前言
不得不说springboot的开发者是在为大众程序猿谋福利，把大家都惯成了懒汉，xml不配置了，连tomcat也懒的配置了，典型的一键启动系统，那么tomcat在springboot是怎么启动的呢？
内置tomcat
开发阶段对我们来说使用内置的tomcat是非常够用了，当然也可以使用jetty。
<dependency> <groupid>org.springframework.boot</groupid> <artifactid>spring-boot-starter-web</artifactid> <version>2.1.6.release</version> </dependency>
@springbootapplication
public class myspringboottomcatstarter{
public static void main(string[] args) {
long time=system.currenttimemillis();
springapplication.run(myspringboottomcatstarter.class);
system.out.println("===应用启动耗时："+(system.currenttimemillis()-time)+"===");
}
}
这里是main函数入口，两句代码最耀眼，分别是springbootapplication注解和springapplication.run()方法。
发布生产
发布的时候，目前大多数的做法还是排除内置的tomcat，打瓦包（war）然后部署在生产的tomcat中，好吧，那打包的时候应该怎么处理？
<dependency>
<groupid>org.springframework.boot</groupid>
<artifactid>spring-boot-starter-web</artifactid>
<!-- 移除嵌入式tomcat插件 -->
<exclusions>
<exclusion>
<groupid>org.springframework.boot</groupid>
<artifactid>spring-boot-starter-tomcat</artifactid>
</exclusion>
</exclusions>
</dependency>
<!--添加servlet-api依赖--->
<dependency>
<groupid>javax.servlet</groupid>
<artifactid>javax.servlet-api</artifactid>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>
更新main函数，主要是继承springbootservletinitializer，并重写configure()方法。
@springbootapplication
public class myspringboottomcatstarter extends springbootservletinitializer {
public static void main(string[] args) {
long time=system.currenttimemillis();
springapplication.run(myspringboottomcatstarter.class);
system.out.println("===应用启动耗时："+(system.currenttimemillis()-time)+"===");
}
@override
protected springapplicationbuilder configure(springapplicationbuilder builder) {
return builder.sources(this.getclass());
}
}
从main函数说起
public static configurableapplicationcontext run(class<?> primarysource, string... args) {
return run(new class[]{primarysource}, args);
}
--这里run方法返回的是configurableapplicationcontext
public static configurableapplicationcontext run(class<?>[] primarysources, string[] args) {
return (new springapplication(primarysources)).run(args);
}
public configurableapplicationcontext run(string... args) {
configurableapplicationcontext context = null;
collection<springbootexceptionreporter> exceptionreporters = new arraylist();
this.configureheadlessproperty();
springapplicationrunlisteners listeners = this.getrunlisteners(args);
listeners.starting();
collection exceptionreporters;
try {
applicationarguments applicationarguments = new defaultapplicationarguments(args);
configurableenvironment environment = this.prepareenvironment(listeners, applicationarguments);
this.configureignorebeaninfo(environment);
//打印banner，这里你可以自己涂鸦一下，换成自己项目的logo
banner printedbanner = this.printbanner(environment);
//创建应用上下文
context = this.createapplicationcontext();
exceptionreporters = this.getspringfactoriesinstances(springbootexceptionreporter.class, new class[]{configurableapplicationcontext.class}, context);
//预处理上下文
this.preparecontext(context, environment, listeners, applicationarguments, printedbanner);
//刷新上下文
this.refreshcontext(context);
//再刷新上下文
this.afterrefresh(context, applicationarguments);
listeners.started(context);
this.callrunners(context, applicationarguments);
} catch (throwable var10) {
}
try {
listeners.running(context);
return context;
} catch (throwable var9) {
}
}
既然我们想知道tomcat在springboot中是怎么启动的，那么run方法中，重点关注创建应用上下文（createapplicationcontext）和刷新上下文（refreshcontext）。
创建上下文
//创建上下文
protected configurableapplicationcontext createapplicationcontext() {
class<?> contextclass = this.applicationcontextclass;
if (contextclass == null) {
try {
switch(this.webapplicationtype) {
case servlet:
//创建annotationconfigservletwebserverapplicationcontext
contextclass = class.forname("org.springframework.boot.web.servlet.context.annotationconfigservletwebserverapplicationcontext");
break;
case reactive:
contextclass = class.forname("org.springframework.boot.web.reactive.context.annotationconfigreactivewebserverapplicationcontext");
break;
default:
contextclass = class.forname("org.springframework.context.annotation.annotationconfigapplicationcontext");
}
} catch (classnotfoundexception var3) {
throw new illegalstateexception("unable create a default applicationcontext, please specify an applicationcontextclass", var3);
}
}
return (configurableapplicationcontext)beanutils.instantiateclass(contextclass);
}
这里会创建annotationconfigservletwebserverapplicationcontext类。
而annotationconfigservletwebserverapplicationcontext类继承了servletwebserverapplicationcontext，而这个类是最终集成了abstractapplicationcontext。
刷新上下文
//springapplication.java
//刷新上下文
private void refreshcontext(configurableapplicationcontext context) {
this.refresh(context);
if (this.registershutdownhook) {
try {
context.registershutdownhook();
} catch (accesscontrolexception var3) {
}
}
}
//这里直接调用最终父类abstractapplicationcontext.refresh()方法
protected void refresh(applicationcontext applicationcontext) {
((abstractapplicationcontext)applicationcontext).refresh();
}
//abstractapplicationcontext.java
public void refresh() throws beansexception, illegalstateexception {
synchronized(this.startupshutdownmonitor) {
this.preparerefresh();
configurablelistablebeanfactory beanfactory = this.obtainfreshbeanfactory();
this.preparebeanfactory(beanfactory);
try {
this.postprocessbeanfactory(beanfactory);
this.invokebeanfactorypostprocessors(beanfactory);
this.registerbeanpostprocessors(beanfactory);
this.initmessagesource();
this.initapplicationeventmulticaster();
//调用各个子类的onrefresh()方法，也就说这里要回到子类：servletwebserverapplicationcontext，调用该类的onrefresh()方法
this.onrefresh();
this.registerlisteners();
this.finishbeanfactoryinitialization(beanfactory);
this.finishrefresh();
} catch (beansexception var9) {
this.destroybeans();
this.cancelrefresh(var9);
throw var9;
} finally {
this.resetcommoncaches();
}
}
}
//servletwebserverapplicationcontext.java
//在这个方法里看到了熟悉的面孔，this.createwebserver，神秘的面纱就要揭开了。
protected void onrefresh() {
super.onrefresh();
try {
this.createwebserver();
} catch (throwable var2) {
}
}
//servletwebserverapplicationcontext.java
//这里是创建webserver，但是还没有启动tomcat，这里是通过servletwebserverfactory创建，那么接着看下servletwebserverfactory
private void createwebserver() {
webserver webserver = this.webserver;
servletcontext servletcontext = this.getservletcontext();
if (webserver == null && servletcontext == null) {
servletwebserverfactory factory = this.getwebserverfactory();
this.webserver = factory.getwebserver(new servletcontextinitializer[]{this.getselfinitializer()});
} else if (servletcontext != null) {
try {
this.getselfinitializer().onstartup(servletcontext);
} catch (servletexception var4) {
}
}
this.initpropertysources();
}
//接口
public interface servletwebserverfactory {
webserver getwebserver(servletcontextinitializer... initializers);
}
//实现
abstractservletwebserverfactory
jettyservletwebserverfactory
tomcatservletwebserverfactory
undertowservletwebserverfactory
这里servletwebserverfactory接口有4个实现类
而其中我们常用的有两个：tomcatservletwebserverfactory和jettyservletwebserverfactory。
//tomcatservletwebserverfactory.java
//这里我们使用的tomcat，所以我们查看tomcatservletwebserverfactory。到这里总算是看到了tomcat的踪迹。
@override
public webserver getwebserver(servletcontextinitializer... initializers) {
tomcat tomcat = new tomcat();
file basedir = (this.basedirectory != null) ? this.basedirectory : createtempdir("tomcat");
tomcat.setbasedir(basedir.getabsolutepath());
//创建connector对象
connector connector = new connector(this.protocol);
tomcat.getservice().addconnector(connector);
customizeconnector(connector);
tomcat.setconnector(connector);
tomcat.gethost().setautodeploy(false);
configureengine(tomcat.getengine());
for (connector additionalconnector : this.additionaltomcatconnectors) {
tomcat.getservice().addconnector(additionalconnector);
}
preparecontext(tomcat.gethost(), initializers);
return gettomcatwebserver(tomcat);
}
protected tomcatwebserver gettomcatwebserver(tomcat tomcat) {
return new tomcatwebserver(tomcat, getport() >= 0);
}
//tomcat.java
//返回engine容器，看到这里，如果熟悉tomcat源码的话，对engine不会感到陌生。
public engine getengine() {
service service = getserver().findservices()[0];
if (service.getcontainer() != null) {
return service.getcontainer();
}
engine engine = new standardengine();
engine.setname( "tomcat" );
engine.setdefaulthost(hostname);
engine.setrealm(createdefaultrealm());
service.setcontainer(engine);
return engine;
}
//engine是最高级别容器，host是engine的子容器，context是host的子容器，wrapper是context的子容器
getwebserver这个方法创建了tomcat对象，并且做了两件重要的事情：把connector对象添加到tomcat中，configureengine(tomcat.getengine());
getwebserver方法返回的是tomcatwebserver。
//tomcatwebserver.java
//这里调用构造函数实例化tomcatwebserver
public tomcatwebserver(tomcat tomcat, boolean autostart) {
assert.notnull(tomcat, "tomcat server must not be null");
this.tomcat = tomcat;
this.autostart = autostart;
initialize();
}
private void initialize() throws webserverexception {
//在控制台会看到这句日志
logger.info("tomcat initialized with port(s): " + getportsdescription(false));
synchronized (this.monitor) {
try {
addinstanceidtoenginename();
context context = findcontext();
context.addlifecyclelistener((event) -> {
if (context.equals(event.getsource()) && lifecycle.start_event.equals(event.gettype())) {
removeserviceconnectors();
}
});
//===启动tomcat服务===
this.tomcat.start();
rethrowdeferredstartupexceptions();
try {
contextbindings.bindclassloader(context, context.getnamingtoken(), getclass().getclassloader());
}
catch (namingexception ex) {
}
//开启阻塞非守护进程
startdaemonawaitthread();
}
catch (exception ex) {
stopsilently();
destroysilently();
throw new webserverexception("unable to start embedded tomcat", ex);
}
}
}
//tomcat.java
public void start() throws lifecycleexception {
getserver();
server.start();
}
//这里server.start又会回到tomcatwebserver的
public void stop() throws lifecycleexception {
getserver();
server.stop();
}
//tomcatwebserver.java
//启动tomcat服务
@override
public void start() throws webserverexception {
synchronized (this.monitor) {
if (this.started) {
return;
}
try {
addpreviouslyremovedconnectors();
connector connector = this.tomcat.getconnector();
if (connector != null && this.autostart) {
performdeferredloadonstartup();
}
checkthatconnectorshavestarted();
this.started = true;
//在控制台打印这句日志，如果在yml设置了上下文，这里会打印
logger.info("tomcat started on port(s): " + getportsdescription(true) + " with context path '"
+ getcontextpath() + "'");
}
catch (connectorstartfailedexception ex) {
stopsilently();
throw ex;
}
catch (exception ex) {
throw new webserverexception("unable to start embedded tomcat server", ex);
}
finally {
context context = findcontext();
contextbindings.unbindclassloader(context, context.getnamingtoken(), getclass().getclassloader());
}
}
}
//关闭tomcat服务
@override
public void stop() throws webserverexception {
synchronized (this.monitor) {
boolean wasstarted = this.started;
try {
this.started = false;
try {
stoptomcat();
this.tomcat.destroy();
}
catch (lifecycleexception ex) {
}
}
catch (exception ex) {
throw new webserverexception("unable to stop embedded tomcat", ex);
}
finally {
if (wasstarted) {
containercounter.decrementandget();
}
}
}
}
附：tomcat顶层结构图
tomcat最顶层容器是server，代表着整个服务器，一个server包含多个service。从上图可以看除service主要包括多个connector和一个container。connector用来处理连接相关的事情，并提供socket到request和response相关转化。container用于封装和管理servlet，以及处理具体的request请求。那么上文提到的engine>host>context>wrapper容器又是怎么回事呢？ 我们来看下图：
综上所述，一个tomcat只包含一个server，一个server可以包含多个service，一个service只有一个container，但有多个connector，这样一个服务可以处理多个连接。
多个connector和一个container就形成了一个service，有了service就可以对外提供服务了，但是service要提供服务又必须提供一个宿主环境，那就非server莫属了，所以整个tomcat的声明周期都由server控制。
总结
springboot的启动主要是通过实例化springapplication来启动的，启动过程主要做了以下几件事情：配置属性、获取监听器，发布应用开始启动事件初、始化输入参数、配置环境，输出banner、创建上下文、预处理上下文、刷新上下文、再刷新上下文、发布应用已经启动事件、发布应用启动完成事件。在springboot中启动tomcat的工作在刷新上下这一步。而tomcat的启动主要是实例化两个组件：connector、container，一个tomcat实例就是一个server，一个server包含多个service，也就是多个应用程序，每个service包含多个connector和一个container，而一个container下又包含多个子容器。
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