Demo.class);
    }
}

classInfo:
DemoClass::A demo class for annotation
methodInfo:
DemoMethod::A demo method for annotation
methodInfo:
DemoField::A demo field for annotation

---

参考资料：
Java官方Tutorial