请尊重作者劳动成果，转载请标明原文链接：http://www.cnblogs.com/dylan-java/p/7450914.html
启动SpringBoot，需要在入口函数所在的类上添加@SpringBootApplication注解
1 @SpringBootApplication2 public class Application {3 public static void main(String[] args) {4 SpringApplication.run(Application.class, args);5 }6 }
我们来看一下@SpringBootApplication注解
1 @Target(ElementType.TYPE) 2 @Retention(RetentionPolicy.RUNTIME) 3 @Documented 4 @Inherited 5 @SpringBootConfiguration 6 @EnableAutoConfiguration 7 @ComponentScan(excludeFilters = { 8 @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), 9 @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })10 public @interface SpringBootApplication {11 @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "exclude")12 Class<?>[] exclude() default {};13 14 @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "excludeName")15 String[] excludeName() default {};16 17 @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")18 String[] scanBasePackages() default {};19 20 @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")21 Class<?>[] scanBasePackageClasses() default {};22 }
1 @Target(ElementType.TYPE)2 @Retention(RetentionPolicy.RUNTIME)3 @Documented4 @Configuration5 public @interface SpringBootConfiguration {6 }
从上面的代码可以看出@SpringBootApplication = @Configuration + @EnableAutoConfiguration + @ComponentScan
@Configuration注解(可以理解为xml里面的<beans>标签)，一般和@Bean注解(可以理解为xml里面的<bean>标签)搭配使用。使用这2个注解可以创建一个配置类，示例如下
1 @Configuration 2 public class Config { 3 @Bean 4 public People people() { 5 People people = new People(); 6 people.setAge(26); 7 people.setName("Dylan"); 8 people.setGender(1); 9 return people;10 }11 }
可以替代xml配置文件里
1 <beans>2 <bean id="people" class="com.dylan.java.beans.People">3 <property name="age" value="26"></property>4 <property name="name" value="Dylan"></property>5 <property name="gender" value="1"></property>6 </bean>7 </beans>
@EnableAutoConfiguration注解自动载入应用程序所需要的所有Bean，这依赖于SpringBoot在类路径中的查找
1 @SuppressWarnings("deprecation") 2 @Target(ElementType.TYPE) 3 @Retention(RetentionPolicy.RUNTIME) 4 @Documented 5 @Inherited 6 @AutoConfigurationPackage 7 @Import(EnableAutoConfigurationImportSelector.class) 8 public @interface EnableAutoConfiguration { 9 String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";10 11 Class<?>[] exclude() default {};12 13 String[] excludeName() default {};14 }
@EnableAutoConfiguration注解使用@Import注解导入EnableAutoConfigurationImportSelector类，此类继承了AutoConfigurationImportSelector类，而AutoConfigurationImportSelector类的selectImports方法就是关键所在
1 @Override 2 public String[] selectImports(AnnotationMetadata annotationMetadata) { 3 if (!isEnabled(annotationMetadata)) { 4 return NO_IMPORTS; 5 } 6 try { 7 AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader 8 .loadMetadata(this.beanClassLoader); 9 AnnotationAttributes attributes = getAttributes(annotationMetadata);10 List<String> configurations = getCandidateConfigurations(annotationMetadata,11 attributes);12 configurations = removeDuplicates(configurations);13 configurations = sort(configurations, autoConfigurationMetadata);14 Set<String> exclusions = getExclusions(annotationMetadata, attributes);15 checkExcludedClasses(configurations, exclusions);16 configurations.removeAll(exclusions);17 configurations = filter(configurations, autoConfigurationMetadata);18 fireAutoConfigurationImportEvents(configurations, exclusions);19 return configurations.toArray(new String[configurations.size()]);20 }21 catch (IOException ex) {22 throw new IllegalStateException(ex);23 }24 }
1 protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,2 AnnotationAttributes attributes) {3 List<String> configurations = SpringFactoriesLoader.loadFactoryNames(4 getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());5 Assert.notEmpty(configurations,6 "No auto configuration classes found in META-INF/spring.factories. If you "7 + "are using a custom packaging, make sure that file is correct.");8 return configurations;9 }
1 protected Class<?> getSpringFactoriesLoaderFactoryClass() {2 return EnableAutoConfiguration.class;3 }
可以看出，该方法使用了Spring Core包的SpringFactoriesLoader类的loadFactoryNames方法，该方法会查询classpath下的JAR文件中包含的/META/spring.factories文件，从文件中读取配置文件名(这里是org.springframework.boot.autoconfigure.EnableAutoConfiguration)的属性，例如
在jar:file:/C:/Users/guiqingqing/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/1.5.6.RELEASE/spring-boot-autoconfigure-1.5.6.RELEASE.jar!/META-INF/spring.factories文件找到如下配置
# 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.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,\org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\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.flyway.FlywayAutoConfiguration,\org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\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.mobile.DeviceResolverAutoConfiguration,\org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration,\org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration,\org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration,\org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration,\org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration,\org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration,\org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration,\org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration,\org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration,\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.DispatcherServletAutoConfiguration,\org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration
获取自动配置的类之后调用removeDuplicates方法先去除重复，然后调用sort方法进行排序，接下来调用getExclusions获取配置的exclude的类，比如@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})，然后这些exclude的类也会被排除
然后是调用filter方法，该方法决定哪些bean自动配置，哪些不配置。去classpath下的JAR文件中包含的/META/spring.factories文件里查询org.springframework.boot.autoconfigure.AutoConfigurationImportFilter对应的配置，这里找到的是org.springframework.boot.autoconfigure.condition.OnClassCondition，检查每个bean，看是否有@ConditionalOnClass注解，并且依赖的类不为空，则符合条件，那么需要自动配置，否则不配置。例如FreeMarkerAutoConfiguration类
1 @Configuration2 @ConditionalOnClass({ freemarker.template.Configuration.class, FreeMarkerConfigurationFactory.class })4 @AutoConfigureAfter(WebMvcAutoConfiguration.class)5 @EnableConfigurationProperties(FreeMarkerProperties.class)6 public class FreeMarkerAutoConfiguration {7 }
该类的@ConditionalOnClass注解里有freemarker.template.Configuration.class和FreeMarkerConfigurationFactory.class类，如果classpath下能找到这2个类，那么就会自动加载FreeMarkerAutoConfiguration类
最后发布一个AutoConfigurationImportEvent事件
@ComponentScan注解会自动扫描指定包下的全部标有@Component(包括@Service、@Repository、@Controller等子注解)的类，并注册成bean
生活不要太劳累，弄得自己很疲惫，快乐幸福多体会，
