SpringBoot02-自动配置原理

自动配置原理 

原理

1. SpringBoot启动时加载主配置类, 开启了自动配置功能@EnableAutoConfiguration.
2. @EnableAutoConfiguration作用
   1. 利用@Import({AutoConfigurationImportSelector.class})给容器导入了一些组件.
   2. 查看selectImports()方法

      List<String> configurations = getCandidateConfigurations(annotationMetadata,attributes); //获取了候选的配置

   3. getCandidateConfigurations()中

      List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());

   4. loadFactoryNames()中

      try {
                  //扫描了所有jar包类路径下: META-INF/spring.factories
                  Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
                  ArrayList result = new ArrayList();
                  //把扫描到的文件包装成properties对象
                  while(urls.hasMoreElements()) {
                      URL url = (URL)urls.nextElement();
                      Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
                      String factoryClassNames = properties.getProperty(factoryClassName);
                      //从properties中获取到EnableAutoConfiguration.class类（类名）对应的值，然后把他们添加在容器 中
                      result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
                  }
      
                  return result;
              } 

   • • 将类路径下 META-INF/spring.factories 里面配置的所有EnableAutoConfiguration的值加入到了容器中

       # 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.ElasticsearchRepositoriesAutoConfi guration, 
       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.WebServicesAutoConfiguratio

     • 每一个这样的xxxAutoConfiguration类都是容器中的一个组件, 都加入到容器中, 用他们来做自动配置.
3. 每个自动配置类进入容器中后, 进行自动配置功能.
4. 以HttpEncodingAutoConfiguration为例解释自动配置原理

   @Configuration //表示这是一个配置类
   /*
    * 启动指定类的 ConfigurationProperties功能；将配置文件中对应的值和HttpEncodingProperties绑定起来；
    * 并把 HttpEncodingProperties加入到ioc容器中.
   */
   @EnableConfigurationProperties(HttpEncodingProperties.class)
   @ConditionalOnWebApplication //判断当前应用是否是web应用, 如果是, 当前配置类生效 
   /*
    * 判断当前项目有没有这个类
    * CharacterEncodingFilter: SpringMVC中进行乱码解决的过滤器
   */
   @ConditionalOnClass(CharacterEncodingFilter.class)
   /*
    * 判断配置文件中是否存在某个配置
   */
   @ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true) //即使我们配置文件中不配置pring.http.encoding.enabled=true，也是默认生效的；
   public class HttpEncodingAutoConfiguration {
   
       private final HttpEncodingProperties properties;
   
       //只有一个有参构造器的情况下，参数的值就会从容器中拿
       public HttpEncodingAutoConfiguration(HttpEncodingProperties properties) {
           this.properties = properties;
       }
   
       //给容器中添加一个组件，这个组件的某些值需要从properties中获取
       @Bean
       @ConditionalOnMissingBean(CharacterEncodingFilter.class) //判断容器没有这个组件
       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;
       }

   1. 根据当前不同的条件判断, 觉得这个配置类是否生效.
   2. 一旦该配置类生效, 就会给容器添加各种组件, 这些组件的属性是从对应的properties类中获取的，这些类里面的每一个属性又是和配置文件绑定的.

5. 所有在配置文件中能配置的属性都是在xxxxProperties类中封装的, 配置文件能配置什么就可以参照某个功能对应的这个属性类.

   @ConfigurationProperties(prefix = "spring.http.encoding")
   public class HttpEncodingProperties {
   
       public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
   
       private Charset charset = DEFAULT_CHARSET;
   
       private Boolean force;
   
       private Boolean forceRequest;
   
       private Boolean forceResponse;
   
       ......

6. 总结
   1. SpringBoot启动时会加载大量的自动配置类.
   2. 我们看我们需要的功能有没有被SpringBoot写入默认的自动配置类.
   3. 我们再来看这个自动配置类中到底配置了哪些组件(只要我们要用的组件有, 我们就不需要再来配置了)
   4. 给容器中自动配置类添加组件的时候, 会从properties类中获取某些属性, 我们就可以在配置文件中指定这些属性的值.

细节

1. @Conditional派生注解
2. 
3.  自动配置类只有在一定条件下才能生效
   1. 在application.properties/yml中启用debug=true属性, 来让控制台打印自动配置报告, 这样就可以很方便的知道哪些自动配置类生效.
   2. 
   3.