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- 版本：2.0.4
- 文章中使用/* */注释的方法会做深入分析
正文
自动配置是Spring boot的一大亮点，让我们从Spring繁杂的配置中脱身而出，本篇文章我们就来分析一下Spring boot自动配置的源码。不知道读者是否有注意到，在分析Spring boot启动流程时，我们没有看到示例代码中@SpringBootApplication注解的解析过程，其实Spring boot的自动配置就和这个注解息息相关，我们来看下这个注解的结构：
@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 {
这里我们发现了两个陌生的注解@SpringBootConfiguration和@EnableAutoConfiguration，其中@SpringBootConfiguration注解了@Configuration，这个注解我们很熟悉，在Spring源码解析之@Configuration注解解析这篇文章中我们详细分析了@Configuration、@Bean、@Import等注解的解析流程（这篇文章中的内容对于分析Spring boot自动配置源码非常重要，建议先了解一下）。接着我们来看@EnableAutoConfiguration注解的结构：
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
我们看到这里用@Import注解导入了AutoConfigurationImportSelector，而@AutoConfigurationPackage则是用@Import注解导入了AutoConfigurationPackages.Registrar，AutoConfigurationPackages.Registrar实现了ImportBeanDefinitionRegistrar，这个接口我们在分析@Configuration注解的解析流程时看到过ImportBeanDefinitionRegistrar的调用过程，我们可以实现ImportBeanDefinitionRegistrar来注册额外的BeanDefinition，我们来看一下AutoConfigurationPackages.Registrar注册了什么BeanDefinition：
public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
register(registry, new PackageImport(metadata).getPackageName());
}
这里的metadata也就是我们实例中的启动类，包名也就是示例启动类所在的包了。
AutoConfigurationPackages：
public static void register(BeanDefinitionRegistry registry, String... packageNames) {
// BEAN就是AutoConfigurationPackages，用于存储自动配置包以供稍后引用
if (registry.containsBeanDefinition(BEAN)) {
BeanDefinition beanDefinition = registry.getBeanDefinition(BEAN);
ConstructorArgumentValues constructorArguments = beanDefinition
.getConstructorArgumentValues();
// 将构造函数的第一个参数设置为包名列表
constructorArguments.addIndexedArgumentValue(0,
addBasePackages(constructorArguments, packageNames));
}
else {
GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
// 将beanClass设置为BasePackages
beanDefinition.setBeanClass(BasePackages.class);
// 将构造函数的第一个参数设置为包名列表，也就是BasePackages的构造函数
beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0,
packageNames);
beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
// 注册beanDefinition
registry.registerBeanDefinition(BEAN, beanDefinition);
}
}
所以AutoConfigurationPackages.Registrar的主要作用就是注册BasePackages类型的BeanDefinition。我们再来分析AutoConfigurationImportSelector的作用，它实现了DeferredImportSelector，我们在分析@Configuration注解的解析流程时同样也看到过DeferredImportSelector的调用过程，我们可以实现DeferredImportSelector来决定导入哪些配置，所以我们猜测，Spring boot的自动配置就是在这里导入的，我们来看实现：
AutoConfigurationImportSelector：
public String[] selectImports(AnnotationMetadata annotationMetadata) {
if (!isEnabled(annotationMetadata)) {
return NO_IMPORTS;
}
AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
.loadMetadata(this.beanClassLoader);
AnnotationAttributes attributes = getAttributes(annotationMetadata);
/* 获取所有候选的配置 */
List<String> configurations = getCandidateConfigurations(annotationMetadata,
attributes);
// 将List放入Set在放入List，去重
configurations = removeDuplicates(configurations);
// 提取exclude和excludeName配置，可以用来排除我们不需要的配置
Set<String> exclusions = getExclusions(annotationMetadata, attributes);
// 检查需要移除的配置是否在候选配置列表中，如果有不存在的则抛出异常
checkExcludedClasses(configurations, exclusions);
// 从候选配置中移除所有需要排除的配置
configurations.removeAll(exclusions);
/* 过滤掉不需要的配置 */
configurations = filter(configurations, autoConfigurationMetadata);
/* 将自动配置导入事件通知监听器 */
fireAutoConfigurationImportEvents(configurations, exclusions);
return StringUtils.toStringArray(configurations);
}
AutoConfigurationImportSelector：
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
AnnotationAttributes attributes) {
/* 加载配置名称 */
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;
}
SpringFactoriesLoader：
public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
/* 加载配置，通过给定的key获取配置名称集合 */
return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}
SpringFactoriesLoader：
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
// 首先尝试从缓存中获取
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
// 加载资源，FACTORIES_RESOURCE_LOCATION = META-INF/spring.factories
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);
// 加载成为properties
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?> entry : properties.entrySet()) {
List<String> factoryClassNames = Arrays.asList(
StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
// 添加映射关系
result.addAll((String) entry.getKey(), factoryClassNames);
}
}
// 缓存
cache.put(classLoader, result);
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
这里我们看到加载配置的文件是META-INF/spring.factories，我们来看一下这个文件中都有些什么配置：
# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer
# Auto Configuration Import Listeners
org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener
# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnClassCondition
# 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.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
# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer,\
org.springframework.boot.autoconfigure.session.NonUniqueSessionRepositoryFailureAnalyzer
# Template availability providers
org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.web.servlet.JspTemplateAvailabilityProvider
文件里我们发现有很多配置，其中org.springframework.boot.autoconfigure.EnableAutoConfiguration这个key对应的value就是上文中要获取的候选配置集合了，非常多，所以接下来就需要在这些配置中过滤掉一些不需要的配置：
AutoConfigurationImportSelector：
private List<String> filter(List<String> configurations,
AutoConfigurationMetadata autoConfigurationMetadata) {
long startTime = System.nanoTime();
String[] candidates = StringUtils.toStringArray(configurations);
// 需要跳过的配置下标boolean数组
boolean[] skip = new boolean[candidates.length];
boolean skipped = false;
// 从上面的配置中获取filter，默认只有一个OnClassCondition
for (AutoConfigurationImportFilter filter : getAutoConfigurationImportFilters()) {
// 为filter设置所需的Aware
invokeAwareMethods(filter);
// filter进行过滤
boolean[] match = filter.match(candidates, autoConfigurationMetadata);
for (int i = 0; i < match.length; i++) {
if (!match[i]) {
skip[i] = true;
skipped = true;
}
}
}
// 没有需要跳过的配置直接返回
if (!skipped) {
return configurations;
}
List<String> result = new ArrayList<>(candidates.length);
for (int i = 0; i < candidates.length; i++) {
// 将不需要跳过的配置添加的集合中返回
if (!skip[i]) {
result.add(candidates[i]);
}
}
if (logger.isTraceEnabled()) {
int numberFiltered = configurations.size() - result.size();
logger.trace("Filtered " + numberFiltered + " auto configuration class in "
+ TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime)
+ " ms");
}
return new ArrayList<>(result);
}
默认的OnClassCondition通过检查指定的类是否存在于classpath中来判断是否加载配置，具体代码实现可以自行查阅。最后就是将自动配置导入事件通知监听器：
AutoConfigurationImportSelector：
private void fireAutoConfigurationImportEvents(List<String> configurations,
Set<String> exclusions) {
// 从上面的配置中提取listener，默认只有一个ConditionEvaluationReportAutoConfigurationImportListener
List<AutoConfigurationImportListener> listeners = getAutoConfigurationImportListeners();
if (!listeners.isEmpty()) {
AutoConfigurationImportEvent event = new AutoConfigurationImportEvent(this,
configurations, exclusions);
for (AutoConfigurationImportListener listener : listeners) {
// 为listener设置所需的Aware
invokeAwareMethods(listener);
// 通知listener
listener.onAutoConfigurationImportEvent(event);
}
}
}
获取到的所有配置类都是通过@Configuration注解这种方式来进行配置，文章开始给出的文章中已经进行了详细的介绍。到这里，整个Spring boot自动配置的流程就分析完了。
