spring boot容器启动流程

一、前言

spring cloud大行其道的当下，如果不了解基本原理那么是很纠结的(看见的都是 约定大于配置 ，但是原理呢？为什么要这么做？)。spring cloud是基于spring boot快速搭建的，今天咱们就看看spring boot容器启动流程。(本文不讲解如何快速启动spring boot，那些直接官方看即可， )

二、容器启动

spring boot一般是 指定容器启动main方法，然后以命令行方式启动jar包 ，如下图：

 @springbootapplication
public class application {
 public static void main(string[] args) {
 springapplication.run(application.class, args);
 }
 }

这里核心关注2个东西：

1.@springbootapplication注解

2. springapplication.run()静态方法

下面我们就分别探究这两块内容。

2.1 @springbootapplication注解

源码如下：  

 @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 {

核心注解：

@springbootconfiguration（实际就是个@configuration）：表示这是一个javaconfig配置类，可以在这个类中自定义bean,依赖关系等。-》这个是spring-boot特有的注解，常用到。

@enableautoconfiguration：借助@import的帮助，将所有符合自动配置条件的bean定义加载到ioc容器（建议放在根包路径下，这样可以扫描子包和类）。-》这个需要详细深挖！

@componentscan：spring的自动扫描注解，可定义扫描范围，加载到ioc容器。-》这个不多说，spring的注解大家肯定眼熟

其中@enableautoconfiguration这个注解的源码：

 @suppresswarnings("deprecation")
 @target(elementtype.type)
 @retention(retentionpolicy.runtime)
 @documented
 @inherited
 @autoconfigurationpackage
 @import(enableautoconfigurationimportselector.class)
 public @interface enableautoconfiguration {

核心是一个enableautoconfigurationimportselector类图如下：

 

核心方法在*接口 importselector 的 selectimports（） ，源码如下：

 @override
 public string[] selectimports(annotationmetadata annotationmetadata) {
 if (!isenabled(annotationmetadata)) {
 return no_imports;
 }
 try { //1.从meta-inf/spring-autoconfigure-metadata.properties文件中载入483条配置属性（有一些有默认值），
 autoconfigurationmetadata autoconfigurationmetadata = autoconfigurationmetadataloader
  .loadmetadata(this.beanclassloader);
 annotationattributes attributes = getattributes(annotationmetadata);//2.获取注解属性
 list<string> configurations = getcandidateconfigurations(annotationmetadata,//3.获取97个自动配置类
  attributes);
 configurations = removeduplicates(configurations);//4.移除重复的
 configurations = sort(configurations, autoconfigurationmetadata);//5.排序
 set<string> exclusions = getexclusions(annotationmetadata, attributes);//6.获取需要排除的
 checkexcludedclasses(configurations, exclusions);//7.校验排除类
 configurations.removeall(exclusions);//8.删除所有需要排除的
 configurations = filter(configurations, autoconfigurationmetadata);//9.过滤器onclasscondition（注解中配置的当存在某类才生效）
 fireautoconfigurationimportevents(configurations, exclusions);//10.触发自动配置导入监听事件
 return configurations.toarray(new string[configurations.size()]);
 }
 catch (ioexception ex) {
 throw new illegalstateexception(ex);
 }
 }

这里注意3个核心方法：

1） loadmetadata 加载配置

其实就是用类加载器去加载： meta-inf/spring-autoconfigure-metadata.properties （spring-boot-autoconfigure-1.5.9.release-sources.jar） 文件中定义的配置，返回propertiesautoconfigurationmetadata（实现了autoconfigurationmetadata接口，封装了属性的get set方法）

2） getcandidateconfigurations 获取默认支持的自动配置类名列表

自动配置灵魂方法， springfactoriesloader.loadfactorynames 从 meta-inf/spring.factories （spring-boot-autoconfigure-1.5.9.release-sources.jar）文件中获取自动配置类key=enableautoconfiguration.class的配置。 

protected list<string> getcandidateconfigurations(annotationmetadata metadata,
 annotationattributes attributes) {//话说这里2个入参没啥用啊...谁来给我解释一下...
 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;
 }
 //返回的是enableautoconfiguration类
 protected class<?> getspringfactoriesloaderfactoryclass() {
 return enableautoconfiguration.class;
 }

实际获取了什么？ spring.factories 文件如下，实际获取了 # auto configure 自动配置模块的所有类。

# initializers
org.springframework.context.applicationcontextinitializer=\
org.springframework.boot.autoconfigure.sharedmetadatareaderfactorycontextinitializer,\
org.springframework.boot.autoconfigure.logging.autoconfigurationreportlogginginitializer
# 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 这里就是全部的自动配置类
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
# 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
# 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.jsptemplateavailabilityprovider

3）filter过滤器 根据 onclasscondition 注解把不满足条件的过滤掉

 private list<string> filter(list<string> configurations,
 autoconfigurationmetadata autoconfigurationmetadata) {
 long starttime = system.nanotime();
 string[] candidates = configurations.toarray(new string[configurations.size()]);
 boolean[] skip = new boolean[candidates.length];
 boolean skipped = false;
 //获取需要过滤的自动配置导入拦截器，spring.factories配置中就一个：org.springframework.boot.autoconfigure.condition.onclasscondition
 for (autoconfigurationimportfilter filter : getautoconfigurationimportfilters()) {
 invokeawaremethods(filter);
 boolean[] match = filter.match(candidates, autoconfigurationmetadata);
 for (int i = 0; i < match.length; i++) {
  if (!match[i]) {
  skip[i] = true;
  skipped = true;
  }
 }
 }
 if (!skipped) {//多条件只要有一个不匹配->skipped = true，全部匹配-》skipped = false->直接返回
 return configurations;
 }
 list<string> result = new arraylist<string>(candidates.length);
 for (int i = 0; i < candidates.length; i++) {
 if (!skip[i]) {//匹配-》不跳过-》添加进result
  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<string>(result);
 }

2.2 springapplication .run()静态方法

springapplication.run 

 public configurableapplicationcontext run(string... args) {
 stopwatch stopwatch = new stopwatch();
 stopwatch.start();
 configurableapplicationcontext context = null;
 failureanalyzers analyzers = null;
 configureheadlessproperty();
 springapplicationrunlisteners listeners = getrunlisteners(args);//1.获取监听器
 listeners.starting();-->启动！
 try {
 applicationarguments applicationarguments = new defaultapplicationarguments(
  args);
 configurableenvironment environment = prepareenvironment(listeners,//2.准备好环境，触发applicationenvironmentpreparedevent事件
  applicationarguments);
 banner printedbanner = printbanner(environment);//打印启动提示字符，默认spring的字符图
 context = createapplicationcontext();//实例化一个可配置应用上下文
 analyzers = new failureanalyzers(context);
 preparecontext(context, environment, listeners, applicationarguments,//3.准备上下文
  printedbanner);
 refreshcontext(context);//4.刷新上下文
 afterrefresh(context, applicationarguments);//5.刷新上下文后
 listeners.finished(context, null);--关闭！
 stopwatch.stop();
 if (this.logstartupinfo) {
  new startupinfologger(this.mainapplicationclass)
  .logstarted(getapplicationlog(), stopwatch);
 }
 return context;
 }
 catch (throwable ex) {
 handlerunfailure(context, listeners, analyzers, ex);
 throw new illegalstateexception(ex);
 }
 }

1. getrunlisteners 获取监听器（ springapplicationrunlisteners ）

实际是 springapplicationrunlistener 类

 private springapplicationrunlisteners getrunlisteners(string[] args) {
 class<?>[] types = new class<?>[] { springapplication.class, string[].class };
 return new springapplicationrunlisteners(logger, getspringfactoriesinstances(
 springapplicationrunlistener.class, types, this, args));
 }
 private <t> collection<? extends t> getspringfactoriesinstances(class<t> type) {
 return getspringfactoriesinstances(type, new class<?>[] {});
 }
 private <t> collection<? extends t> getspringfactoriesinstances(class<t> type,
 class<?>[] parametertypes, object... args) {
 classloader classloader = thread.currentthread().getcontextclassloader();
 // 使用set确保的字符串的唯一性
 set<string> names = new linkedhashset<string>(
 springfactoriesloader.loadfactorynames(type, classloader));// 1.载入工厂名称集合
 list<t> instances = createspringfactoriesinstances(type, parametertypes,// 2.创建工厂实例
 classloader, args, names);
 annotationawareordercomparator.sort(instances);// 排序
 return instances;
 }

1.1 载入工厂名称（loadfactorynames）

当前类的类加载器从 meta-inf/spring.factories 文件中获取springapplicationrunlistener类的配置

public static list<string> loadfactorynames(class<?> factoryclass, classloader classloader) {
 string factoryclassname = factoryclass.getname();
 try {
 enumeration<url> urls = (classloader != null ? classloader.getresources(factories_resource_location) :
  classloader.getsystemresources(factories_resource_location));
 list<string> result = new arraylist<string>();
 while (urls.hasmoreelements()) {
  url url = urls.nextelement();
  properties properties = propertiesloaderutils.loadproperties(new urlresource(url));
  string factoryclassnames = properties.getproperty(factoryclassname);
  result.addall(arrays.aslist(stringutils.commadelimitedlisttostringarray(factoryclassnames)));
 }
 return result;
 }
 catch (ioexception ex) {
 throw new illegalargumentexception("unable to load [" + factoryclass.getname() +
  "] factories from location [" + factories_resource_location + "]", ex);
 }
 }

上图，获取到工厂类名后，下面来看看meta-inf/spring.factories中定义了啥：

# propertysource loaders
org.springframework.boot.env.propertysourceloader=\
org.springframework.boot.env.propertiespropertysourceloader,\
org.springframework.boot.env.yamlpropertysourceloader
# run listeners 这里呢，看这里！！！！
org.springframework.boot.springapplicationrunlistener=\
org.springframework.boot.context.event.eventpublishingrunlistener
# application context initializers
org.springframework.context.applicationcontextinitializer=\
org.springframework.boot.context.configurationwarningsapplicationcontextinitializer,\
org.springframework.boot.context.contextidapplicationcontextinitializer,\
org.springframework.boot.context.config.delegatingapplicationcontextinitializer,\
org.springframework.boot.context.embedded.serverportinfoapplicationcontextinitializer
# application listeners
org.springframework.context.applicationlistener=\
org.springframework.boot.clearcachesapplicationlistener,\
org.springframework.boot.builder.parentcontextcloserapplicationlistener,\
org.springframework.boot.context.fileencodingapplicationlistener,\
org.springframework.boot.context.config.ansioutputapplicationlistener,\
org.springframework.boot.context.config.configfileapplicationlistener,\
org.springframework.boot.context.config.delegatingapplicationlistener,\
org.springframework.boot.liquibase.liquibaseservicelocatorapplicationlistener,\
org.springframework.boot.logging.classpathloggingapplicationlistener,\
org.springframework.boot.logging.loggingapplicationlistener
# environment post processors
org.springframework.boot.env.environmentpostprocessor=\
org.springframework.boot.cloud.cloudfoundryvcapenvironmentpostprocessor,\
org.springframework.boot.env.springapplicationjsonenvironmentpostprocessor
# failure analyzers
org.springframework.boot.diagnostics.failureanalyzer=\
org.springframework.boot.diagnostics.analyzer.beancurrentlyincreationfailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.beannotofrequiredtypefailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.bindfailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.connectorstartfailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.nouniquebeandefinitionfailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.portinusefailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.validationexceptionfailureanalyzer
# failureanalysisreporters
org.springframework.boot.diagnostics.failureanalysisreporter=\
org.springframework.boot.diagnostics.loggingfailureanalysisreporter

哇，都是些类全名称，且key都是接口，value都是实现类。我们根据key=“ org.springframework.boot.springapplicationrunlistener ”查询得到实现类value=" org.springframework.boot.context.event.eventpublishingrunlistener" 事件发布启动监听器 ， 一猜也知道肯定要用” 反射 ”根据类名获取类实例，下面很快得到验证...

1.2 创建spring工厂实例（createspringfactoriesinstances）

根据第一步得到的set<string> names（springapplicationrunlistener的唯一实现类 eventpublishingrunlistener ）生成" 事件发布启动监听器 " 工厂实例

 @suppresswarnings("unchecked")
 private <t> list<t> createspringfactoriesinstances(class<t> type,
 class<?>[] parametertypes, classloader classloader, object[] args,
 set<string> names) {
 list<t> instances = new arraylist<t>(names.size());
 for (string name : names) {
 try {
  class<?> instanceclass = classutils.forname(name, classloader);// 利用反射获取类
  assert.isassignable(type, instanceclass);
  constructor<?> constructor = instanceclass
  .getdeclaredconstructor(parametertypes);// 得到构造器
  t instance = (t) beanutils.instantiateclass(constructor, args);// 根据构造器和参数构造实例
  instances.add(instance);
 }
 catch (throwable ex) {
  throw new illegalargumentexception(
  "cannot instantiate " + type + " : " + name, ex);
 }
 }
 return instances;
 }

准备上下文

 private void preparecontext(configurableapplicationcontext context,
 configurableenvironment environment, springapplicationrunlisteners listeners,
 applicationarguments applicationarguments, banner printedbanner) {
 context.setenvironment(environment);
 postprocessapplicationcontext(context);//单例一个beannamegenerator，把resourceloader设置进应用上下文
 applyinitializers(context);//执行初始化器
 listeners.contextprepared(context);// 监听器执行上下文"已准备好"方法
 if (this.logstartupinfo) {
 logstartupinfo(context.getparent() == null);
 logstartupprofileinfo(context);
 } 
 // 添加spring boot特殊单例bean
 context.getbeanfactory().registersingleton("springapplicationarguments",
  applicationarguments);
 if (printedbanner != null) {
 context.getbeanfactory().registersingleton("springbootbanner", printedbanner);
 }
 // 载入资源
 set<object> sources = getsources();
 assert.notempty(sources, "sources must not be empty");
 load(context, sources.toarray(new object[sources.size()]));
 listeners.contextloaded(context);// 监听器执行"上下文已加载"方法
 }

刷新上下文

 private void refreshcontext(configurableapplicationcontext context) {
 refresh(context);//核心类
 if (this.registershutdownhook) {
 try {
 context.registershutdownhook();//注册关闭钩子，容器关闭时执行
 }
 catch (accesscontrolexception ex) {
 // not allowed in some environments.
 }
 }
 }
 protected void refresh(applicationcontext applicationcontext) {
 assert.isinstanceof(abstractapplicationcontext.class, applicationcontext);
 ((abstractapplicationcontext) applicationcontext).refresh();
 }

最终执行的是abstractapplicationcontext抽象类的 refresh 方法。

 public void refresh() throws beansexception, illegalstateexception {
 synchronized (this.startupshutdownmonitor) {
 //准备刷新的上下文环境，例如对系统属性或者环境变量进行准备及验证。
 preparerefresh();
 //启动子类的refreshbeanfactory方法.解析xml
 configurablelistablebeanfactory beanfactory = obtainfreshbeanfactory();
 //为beanfactory配置容器特性，例如类加载器、事件处理器等.
 preparebeanfactory(beanfactory);
 try {
  //设置beanfactory的后置处理. 空方法，留给子类拓展用。 
  postprocessbeanfactory(beanfactory);
  //调用beanfactory的后处理器, 这些后处理器是在bean定义中向容器注册的. 
  invokebeanfactorypostprocessors(beanfactory);
  //注册bean的后处理器, 在bean创建过程中调用. 
  registerbeanpostprocessors(beanfactory);
  //初始化上下文中的消息源，即不同语言的消息体进行国际化处理 
  initmessagesource();
  //初始化applicationeventmulticaster bean,应用事件广播器
  initapplicationeventmulticaster();
  //初始化其它特殊的bean， 空方法，留给子类拓展用。 
  onrefresh();
  //检查并向容器注册监听器bean
  registerlisteners();
  //实例化所有剩余的(non-lazy-init) 单例bean.
  finishbeanfactoryinitialization(beanfactory);
  //发布容器事件, 结束refresh过程. 
  finishrefresh();
 }
 catch (beansexception ex) {
  if (logger.iswarnenabled()) {
  logger.warn("exception encountered during context initialization - " +
  "cancelling refresh attempt: " + ex);
  }
  //销毁已经创建的单例bean, 以避免资源占用.
  destroybeans();
  //取消refresh操作, 重置active标志. 
  cancelrefresh(ex);
  // propagate exception to caller.
  throw ex;
 }
 finally {
  //重置spring的核心缓存
  resetcommoncaches();
 }
 }
 }

刷新完上下文后

spring boot提供的2个供用户自己拓展的接口： applicationrunner和 commandlinerunner。可以在容器启动完毕后（上下文刷新后）执行，做一些类似数据初始化的操作。

 private void callrunners(applicationcontext context, applicationarguments args) {
 list<object> runners = new arraylist<object>();
 runners.addall(context.getbeansoftype(applicationrunner.class).values());//从上下文中获取applicationrunner类型的bean
 runners.addall(context.getbeansoftype(commandlinerunner.class).values());//从上下文中获取commandlinerunner类型的bean
 annotationawareordercomparator.sort(runners);//排序
 for (object runner : new linkedhashset<object>(runners)) {
 if (runner instanceof applicationrunner) {
  callrunner((applicationrunner) runner, args);//执行
 }
 if (runner instanceof commandlinerunner) {
  callrunner((commandlinerunner) runner, args);
 }
 }
 }

两个区别在于入参不同，根据实际情况自己选择。

 public interface commandlinerunner {
 void run(string... args) throws exception;
 }
 public interface applicationrunner {
 void run(applicationarguments args) throws exception;
 }

commandlinerunner中执行参数是原始的 java启动类main方法的string[] args字符串数组参数； applicationrunner中的参数经过处理提供一些方法例如:

 list<string> getoptionvalues(string name);

根据名称获取值list,java 启动命令中 --foo=bar --foo=baz，则根据foo参数名返回list ["bar", "baz"]

三、总结

 

按照前面的分析，spring-boot容器启动流程总体可划分为2部分：

1） 执行注解 ：扫描指定范围下的bean、载入自动配置类对应的bean加载到ioc容器。

2）man方法中具体springappliocation.run() ，全流程贯穿springapplicationevent,有6个子类：

applicationfailedevent.class
applicationpreparedevent.class
applicationreadyevent.class
applicationstartedevent.class
applicationstartingevent.class
springapplicationevent.class

这里用到了很经典的 spring事件驱动模型 ，飞机票： spring事件驱动模型和观察者模式

类图如下：

 

如上图，就是一个经典spring 事件驱动模型，包含3种角色：事件发布者、事件、监听者。对应到spring-boot中就是：

1 .eventpublishingrunlistener 这个类封装了 事件发布 ，

2. springapplicationevent 是spring-boot中定义的事件（上面说的6种事件），继承自 applicationevent （spring中定义的）

3. 监听者 spring-boot并没有实现针对上述6种事件的监听者（我没找到...）， 这里用户可以自己实现监听者（上述6种事件）来注入spring boot容器启动流程，触发相应的事件。

例如：实现applicationlistener<applicationreadyevent>这个接口，在容器启动完毕时最后一步listener.finished时，如果启动没有异常，就会执行！可以做一些数据初始化之类的操作。

总结

以上所述是小编给大家介绍的spring boot容器启动的相关知识，希望对大家有所帮助