Spring Boot 自動配置的實現

2024-07-14 08:41:59

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Spring Boot 自動配置

來看下 spring boot中自動配置的注解

@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 {};}

exclude() 可以排除一些自動配置的內容
excludeName 通過名稱排除自動配置內容

再來看下， @EnableAutoConfiguration 是怎么處理自動配置的呢？

注意到@Import(EnableAutoConfigurationImportSelector.class)

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

再來看下 AutoConfigurationImportSelector ，主要是接口的 ImportSelector 的實現

@Override  public String[] selectImports(AnnotationMetadata annotationMetadata) {    if (!isEnabled(annotationMetadata)) {      return NO_IMPORTS;    }    try {      //1、 自動配置的元數據 spring-autocomfigure-metadata.properties      // 自動配置的開啟條件      AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader          .loadMetadata(this.beanClassLoader);      AnnotationAttributes attributes = getAttributes(annotationMetadata);      // 獲取設置的自動配置列表 spring.factories      List<String> configurations = getCandidateConfigurations(annotationMetadata,          attributes);      configurations = removeDuplicates(configurations);      configurations = sort(configurations, autoConfigurationMetadata);      // 獲取要排除的自動配置列表，可以通過 注解@EnableAutoConfiguration 的exclude和       // 配置文件設置 spring.autoconfigure.exclude key的值      Set<String> exclusions = getExclusions(annotationMetadata, attributes);      checkExcludedClasses(configurations, exclusions);      configurations.removeAll(exclusions);       // 通過 spring-autocomfigure-metadata.properties ConditionOnClass 條件進行過濾      configurations = filter(configurations, autoConfigurationMetadata);      fireAutoConfigurationImportEvents(configurations, exclusions);      return configurations.toArray(new String[configurations.size()]);    }    catch (IOException ex) {      throw new IllegalStateException(ex);    }  }

看下 spring.factories 文件

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,/

再看下 spring framework中 ConfigurationClassParser 的處理方式，會解析 @Import 里的接口 ImportSelector返回的所有配置類,那是怎么配置的呢，如 JpaRepositoriesAutoConfiguration

@Configuration@ConditionalOnBean(DataSource.class)@ConditionalOnClass(JpaRepository.class)@ConditionalOnMissingBean({ JpaRepositoryFactoryBean.class,    JpaRepositoryConfigExtension.class })@ConditionalOnProperty(prefix = "spring.data.jpa.repositories", name = "enabled", havingValue = "true", matchIfMissing = true)@Import(JpaRepositoriesAutoConfigureRegistrar.class)@AutoConfigureAfter(HibernateJpaAutoConfiguration.class)public class JpaRepositoriesAutoConfiguration {}

從上面可以看到，有很多的@ConditionalOn**的注解，我們來看下 ConditionEvaluator這個條件計算器，會去計算出當前這個配置類是否要開啟，而這些 @ConditionalOn** 是依賴于 @Conditional 這個注解，如 @ConditionalOnBean 最終是通過 Condition 接口來作條件選擇

@Target({ ElementType.TYPE, ElementType.METHOD })@Retention(RetentionPolicy.RUNTIME)@Documented@Conditional(OnBeanCondition.class)public @interface ConditionalOnBean {  /**   * The class type of bean that should be checked. The condition matches when any of   * the classes specified is contained in the {@link ApplicationContext}.   * @return the class types of beans to check   */  Class<?>[] value() default {};  /**   * The class type names of bean that should be checked. The condition matches when any   * of the classes specified is contained in the {@link ApplicationContext}.   * @return the class type names of beans to check   */  String[] type() default {};  /**   * The annotation type decorating a bean that should be checked. The condition matches   * when any of the annotations specified is defined on a bean in the   * {@link ApplicationContext}.   * @return the class-level annotation types to check   */  Class<? extends Annotation>[] annotation() default {};  /**   * The names of beans to check. The condition matches when any of the bean names   * specified is contained in the {@link ApplicationContext}.   * @return the name of beans to check   */  String[] name() default {};  /**   * Strategy to decide if the application context hierarchy (parent contexts) should be   * considered.   * @return the search strategy   */  SearchStrategy search() default SearchStrategy.ALL;}

Spring boot 的autoconfigure 是囊括了所有可以和spring 整合的項目，但大部分情況下，并不是所以的項目都會啟用，通過 Condition和@Conditional 來判斷條件