Spring Boot 自动配置的实现

时间：2022-09-03 21:55:42

spring boot 自动配置

来看下 spring boot中自动配置的注解

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@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 {};
 
}
  1. exclude() 可以排除一些自动配置的内容
  2. excludename 通过名称排除自动配置内容

再来看下， @enableautoconfiguration 是怎么处理自动配置的呢？

注意到@import(enableautoconfigurationimportselector.class)

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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;
  }
}
 
}

再来看下 autoconfigurationimportselector ，主要是 接口的 importselector 的实现

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@override
  public string[] selectimports(annotationmetadata annotationmetadata) {
    if (!isenabled(annotationmetadata)) {
      return no_imports;
    }
    try {
      //1、 自动配置的元数据 spring-autocomfigure-metadata.properties
      // 自动配置的开启条件
      autoconfigurationmetadata autoconfigurationmetadata = autoconfigurationmetadataloader
          .loadmetadata(this.beanclassloader);
      annotationattributes attributes = getattributes(annotationmetadata);
      // 获取设置的自动配置列表 spring.factories
      list<string> configurations = getcandidateconfigurations(annotationmetadata,
          attributes);
      configurations = removeduplicates(configurations);
      configurations = sort(configurations, autoconfigurationmetadata);
      // 获取要排除的自动配置列表，可以通过 注解@enableautoconfiguration 的exclude和
       // 配置文件设置 spring.autoconfigure.exclude key的值
      set<string> exclusions = getexclusions(annotationmetadata, attributes);
      checkexcludedclasses(configurations, exclusions);
      configurations.removeall(exclusions);
       // 通过 spring-autocomfigure-metadata.properties conditiononclass 条件进行过滤
      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

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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 的处理方式，会解析 @import 里的接口 importselector 返回的所有配置类,那是怎么配置的呢，如 jparepositoriesautoconfiguration

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@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 {
 
}

从上面可以看到，有很多的@conditionalon**的注解，我们来看下 conditionevaluator这个 条件计算器，会去计算出当前这个配置类 是否要开启，而这些 @conditionalon** 是依赖于 @conditional 这个注解，如  @conditionalonbean 最终是通过 condition 接口来作条件选择

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@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 整合的项目，但大部分情况下，并不是所以的项目都会启用，通过 condition和@conditional 来判断条件

  1. 判断classpath 是否存在指定的类  @conditionalonclass
  2. 判断 applicationcontext 中是否存在指定的 bean  @conditionalonbean
  3. 配置环境中是否存在特定的配置项  @conditionalonproperty
  4. 配置环境中指定的配置项是否存在指定的值

禁用配置

当前 也是可以禁用某些我们不想要的默认配置，如上面加载时说到，会排除一些配置(exclude)

  1. 设置 @enableautoconfiguration 的exclude 配置
  2. 在配置文件增加 spring.autoconfigure.exclude 配置

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。

原文链接：https://www.jianshu.com/p/7261521394e7

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