Spring Boot自动装配原理源码分析

Spring Boot自动装配原理源码分析

1.环境准备

使用IDEA Spring Initializr快速创建一个Spring Boot项目

添加一个Controller类

@RestController

public class HelloController {
@RequestMapping(“hello”)


public String hello() {<br/>
    return &#34;hello&#34;;<br/>
}<br/>


}

主配置类如下

@SpringBootApplication

public class SpringbootQuickstartApplication {
public static void main(String[] args) {


    SpringApplication.run(SpringbootQuickstartApplication.class, args);<br/>
}


}

2.注解分析

@SpringBootApplication

@SpringBootConfiguration

@EnableAutoConfiguration

@ComponentScan(excludeFilters = {


@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),<br/>
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class)<br/>


})

public @interface SpringBootApplication {

@SpringBootApplication

@Configuration

public @interface SpringBootConfiguration {

@AutoConfigurationPackage

@Import(AutoConfigurationImportSelector.class)

public @interface EnableAutoConfiguration {

3.自动装配的主角

@EnableAutoConfiguration@AutoConfigurationPackage@Import

(1)、@AutoConfigurationPackage

点进该注解

@Import(AutoConfigurationPackages.Registrar.class)

public @interface AutoConfigurationPackage {

}

在点进Register，这是一个静态内部类

static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
@Override

  public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {


  register(registry, new PackageImport(metadata).getPackageName());<br/>


}
@Override

  public Set&lt;Object&gt; determineImports(AnnotationMetadata metadata) {


 return Collections.singleton(new PackageImport(metadata));<br/>


}
}

new PackageImport(metadata).getPackageName()

再看一眼metadata，果然，就是主配置类

因此，这个注解的作用就是将主配置类所在的包作为自动配置包进行管理

(2)、@Import(AutoConfigurationImportSelector.class)

@Import

selectImports

@Override

public String[] selectImports(AnnotationMetadata annotationMetadata) {

   if (!isEnabled(annotationMetadata)) {


  return NO_IMPORTS;<br/>


}

   AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader


     .loadMetadata(this.beanClassLoader);<br/>


AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,


     annotationMetadata);<br/>


return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());

}

getAutoConfigurationEntry

protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,


  AnnotationMetadata annotationMetadata) {<br/>


if (!isEnabled(annotationMetadata)) {


  return EMPTY_ENTRY;<br/>


}

   AnnotationAttributes attributes = getAttributes(annotationMetadata);

   List&lt;String&gt; configurations = getCandidateConfigurations(annotationMetadata, attributes);

   configurations = removeDuplicates(configurations);

   Set&lt;String&gt; exclusions = getExclusions(annotationMetadata, attributes);

   checkExcludedClasses(configurations, exclusions);

   configurations.removeAll(exclusions);

   configurations = filter(configurations, autoConfigurationMetadata);

   fireAutoConfigurationImportEvents(configurations, exclusions);

   return new AutoConfigurationEntry(configurations, exclusions);

}

getCandidateConfigurationsxxxAtuoConfiguration

那么这些自动配置类是如何获取的呢，从哪里获取的呢？

getCandidateConfigurations

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {


List&lt;String&gt; configurations =<br/>
    SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),<br/>
     getBeanClassLoader());<br/>


Assert.notEmpty(configurations, “… …”);

   return configurations;

}

loadFactoryNamesFACTORIES_RESOURCE_LOCATIONMETA-INF/spring.factories

public static final String FACTORIES_RESOURCE_LOCATION = “META-INF/spring.factories”;

public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {


	String factoryTypeName = factoryType.getName();<br/>
	return loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());<br/>
}
private static Map&lt;String, List&lt;String&gt;&gt; loadSpringFactories(@Nullable ClassLoader classLoader) {<br/>
	MultiValueMap&lt;String, String&gt; result = cache.get(classLoader);<br/>
	if (result != null) {<br/>
		return result;<br/>
	}<br/>
	try {<br/>
		Enumeration&lt;URL&gt; urls = (classLoader != null ?<br/>
				classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :<br/>
				ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));<br/>
		result = new LinkedMultiValueMap&lt;&gt;();<br/>
		while (urls.hasMoreElements()) {<br/>
			URL url = urls.nextElement();<br/>
			UrlResource resource = new UrlResource(url);<br/>
			Properties properties = PropertiesLoaderUtils.loadProperties(resource);<br/>
			for (Map.Entry&lt;?, ?&gt; entry : properties.entrySet()) {<br/>
				String factoryTypeName = ((String) entry.getKey()).trim();<br/>
				for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {<br/>
					result.add(factoryTypeName, factoryImplementationName.trim());<br/>
				}<br/>
			}<br/>
		}<br/>
		cache.put(classLoader, result);<br/>
		return result;<br/>
	}<br/>
	catch (IOException ex) {<br/>
		throw new IllegalArgumentException(&#34;Unable to load factories from location [&#34; +<br/>
				FACTORIES_RESOURCE_LOCATION + &#34;]&#34;, ex);<br/>
	}<br/>
}<br/>

spring-boot-autoconfigure-2.2.4.RELEASE.jar/META-INF/spring.factories

# Auto Configure

org.springframework.boot.autoconfigure.EnableAutoConfiguration=<br/>
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,<br/>
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration

… …

4.类的加载时机

ConditionalOnClass@ConditionaOn xxx

WebMvcAutoConfiguration