引言：

大家在使用springboot的时候不得不感叹它的功能强大和方便，但是作为一个合格的程序员，单纯只是去使用框架是远远不够的！

我们知道，Spring Boot 项目创建完成后，即使不进行任何的配置，也能够顺利地运行，这都要归功于 Spring Boot 的自动化配置。

Spring Boot 默认使用 application.properties 或 application.yml 作为其全局配置文件，我们可以在该配置文件中对各种自动配置属性（server.port、logging.level.* 、spring.config.active.no-profile 等等）进行修改，并使之生效，那么您有没有想过这些属性是否有据可依呢？

而这个答案的回答是"是，肯定有据可依"，当我们感叹框架功能之强大、使用之便捷之余，我们也要有深究原理的精神，任何框架的功能的强大和方便都是由一行行的代码所支撑的。

Spring Factories 实现原理

springboot的自动装箱功能的实现是基于spring factories机制所实现的。Spring Factories 机制是 Spring Boot 中的一种服务发现机制，这种扩展机制与 Java SPI 机制十分相似（而java的SPI机制这篇博客，我之前想着发表的，但是因为一些原因导致没有发表成功，在之后这段时间，我会找个时间发布，如果有不懂SPI服务的到时候可以去看一看）。Spring Boot 会自动扫描所有 Jar 包类路径下 META-INF/spring.factories 文件，并读取其中的内容，进行实例化，这种机制也是 Spring Boot Starter 的基础。

而spring factories机制的实现主要依赖一个SpringFactoriesLoader类和多个spring.factories 文件。

spring.factories

spring.factories文件和java属性文件（.properties）差不多，其中包含一组或多组键值对（key=vlaue），其中，key 的取值为接口的完全限定名；value 的取值为接口实现类的完全限定名，一个接口可以设置多个实现类，不同实现类之间使用“，”隔开，例如：

org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition

SpringFactoriesLoader

spring-core 包里定义了 SpringFactoriesLoader 类，这个类会扫描所有 Jar 包类路径下的 META-INF/spring.factories 文件，并获取指定接口的配置。在 SpringFactoriesLoader 类中定义了两个对外的方法，如下表。

方法	描述
loadFactories(Class factoryType, @Nullable ClassLoader classLoader)	根据接口获取其实现类的实例；该方法返回的是实现类对象列表
loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader)	根据接口l获取其实现类的名称；该方法返回的是实现类的类名的列表

以上两个方法的关键都是从指定的 ClassLoader 中获取 spring.factories 文件，并解析得到类名列表，具体代码如下：

loadFactories方法：能够获取指定接口的实现类对象

 public static <T> List<T> loadFactories(Class<T> factoryType, @Nullable ClassLoader classLoader) {
    
        Assert.notNull(factoryType, "'factoryType' must not be null");
        ClassLoader classLoaderToUse = classLoader;
        if (classLoader == null) {
    
            classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
        }

        List<String> factoryImplementationNames = loadFactoryNames(factoryType, classLoaderToUse);
        if (logger.isTraceEnabled()) {
    
            logger.trace("Loaded [" + factoryType.getName() + "] names: " + factoryImplementationNames);
        }

        List<T> result = new ArrayList(factoryImplementationNames.size());
        Iterator var5 = factoryImplementationNames.iterator();

        while(var5.hasNext()) {
    
            String factoryImplementationName = (String)var5.next();
            result.add(instantiateFactory(factoryImplementationName, factoryType, classLoaderToUse));
        }

        AnnotationAwareOrderComparator.sort(result);
        return result;
    }

loadFactoryNames方法:能够根据接口获取其实现类类名的集合

public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
    
        ClassLoader classLoaderToUse = classLoader;
        if (classLoader == null) {
    
            classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
        }

        String factoryTypeName = factoryType.getName();
        return (List)loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());
    }

而在上面的loadFactoryNames方法中调用了一个内部方法loadSpringFactories方法，这个方法的作用能够读取该项目中所有 Jar 包类路径下 META-INF/spring.factories 文件的配置内容，并以 Map 集合的形式返回。

private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
    
        Map<String, List<String>> result = (Map)cache.get(classLoader);
        if (result != null) {
    
            return result;
        } else {
    
            HashMap result = new HashMap();

            try {
    
                Enumeration urls = classLoader.getResources("META-INF/spring.factories");

                while(urls.hasMoreElements()) {
    
                    URL url = (URL)urls.nextElement();
                    UrlResource resource = new UrlResource(url);
                    Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                    Iterator var6 = properties.entrySet().iterator();

                    while(var6.hasNext()) {
    
                        Entry<?, ?> entry = (Entry)var6.next();
                        String factoryTypeName = ((String)entry.getKey()).trim();
                        String[] factoryImplementationNames = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
                        String[] var10 = factoryImplementationNames;
                        int var11 = factoryImplementationNames.length;

                        for(int var12 = 0; var12 < var11; ++var12) {
    
                            String factoryImplementationName = var10[var12];
                            ((List)result.computeIfAbsent(factoryTypeName, (key) -> {
    
                                return new ArrayList();
                            })).add(factoryImplementationName.trim());
                        }
                    }
                }

                result.replaceAll((factoryType, implementations) -> {
    
                    return (List)implementations.stream().distinct().collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList));
                });
                cache.put(classLoader, result);
                return result;
            } catch (IOException var14) {
    
                throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var14);
            }
        }
    }

到此，我们就已经了解了spring factories的基本原理。下面我们再来了解自动配置的加载是如何实现的

自动配置的加载

Spring Boot 自动化配置也是基于 Spring Factories 机制实现的，在 spring-boot-autoconfigure-xxx.jar 类路径下的 META-INF/spring.factories 中设置了 Spring Boot 自动配置的内容 ，如下。

# 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.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.LifecycleAutoConfiguration,\
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.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
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.Neo4jReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcRepositoriesAutoConfiguration,\
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.ElasticsearchRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
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.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration,\
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.neo4j.Neo4jAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\
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.security.rsocket.RSocketSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\
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.ClientHttpConnectorAutoConfiguration,\
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,\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

以上配置中，value 取值是由多个 xxxAutoConfiguration （使用逗号分隔）组成，每个 xxxAutoConfiguration 都是一个自动配置类。Spring Boot 启动时，会利用 Spring-Factories 机制，将这些 xxxAutoConfiguration 实例化并作为组件加入到容器中，以实现 Spring Boot 的自动配置。

@EnableAutoConfiguration注解

@EnableAutoConfiguration 注解用于开启 Spring Boot 的自动配置功能， 它使用 Spring 框架提供的 @Import 注解通过 AutoConfigurationImportSelector类（选择器）给容器中导入自动配置组件。而这个注解是SpringBootApplication的元注解之一。

而这个能够帮助SpringBootApplication这个注解实现自动装配的功能，当然，SpringBootApplication这个注解不单纯只有这一个功能，本文不对其他功能进行一个解释，再提一嘴SpringBootApplication注解的功能主要都是由它的元注解所完成。

好了，回到正题，我们知道SpringBootApplication的自动配置功能是由EnableAutoConfiguration 注解所实现的，我们现在就去看看这个注解

在这个注解中我们需要关注其中的Import元注解，它导入了一个AutoConfigurationImportSelector配置类，这个配置类会帮我们的EnableAutoConfiguration 注解完成自动配置功能。

AutoConfigurationImportSelector

AutoConfigurationImportSelector 类实现了 DeferredImportSelector 接口，AutoConfigurationImportSelector 中还包含一个静态内部类 AutoConfigurationGroup，它实现了 DeferredImportSelector 接口的内部接口 Group（Spring 5 新增）

在这个类中，我们需要重点关注三个方法：

• getImportGroup():该方法获取实现了 Group 接口的类，并实例化
• process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector):该方法用于引入自动配置的集合
• selectImports():遍历自动配置类集合（Entry 类型的集合），并逐个解析集合中的配置类

他们的执行顺序是:getImportGroup—>process—>selectImports

下面我们将分别对以上 3 个方法及其调用过程进行介绍。

1.getImportGroup

AutoConfigurationImportSelector 类中 getImportGroup() 方法主要用于获取实现了 DeferredImportSelector.Group 接口的类，代码如下

 public Class<? extends Group> getImportGroup() {
    
        return AutoConfigurationImportSelector.AutoConfigurationGroup.class;
    }

2.process

静态内部类 AutoConfigurationGroup 中的核心方法是 process()，该方法通过调用 getAutoConfigurationEntry() 方法读取 spring.factories 文件中的内容，获得自动配置类的集合，代码如下

public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) {
    
            Assert.state(deferredImportSelector instanceof AutoConfigurationImportSelector, () -> {
    
                return String.format("Only %s implementations are supported, got %s", AutoConfigurationImportSelector.class.getSimpleName(), deferredImportSelector.getClass().getName());
            });
            AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector)deferredImportSelector).getAutoConfigurationEntry(annotationMetadata);
            this.autoConfigurationEntries.add(autoConfigurationEntry);
            Iterator var4 = autoConfigurationEntry.getConfigurations().iterator();

            while(var4.hasNext()) {
    
                String importClassName = (String)var4.next();
                this.entries.putIfAbsent(importClassName, annotationMetadata);
            }

        }

getAutoConfigurationEntry() 方法通过调用 getCandidateConfigurations() 方法来获取自动配置类的完全限定名，并在经过排除、过滤等处理后，将其缓存到成员变量中，具体代码如下。

protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
    
        if (!this.isEnabled(annotationMetadata)) {
    
            return EMPTY_ENTRY;
        } else {
    
            AnnotationAttributes attributes = this.getAttributes(annotationMetadata);
            List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);
            configurations = this.removeDuplicates(configurations);
            Set<String> exclusions = this.getExclusions(annotationMetadata, attributes);
            this.checkExcludedClasses(configurations, exclusions);
            configurations.removeAll(exclusions);
            configurations = this.getConfigurationClassFilter().filter(configurations);
            this.fireAutoConfigurationImportEvents(configurations, exclusions);
            return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions);
        }
    }

在 getCandidateConfigurations() 方法中，根据 Spring Factories 机制调用 SpringFactoriesLoader 的 loadFactoryNames() 方法，根据 EnableAutoConfiguration.class （自动配置接口）获取其实现类（自动配置类）的类名的集合

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
    
        List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.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;
    }

    protected Class<?> getSpringFactoriesLoaderFactoryClass() {
    
        return EnableAutoConfiguration.class;
    }

3.selectImports

以上所有方法执行完成后，selectImports() 会将 process() 方法处理后得到的自动配置类，进行过滤、排除，最后将所有自动配置类添加到容器中

 public Iterable<Entry> selectImports() {
    
            if (this.autoConfigurationEntries.isEmpty()) {
    
                return Collections.emptyList();
            } else {
    
                Set<String> allExclusions = (Set)this.autoConfigurationEntries.stream().map(AutoConfigurationImportSelector.AutoConfigurationEntry::getExclusions).flatMap(Collection::stream).collect(Collectors.toSet());
                Set<String> processedConfigurations = (Set)this.autoConfigurationEntries.stream().map(AutoConfigurationImportSelector.AutoConfigurationEntry::getConfigurations).flatMap(Collection::stream).collect(Collectors.toCollection(LinkedHashSet::new));
                processedConfigurations.removeAll(allExclusions);
                return (Iterable)this.sortAutoConfigurations(processedConfigurations, this.getAutoConfigurationMetadata()).stream().map((importClassName) -> {
    
                    return new Entry((AnnotationMetadata)this.entries.get(importClassName), importClassName);
                }).collect(Collectors.toList());
            }
        }

好了，到此，我们的springboot的自动装箱原理就已经讲解完毕，如果觉得有收获的话，就给博主点点赞吧（o(￣︶￣)o）。