亲宝软件园·资讯

展开

spring-boot-autoconfigure模块用法详解

五克松 人气:0

       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

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

    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。

     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。

加载全部内容

相关教程
猜你喜欢
用户评论