01.SpringBoot自动配置简析

环境说明

此博客中，所有Springboot的笔记都是基于SpringBoot 2.0.2版本

从入口说起

1. 入口方法声明：

   @SpringBootApplication
   public class StaffingSystemApplication {
   
   	public static void main(String[] args) {
   		SpringApplication.run(StaffingSystemApplication.class, args);
   	}
   }

   @SpringBootApplication注解声明：

   @Target(ElementType.TYPE)
   @Retention(RetentionPolicy.RUNTIME)
   @Documented
   @Inherited
   @SpringBootConfiguration
   @EnableAutoConfiguration
   @ComponentScan(excludeFilters = {
   		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
   		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
   public @interface SpringBootApplication {
     
   }

   • @SpringBootConfiguration注解声明：

     @Target(ElementType.TYPE)
     @Retention(RetentionPolicy.RUNTIME)
     @Documented
     @Configuration
     public @interface SpringBootConfiguration {
     
     }

     • @Configuration注解为Spring3.0新增，用于替换xml配置。
     • 从代码来看，@SpringBootConfiguration只是封装了一层@Configuration。来说明SpringBootApplication是一个配置类。

   • @EnableAutoConfiguration注解 ——自动配置的核心。代码声明如下：

     @Target(ElementType.TYPE)
     @Retention(RetentionPolicy.RUNTIME)
     @Documented
     @Inherited
     @AutoConfigurationPackage
     @Import(AutoConfigurationImportSelector.class)
     public @interface EnableAutoConfiguration {
       
     }

     • @AutoConfigurationPackage

       @Target(ElementType.TYPE)
       @Retention(RetentionPolicy.RUNTIME)
       @Documented
       @Inherited
       @Import(AutoConfigurationPackages.Registrar.class)
       public @interface AutoConfigurationPackage {
       
       }

       • @Import:用于依赖第三方包中bean的配置和加载
       • 从代码上看，@AutoConfigurationPackage引入了AutoConfigurationPackages.Registrar这个类。而这个类做的就是将主配置类（@SpringBootApplication标注的类）的所在包及下面所有子包里面的所有组件扫描到Spring容器；

     • @Import(AutoConfigurationImportSelector.class)：加载AutoConfigurationImportSelector类。将所有需要导入的组件以全类名的方式返回；这些组件就会被添加到容器中；其中主要的方法为selectImports。如下：

       @Override
       public String[] selectImports(AnnotationMetadata annotationMetadata) {
           if (!isEnabled(annotationMetadata)) {
               return NO_IMPORTS;
           }
           AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
               .loadMetadata(this.beanClassLoader);
           AnnotationAttributes attributes = getAttributes(annotationMetadata);
           //获取需要导入的组件全类名。
           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 StringUtils.toStringArray(configurations);
       }
       //  getCandidateConfigurations 方法体
       protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,AnnotationAttributes attributes) {
           List<String> configurations = SpringFactoriesLoader.loadFactoryNames(// 方法体如下
               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;
       }
       
       public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
           String factoryClassName = factoryClass.getName();
           return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
       }
       
       private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
           MultiValueMap<String, String> result = cache.get(classLoader);
           if (result != null) {
               return result;
           }
       
           try {
               Enumeration<URL> urls = (classLoader != null ?
                                        // FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"
                                        classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
                                        ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
               result = new LinkedMultiValueMap<>();
               while (urls.hasMoreElements()) {
                   URL url = urls.nextElement();
                   UrlResource resource = new UrlResource(url);
                   Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                   for (Map.Entry<?, ?> entry : properties.entrySet()) {
                       List<String> factoryClassNames = Arrays.asList(
                           StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
                       result.addAll((String) entry.getKey(), factoryClassNames);
                   }
               }
               cache.put(classLoader, result);
               return result;
           }
           catch (IOException ex) {
               throw new IllegalArgumentException("Unable to load factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
           }
       }

### 自动配置总结

​	SpringBoot在启动的时候，先会把主配置类（@SpringBootApplication标注的类）的所在包及下面所有子包里面的所有组件扫描到Spring容器；然后读取spring-boot-autoconfigure-2.0.2.RELEASE.jar中的/META-INF/spring.factories里面需要自动配置组件的全类名，然后加载。达到自动配置的目的。

​	spring.factories

​```properties
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration

从HttpEncodingAutoConfiguration中看自动配置

@Configuration  //声明该此类为配置类
/**
@EnableConfigurationProperties:把properties配置中的属性绑定到类上。
*/
@EnableConfigurationProperties(HttpEncodingProperties.class)
//@ConditionalOnWebApplication：只有在web应用，该类才生效
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
//ConditionalOnClass：只有在classPath中有CharacterEncodingFilter这个类才生效
@ConditionalOnClass(CharacterEncodingFilter.class)
//@ConditionalOnProperty:只有在配置文件中配置了spring.http.encoding=enable才生效，但是这里缺省值是true。不管你配没配都生效
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)
public class HttpEncodingAutoConfiguration {
	//引用上面的配置类
	private final HttpEncodingProperties properties;
	//构造注入
	public HttpEncodingAutoConfiguration(HttpEncodingProperties properties) {
		this.properties = properties;
	}

	@Bean  //往容器中加入一个对象，默认id为方法名。类似于xml配置中的<bean id="xxx" class="xxx" />
	@ConditionalOnMissingBean //只有在容器中没有这个Bean才会自动配置。有就忽略
	public CharacterEncodingFilter characterEncodingFilter() {
		CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
		filter.setEncoding(this.properties.getCharset().name());
		filter.setForceRequestEncoding(this.properties.shouldForce(Type.REQUEST));
		filter.setForceResponseEncoding(this.properties.shouldForce(Type.RESPONSE));
		return filter;
	}

	@Bean
	public LocaleCharsetMappingsCustomizer localeCharsetMappingsCustomizer() {
		return new LocaleCharsetMappingsCustomizer(this.properties);
	}

	private static class LocaleCharsetMappingsCustomizer implements
			WebServerFactoryCustomizer<ConfigurableServletWebServerFactory>, Ordered {

		private final HttpEncodingProperties properties;

		LocaleCharsetMappingsCustomizer(HttpEncodingProperties properties) {
			this.properties = properties;
		}

		@Override
		public void customize(ConfigurableServletWebServerFactory factory) {
			if (this.properties.getMapping() != null) {
				factory.setLocaleCharsetMappings(this.properties.getMapping());
			}
		}

		@Override
		public int getOrder() {
			return 0;
		}

	}

}