SpringBoot启动过程的实现
springboot启动过程分析,首先打开springboot的启用入口main类:
@springbootapplication public class applicationmain{ public static void main(string[] args) { springapplication.run(applicationmain.class, args); } }
可以看到main方法里面只有一行核心启用类:springapplication.run(applicationmain.class, args);这个是关键,在改行打上断点,debug模式启动该main类。点击下一步进入springapplication的源码对应的run方法:
public static configurableapplicationcontext run(object[] sources, string[] args) { return (new springapplication(sources)).run(args); }
初始化springapplication
springapplication实例化之前会调用构造方法进行初始化:
public springapplication(object... sources) { this.bannermode = mode.console; this.logstartupinfo = true; this.addcommandlineproperties = true; this.headless = true; this.registershutdownhook = true; this.additionalprofiles = new hashset(); this.initialize(sources); }
而springapplication构造方法的核心是:this.initialize(sources);初始化方法,springapplication通过调用该方法来初始化。
private void initialize(object[] sources) { if (sources != null && sources.length > 0) { this.sources.addall(arrays.aslist(sources)); } this.webenvironment = deducewebenvironment(); setinitializers((collection) getspringfactoriesinstances( applicationcontextinitializer.class)); setlisteners((collection) getspringfactoriesinstances(applicationlistener.class)); this.mainapplicationclass = deducemainapplicationclass(); }
1.deducewebenvironment方法是用来判断当前应用的环境,该方法通过获取这两个类来判断当前环境是否是web环境,如果能获得这两个类说明是web环境,否则不是。
javax.servlet.servlet org.springframework.web.context.configurablewebapplicationcontext
2.getspringfactoriesinstances方法主要用来从spring.factories文件中找出key为applicationcontextinitializer的类并实例化,然后调用setinitializers方法设置到springapplication的initializers属性中。这个过程就是找出所有的应用程序初始化器。
private <t> collection<? extends t> getspringfactoriesinstances(class<t> type, class<?>[] parametertypes, object... args) { classloader classloader = thread.currentthread().getcontextclassloader(); set<string> names = new linkedhashset(springfactoriesloader.loadfactorynames(type, classloader)); list<t> instances = this.createspringfactoriesinstances(type, parametertypes, classloader, args, names); annotationawareordercomparator.sort(instances); return instances; }
public static list<string> loadfactorynames(class<?> factoryclass, classloader classloader) { string factoryclassname = factoryclass.getname(); try { //从spring.factories文件中找出key为applicationcontextinitializer的类 enumeration<url> urls = classloader != null ? classloader.getresources("meta-inf/spring.factories") : classloader.getsystemresources("meta-inf/spring.factories"); arraylist result = new arraylist(); while(urls.hasmoreelements()) { url 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 var8) { throw new illegalargumentexception("unable to load [" + factoryclass.getname() + "] factories from location [" + "meta-inf/spring.factories" + "]", var8); } }
当前的初始化器有如下几个:
3.同理调用getspringfactoriesinstances从spring.factories文件中找出key为applicationlistener的类并实例化,然后调用setlisteners方法设置到springapplication的listeners属性中。这个过程就是找出所有的应用程序事件监听器。
当前的事件监听器有如下几个:
4.调用deducemainapplicationclass方法找出main类,就是这里的applicationmain类。
运行springapplication
初始化springapplication完成之后,调用run方法运行:
public configurableapplicationcontext run(string... args) { //计时器,统计任务的执行时间 stopwatch stopwatch = new stopwatch(); //开始执行 stopwatch.start(); configurableapplicationcontext context = null; failureanalyzers analyzers = null; this.configureheadlessproperty(); // 获取springapplicationrunlisteners启动事件监听器,这里只有一个eventpublishingrunlistener springapplicationrunlisteners listeners = this.getrunlisteners(args); // 封装成springapplicationevent事件然后广播出去给springapplication中的listeners所监听 listeners.starting(); try { // 构造一个应用程序参数持有类 applicationarguments applicationarguments = new defaultapplicationarguments(args); // 准备并配置环境 configurableenvironment environment = this.prepareenvironment(listeners, applicationarguments); // 打印banner图形 banner printedbanner = this.printbanner(environment); // 创建spring容器 context = this.createapplicationcontext(); new failureanalyzers(context); // 配置spring容器 this.preparecontext(context, environment, listeners, applicationarguments, printedbanner); // 容器上下文刷新 this.refreshcontext(context); // 容器创建完成之后调用afterrefresh方法 this.afterrefresh(context, applicationarguments); // 调用监听器,广播spring启动结束的事件 listeners.finished(context, (throwable)null); // 停止计时器 stopwatch.stop(); if (this.logstartupinfo) { (new startupinfologger(this.mainapplicationclass)).logstarted(this.getapplicationlog(), stopwatch); } return context; } catch (throwable var9) { this.handlerunfailure(context, listeners, (failureanalyzers)analyzers, var9); throw new illegalstateexception(var9); } }
springapplicationrunlisteners
1.获取启动事件监听器,可以看看该方法:
springapplicationrunlisteners listeners = this.getrunlisteners(args);
private springapplicationrunlisteners getrunlisteners(string[] args) { class<?>[] types = new class[]{springapplication.class, string[].class}; return new springapplicationrunlisteners(logger, this.getspringfactoriesinstances(springapplicationrunlistener.class, types, this, args)); }
同样的通过调用getspringfactoriesinstances方法去meta-inf/spring.factories文件中拿到springapplicationrunlistener监听器,当前的springapplicationrunlistener事件监听器只有一个eventpublishingrunlistener广播事件监听器:
springapplicationrunlisteners内部持有springapplicationrunlistener集合和1个log日志类。用于springapplicationrunlistener监听器的批量执行。
springapplicationrunlistener用于监听springapplication的run方法的执行,它定义了5个步骤:
1.starting:run方法执行的时候立马执行,对应的事件类型是applicationstartedevent
2.environmentprepared:applicationcontext创建之前并且环境信息准备好的时候调用,对应的事件类型是applicationenvironmentpreparedevent
3.contextprepared:applicationcontext创建好并且在source加载之前调用一次,没有具体的对应事件
4.contextloaded:applicationcontext创建并加载之后并在refresh之前调用,对应的事件类型是applicationpreparedevent
5.finished:run方法结束之前调用,对应事件的类型是applicationreadyevent或applicationfailedevent
springapplicationrunlistener目前只有一个实现类eventpublishingrunlistener,详见获取springapplicationrunlisteners。它把监听的过程封装成了springapplicationevent事件并让内部属性applicationeventmulticaster接口的实现类simpleapplicationeventmulticaster广播出去,广播出去的事件对象会被springapplication中的listeners属性进行处理。
所以说springapplicationrunlistener和applicationlistener之间的关系是通过applicationeventmulticaster广播出去的springapplicationevent所联系起来的
2.启动事件监听器
通过listeners.starting()可以启动事件监听器springapplicationrunlistener ,springapplicationrunlistener 是一个启动事件监听器接口:
public interface springapplicationrunlistener { void starting(); void environmentprepared(configurableenvironment var1); void contextprepared(configurableapplicationcontext var1); void contextloaded(configurableapplicationcontext var1); void finished(configurableapplicationcontext var1, throwable var2); }
springapplicationrunlistener 接口的具体实现就是eventpublishingrunlistener类,我们主要来看一下它的startting方法,该方法会封装成springapplicationevent事件然后广播出去给springapplication中的listeners所监听。
public void starting() { this.initialmulticaster.multicastevent(new applicationstartedevent(this.application, this.args)); }
配置并准备环境
private configurableenvironment prepareenvironment( springapplicationrunlisteners listeners, applicationarguments applicationarguments) { // 创建应用程序的环境信息。如果是web程序,创建standardservletenvironment;否则,创建standardenvironment configurableenvironment environment = getorcreateenvironment(); // 配置环境信息。比如profile,命令行参数 configureenvironment(environment, applicationarguments.getsourceargs()); // 广播出applicationenvironmentpreparedevent事件给相应的监听器执行 listeners.environmentprepared(environment); // 环境信息的校对 if (!this.webenvironment) { environment = new environmentconverter(getclassloader()) .converttostandardenvironmentifnecessary(environment); } return environment; }
判断环境,如果是web程序,创建standardservletenvironment;否则,创建standardenvironment。
private configurableenvironment getorcreateenvironment() { if (this.environment != null) { return this.environment; } else { return (configurableenvironment)(this.webenvironment ? new standardservletenvironment() : new standardenvironment()); } }
创建spring容器上下文
protected configurableapplicationcontext createapplicationcontext() { class<?> contextclass = this.applicationcontextclass; if (contextclass == null) { try { // 判断是否是web应用, // 如果是则创建annotationconfigembeddedwebapplicationcontext,否则创建annotationconfigapplicationcontext contextclass = class.forname(this.webenvironment ? default_web_context_class : default_context_class); } catch (classnotfoundexception ex) { throw new illegalstateexception( "unable create a default applicationcontext, " + "please specify an applicationcontextclass", ex); } } return (configurableapplicationcontext) beanutils.instantiate(contextclass); }
配置spring容器上下文
private void preparecontext(configurableapplicationcontext context, configurableenvironment environment, springapplicationrunlisteners listeners, applicationarguments applicationarguments, banner printedbanner) { // 设置spring容器上下文的环境信息 context.setenvironment(environment); // spring容器创建之后做一些额外的事 postprocessapplicationcontext(context); // springapplication的初始化器开始工作 applyinitializers(context); // 遍历调用springapplicationrunlistener的contextprepared方法。目前只是将这个事件广播器注册到spring容器中 listeners.contextprepared(context); if (this.logstartupinfo) { logstartupinfo(context.getparent() == null); logstartupprofileinfo(context); } // 把应用程序参数持有类注册到spring容器中,并且是一个单例 context.getbeanfactory().registersingleton("springapplicationarguments", applicationarguments); if (printedbanner != null) { context.getbeanfactory().registersingleton("springbootbanner", printedbanner); } // 加载sources,sources是main方法所在的类 set<object> sources = getsources(); assert.notempty(sources, "sources must not be empty"); // 将sources加载到应用上下文中。最终调用的是annotatedbeandefinitionreader.registerbean方法 load(context, sources.toarray(new object[sources.size()])); // 广播出applicationpreparedevent事件给相应的监听器执行 // 执行eventpublishingrunlistener.contextloaded方法 listeners.contextloaded(context); }
spring容器创建之后回调方法postprocessapplicationcontext
protected void postprocessapplicationcontext(configurableapplicationcontext context) { // 如果springapplication设置了实例命名生成器,则注册到spring容器中 if (this.beannamegenerator != null) { context.getbeanfactory().registersingleton( annotationconfigutils.configuration_bean_name_generator, this.beannamegenerator); } // 如果springapplication设置了资源加载器,设置到spring容器中 if (this.resourceloader != null) { if (context instanceof genericapplicationcontext) { ((genericapplicationcontext) context) .setresourceloader(this.resourceloader); } if (context instanceof defaultresourceloader) { ((defaultresourceloader) context) .setclassloader(this.resourceloader.getclassloader()); } } }
初始化器开始工作
protected void applyinitializers(configurableapplicationcontext context) { // 遍历每个初始化器,调用对应的initialize方法 for (applicationcontextinitializer initializer : getinitializers()) { class<?> requiredtype = generictyperesolver.resolvetypeargument( initializer.getclass(), applicationcontextinitializer.class); assert.isinstanceof(requiredtype, context, "unable to call initializer."); initializer.initialize(context); } }
spring容器创建完成之后会调用afterrefresh方法
applicationrunner、commandlinerunner类都是在在afterrefresh方法中调用的,也就是说在spring容器创建之后执行的。
protected void applyinitializers(configurableapplicationcontext context) { // 遍历每个初始化器,调用对应的initialize方法 for (applicationcontextinitializer initializer : getinitializers()) { class<?> requiredtype = generictyperesolver.resolvetypeargument( initializer.getclass(), applicationcontextinitializer.class); assert.isinstanceof(requiredtype, context, "unable to call initializer."); initializer.initialize(context); } }
参考:https://blog.wangqi.love/articles/spring/springboot启动过程.html
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