spring-boot-autoconfigure ╰半夏微凉° 2022-03-26 08:56 123阅读 0赞 初次接触spring-boot的时候，我们经常会看到这样的文章：“为什么要使用spring-boot” "spring-boot与spring mvc有什么区别"，在这些文章中几乎都会出现这样的一句话“约定优于配置”，确实是这样的，spring-boot与spring-mvc的一个重要区别就是spring-boot遵循“约定优于配置”这一原则，而spring-boot-autoconfigure模块正是完美的实现这个原则，所以我们今天就来说一说spring-boot-autoconfigure这个模块。 顾名思义，autoconfigure就是自动配置的意思，我们先看一个比较常用的例子，我们都知道，对于90%的web项目我们都需要使用数据库(比如mysql)，所以就需要用到datasource，我们就先以datasource的自动配置为例吧。 使用过spring-boot的都知道，我们只需要在application.yml中进行以下配置即可在应用中使用对应的数据库连接 spring: datasource: driver-class-name: com.mysql.jdbc.Driver url: "jdbc:mysql://127.0.0.1/crs_db?useUnicode=true&characterEncoding=utf" username: root password: 123456 对于习惯了spring-mvc的同学来说，这真是太简洁了！我们下面来看一下spring-boot-autoconfigure是怎样简化这些步骤的，话不多说，直奔关键代码: org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration @Configuration // 备注1 @ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class }) //备注2 @EnableConfigurationProperties(DataSourceProperties.class) //备注3 @Import({ DataSourcePoolMetadataProvidersConfiguration.class, DataSourceInitializationConfiguration.class }) //备注4 public class DataSourceAutoConfiguration { // 这里是为了开启一个内嵌的datasource,因为不满足某些条件,因此最终不会实例化一个dataSource @Configuration @Conditional(EmbeddedDatabaseCondition.class) @ConditionalOnMissingBean({ DataSource.class, XADataSource.class }) @Import(EmbeddedDataSourceConfiguration.class) protected static class EmbeddedDatabaseConfiguration { } @Configuration @Conditional(PooledDataSourceCondition.class) // 由于上面的EmbeddedDatabase没有实例化成功,所以在这里还没有dataSource,所以还可以往下玩 @ConditionalOnMissingBean({ DataSource.class, XADataSource.class }) @Import({ DataSourceConfiguration.Hikari.class, DataSourceConfiguration.Tomcat.class, DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.Generic.class, DataSourceJmxConfiguration.class }) // 备注5 protected static class PooledDataSourceConfiguration { } // 其它代码省略 备注1： @Configuration 这个注解我就不解释了，用过spring-boot的都知道是干啥的 备注2: @ConditionalOnClass表示只有classpath中能找到DataSource.class和EmbeddedDatabaseType.class时，DataSourceAutoConfiguration这个类才会被spring容器实例化，这其实也解释了为什么我们有时候只需要在pom.xml添加某些依赖包，某些功能就自动打开了，就是这个注解干的好事儿。 备注3： @EnableConfigurationProperties引入了DataSourceProperties的配置，简单看一下代码，是不是有一种似曾相识的感觉， spring.datasource.url这些不就是application.yml中的配置吗，所以从这里我们就知道我们的配置是用在这里的。 @ConfigurationProperties(prefix = "spring.datasource") public class DataSourceProperties implements BeanClassLoaderAware, InitializingBean { private ClassLoader classLoader; private String name; private boolean generateUniqueName; private Class<? extends DataSource> type; private String driverClassName; private String url; private String username; private String password; private String jndiName; private DataSourceInitializationMode initializationMode = DataSourceInitializationMode.EMBEDDED; private String platform = "all"; private List<String> schema; private String schemaUsername; private String schemaPassword; private List<String> data; private String dataUsername; private String dataPassword; private boolean continueOnError = false; private String separator = ";"; private Charset sqlScriptEncoding; 备注4： 使用了 @Import注解引入了DataSourcePoolMetadataProvidersConfiguration 和DataSourceInitializationConfiguration,这里我们重点关注一下DataSourceInitializationConfiguration @Configuration public class DataSourcePoolMetadataProvidersConfiguration { // tomcat自带的datasource连接池,由于默认情况下spring-boot未引入org.apache.tomcat.jdbc.pool.DataSource对应的依赖包, // 根据@ConditionalOnClass注解的作用，这个配置不会生效 @Configuration @ConditionalOnClass(org.apache.tomcat.jdbc.pool.DataSource.class) static class TomcatDataSourcePoolMetadataProviderConfiguration { @Bean public DataSourcePoolMetadataProvider tomcatPoolDataSourceMetadataProvider() { return (dataSource) -> { if (dataSource instanceof org.apache.tomcat.jdbc.pool.DataSource) { return new TomcatDataSourcePoolMetadata( (org.apache.tomcat.jdbc.pool.DataSource) dataSource); } return null; }; } } // hikaricp是spring-boot默认的连接池(据说速度超快),HikariDataSource的包默认在spring-boot的全家桶中, //所以最终会实例化DataSourcePoolMetadataProvider 的一个bean @Configuration @ConditionalOnClass(HikariDataSource.class) static class HikariPoolDataSourceMetadataProviderConfiguration { @Bean public DataSourcePoolMetadataProvider hikariPoolDataSourceMetadataProvider() { return (dataSource) -> { if (dataSource instanceof HikariDataSource) { return new HikariDataSourcePoolMetadata( (HikariDataSource) dataSource); } return null; }; } } // dbcp2连接池的配置，很不幸,BasicDataSource不在默认包中，所以这个连接池不会生效 @Configuration @ConditionalOnClass(BasicDataSource.class) static class CommonsDbcp2PoolDataSourceMetadataProviderConfiguration { @Bean public DataSourcePoolMetadataProvider commonsDbcp2PoolDataSourceMetadataProvider() { return (dataSource) -> { if (dataSource instanceof BasicDataSource) { return new CommonsDbcp2DataSourcePoolMetadata( (BasicDataSource) dataSource); } return null; }; } } } 从上面的代码可以知道spring-boot默认实现了hikari连接池。 备注5： @Import引入了DataSourceConfiguration的几个内部类(Hikari、Tomcat、Dbcp2、Generic) ，上面我们也说了Hikari是亲儿子，所以Tomcat和Dbcp2肯定是死在了@ConditionalOnClass上了，所以我们只看Hikari和Generic abstract class DataSourceConfiguration { //HikariDataSource肯定存在,往下走 @ConditionalOnClass(HikariDataSource.class) // 在此之前还没有实例化DataSource,往下走(如果我们在应用中主动实现了datasource,那默认的hikari就不会实现, //这个也很常见,比如我们使用阿里巴巴的durid连接池,也是基于类似的原理,当然比这要稍微复杂些) @ConditionalOnMissingBean(DataSource.class) // 当配置 spring.datasource.type=com.zaxxer.hikari.HikariDataSource或该配置不存在时,往下走 @ConditionalOnProperty(name = "spring.datasource.type", havingValue = "com.zaxxer.hikari.HikariDataSource", matchIfMissing = true) static class Hikari { // 若以上4个注解的条件都满足,则在这里实例化一个HikariDataSource的bean,很显然它也是DataSource的子类 @Bean @ConfigurationProperties(prefix = "spring.datasource.hikari") public HikariDataSource dataSource(DataSourceProperties properties) { HikariDataSource dataSource = createDataSource(properties, HikariDataSource.class); if (StringUtils.hasText(properties.getName())) { dataSource.setPoolName(properties.getName()); } return dataSource; } } // 若DataSource没有bean存在,则往下走,很不幸,在上面已经实例化过HikariDataSource,止步于此， // 看去来这只是为了避免之前都没有实例化dataSource,这里来默认一个dataSource @ConditionalOnMissingBean(DataSource.class) @ConditionalOnProperty(name = "spring.datasource.type") static class Generic { @Bean public DataSource dataSource(DataSourceProperties properties) { return properties.initializeDataSourceBuilder().build(); } } 至此，数据源和连接池都已实例化完成。讲解的非常粗糙，但是这不重要，因为我们今天的主角可不是dataSource，别忘了我们要讲的是spring-boot-autoconfigure，通过上面的例子，其实最关键的是几个注解 **@ConditionalOnClass : **当对应的类存在时则表示满足条件,一个典型的例子，spring-boot中经常会在你添加了某一个模块的maven依赖之后,该功能就自动开启了,比如添加org.flywaydb.flyway-core的依赖包后会默认开启flyway。 **@Import : ** 类似于spring-mvc的import标签 **@ConditionalOnMissingBean: ** 当对应的bean在beanFactory不存在时表示满足条件，一般用于只允许类的一个bean存在 ** @ConditionalOnBean: **与ConditionalOnMissingBean的作用相反,一般用于依赖的bean存在时才会实例化 **@ConditionalOnProperty: ** 当对应的属性值为指定值时表示满足条件 因此我们在接触到一个新的模块后，如果spring-boot会自动配置它,那么我们可以在spring-boot-autoconfigure模块下找到对应的包，然后找到以AutoConfiguration结尾的类，比如flyway的FlywayAutoConfiguration,cassandra的CassandraAutoConfiguration等等，然后再配合上面的几个注解,就能很快了解新模块的加载过程。 有些爱思考的同学就要问了，你怎么知道要去找以AutoConfiguration结尾的类，这个就引入了另一个话题,spring-boot是如何实现自动配置的,它怎么知道需要加载哪些AutoConfiguration，这个其实是用到了spring-factories机制,关于spring-factories的详细原理需要单独写一篇文章来介绍，这里只是简单说一下它在autoconfigure中的应用，我们直接来看一下spring-boot-autoconfigure-2.0.6.RELEASE.jar包下的spring.factories文件 ![20190117105857485.png][] 里面有这样的一部分配置（如下）,key是org.springframework.boot.autoconfigure.EnableAutoConfiguration，value是各个以逗号隔开的\*AutoConfiguration，结合spring-factories的运行原理,我们就可以知道所有的自动配置是从这里开始加载的。 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.CassandraReactiveDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\ 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.MongoReactiveDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\ 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.RedisReactiveAutoConfiguration,\ 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.flyway.FlywayAutoConfiguration,\ 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.http.HttpMessageConvertersAutoConfiguration,\ org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\ org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\ 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.groovy.template.GroovyTemplateAutoConfiguration,\ org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\ org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\ org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\ 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.mongo.embedded.EmbeddedMongoAutoConfiguration,\ org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\ org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\ org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\ org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\ org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\ org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,\ org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\ org.springframework.boot.autoconfigure.security.servlet.SecurityRequestMatcherProviderAutoConfiguration,\ org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\ org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\ org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\ org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\ org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\ org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\ org.springframework.boot.autoconfigure.security.oauth2.client.OAuth2ClientAutoConfiguration,\ 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.client.RestTemplateAutoConfiguration,\ org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\ org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\ org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\ org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\ org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration 知道了原理后，我们也可以自己定义自己的自动配置模块，只需要在自己的jar包下添加 MATA-INF/spring.factories文件,然后加上配置org.springframework.boot.autoconfigure.EnableAutoConfiguration=\[我们自己写的autoconfigure\]，举个常用的例子，上面我们提到了阿里巴巴的durid数据库连接池,durid也专门提供了自动配置支持 ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvbmdfamF2YQ_size_16_color_FFFFFF_t_70][] 其中spring.factories中的内容是这样的 org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ com.alibaba.druid.spring.boot.autoconfigure.DruidDataSourceAutoConfigure DruidDataSourceAutoConfigure.java中的内容如下，跟我们之前介绍的dataSource的例子差不多，都是使用了几个常用的注解来实现自动配置。![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvbmdfamF2YQ_size_16_color_FFFFFF_t_70 1][] 总结一下，spring-boot通过spring-boot-autoconfigure体现了"约定优于配置"这一设计原则,而spring-boot-autoconfigure主要用到了spring.factories和几个常用的注解条件来实现自动配置，思路很清晰也很简单。 但是我特别偏爱spring-boot-autoconfigure这个模块，其中一个最大的好处就是，当我在使用一个新的功能或模块时，比如spring内置的flyway,cassandra或是阿里巴巴第三方的durid，我只需要顺着spring-boot-autoconfigure的自动配置，就能大致了解新模块的加载过程以及运行的原理，这对于我们熟悉新的模块确实起到了事半功倍的效果，希望spring-boot-autoconfigure也能给各位带来更好的学习体验。 [20190117105857485.png]: /images/20220326/faa896ef038c4ec7a6f80cff68042a45.png [watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvbmdfamF2YQ_size_16_color_FFFFFF_t_70]: /images/20220326/0eec55dffeab497f90d20db6f4e5bb16.png [watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvbmdfamF2YQ_size_16_color_FFFFFF_t_70 1]: /images/20220326/5ebf25364f23470193a64c49d5ad8455.png
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