一、前言
- Springboot源码解析是一件大工程，逐行逐句的去钻研代码，会很干燥，也不容易坚持下去。
- 咱们不谋求大而全，而是试着每次去钻研一个小知识点，最终聚沙成塔，这就是咱们的springboot源码管中窥豹系列。
二、何为主动拆卸？
- 咱们想用redis，间接引入spring-boot-starter-data-redis的依赖，配置加上就能用。
- 咱们想用mongodb, 间接引入mongodb的依赖
- 咱们想用缓存，间接引入cache的依赖
- 咱们在：springboot源码解析-管中窥豹系列之web服务器（七） 外面想更换不同的web服务器，更换不同的依赖，那里也是用到主动拆卸
三、源码剖析
咱们从main办法所在类开始看：
import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic class MyprojectApplication { public static void main(String[] args) { SpringApplication.run(MyprojectApplication.class, args); }}这次不进main办法，咱们看注解：@SpringBootApplication
@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@SpringBootConfiguration@EnableAutoConfiguration@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })public @interface SpringBootApplication { ...}- 咱们看这个注解：@EnableAutoConfiguration
- 留神这个注解是在：spring-boot-autoconifgure依赖包外面
@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@AutoConfigurationPackage@Import(AutoConfigurationImportSelector.class)public @interface EnableAutoConfiguration { String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration"; Class<?>[] exclude() default {}; String[] excludeName() default {};}- spring.boot.enableautoconfiguration：主动拆卸的开关，默认开
- 咱们看这个：@Import(AutoConfigurationImportSelector.class)
- springboot会加载@Import 和 继承ImportSelector的类 到bean汇合外面
public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered { ...}- 继承的各种Aware，咱们之前说过：springboot源码解析-管中窥豹系列之aware（六）
- Ordered：咱们在之前排序那一节也说过：springboot源码解析-管中窥豹系列之排序（五）
- ImportSelector是把继承的selectImports办法的返回数组转换成加载的bean
public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered { .... private static final String[] NO_IMPORTS = {}; @Override public String[] selectImports(AnnotationMetadata annotationMetadata) { if (!isEnabled(annotationMetadata)) { return NO_IMPORTS; } AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata); return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations()); } protected boolean isEnabled(AnnotationMetadata metadata) { if (getClass() == AutoConfigurationImportSelector.class) { return getEnvironment().getProperty(EnableAutoConfiguration.ENABLED_OVERRIDE_PROPERTY, Boolean.class, true); } return true; } ....}- 先判断开关，没关上就返回空数组
- getAutoConfigurationEntry() 拿到要加载成bean的对象
- 转换成数组返回
- 咱们看看这个办法：getAutoConfigurationEntry()
protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) { if (!isEnabled(annotationMetadata)) { return EMPTY_ENTRY; } AnnotationAttributes attributes = getAttributes(annotationMetadata); List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes); configurations = removeDuplicates(configurations); Set<String> exclusions = getExclusions(annotationMetadata, attributes); checkExcludedClasses(configurations, exclusions); configurations.removeAll(exclusions); configurations = getConfigurationClassFilter().filter(configurations); fireAutoConfigurationImportEvents(configurations, exclusions); return new AutoConfigurationEntry(configurations, exclusions);}- 其它行都是加工数据的，或者exlusions(排除)，filter(过滤)
- 最重要的是：List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
- 咱们看这个办法：getCandidateConfigurations
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) { List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader()); Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you " + "are using a custom packaging, make sure that file is correct."); return configurations;}protected Class<?> getSpringFactoriesLoaderFactoryClass() { return EnableAutoConfiguration.class;}- SpringFactoriesLoader.loadFactoryNames, 咱们之前说过，是从spring.factories外面加载对应的class
- 这次要加载的class: EnableAutoConfiguration
- 咱们到spring.factories外面找找
# Auto Configureorg.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.context.ConfigurationPropertiesAutoConfiguration,\org.springframework.boot.autoconfigure.context.LifecycleAutoConfiguration,\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.ElasticsearchDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRestClientAutoConfiguration,\org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\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.r2dbc.R2dbcDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.r2dbc.R2dbcRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.r2dbc.R2dbcTransactionManagerAutoConfiguration,\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.ElasticsearchRestClientAutoConfiguration,\org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\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.jersey.JerseyAutoConfiguration,\org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration,\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.r2dbc.R2dbcAutoConfiguration,\org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\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.security.rsocket.RSocketSecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\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.ClientHttpConnectorAutoConfiguration,\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,\org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration- 咱们罕用的各种工具都曾经封装好了
- 比方redis: RedisAutoConfiguration
- 比方mongo: MongoDataAutoConfiguration
- 咱们看看RedisAutoConfiguration
import org.springframework.data.redis.core.RedisOperations;@Configuration(proxyBeanMethods = false)@ConditionalOnClass(RedisOperations.class)@EnableConfigurationProperties(RedisProperties.class)@Import({ LettuceConnectionConfiguration.class, JedisConnectionConfiguration.class })public class RedisAutoConfiguration { @Bean @ConditionalOnMissingBean(name = "redisTemplate") public RedisTemplate<Object, Object> redisTemplate(RedisConnectionFactory redisConnectionFactory) throws UnknownHostException { RedisTemplate<Object, Object> template = new RedisTemplate<>(); template.setConnectionFactory(redisConnectionFactory); return template; } @Bean @ConditionalOnMissingBean public StringRedisTemplate stringRedisTemplate(RedisConnectionFactory redisConnectionFactory) throws UnknownHostException { StringRedisTemplate template = new StringRedisTemplate(); template.setConnectionFactory(redisConnectionFactory); return template; }}- @EnableConfigurationProperties(RedisProperties.class)是加载配置的
- @ConditionalOnClass(RedisOperations.class)是另一个开关，必须存在RedisOperations这个类
- 办法是封装好的RedisTemplate
@ConfigurationProperties(prefix = "spring.redis")public class RedisProperties { private int database = 0; private String url; private String host = "localhost"; private String password; private int port = 6379; private boolean ssl; private Duration timeout; private String clientName; private Sentinel sentinel; private Cluster cluster; ...}- RedisOperations这个类在哪呢？上面这个jar外面
<dependency> <groupId>org.springframework.data</groupId> <artifactId>spring-data-redis</artifactId></dependency> - 这个依赖又怎么加载进springboot呢？
<?xml version="1.0" encoding="UTF-8"?><project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starters</artifactId> <version>2.0.8.RELEASE</version> </parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> <version>2.0.8.RELEASE</version> <name>Spring Boot Data Redis Starter</name> <description>Starter for using Redis key-value data store with Spring Data Redis and the Lettuce client</description> <url>https://projects.spring.io/spring-boot/#/spring-boot-parent/spring-boot-starters/spring-boot-starter-data-redis</url> <organization> <name>Pivotal Software, Inc.</name> <url>https://spring.io</url> </organization> <licenses> <license> <name>Apache License, Version 2.0</name> <url>http://www.apache.org/licenses/LICENSE-2.0</url> </license> </licenses> <developers> <developer> <name>Pivotal</name> <email>info@pivotal.io</email> <organization>Pivotal Software, Inc.</organization> <organizationUrl>http://www.spring.io</organizationUrl> </developer> </developers> <scm> <connection>scm:git:git://github.com/spring-projects/spring-boot.git/spring-boot-starters/spring-boot-starter-data-redis</connection> <developerConnection>scm:git:ssh://git@github.com/spring-projects/spring-boot.git/spring-boot-starters/spring-boot-starter-data-redis</developerConnection> <url>http://github.com/spring-projects/spring-boot/spring-boot-starters/spring-boot-starter-data-redis</url> </scm> <issueManagement> <system>Github</system> <url>https://github.com/spring-projects/spring-boot/issues</url> </issueManagement> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> <version>2.0.8.RELEASE</version> <scope>compile</scope> </dependency> <dependency> <groupId>org.springframework.data</groupId> <artifactId>spring-data-redis</artifactId> <version>2.0.13.RELEASE</version> <scope>compile</scope> <exclusions> <exclusion> <artifactId>jcl-over-slf4j</artifactId> <groupId>org.slf4j</groupId> </exclusion> </exclusions> </dependency> <dependency> <groupId>io.lettuce</groupId> <artifactId>lettuce-core</artifactId> <version>5.0.5.RELEASE</version> <scope>compile</scope> </dependency> </dependencies></project>- spring-boot-starter-data-redis这个依赖外面有
到此，曾经很分明了，咱们总结一下：
- 通过@SpringBootApplication注解引入@EnableAutoConfiguration注解
- 通过@EnableAutoConfiguration注解引入AutoConfigurationImportSelector
- 进入AutoConfigurationImportSelector的selectImports办法
- 通过SpringFactoriesLoader把所有的EnableAutoConfiguration加载进来
- 这些主动拆卸的类还有一道@ConditionalOnClass拦着，必须加载相应的jar能力加载进springboot, 实现可插拔
- 咱们应用就两步，加载相应的依赖，写好配置
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