Spring Boot启动原理解析（注解篇）

骑猪看日落 2022-01-22 01:35 230阅读 0赞

**    SpringBoot内置的自动配置使开发变得很方便，所以这次就来看看它的启动源码和它的自动化配置的实现原理。**

启动类：

@SpringBootApplication
    public class DemoApplication {
    
        public static void main(String[] args) {
            SpringApplication.run(DemoApplication.class, args);
        }
    }

可以看到这个启动类中有两部分：**@SpringBootApplication**和**SpringApplication.run(DemoApplication.class, args)**两部分。每个Spring Boot项目都包含这两部分。

# @SpringBootApplication #

@Target(ElementType.TYPE)            // 注解的适用范围，TYPE用于描述类、接口、enum声明
    @Retention(RetentionPolicy.RUNTIME)  // 注解的生命周期
    @Documented                          // 表明这个注解应该被javadoc记录
    @Inherited                           // 子类可以继承该注解
    @SpringBootConfiguration             // 继承了Configuration，表示当前是注解类
    @EnableAutoConfiguration             // 开启SpringBoot的注解功能，借助@import的帮助
    @ComponentScan(excludeFilters = {    // 包扫描路径设置
            @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
            @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
    public @interface SpringBootApplication {
        ……
    }

这块最重要的三个注解是：

*  @Configuration：IoC容器的配置类（@SpringBootConfiguration内部有@Configuration）
 *  @EnableAutoConfiguration：借助@Import的支持，将所有符合自动配置条件的bean定义加载到IoC容器。
 *  @ComponentScan：自动扫描并加载符合条件的组件或者bean，最终将这些bean加载到IoC容器中

这里主要研究下@EnableAutoConfiguration注解：

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @AutoConfigurationPackage
    @Import(AutoConfigurationImportSelector.class)
    public @interface EnableAutoConfiguration {
    
    	String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
    
        ……
    
    }

这个注解主要有两个注解组成：

*  @AutoConfigurationPackage：返回了当前主程序类的*同级以及子级*的包组件。
 *  @Import(AutoConfigurationImportSelector.class)：导入自动配置的组件

先来看看@AutoConfigurationPackage的实现：

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @Import(AutoConfigurationPackages.Registrar.class)
    public @interface AutoConfigurationPackage {
    
    }
    
    
    	static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
    
    		@Override
    		public void registerBeanDefinitions(AnnotationMetadata metadata,
    				BeanDefinitionRegistry registry) {
    			register(registry, new PackageImport(metadata).getPackageName());
    		}
    
    		@Override
    		public Set<Object> determineImports(AnnotationMetadata metadata) {
    			return Collections.singleton(new PackageImport(metadata));
    		}
    
    	}

**    它其实是注册了一个Bean的定义。new PackageImport(metadata).getPackageName()，它会返回当前主程序类的同级以及子级的包组件。**

**   这就是为什么要把主程序放在项目的顶层节点的原因。**

下面再来看看@Import(AutoConfigurationImportSelector.class)的作用：

public String[] selectImports(AnnotationMetadata annotationMetadata) {
    		if (!isEnabled(annotationMetadata)) {
    			return NO_IMPORTS;
    		}
    		AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
    				.loadMetadata(this.beanClassLoader);
    		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 = filter(configurations, autoConfigurationMetadata);
    		fireAutoConfigurationImportEvents(configurations, exclusions);
    		return StringUtils.toStringArray(configurations);
    	}
    
    
    
    	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;
    	}
    
    
    
    	public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
    		String factoryClassName = factoryClass.getName();
    		return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
    	}
    
    
    
    	private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
    		MultiValueMap<String, String> result = cache.get(classLoader);
    		if (result != null) {
    			return result;
    		}
    
    		try {
    			Enumeration<URL> urls = (classLoader != null ?
    					classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
    					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
    			result = new LinkedMultiValueMap<>();
    			while (urls.hasMoreElements()) {
    				URL url = urls.nextElement();
    				UrlResource resource = new UrlResource(url);
    				Properties properties = PropertiesLoaderUtils.loadProperties(resource);
    				for (Map.Entry<?, ?> entry : properties.entrySet()) {
    					List<String> factoryClassNames = Arrays.asList(
    							StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
    					result.addAll((String) entry.getKey(), factoryClassNames);
    				}
    			}
    			cache.put(classLoader, result);
    			return result;
    		}
    		catch (IOException ex) {
    			throw new IllegalArgumentException("Unable to load factories from location [" +
    					FACTORIES_RESOURCE_LOCATION + "]", ex);
    		}
    	}

** **![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NTk4MDEx_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NTk4MDEx_size_16_color_FFFFFF_t_70 1][]

**    可以看到它会从spring-boot-autoconfigure/2.0.2.RELEASE/spring-boot-autoconfigure-2.0.2.RELEASE.jar!/META-INF/spring.factories中去获取自动配置类，然后根据反射将其实例化为JavaConfig形式的IoC容器配置类，然后将其加载到IoC容器中。**

![1112095-20181115230505205-305138350.png][]

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.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

执行流程篇：[https://blog.csdn.net/qq\_37598011/article/details/90969634][https_blog.csdn.net_qq_37598011_article_details_90969634]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NTk4MDEx_size_16_color_FFFFFF_t_70]: /images/20220122/042470fc07ea4ac5a32d0ebaab454b52.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NTk4MDEx_size_16_color_FFFFFF_t_70 1]: /images/20220122/ed3b19ff45754fb38d47c319bec8cb95.png
[1112095-20181115230505205-305138350.png]: /images/20220122/70a10cbbb6c845308fbb091bd2aa21d9.png
[https_blog.csdn.net_qq_37598011_article_details_90969634]: https://blog.csdn.net/qq_37598011/article/details/90969634