注释嵌套注释

从Java 5开始，Java中出现了注释。我想做一个自己的注释，只是为了看看需要什么。但是，我发现它们只是接口。

有擦

接口后面没有牙。必须执行一些代码。我认为这是橡胶行之有效的方法，我真的找到了解决方法。

首先，我需要一个目标

我选择了一个最近的热门话题：缓存。我不想实现JSR 109（JCache），但也不想做典型的“ Hello World”。我选择实现两个注释，一个注释不带任何参数，另一个注释不带参数。我还需要一个缓存提供程序。如果我要这样做的话，还可以将真正的缓存库加入其中。它还遵循我的设计理念，即使用产品/库来达成目标，而不是将所有内容都进行家庭纺。经过仔细考虑，我选择了hazelcast作为我的缓存引擎。它是市场上最快的，而且是免费的。

同时，回到AOP牧场

虽然我知道AOP是适合我的地方，但我对此并不了解。我发现Spring有一个AOP库，而众所周知的库是AspectJ。 AspectJ对我不熟悉，需要运行时引擎才能工作。我对Spring更加熟悉，所以选择了它。在研究Spring的AOP时，我发现我必须深入研究AspectJ的注释，因此无论如何我还是以某种形式或方式被AspectJ所困。

新概念，新词汇

编写方面不像编写对象。它们是对象，但并非如此，因此当然需要一组新的术语。我使用的是Spring AOP文档中的内容

我确实需要阅读几次该页面才能理解所讲的内容。强烈建议您执行相同的操作，否则其余帖子听起来像胡言乱语。

切入点的构成和建议

切入点设计很容易，因为我只对带有注释的方法感兴趣。它需要的建议是周围的建议，因为如果已经进行了匹配的调用，我就需要能够避免调用该方法。

最后的代码

Maven Pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.darylmathison</groupId><artifactId>annotation-implementation</artifactId><version>1.0-SNAPSHOT</version><properties><project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><maven.compiler.source>1.8</maven.compiler.source><maven.compiler.target>1.8</maven.compiler.target><spring.version>4.2.4.RELEASE</spring.version></properties><description>This project is an example of how to implement an annotation via Spring AOP.</description><scm><url>https://github.com/darylmathison/annotation-implementation-example.git</url><connection>scm:git:https://github.com/darylmathison/annotation-implementation-example.git</connection><developerConnection>scm:git:git@github.com:darylmathison/annotation-implementation-example.git</developerConnection></scm><issueManagement><system>GitHub</system><url>https://github.com/darylmathison/annotation-implementation-example/issues</url></issueManagement><dependencies><dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>${spring.version}</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-aop</artifactId><version>${spring.version}</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-test</artifactId><version>${spring.version}</version><scope>test</scope></dependency><dependency><groupId>org.aspectj</groupId><artifactId>aspectjweaver</artifactId><version>1.8.8</version></dependency><dependency><groupId>com.hazelcast</groupId><artifactId>hazelcast</artifactId><version>3.6</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version><scope>test</scope></dependency></dependencies><reporting><plugins><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-project-info-reports-plugin</artifactId><version>2.7</version><reportSets><reportSet><reports><report>dependencies</report><report>index</report><report>project-team</report><report>issue-tracking</report><report>scm</report></reports></reportSet></reportSets></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-surefire-report-plugin</artifactId><version>2.18.1</version></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-javadoc-plugin</artifactId><version>2.10.3</version><reportSets><reportSet><reports><report>javadoc</report><report>test-javadoc</report></reports></reportSet></reportSets></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-jxr-plugin</artifactId><version>2.5</version><configuration><linkJavadoc>true</linkJavadoc></configuration><reportSets><reportSet><reports><report>jxr</report><report>test-jxr</report></reports></reportSet></reportSets></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-changelog-plugin</artifactId><version>2.3</version><configuration><type>range</type><range>90</range></configuration></plugin></plugins></reporting>
</project>

注释

快取

缓存注释的可爱名称，对吗？

package com.darylmathison.ai.annotation;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;/*** Created by Daryl on 2/19/2016.*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface CacheMe {
}

CacheMeNow

package com.darylmathison.ai.annotation;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;/*** Created by Daryl on 2/19/2016.*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface CacheMeNow {String key();
}

弹簧配置

我决定使用基于Java的配置，而不是像通常为了改变速度而使用的XML。 EnableAspectJAutoProxy批注是使Spring AOP开始工作的关键。我一直在我旁边，直到我读到有关这颗小宝石的这篇文章。有时，这是一天中最容易燃烧的事情。

AppConfig

package com.darylmathison.ai.config;import com.darylmathison.ai.cache.CacheAspect;
import com.darylmathison.ai.service.FibonacciService;
import com.darylmathison.ai.service.FibonacciServiceImpl;
import com.hazelcast.config.Config;
import com.hazelcast.config.EvictionPolicy;
import com.hazelcast.config.MapConfig;
import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.HazelcastInstance;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;import java.util.HashMap;
import java.util.Map;/*** Created by Daryl on 2/20/2016.*/
@Configuration
@ComponentScan(basePackages = "com.darylmathison.ai")
@EnableAspectJAutoProxy
public class AppConfig {@Beanpublic Map<String, Object> cache() {Config config = new Config();MapConfig mapConfig = new MapConfig();mapConfig.setEvictionPercentage(50);mapConfig.setEvictionPolicy(EvictionPolicy.LFU);mapConfig.setTimeToLiveSeconds(300);Map<String, MapConfig> mapConfigMap = new HashMap<>();mapConfigMap.put("cache", mapConfig);config.setMapConfigs(mapConfigMap);HazelcastInstance instance = Hazelcast.newHazelcastInstance(config);return instance.getMap("cache");}@Beanpublic FibonacciService fibonacci() {return new FibonacciServiceImpl();}@Beanpublic CacheAspect cacheAspect() {return new CacheAspect();}
}

服务编号

基于经典Spring的设计需要服务吗？由于Spring使用代理来实现其AOP，因此强烈建议为带注释的类定义一个接口以实现。

斐波那契服务

package com.darylmathison.ai.service;/*** Created by Daryl on 2/20/2016.*/
public interface FibonacciService {long calculate(int rounds);long calculateWithKey(int rounds);
}

FibonacciServiceImpl

package com.darylmathison.ai.service;import com.darylmathison.ai.annotation.CacheMe;
import com.darylmathison.ai.annotation.CacheMeNow;/*** Created by Daryl on 2/20/2016.*/
public class FibonacciServiceImpl implements FibonacciService {@Override@CacheMepublic long calculate(int rounds) {return sharedCalculate(rounds);}@Override@CacheMeNow(key = "now")public long calculateWithKey(int rounds) {return sharedCalculate(rounds);}private static long sharedCalculate(int rounds) {long[] lastTwo = new long[] {1, 1};for(int i = 0; i < rounds; i++) {long last = lastTwo[1];lastTwo[1] = lastTwo[0] + lastTwo[1];lastTwo[0] = last;}return lastTwo[1];}
}

AOP的东西

这是注释实现的核心。其他所有内容都可以用来支持后续的工作。

系统存档

根据Spring文档，集中化切入点定义是一个好主意。

package com.darylmathison.ai.cache;import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;/*** Created by Daryl on 2/20/2016.*/
@Aspect
public class SystemArch {@Pointcut("@annotation(com.darylmathison.ai.annotation.CacheMe)")public void cacheMeCut() {}@Pointcut("@annotation(com.darylmathison.ai.annotation.CacheMeNow)")public void cacheMeNowCut() {}
}

缓存方面

周围注释使用切入点类的完整方法名称来定义建议的内容。 CacheMeNow批注的建议包括一个额外条件，因此可以定义批注，以便可以读取关键参数。测试代码中揭示了CacheMeNow中的一个设计错误。

package com.darylmathison.ai.cache;import com.darylmathison.ai.annotation.CacheMeNow;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.springframework.beans.factory.annotation.Autowired;import java.util.Map;/*** Created by Daryl on 2/20/2016.*/
@Aspect
public class CacheAspect {@Autowiredprivate Map<String, Object> cache;@Around("com.darylmathison.ai.cache.SystemArch.cacheMeCut()")public Object simpleCache(ProceedingJoinPoint proceedingJoinPoint) throws Throwable {StringBuffer keyBuffer = new StringBuffer();for(Object o: proceedingJoinPoint.getArgs()) {keyBuffer.append(o.hashCode());}String key = keyBuffer.toString();Object ret = cache.get(key);if(ret == null) {ret = proceedingJoinPoint.proceed();cache.put(key, ret);}return ret;}@Around("com.darylmathison.ai.cache.SystemArch.cacheMeNowCut() && @annotation(cacheMeNow)")public Object simpleCacheWithParam(ProceedingJoinPoint proceedingJoinPoint, CacheMeNow cacheMeNow) throws Throwable {Object ret = cache.get(cacheMeNow.key());if(ret == null) {ret = proceedingJoinPoint.proceed();cache.put(cacheMeNow.key(), ret);}return ret;}
}

测试代码

显示注释确实引起缓存的驱动程序代码。

斐波那契检验

package com.darylmathison.ai.service;import com.darylmathison.ai.config.AppConfig;
import org.junit.Assert;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;/*** Created by Daryl on 2/20/2016.*/
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = {AppConfig.class})
public class FibonacciTest {private static final int ROUNDS = 12;private static final long ANSWER = 377;@Autowiredprivate FibonacciService fibonacci;@org.junit.Testpublic void testCalculate() throws Exception {long start = System.currentTimeMillis();Assert.assertEquals(ANSWER, fibonacci.calculate(ROUNDS));long middle = System.currentTimeMillis();Assert.assertEquals(ANSWER, fibonacci.calculate(ROUNDS));long end = System.currentTimeMillis();Assert.assertTrue((end - middle) < (middle - start));}@org.junit.Testpublic void testCalculateWithKey() throws Exception {Assert.assertEquals(ANSWER, fibonacci.calculateWithKey(ROUNDS));// This test should not passAssert.assertEquals(ANSWER, fibonacci.calculateWithKey(13));}
}

结论

注释不必很难实现。使用AOP编程，我可以用很少的代码来实现两个注释。

翻译自: https://www.javacodegeeks.com/2016/03/diy-annotations-3.html

注释嵌套注释