SpringBoot实现自动化装配解析

自动化装配步骤：

                 1.新建一个组件项目2.在resources下新建META-INF/spring.factories新建META-INF/spring-autoconfigure-metadata.properties （可选）（可由                                                                    条件注解替代）         3.写一个JavaConfig配置类，并在类中写入需要注入的BeanX4.maven-intall 生成 jar包5.在新项目中引入该jar包的依赖6.直接注入BeanX即可。（IOC容器自动加载）

源码解析

AutoConfigurationImportSelector源码解析

AutoConfigurationImportSelector是Spring实现自动装配Bean的核心类，selectImports是其核心方法。方法作用：加载spring-autoconfigure-metadata.properties的条件，加载sprng.factories的配置类。然后加入过滤条件，交给IOC去创建对象。

@Overridepublic String[] selectImports(AnnotationMetadata annotationMetadata) {if (!isEnabled(annotationMetadata)) {return NO_IMPORTS;}//1.获取classpath下META-INF所有的spring-autoconfidure-metadata.propeerties所有过滤条件AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);//2.获取classpath下META-INF下所有的spring.factories         AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,annotationMetadata);//返回所有需要加载的类的全路径，交给IOC去创建对象     return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());}

2.通过FactoriesClassLoad工具加载META-INF下所有的spring.factories，通过key（注解全路径作为key），获取所有的value，value值为自动注入Bean的全路径，然后加入过滤条件，返回。

/*** Return the {@link AutoConfigurationEntry} based on the {@link AnnotationMetadata}* of the importing {@link Configuration @Configuration} class.* @param autoConfigurationMetadata the auto-configuration metadata* @param annotationMetadata the annotation metadata of the configuration class* @return the auto-configurations that should be imported*/protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,AnnotationMetadata annotationMetadata) {if (!isEnabled(annotationMetadata)) {return EMPTY_ENTRY;}AnnotationAttributes attributes = getAttributes(annotationMetadata);List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);configurations = removeDuplicates(configurations);Set<String> exclusions = getExclusions(annotationMetadata, attributes);checkExcludedClasses(configurations, exclusions);configurations.removeAll(exclusions);configurations = filter(configurations, autoConfigurationMetadata);fireAutoConfigurationImportEvents(configurations, exclusions);return new AutoConfigurationEntry(configurations, exclusions);}

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),getBeanClassLoader());Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you "+ "are using a custom packaging, make sure that file is correct.");return configurations;}

自动化装配实现

根据条件注入Bean

根据条件注入Bean实现方式：

基于spring-autoconfigure-metadata.properties配置文件实现
新建项目 gupao-core ，作为一个组件进行编写。无需注入完整的依赖。
包结构：

pom.xml
只需要可以使用@Configuration注解、@Bean注解即可，所以只注入了context包，无需注入完整的spring包

<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</groupId><artifactId>gupao-core</artifactId><version>0.0.1-SNAPSHOT</version><dependencies><!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
<dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>5.1.9.RELEASE</version>
</dependency></dependencies></project>

java代码

@Configuration
@Configuration
public class GuPaoConfig {@Beanpublic Student   student(){return new Student();}
}

@Configuration
public class GuPaoOtherConfig {@Beanpublic People   people(){return new People();}
}

在resources下新建/META-INF/spring.factories

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.gupao.core.GuPaoConfig,\
com.gupao.core.GuPaoOtherConfig

在resources下新建/META-INF/spring-autoconfigure-metadata.properties

com.gupao.core.GuPaoConfig.ConditionalOnClass=com.differ.demo5.Test

然后使用maven工具 install生成jar包

新建项目 gupao ，引入组件gupao-core，实现自动装配
在gupao的pom.xml中引入组件的依赖。

     <dependency><groupId>com</groupId><artifactId>gupao-core</artifactId><version>0.0.1-SNAPSHOT</version></dependency>

@SpringBootApplication
public class App {public static void main(String[] args) {ConfigurableApplicationContext ca = SpringApplication.run(App.class, args);People bean = ca.getBean(People.class);Student dog = ca.getBean(Student.class);System.out.println(bean.say());System.out.println(dog.say());}
}

Console控制台打印

2019-09-03 19:22:05.449  INFO 5640 --- [           main] com.differ.demo5.App                     : No active profile set, falling back to default profiles: default
2019-09-03 19:22:09.090  INFO 5640 --- [           main] com.differ.demo5.App                     : Started App in 11.176 seconds (JVM running for 21.484)
Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.gupao.core.Student' availableat org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:346)at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:337)at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1123)at com.differ.demo5.App.main(App.java:17)

报错原因：由于组件加入了条件。所以必须在主项目中加入相应的条件才不会报错。

在guapo项目中，新建一个类即可。
com.differ.demo5.Test

基于条件注解，实现自动装配
　
基于注解实现—> 条件注解
@ConditionOnClass
@Condi…
…
新建项目 gupao-core ，作为一个组件进行编写。无需注入完整的依赖。
包结构：

pom.xml

<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-gupao</groupId><artifactId>gupao-core2</artifactId><version>0.0.1-SNAPSHOT</version><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.1.7.RELEASE</version><relativePath/> <!-- lookup parent from repository --></parent><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter</artifactId></dependency></dependencies>
</project>