Spring自定义注解的使用和解析

自定义的注解 ，可通过Spring快速的获取所有使用该注解的类或方法或属性，以及注解内的值。

自定义一个注解

@Target({ ElementType.TYPE, ElementType.METHOD }) //可以用在方法或者类上面
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Fooish {

    String[] tags() default { "all" };
}

定义一个接口，以及两个实现类

public interface Foo{
  void bar();
}
/** FooA **/
public class FooA implements Foo{
  @Override
  @Fooish(tags={"this_is_method"})
  public void bar(){
    System.out.println("I am number 6!");
  }
}
/** FooB **/
@Fooish(tags= {"this_is_class"})
@Component // 一定得写，有这个注解，Spring才会将这个类实例化
public class FooB implements Foo{
  @Override
  public void bar(){
    System.out.println("I am not a number, I am a free man!");
  }
}

配置Spring

首先引入Spring的依赖包，
配置文件添加,通过注解实例化Bean
<mvc:annotation-driven />或者<context:component-scan />

<!-- 让Spring扫描我们的自定义注解-->
<context:component-scan base-package="cn.itenlee">
  <context:include-filter type="annotation" expression="cn.itenlee.annotation.Fooish" />
</context:component-scan>

测试

加上@Component，当Spring启动并实例化该类的时候，会调用afterPropertiesSet方法

@Component
public class MyFooishHandler implements ApplicationContextAware, InitializingBean {
    private ApplicationContext applicationContext;

    private List<String> allFooish = new ArrayList<>();

    @Override
    public void afterPropertiesSet() throws Exception {
        scanFooishClass();
        scanFooishMethod();
        System.out.println(allFooish);
    }

    /**
     * 查找 用 Fooish 注解的 类
     * @throws Exception
     */
    private void scanFooishClass() throws Exception {
        final Map<String, Object> permissionMap = applicationContext.getBeansWithAnnotation(Fooish.class);
        for (final Object permissionObject : permissionMap.values()) {
            final Class<? extends Object> permissionClass = permissionObject.getClass();
            final Fooish annotation = permissionClass.getAnnotation(Fooish.class);
            if(annotation != null) {
                allFooish.addAll(Arrays.asList(annotation.tags()));
            }
        }
    }


    /**
     * 查找 用 Component 注解的 类 下面 用 Fooish 注解的方法
     * @throws Exception
     */
    private void scanFooishMethod() throws Exception{
        final Map<String, Object> controllerMap = applicationContext.getBeansWithAnnotation(Component.class);
        for (final Object controllerObject : controllerMap.values()) {
            final Class<? extends Object> controllerClass = controllerObject.getClass();
            for (Method method : controllerClass.getDeclaredMethods()) {
                Fooish fooish = method.getAnnotation(Fooish.class);
              if (fooish != null) {
                    allFooish.addAll(Arrays.asList(fooish.tags()));
                }
            }
        }
    }

    @Override
    public void setApplicationContext(final ApplicationContext applicationContext)
            throws BeansException {
        this.applicationContext = applicationContext;
    }
}

通过AOP以该注解为切入点

Spring配置

<aop:aspectj-autoproxy proxy-target-class="true"/>

如果使用了SpringMVC，且想在Controller实现切入，则该配置需和SpringMVC配置在同一上下文中。
切面代码

@Aspect
@Component
public class PermissionAspect {

    @Pointcut("@annotation(cn.itenlee.annotation.PermissionCode)")
    public void permissionCodeAspect() {
    }

    @Before("permissionCodeAspect()")
    public void doBefore(JoinPoint joinPoint) {
        try {
            //*========控制台输出=========*//
            System.out.println("=====前置通知开始=====");
            System.out.println("###请求方法:" + (joinPoint.getTarget().getClass().getName() + "." + joinPoint.getSignature().getName() + "()"));
            System.out.println("=====前置通知结束=====");
        }  catch (Exception e) {
            //记录本地异常日志
            e.printStackTrace();
        }
    }
    @After("permissionCodeAspect()")
    public void doAfterTask(JoinPoint joinPoint){
        System.out.println("=====后置通知=====");
        System.out.println("###请求方法:" + (joinPoint.getTarget().getClass().getName() + "." + joinPoint.getSignature().getName() + "()"));
        System.out.println("=====后置通知end=====");
    }
}

google 大法好，感谢来自国外的博主 http://techo-ecco.com/blog/spring-custom-annotations/