SpringBoot之自动配置

---

title: SpringBoot之自动配置 tags:

• SpringBoot
• springfactories
• autoconfig
• 配置 categories: springboot date: 2017-11-15 21:31:33

---

背景

提到SpringBoot各位开发者大概能想到一些标签 “新” “快” “FatJar” “微服务” “SpringCloud” “约定大约配置” “开箱即用” “starter" "EmbedTomcat" ”Spring全家桶“ ”profile“ ”注解“

事实上SpringBoot基于Spring提供了大量的配置帮开发者做了许多默认配置【一定程度上帮开发者搞定了许多默认配置 但是稍有不慎也可能导致出现一些奇怪的问题】

本篇简单梳理一下自动配置的实现

源码

SpringBoot的启动代码 通常都是一句

    public static void main(String[] args) {
       SpringApplication.run(ZeusApplication.class, args);
    }
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我们来关注一下做了哪些操作

    /**
     * Static helper that can be used to run a {@link SpringApplication} from the
     * specified source using default settings.
     * @param source the source to load
     * @param args the application arguments (usually passed from a Java main method)
     * @return the running {@link ApplicationContext}
     */
    public static ConfigurableApplicationContext run(Object source, String... args) {
       return run(new Object[] { source }, args);
    }
    /**
     * Static helper that can be used to run a {@link SpringApplication} from the
     * specified sources using default settings and user supplied arguments.
     * @param sources the sources to load
     * @param args the application arguments (usually passed from a Java main method)
     * @return the running {@link ApplicationContext}
     */
    public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
       return new SpringApplication(sources).run(args);
    }
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首先创建了SpringApplication实例 其次调用对应的run方法

    @SuppressWarnings({ "unchecked", "rawtypes" })
    private void initialize(Object[] sources) {
       if (sources != null && sources.length > 0) {
          this.sources.addAll(Arrays.asList(sources));
       }
       this.webEnvironment = deduceWebEnvironment();
       setInitializers((Collection) getSpringFactoriesInstances(
             ApplicationContextInitializer.class));
       setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
       this.mainApplicationClass = deduceMainApplicationClass();
    }
     
    private boolean deduceWebEnvironment() {
       for (String className : WEB_ENVIRONMENT_CLASSES) {
          if (!ClassUtils.isPresent(className, null)) {
             return false;
          }
       }
       return true;
    }
     
    private Class<?> deduceMainApplicationClass() {
       try {
          StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
          for (StackTraceElement stackTraceElement : stackTrace) {
             if ("main".equals(stackTraceElement.getMethodName())) {
                return Class.forName(stackTraceElement.getClassName());
             }
          }
       }
       catch (ClassNotFoundException ex) {
          // Swallow and continue
       }
       return null;
    }
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首先根据当前classpath中是否包含WEB_ENVIRONMENT_CLASSES判断是否是web环境

Spring利用spring.factories文件做了许多事情  比如一些初始化 比如一些监听器

比如SpringBoot jar中提供了如下的spring.factories

    # PropertySource Loaders
    org.springframework.boot.env.PropertySourceLoader=\
    org.springframework.boot.env.PropertiesPropertySourceLoader,\
    org.springframework.boot.env.YamlPropertySourceLoader
     
    # Run Listeners
    org.springframework.boot.SpringApplicationRunListener=\
    org.springframework.boot.context.event.EventPublishingRunListener
     
    # Application Context Initializers
    org.springframework.context.ApplicationContextInitializer=\
    org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
    org.springframework.boot.context.ContextIdApplicationContextInitializer,\
    org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
    org.springframework.boot.context.embedded.ServerPortInfoApplicationContextInitializer
     
    # Application Listeners
    org.springframework.context.ApplicationListener=\
    org.springframework.boot.ClearCachesApplicationListener,\
    org.springframework.boot.builder.ParentContextCloserApplicationListener,\
    org.springframework.boot.context.FileEncodingApplicationListener,\
    org.springframework.boot.context.config.AnsiOutputApplicationListener,\
    org.springframework.boot.context.config.ConfigFileApplicationListener,\
    org.springframework.boot.context.config.DelegatingApplicationListener,\
    org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\
    org.springframework.boot.logging.ClasspathLoggingApplicationListener,\
    org.springframework.boot.logging.LoggingApplicationListener
     
    # Environment Post Processors
    org.springframework.boot.env.EnvironmentPostProcessor=\
    org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
    org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor
     
    # Failure Analyzers
    org.springframework.boot.diagnostics.FailureAnalyzer=\
    org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\
    org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\
    org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\
    org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\
    org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\
    org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\
    org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer
     
    # FailureAnalysisReporters
    org.springframework.boot.diagnostics.FailureAnalysisReporter=\
    org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter
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相对扩展了spi的思想【dubbo也是类似实现】

从SpringBoot的autoConfig包下面的spring.factories我们发现了更多信息

    # Initializers
    org.springframework.context.ApplicationContextInitializer=\
    org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
    org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer
     
    # Application Listeners
    org.springframework.context.ApplicationListener=\
    org.springframework.boot.autoconfigure.BackgroundPreinitializer
     
    # Auto Configuration Import Listeners
    org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
    org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener
     
    # Auto Configuration Import Filters
    org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
    org.springframework.boot.autoconfigure.condition.OnClassCondition
     
    # 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.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 analyzers
    org.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 providers
    org.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

    EnableAutoConfiguration这个注解表示打开自动配置
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而我们通常在SpringBoot第一行就是如下

    @SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
    public class ZeusApplication {
     
       public static void main(String[] args) {
          SpringApplication.run(ZeusApplication.class, args);
       }
    }
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SpringBootApplication注解实现了大部分的功能【事实上是一个注解的聚合】

    /**
     * Indicates a {@link Configuration configuration} class that declares one or more
     * {@link Bean @Bean} methods and also triggers {@link EnableAutoConfiguration
     * auto-configuration} and {@link ComponentScan component scanning}. This is a convenience
     * annotation that is equivalent to declaring {@code @Configuration},
     * {@code @EnableAutoConfiguration} and {@code @ComponentScan}.
     *
     * @author Phillip Webb
     * @author Stephane Nicoll
     * @since 1.2.0
     */
    @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 {
     
       /**
        * Exclude specific auto-configuration classes such that they will never be applied.
        * @return the classes to exclude
        */
       @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "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
        */
       @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "excludeName")
       String[] excludeName() default {};
     
       /**
        * Base packages to scan for annotated components. Use {@link #scanBasePackageClasses}
        * for a type-safe alternative to String-based package names.
        * @return base packages to scan
        * @since 1.3.0
        */
       @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
       String[] scanBasePackages() default {};
     
       /**
        * Type-safe alternative to {@link #scanBasePackages} for specifying the packages to
        * scan for annotated components. The package of each class specified will be scanned.
        * <p>
        * Consider creating a special no-op marker class or interface in each package that
        * serves no purpose other than being referenced by this attribute.
        * @return base packages to scan
        * @since 1.3.0
        */
       @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
       Class<?>[] scanBasePackageClasses() default {};
     
    }
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SpringBoot将对应的Application注册到Spring容器中通过调用Spring的ApplicationContext refresh方法实现对应备案的处理【包括初始化 注入等等 】

其中也包括了处理注解。

比如针对CompomentScan的处理如下

    private void addComponentScanningPackages(Set<String> packages,
          AnnotationMetadata metadata) {
       AnnotationAttributes attributes = AnnotationAttributes.fromMap(metadata
             .getAnnotationAttributes(ComponentScan.class.getName(), true));
       if (attributes != null) {
          addPackages(packages, attributes.getStringArray("value"));
          addPackages(packages, attributes.getStringArray("basePackages"));
          addClasses(packages, attributes.getStringArray("basePackageClasses"));
          if (packages.isEmpty()) {
             packages.add(ClassUtils.getPackageName(metadata.getClassName()));
          }
       }
    }
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从上述代码中可以得知 当CompomentScan没有配置value时默认注册为对应的包名【小知识点】

同样的道理对于如下注解

    /**
     * Enable auto-configuration of the Spring Application Context, attempting to guess and
     * configure beans that you are likely to need. Auto-configuration classes are usually
     * applied based on your classpath and what beans you have defined. For example, If you
     * have {@code tomcat-embedded.jar} on your classpath you are likely to want a
     * {@link TomcatEmbeddedServletContainerFactory} (unless you have defined your own
     * {@link EmbeddedServletContainerFactory} bean).
     * <p>
     * When using {@link SpringBootApplication}, the auto-configuration of the context is
     * automatically enabled and adding this annotation has therefore no additional effect.
     * <p>
     * Auto-configuration tries to be as intelligent as possible and will back-away as you
     * define more of your own configuration. You can always manually {@link #exclude()} any
     * configuration that you never want to apply (use {@link #excludeName()} if you don't
     * have access to them). You can also exclude them via the
     * {@code spring.autoconfigure.exclude} property. Auto-configuration is always applied
     * after user-defined beans have been registered.
     * <p>
     * The package of the class that is annotated with {@code @EnableAutoConfiguration},
     * usually via {@code @SpringBootApplication}, has specific significance and is often used
     * as a 'default'. For example, it will be used when scanning for {@code @Entity} classes.
     * It is generally recommended that you place {@code @EnableAutoConfiguration} (if you're
     * not using {@code @SpringBootApplication}) in a root package so that all sub-packages
     * and classes can be searched.
     * <p>
     * Auto-configuration classes are regular Spring {@link Configuration} beans. They are
     * located using the {@link SpringFactoriesLoader} mechanism (keyed against this class).
     * Generally auto-configuration beans are {@link Conditional @Conditional} beans (most
     * often using {@link ConditionalOnClass @ConditionalOnClass} and
     * {@link ConditionalOnMissingBean @ConditionalOnMissingBean} annotations).
     *
     * @author Phillip Webb
     * @author Stephane Nicoll
     * @see ConditionalOnBean
     * @see ConditionalOnMissingBean
     * @see ConditionalOnClass
     * @see AutoConfigureAfter
     * @see SpringBootApplication
     */
    @SuppressWarnings("deprecation")
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @AutoConfigurationPackage
    @Import(EnableAutoConfigurationImportSelector.class)
    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 {};
     
    }
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其中引入了一个很关键的import

    EnableAutoConfigurationImportSelector
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对于AutoConfigurationImportSelector

    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
       if (!isEnabled(annotationMetadata)) {
          return NO_IMPORTS;
       }
       try {
          AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
                .loadMetadata(this.beanClassLoader);
          AnnotationAttributes attributes = getAttributes(annotationMetadata);
          List<String> configurations = getCandidateConfigurations(annotationMetadata,
                attributes);
          configurations = removeDuplicates(configurations);
          configurations = sort(configurations, autoConfigurationMetadata);
          Set<String> 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);
       }
    }
    /**
     * Return the auto-configuration class names that should be considered. By default
     * this method will load candidates using {@link SpringFactoriesLoader} with
     * {@link #getSpringFactoriesLoaderFactoryClass()}.
     * @param metadata the source metadata
     * @param attributes the {@link #getAttributes(AnnotationMetadata) annotation
     * attributes}
     * @return a list of candidate configurations
     */
    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;
    }
     
    /**
     * Return the class used by {@link SpringFactoriesLoader} to load configuration
     * candidates.
     * @return the factory class
     */
    protected Class<?> getSpringFactoriesLoaderFactoryClass() {
       return EnableAutoConfiguration.class;
    }
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当调用getCandidateConfigurations 回去获取对spring.factories 中的EnableAutoConfiguration也就是上文中我们列出的一大堆自动配置

其中默认也提供了exclude选项 同时需要判断某些候选者需要排除【毕竟某些主键我们没有用到 比如不使用redis的情况下RedisAutoConfiguration这个就不处理 】

这个涉及到一些条件bean的注册【spring高级用法 条件注入】

那么到了这里基本可以分析出我们需要自动初始化的autoConfig

如果我们要实现一个自动配置的话我们也可以通过如上方法来完成【spring.factories】