SpringBoot的启动过程中自动配置源码

我会带着你远行 2022-04-25 10:36 201阅读 0赞

> 记录一下springboot启动过程，是如何进行加载自动配置的

##### 进入springboot的主程序 #####

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

看到有一个注解`@SpringBootApplication`，接着进入该注解

@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 {

这里出现了一个比较关键的注解`@EnableAutoConfiguration`看注解的字面意思是，开启自动配置。同样，进入该注解，发现它导入了一个类，`EnableAutoConfigurationImportSelector.class`.

@SuppressWarnings("deprecation")
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @AutoConfigurationPackage
    @Import(EnableAutoConfigurationImportSelector.class)
    public @interface EnableAutoConfiguration {

进入`EnableAutoConfigurationImportSelector`这个类（代码如下:）

@Deprecated
    public class EnableAutoConfigurationImportSelector
    		extends AutoConfigurationImportSelector { 
    
    	@Override
    	protected boolean isEnabled(AnnotationMetadata metadata) { 
    		if (getClass().equals(EnableAutoConfigurationImportSelector.class)) { 
    			return getEnvironment().getProperty(
    					EnableAutoConfiguration.ENABLED_OVERRIDE_PROPERTY, Boolean.class,
    					true);
    		}
    		return true;
    	}

进入他的父类，`AutoConfigurationImportSelector`,自动配置导入选择器，现在来走读源码

public class AutoConfigurationImportSelector
    		implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware,
    		BeanFactoryAware, EnvironmentAware, Ordered { 
    
    	private static final String[] NO_IMPORTS = { };
    
    	private static final Log logger = LogFactory
    			.getLog(AutoConfigurationImportSelector.class);
    
    	private ConfigurableListableBeanFactory beanFactory;
    
    	private Environment environment;
    
    	private ClassLoader beanClassLoader;
    
    	private ResourceLoader resourceLoader;
    
    	@Override
    	public String[] selectImports(AnnotationMetadata annotationMetadata) { 
    		if (!isEnabled(annotationMetadata)) { 
    			return NO_IMPORTS;
    		}
    		try { 
    			# 获得注解属性信息
    			AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
    					.loadMetadata(this.beanClassLoader);
    			AnnotationAttributes attributes = getAttributes(annotationMetadata);
    			
    			# 获得候选的将要导入的配置类名的list集合，这个方法比较重要
    			List<String> configurations = getCandidateConfigurations(annotationMetadata,
    					attributes);
    			
    			# 下面的操作就是对返回的 List集合，进行排序，然后根据属性的设置，取出一些值，最后转为一个数组返回
    			configurations = removeDuplicates(configurations);
    			configurations = sort(configurations, autoConfigurationMetadata);
    			Set<String> exclusions = getExclusions(annotationMetadata, attributes);
    			checkExcludedClasses(configurations, exclusions);
    			configurations.removeAll(exclusions);
    			configurations = filter(configurations, autoConfigurationMetadata);
    			fireAutoConfigurationImportEvents(configurations, exclusions);
    			return configurations.toArray(new String[configurations.size()]);
    		}
    		catch (IOException ex) { 
    			throw new IllegalStateException(ex);
    		}
    	}

进入`getCandidateConfigurations(annotationMetadata,attributes)`方法的源码当中看一下。

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;
    	}

接着进入`SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader())`

public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) { 
    	
    		// 值为org.springframework.boot.autoconfigure.EnableAutoConfiguration，也就是自动配置类。
    		String factoryClassName = factoryClass.getName();
    		try { 
    			
    			//# 扫描所有jar包类路径下的FACTORIES_RESOURCE_LOCATION的路径，其中FACTORIES_RESOURCE_LOCATION为"META-INF/spring.factories"
    			Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
    					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
    			List<String> result = new ArrayList<String>();
    			// 开始遍历所有urls下META-INF/spring.factories文件内容
    			while (urls.hasMoreElements()) { 
    				URL url = urls.nextElement();
    				//将该文件内容封装成 properties对象
    				Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
    				// 获得属性为org.springframework.boot.autoconfigure.EnableAutoConfiguration的值
    				String propertyValue = properties.getProperty(factoryClassName);
    				// 遍历然后添加到result集合当中
    				for (String factoryName : StringUtils.commaDelimitedListToStringArray(propertyValue)) { 
    					result.add(factoryName.trim());
    				}
    			}
    			return result;
    		}
    		catch (IOException ex) { 
    			throw new IllegalArgumentException("Unable to load factories from location [" +
    					FACTORIES_RESOURCE_LOCATION + "]", ex);
    		}
    	}

进入一个spring-boot-autoconfigure-1.5.21.RELEASE.jar的`META-INF/spring.factories`文件中看

# Auto Configure
    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.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

**小结：**  
1）SpringBoot启动的时候加载主配置类，开启了自动配置功能 `@EnableAutoConfiguration`

2）`@EnableAutoConfiguration` 作用：

*  利用`EnableAutoConfigurationImportSelector`给容器中导入一些组件
 *  可以查看`selectImports()`方法的内容；
 *  List configurations = getCandidateConfigurations(annotationMetadata,attributes);//获取候选的配置
    
     *      SpringFactoriesLoader.loadFactoryNames()
            扫描所有jar包类路径下  META-INF/spring.factories
            把扫描到的这些文件的内容包装成properties对象
            从properties中获取到EnableAutoConfiguration.class类（类名）对应的值，然后把他们添加在容器中,

**大多配置类上都会标注注解@Conditionalxxxx，如：@ConditionalOnMissingClass（系统中没有指定的类），@ConditionalOnProperty（系统中指定的属性是否有指定的值），通过这些来判定配置类是否生效。**

下面简单记录一下其中一个自动配置类**WebMvcAutoConfiguration**(web的自动配置类)，代码如下:

*/
    @Configuration
    @ConditionalOnWebApplication //判断是否是，web环境
    @ConditionalOnClass({  Servlet.class, DispatcherServlet.class,
    		WebMvcConfigurerAdapter.class }) //判断项目是否有这几个类
    @ConditionalOnMissingBean(WebMvcConfigurationSupport.class) //判断是否缺少WebMvcConfigurationSupport这个类
    @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
    @AutoConfigureAfter({  DispatcherServletAutoConfiguration.class,
    		ValidationAutoConfiguration.class })
    public class WebMvcAutoConfiguration { 
    
    	public static final String DEFAULT_PREFIX = "";
    
    	public static final String DEFAULT_SUFFIX = "";
    
    	@Bean
    	@ConditionalOnMissingBean(HiddenHttpMethodFilter.class)
    	public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() { 
    		return new OrderedHiddenHttpMethodFilter();
    	}
    
    	@Bean
    	@ConditionalOnMissingBean(HttpPutFormContentFilter.class)
    	@ConditionalOnProperty(prefix = "spring.mvc.formcontent.putfilter", name = "enabled",
    			matchIfMissing = true)
    	public OrderedHttpPutFormContentFilter httpPutFormContentFilter() { 
    		return new OrderedHttpPutFormContentFilter();
    	}
    
    	// Defined as a nested config to ensure WebMvcConfigurerAdapter is not read when not
    	// on the classpath
    	@Configuration
    	@Import(EnableWebMvcConfiguration.class)
    	//启动指定类的ConfigurationProperties功能；将配置文件中对应的值和WebMvcProperties,ResourceProperties绑定起来；
    	//并把WebMvcProperties,ResourceProperties加入到ioc容器中
    	@EnableConfigurationProperties({  WebMvcProperties.class, ResourceProperties.class })
    	public static class WebMvcAutoConfigurationAdapter extends WebMvcConfigurerAdapter {

我们配置文件中配置值能够与`WebMvcProperties`和`ResourceProperties`进行绑定，然后自动配置的属性，又都是获得`ResourceProperties`，`WebMvcProperties`，中的值获取的，所以当我们要设置，某个组件的属性，就可以直接在配置文件中配置对应的属性如`spring.mvc.view.suffix=xxx`,就会与`WebMvcProperties`这个类绑定，然后自动配置的时候，从`WebMvcProperties`就可以获得我们设置的值。  
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