Java自定义注解（二）

绝地灬酷狼 2022-11-05 08:31 145阅读 0赞

上文介绍了如何自定义注解，本篇主要介绍如何使用注解

# 自定义注解 #

package com.example.annotaion;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    //注解保留到什么时候
    @Retention(RetentionPolicy.RUNTIME)
    @Target({
        ElementType.TYPE, ElementType.METHOD})
    public @interface CacheResult {
        
    
        //缓存key
        String key();
    
        //缓存名称
        String cacheName();
    
        //过期时间
        String expireDate() default "";
    
        //是否过期
        boolean expire() default false;
    }

在另外一个controller里面使用这个注解

package com.example.controller;
    
    import com.example.annotaion.CacheResult;
    import org.springframework.stereotype.Controller;
    
    @Controller
    @CacheResult(key = "IndexController-class-key", cacheName = "IndexController-class-cacheName")
    public class IndexController {
        
    
        @CacheResult(key = "IndexController-method-key", cacheName = "IndexController-method-cacheName")
        public String index() {
        
            return "hhh";
        }
    }

# 通过JDK反射来实现获取注解 #

/**
         * 通过JDK的反射的方式来获取注解
         */
        @Test
        void testMyAnnotationByJDK() {
        
            Class<TestController> clazz = TestController.class;
            Class<CacheResult> annoClazz = CacheResult.class;
            //如果在TestController这个类上面使用了CacheResult这个注解
            if (clazz.isAnnotationPresent(annoClazz)) {
        
                CacheResult annotation = clazz.getAnnotation(annoClazz);
                System.out.println(annotation.key());
                System.out.println(annotation.cacheName());
            }
            Method[] methods = clazz.getMethods();
            //遍历所有的方法，如果这个方法上有这个注解，则获取这个注解
            for (Method method : methods) {
        
                if (method.isAnnotationPresent(annoClazz)) {
        
                    CacheResult annotation = method.getAnnotation(annoClazz);
                    System.out.println(annotation.key());
                    System.out.println(annotation.cacheName());
                }
            }
        }

# 运行效果 #

IndexController-class-key
    IndexController-class-cacheName
    IndexController-method-key
    IndexController-method-cacheName

# 通过spring容器来获取注解 #

### 首先需要实现spring的两个接口 ###

package com.example.component;
    
    import com.example.annotaion.CacheResult;
    import org.springframework.beans.BeansException;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.ApplicationContextAware;
    import org.springframework.context.ApplicationListener;
    import org.springframework.context.event.ContextRefreshedEvent;
    import org.springframework.core.annotation.AnnotationUtils;
    import org.springframework.stereotype.Component;
    
    import java.lang.reflect.Method;
    import java.util.Map;
    import java.util.Set;
    
    @Component
    //实现了ApplicationContextAware接口，就可以获取到容器到上下文
    //ApplicationListener<ContextRefreshedEvent>容器启动之后的监听器
    public class MyComponent implements ApplicationContextAware, ApplicationListener<ContextRefreshedEvent> {
        
    
        ApplicationContext applicationContext;
    
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        
            this.applicationContext = applicationContext;
        }
    
        @Override
        public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        
            Class<CacheResult> cacheResultClass = CacheResult.class;
            //spring容器启动之后，spring上下文获取有CacheResult注解的bean
            Map<String, Object> beansWithAnnotation = applicationContext.getBeansWithAnnotation(cacheResultClass);
            //遍历这些有CacheResult注解的bean
            Set<Map.Entry<String, Object>> entries = beansWithAnnotation.entrySet();
            for (Map.Entry<String, Object> entry : entries) {
        
                String beanId = entry.getKey();//获取bean的名字
                Class<?> aClass = entry.getValue().getClass();//获取bean的类对象
                System.out.println("在spring容器中，使用CacheResult注解的beanId："+beanId);
                System.out.println("在spring容器中，使用CacheResult注解的bean名称："+aClass.getName());
    
    
                //获取注解类实例
                CacheResult annotation = AnnotationUtils.findAnnotation(aClass, cacheResultClass);
                System.out.println(annotation.key());
                System.out.println(annotation.cacheName());
    
    
                Method[] methods = aClass.getMethods();
                //遍历带有cacheResult注解的类中的所有方法
                for (Method method : methods) {
        
                    CacheResult annotation1 = AnnotationUtils.findAnnotation(method, cacheResultClass);
                    if (annotation1 != null) {
        
                        System.out.println(annotation1.key());
                        System.out.println(annotation1.cacheName());
                    }
                }
            }
    
        }
    
        public void test() {
        
            System.out.println("TestComponent中的test方法，没有实际意义");
        }
    }

### 注入这个component ###

@SpringBootTest
    class StudyAnnotationApplicationTests {
        
    
        @Resource
        private MyComponent myComponent;
        @Test
        void TestMyAnnotationBySpring() {
        
            myComponent.test();
        }
    }
    
    ### 运行效果
     ```shell
    在spring容器中，使用CacheResult注解的beanId：indexController
    在spring容器中，使用CacheResult注解的bean名称：com.example.controller.IndexController
    IndexController-class-key
    IndexController-class-cacheName
    IndexController-method-key
    IndexController-method-cacheName
    在spring容器中，使用CacheResult注解的beanId：testController
    在spring容器中，使用CacheResult注解的bean名称：com.example.controller.TestController$$EnhancerBySpringCGLIB$$3d4dbf28
    class_key
    class_cacheName
    method_key
    method_cacheName
    2021-03-04 15:47:11.943  INFO 15259 --- [           main] c.e.StudyAnnotationApplicationTests      : Started StudyAnnotationApplicationTests in 1.645 seconds (JVM running for 2.422)
    
    TestComponent中的test方法，没有实际意义
    
    2021-03-04 15:47:12.132  INFO 15259 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'
    
    Process finished with exit code 0