Spring自動(dòng)配置原理

配置文件到底能寫(xiě)什么？怎么寫(xiě)？自動(dòng)配置原理；

配置文件能配置的屬性參照

1、自動(dòng)配置原理：

1、SpringBoot啟動(dòng)的時(shí)候加載主配置類，開(kāi)啟了自動(dòng)配置功能 @EnableAutoConfiguration

2、@EnableAutoConfiguration 作用：

  • 利用EnableAutoConfigurationImportSelector給容器中導(dǎo)入一些組件？

  • 可以查看selectImports()方法的內(nèi)容；

  • List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);獲取候選的配置

  • SpringFactoriesLoader.loadFactoryNames()
    掃描所有jar包類路徑下 META-INF/spring.factories
    把掃描到的這些文件的內(nèi)容包裝成properties對(duì)象
    從properties中獲取到EnableAutoConfiguration.class類（類名）對(duì)應(yīng)的值，然后把他們添加在容器中

  • 將 類路徑下 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.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

每一個(gè)這樣的 xxxAutoConfiguration類都是容器中的一個(gè)組件，都加入到容器中；用他們來(lái)做自動(dòng)配置
3、每一個(gè)自動(dòng)配置類進(jìn)行自動(dòng)配置功能；

4、以HttpEncodingAutoConfiguration（Http編碼自動(dòng)配置）為例解釋自動(dòng)配置原理；

@Configuration   //表示這是一個(gè)配置類，以前編寫(xiě)的配置文件一樣，也可以給容器中添加組件
@EnableConfigurationProperties(HttpEncodingProperties.class)  //啟動(dòng)指定類的ConfigurationProperties功能；將配置文件中對(duì)應(yīng)的值和HttpEncodingProperties綁定起來(lái)；并把HttpEncodingProperties加入到ioc容器中

@ConditionalOnWebApplication //Spring底層@Conditional注解（Spring注解版），根據(jù)不同的條件，如果滿足指定的條件，整個(gè)配置類里面的配置就會(huì)生效；    判斷當(dāng)前應(yīng)用是否是web應(yīng)用，如果是，當(dāng)前配置類生效

@ConditionalOnClass(CharacterEncodingFilter.class)  //判斷當(dāng)前項(xiàng)目有沒(méi)有這個(gè)類CharacterEncodingFilter；SpringMVC中進(jìn)行亂碼解決的過(guò)濾器；

@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)  //判斷配置文件中是否存在某個(gè)配置  spring.http.encoding.enabled；如果不存在，判斷也是成立的
//即使我們配置文件中不配置pring.http.encoding.enabled=true，也是默認(rèn)生效的；
public class HttpEncodingAutoConfiguration {
  
    //他已經(jīng)和SpringBoot的配置文件映射了
    private final HttpEncodingProperties properties;
  
   //只有一個(gè)有參構(gòu)造器的情況下，參數(shù)的值就會(huì)從容器中拿
    public HttpEncodingAutoConfiguration(HttpEncodingProperties properties) {
        this.properties = properties;
    }
  
    @Bean   //給容器中添加一個(gè)組件，這個(gè)組件的某些值需要從properties中獲取
    @ConditionalOnMissingBean(CharacterEncodingFilter.class) //判斷容器沒(méi)有這個(gè)組件？
    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;
    }
根據(jù)當(dāng)前不同的條件判斷，決定這個(gè)配置類是否生效？

一但這個(gè)配置類生效；這個(gè)配置類就會(huì)給容器中添加各種組件；這些組件的屬性是從對(duì)應(yīng)的properties類中獲取的，這些類里面的每一個(gè)屬性又是和配置文件綁定的；

5.所有在配置文件中能配置的屬性都是在xxxxProperties類中封裝者；配置文件能配置什么就可以參照某個(gè)功能對(duì)應(yīng)的這個(gè)屬性類

@ConfigurationProperties(prefix = "spring.http.encoding")  //從配置文件中獲取指定的值和bean的屬性進(jìn)行綁定
public class HttpEncodingProperties {

   public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");

總結(jié)自動(dòng)配置原理：

? 1、SpringBoot啟動(dòng)會(huì)加載大量的自動(dòng)配置類

? 2、我們看我們需要的功能有沒(méi)有SpringBoot默認(rèn)寫(xiě)好的自動(dòng)配置類；

? 3、我們?cè)賮?lái)看這個(gè)自動(dòng)配置類中到底配置了哪些組件；（只要我們要用的組件有，我們就不需要再來(lái)配置了）

? 4、給容器中自動(dòng)配置類添加組件的時(shí)候，會(huì)從properties類中獲取某些屬性。我們就可以在配置文件中指定這些屬性的值；

xxxxAutoConfigurartion：自動(dòng)配置類；

給容器中添加組件

xxxxProperties:封裝配置文件中相關(guān)屬性；

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