一、EnableAutoConfiguration

1、EnableAutoConfiguration原理

springboot程序入口使用注解@SpringBootApplication，SpringBootApplication注解的定义如下

@SpringBootConfiguration@EnableAutoConfiguration@ComponentScan(excludeFilters = {        @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

头部有三个注解，

@SpringBootConfiguration：表示是一个配置类

@ComponentScan：自动扫描，

@EnableAutoConfiguration：

作用：从classpath中搜索所有META-INF/spring.factories配置文件，然后将其中org.springframework.boot.autoconfigure.EnableAutoConfiguration 的key对应的配置项加载到容器中。

只有spring.boot.enableautoconfiguration 为true【默认为true】的时候，才启用自动配置

关键点：1》、ImportSelector改接口的方法的返回值都会被纳入到spring容器管理中；2》、SpringFactoriesLoader该类可以从classpath中搜索所有的 META-INF/spring.factories配置文件，并读取配置，交由ImportSelector接口纳入spring处理

1.5版本以前

@Import(EnableAutoConfigurationImportSelector.class)public @interface EnableAutoConfiguration {

查看EnableAutoConfigurationImportSelector 查看父类AutoConfigurationImportSelector

public String[] selectImports(AnnotationMetadata annotationMetadata) {        if (!isEnabled(annotationMetadata)) {            return NO_IMPORTS;        }        try {            AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader                    .loadMetadata(this.beanClassLoader);            AnnotationAttributes attributes = getAttributes(annotationMetadata);            List
      
        configurations = getCandidateConfigurations(annotationMetadata,                    attributes);            configurations = removeDuplicates(configurations);            configurations = sort(configurations, autoConfigurationMetadata);            Set
       
         exclusions = getExclusions(annotationMetadata, attributes);            checkExcludedClasses(configurations, exclusions);            configurations.removeAll(exclusions);            configurations = filter(configurations, autoConfigurationMetadata);            fireAutoConfigurationImportEvents(configurations, exclusions);            return configurations.toArray(new String[configurations.size()]);        }        catch (IOException ex) {            throw new IllegalStateException(ex);        }    }

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调用了getCandidateConfigurations

protected List
     
       getCandidateConfigurations(AnnotationMetadata metadata,            AnnotationAttributes attributes) {        List
      
        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;    }

可以看到自定义包：found in META-INF/spring.factories

在自定义包的src/main/resource/增加以上META-INF/spring.factories内容

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.lhx.spring.springboot_enableauto_example.RunnableConfiguration

然后这个包就可以自动被导入了。

public @interface EnableAutoConfiguration {    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";    /**     * Exclude specific auto-configuration classes such that they will never be applied.     * @return the classes to exclude     */    Class
     [] exclude() default {};    /**     * Exclude specific auto-configuration class names such that they will never be     * applied.     * @return the class names to exclude     * @since 1.3.0     */    String[] excludeName() default {};}

1、ENABLED_OVERRIDE_PROPERTY 配置项：spring.boot.enableautoconfiguration 控制是否启用此注解，可在application.properties中配置。

@Override    protected boolean isEnabled(AnnotationMetadata metadata) {        if (getClass().equals(EnableAutoConfigurationImportSelector.class)) {            return getEnvironment().getProperty(                    EnableAutoConfiguration.ENABLED_OVERRIDE_PROPERTY, Boolean.class,                    true);        }        return true;    }

2、exclude、excludeName排除

使用：@EnableAutoConfiguration(exclude=UserConfig.class)

@EnableAutoConfiguration(excludeName= {"com.lhx.spring.springboot_enableauto_example.Role"})

1.5版本以后

Deprecated. as of 1.5 in favor of AutoConfigurationImportSelector

DeferredImportSelector to handle auto-configuration. This class can also be subclassed if a custom variant of @EnableAutoConfiguration. is needed.

这里可以看到其实1.5以后是将EnableAutoConfigurationImportSelector 向上提了一个类。

二、spring boot 内部如何使用EnableAutoConfiguration

找到jar：spring-boot-autoconfigure-1.5.9.RELEASE.jar

查看META-INF，其中也存在spring.facetories文件。

# Initializersorg.springframework.context.ApplicationContextInitializer=\org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer# Application Listenersorg.springframework.context.ApplicationListener=\org.springframework.boot.autoconfigure.BackgroundPreinitializer# Auto Configuration Import Listenersorg.springframework.boot.autoconfigure.AutoConfigurationImportListener=\org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener# Auto Configuration Import Filtersorg.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\org.springframework.boot.autoconfigure.condition.OnClassCondition# Auto Configureorg.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.CassandraRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\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.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.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.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.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.flyway.FlywayAutoConfiguration,\org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\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.mobile.DeviceResolverAutoConfiguration,\org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration,\org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration,\org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration,\org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration,\org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration,\org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration,\org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration,\org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration,\org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration,\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.DispatcherServletAutoConfiguration,\org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration# Failure analyzersorg.springframework.boot.diagnostics.FailureAnalyzer=\org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer# Template availability providersorg.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.web.JspTemplateAvailabilityProvider

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示例：

查看：org.springframework.boot.autoconfigure.gson包

1.看META-INFO/spring.factories中存在

2.查看类GsonAutoConfiguration

@Configuration@ConditionalOnClass(Gson.class)public class GsonAutoConfiguration {    @Bean    @ConditionalOnMissingBean    public Gson gson() {        return new Gson();    }}

说明：Configuration是一个配置类，ConditionalOnClass(Gson.class)类存在才加载

@ConditionalOnMissingBean，没有才装配，有就以个人装配为准

代码地址：中的 springboot-enable即可

转载地址：http://xgukl.baihongyu.com/

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