SpringBoot5-spring高级话题-组合注解与元注解，@Enable*注解的工作原理，测试

一：组合注解与元注解

      从spring2开始，为了响应JDK1.5推出的注解供暖，spring开始大量加入注解来替代xml配置。spring的注解主要用来配置和注入bean，以及AOP相关的配置（@Transactional）。随着注解的大量使用，尤其相同的多个注解用到各个类或方法中，会相当繁琐。这就是所谓的样板代码，是spring设计的原则中要消除的代码。

      所谓元注解其实就是可以注解到别的注解上的注解，被注解的注解称之为组合注解，组合注解具备注解其上的元注解的功能。spring的很多注解都可以作为元注解，而且spring本身已经有很多组合注解，如@Configuration就是一个组合@Component注解，表明这个类其实也是一个Bean。

      前面我们大量使用了@Configuration和@ComponentScan注解到配置类上，下面我们把这两个注解组成一个组合注解。

     示例：

package jack.ch3.annotation;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

import java.lang.annotation.*;

/**
 * Created by jack on 2017/7/15.
 * 组合注解
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration //组合@Configuration元注解
@ComponentScan //组合@ComponentScan元注解
public @interface WiselyConfiguration {
    //覆盖value参数
    String [] value() default {};
}

演示服务的Bean：

package jack.ch3.annotation;

import org.springframework.stereotype.Service;

/**
 * Created by jack on 2017/7/15.
 */
@Service
public class DemoService {
    public void outputResult(){
        System.out.println("从组合注解配置照样获取的Bean");
    }
}

  配置类：

package jack.ch3.annotation;

/**
 * Created by jack on 2017/7/15.
 */
//使用@WiselyConfiguration组合注解替代@Configuration和@ComponentScan
@WiselyConfiguration("jack.ch3.annotation")
public class DemoConfig {
}

  测试代码如下：

package jack.ch3.annotation;

import jack.ch3.conditional.ConditionConfig;
import jack.ch3.conditional.ListServer;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * Created by jack on 2017/7/15.
 */
public class MainTest12 {
    public static void main(String [] args){
        //AnnotationConfigApplicationContext作为spring容器，接受一个配置类作为参数
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(DemoConfig.class);
        DemoService demoService = context.getBean(DemoService.class);
        demoService.outputResult();
        context.close();
    }
}

   运行程序，输出如下：

D:\java\jdk1.8.0_111\bin\java -Didea.launcher.port=7535 "-Didea.launcher.bin.path=D:\programmingsoftware\IDEA\JetBrains\IntelliJ IDEA 2016.3.2\bin" -Dfile.encoding=UTF-8 -classpath "D:\java\jdk1.8.0_111\jre\lib\charsets.jar;D:\java\jdk1.8.0_111\jre\lib\deploy.jar;D:\java\jdk1.8.0_111\jre\lib\ext\access-bridge-64.jar;D:\java\jdk1.8.0_111\jre\lib\ext\cldrdata.jar;D:\java\jdk1.8.0_111\jre\lib\ext\dnsns.jar;D:\java\jdk1.8.0_111\jre\lib\ext\jaccess.jar;D:\java\jdk1.8.0_111\jre\lib\ext\jfxrt.jar;D:\java\jdk1.8.0_111\jre\lib\ext\localedata.jar;D:\java\jdk1.8.0_111\jre\lib\ext\nashorn.jar;D:\java\jdk1.8.0_111\jre\lib\ext\sunec.jar;D:\java\jdk1.8.0_111\jre\lib\ext\sunjce_provider.jar;D:\java\jdk1.8.0_111\jre\lib\ext\sunmscapi.jar;D:\java\jdk1.8.0_111\jre\lib\ext\sunpkcs11.jar;D:\java\jdk1.8.0_111\jre\lib\ext\zipfs.jar;D:\java\jdk1.8.0_111\jre\lib\javaws.jar;D:\java\jdk1.8.0_111\jre\lib\jce.jar;D:\java\jdk1.8.0_111\jre\lib\jfr.jar;D:\java\jdk1.8.0_111\jre\lib\jfxswt.jar;D:\java\jdk1.8.0_111\jre\lib\jsse.jar;D:\java\jdk1.8.0_111\jre\lib\management-agent.jar;D:\java\jdk1.8.0_111\jre\lib\plugin.jar;D:\java\jdk1.8.0_111\jre\lib\resources.jar;D:\java\jdk1.8.0_111\jre\lib\rt.jar;E:\webworkspace\IdeaProjects\springstudy1\target\classes;C:\Users\wj\.m2\repository\org\springframework\spring-context\4.1.6.RELEASE\spring-context-4.1.6.RELEASE.jar;C:\Users\wj\.m2\repository\org\springframework\spring-beans\4.1.6.RELEASE\spring-beans-4.1.6.RELEASE.jar;C:\Users\wj\.m2\repository\org\springframework\spring-core\4.1.6.RELEASE\spring-core-4.1.6.RELEASE.jar;C:\Users\wj\.m2\repository\commons-logging\commons-logging\1.2\commons-logging-1.2.jar;C:\Users\wj\.m2\repository\org\springframework\spring-expression\4.1.6.RELEASE\spring-expression-4.1.6.RELEASE.jar;C:\Users\wj\.m2\repository\org\springframework\spring-aop\4.1.6.RELEASE\spring-aop-4.1.6.RELEASE.jar;C:\Users\wj\.m2\repository\aopalliance\aopalliance\1.0\aopalliance-1.0.jar;C:\Users\wj\.m2\repository\org\aspectj\aspectjrt\1.8.5\aspectjrt-1.8.5.jar;C:\Users\wj\.m2\repository\org\aspectj\aspectjweaver\1.8.5\aspectjweaver-1.8.5.jar;C:\Users\wj\.m2\repository\commons-io\commons-io\2.3\commons-io-2.3.jar;C:\Users\wj\.m2\repository\javax\annotation\jsr250-api\1.0\jsr250-api-1.0.jar;D:\programmingsoftware\IDEA\JetBrains\IntelliJ IDEA 2016.3.2\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain jack.ch3.annotation.MainTest12
七月 15, 2017 3:27:09 下午 org.springframework.context.annotation.AnnotationConfigApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@5d099f62: startup date [Sat Jul 15 15:27:09 CST 2017]; root of context hierarchy
从组合注解配置照样获取的Bean
七月 15, 2017 3:27:09 下午 org.springframework.context.annotation.AnnotationConfigApplicationContext doClose
信息: Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@5d099f62: startup date [Sat Jul 15 15:27:09 CST 2017]; root of context hierarchy

Process finished with exit code 0

 

二：@Enable*注解的工作原理

    在前面我们通过@EnableAspectJAutoProxy开启对AspectJ自动代理的支持。

    @EnableAsync开启异步方法的支持

    @EnableScheduling开启计划任务的支持

    @EnableWebMvc开启Web MVC的配置支持

    @EnableConfigurationProperties开启对@ConfigurationProperties注解配置Bean的支持。

    @EnableJpaRepositor开启对Spring Data JPA Repository的支持

    @EnableTransactionManagement开启注解事务的支持

    @EnableCaching开启注解式的缓存支持

        通过简单的@Enable*来开启一项功能的支持，从而避免自己配置大量的代码，大大降低了使用难度。下面看看实现该功能的原理。

       通过观察这些@Enable*注解的源码，我们发现所有的注解都有一个@Import注解，@Import是用来导入配置类的，这也意味着这些自动开启的实现其实是导入一些自动配置的bean。这些导入的配置方式主要分为以下三种类型。

     1，第一类：直接导入配置类

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.scheduling.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;
import org.springframework.scheduling.annotation.SchedulingConfiguration;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Import({SchedulingConfiguration.class})
@Documented
public @interface EnableScheduling {
}

      直接导入配置类SchedulingConfiguration，这个类注解了@Configuration，且注册了一个scheduledAnnotationProcessor的Bean，源码如下：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.scheduling.annotation;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Role;
import org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor;

@Configuration
public class SchedulingConfiguration {
    public SchedulingConfiguration() {
    }

    @Bean(
        name = {"org.springframework.context.annotation.internalScheduledAnnotationProcessor"}
    )
    @Role(2)
    public ScheduledAnnotationBeanPostProcessor scheduledAnnotationProcessor() {
        return new ScheduledAnnotationBeanPostProcessor();
    }
}

   2，第二类：依据条件选择配置类

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.scheduling.annotation;

import java.lang.annotation.Annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.AdviceMode;
import org.springframework.context.annotation.Import;
import org.springframework.scheduling.annotation.AsyncConfigurationSelector;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import({AsyncConfigurationSelector.class})
public @interface EnableAsync {
    Class annotation() default Annotation.class;

    boolean proxyTargetClass() default false;

    AdviceMode mode() default AdviceMode.PROXY;

    int order() default 2147483647;
}

AsyncConfigurationSelector通过条件来选择需要导入的配置类，AsyncConfigurationSelector的根接口为ImportSelector，这个接口需重写selectImports方法，在此方法内进行事先条件判断。此例中，若adviceMode为PORXY,则返回ProxyAsyncConfiguration这个配置类；若activeMode为ASPECTJ,则返回AspectJAsyncConfiguration配置类，源码如下：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.scheduling.annotation;

import org.springframework.context.annotation.AdviceMode;
import org.springframework.context.annotation.AdviceModeImportSelector;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.annotation.ProxyAsyncConfiguration;

public class AsyncConfigurationSelector extends AdviceModeImportSelector {
    private static final String ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME = "org.springframework.scheduling.aspectj.AspectJAsyncConfiguration";

    public AsyncConfigurationSelector() {
    }

    public String[] selectImports(AdviceMode adviceMode) {
        switch(null.$SwitchMap$org$springframework$context$annotation$AdviceMode[adviceMode.ordinal()]) {
        case 1:
            return new String[]{ProxyAsyncConfiguration.class.getName()};
        case 2:
            return new String[]{"org.springframework.scheduling.aspectj.AspectJAsyncConfiguration"};
        default:
            return null;
        }
    }
}

     3，第三类：动态注册Bean

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.context.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.AspectJAutoProxyRegistrar;
import org.springframework.context.annotation.Import;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import({AspectJAutoProxyRegistrar.class})
public @interface EnableAspectJAutoProxy {
    boolean proxyTargetClass() default false;
}

    AspectJAutoProxyRegistrar实现了ImportBeanDefinitionRegistar接口，ImportBeanDefinitionRegistrar的作用是在运行时自动添加Bean到已有的配置类，通过重写方法

public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);
        AnnotationAttributes enableAJAutoProxy = AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class);
        if(enableAJAutoProxy.getBoolean("proxyTargetClass")) {
            AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
        }

    }

        其中AnnotationMetadata参数用来获得当前配置类上的注解；BeanDefinitionRegistry参数用来注册Bean。源码如下：

     

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.context.annotation;

import org.springframework.aop.config.AopConfigUtils;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.annotation.AnnotationConfigUtils;
import org.springframework.context.annotation.EnableAspectJAutoProxy;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.type.AnnotationMetadata;

class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar {
    AspectJAutoProxyRegistrar() {
    }

    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);
        AnnotationAttributes enableAJAutoProxy = AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class);
        if(enableAJAutoProxy.getBoolean("proxyTargetClass")) {
            AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
        }

    }
}

三：测试

        测试是开发中不可缺少的部分，单元测试只针对当前开发的类和方法进行测试，可以简单通过模拟依赖来实现，对运行环境没有依赖。

       spring通过Spring TestContex Framework对集成测试提供顶级支持。它不依赖于特定的测试框架，既可使用Junit，也可以使用TestNG。

       基于Maven构建的项目结构默认有关于测试的目录：src/test/java(测试代码),src/test/resources（测试资源）,区别于src/main/java（项目源码）,src/main/resources（项目资源）

        Spring提供了一个SpringJUnit4ClassRunner类，它提供了Spring TestContext Framework的功能。通过@ContextConfiguration来配置ApplicationContext，通过@ActiveProfiles确定活动的profile。

        在使用了Spring测试后，我们前面例子的运行部分都可以用spring测试来检验功能能否正常运作。

        下面对简单配置的Application Context和在测试中注入Bean做演示。

        1，准备

        增加Spring测试的依赖包到Maven

        
            org.springframework
            spring-test
            4.1.6.RELEASE
        
        
            junit
            junit
            4.11
        

业务代码：

 在src/main/java下的源码：

package jack.ch3.test;

/**
 * Created by jack on 2017/7/16.
 */
public class TestBean {
    private String content;

    public TestBean(String content) {
        this.content = content;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }
}

  配置类：

package jack.ch3.test;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;

/**
 * Created by jack on 2017/7/16.
 */
@Configuration
public class TestConfig {
    @Bean
    @Profile("dev")
    public TestBean devTestBean(){
        return new TestBean("from development profile");
    }
    @Bean
    @Profile("prod")
    public TestBean prodTestBean(){
        return new TestBean("from production profile");
    }
}

测试：

  在src/test/java下的代码：

package jack.ch3.test;

import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

/**
 * Created by jack on 2017/7/16.
 */
@RunWith(SpringJUnit4ClassRunner.class)//SpringJUnit4ClassRunner在JUnit环境下提供Spring TestContext Framework的功能
@ContextConfiguration(classes = {TestConfig.class}) //@ContextConfiguration用来加载配置ApplicationContext，其中classes属性用来加载配置类
@ActiveProfiles("prod") //@ActiveProfiles用来声明活动的profile
public class DemoBeanIntegrationTests {
    @Autowired //可使用普通的@Autowired注入Bean
    private TestBean testBean;
    @Test //测试代码，通过JUnit的Assert来校验是否和预期一致
    public void prodBeanShouldInject(){
        String expected = "from production profile";
        String actual = testBean.getContent();
        Assert.assertEquals(expected,actual);
    }
}

测试结果如下：

将

@ActiveProfiles("prod")

改为

@ActiveProfiles("dev")

将采用开发配置的bean

到目前为止，maven中pom.xml的内容如下：

    4.0.0

    com.jack
    springstudy1
    1.0-SNAPSHOT

    
    
        1.8
    

    
    
        
        
            org.springframework
            spring-context
            4.1.6.RELEASE
        

        
        
            org.springframework
            spring-aop
            4.1.6.RELEASE
        
        
        
            org.aspectj
            aspectjrt
            1.8.5
        
        
            org.aspectj
            aspectjweaver
            1.8.5
        

        
        
            commons-io
            commons-io
            2.3
        

        
        
            javax.annotation
            jsr250-api
            1.0
        

        
        
            org.springframework
            spring-test
            4.1.6.RELEASE
        
        
            junit
            junit
            4.11
        

    

    
    
        
            
                org.apache.maven.plugins
                maven-compiler-plugin
                2.3.2
                
                    ${java.version}
                    ${java.version}