spring-mvc源码分析v3.3.0

分析下springboot内嵌tomcat启动流程，即springboot-mvc

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId><version>3.3.0</version>
</dependency>

环境信息

• Java 22
• Spring Boot v3.3.0
• Apache Tomcat/10.1.24
• spring-boot-starter-web 3.3.0

测试项目主要文件结构：

@RestController
public class Controller {@GetMapping("/test")public String test(){return "test";}
}

参考文章

• springboot启动流程
• tomcat源码分析

下面开始分析源码

1. 创建tomcat服务

要从启动springboot开始说起，在springApplication.run.refreshContext.refresh.onRefresh这一步中，创建tomcat服务。

@Override
protected void onRefresh() {super.onRefresh();//设置springboot主题。主要用于国际化和本地化的场景。它允许应用程序根据用户的区域设置动态地更改界面的外观和感觉try {createWebServer();//创建tomcat}catch (Throwable ex) {throw new ApplicationContextException("Unable to start web server", ex);}
}private void createWebServer() {WebServer webServer = this.webServer;//nullServletContext servletContext = getServletContext();//nullif (webServer == null && servletContext == null) {//trueStartupStep createWebServer = getApplicationStartup().start("spring.boot.webserver.create");//记录web开始创建步骤//webServer创建工厂，这个是重点ServletWebServerFactory factory = getWebServerFactory();createWebServer.tag("factory", factory.getClass().toString());this.webServer = factory.getWebServer(getSelfInitializer());createWebServer.end();getBeanFactory().registerSingleton("webServerGracefulShutdown",new WebServerGracefulShutdownLifecycle(this.webServer));//bean注册webServerStartStopgetBeanFactory().registerSingleton("webServerStartStop",new WebServerStartStopLifecycle(this, this.webServer));}else if (servletContext != null) {try {getSelfInitializer().onStartup(servletContext);}catch (ServletException ex) {throw new ApplicationContextException("Cannot initialize servlet context", ex);}}//初始化配置属性，配置环境initPropertySources();
}

1.1. webServer创建工厂getWebServerFactory()

因为程序执行到这一步的时候，springboot beanFactory已经完成所有的bean定义了，然后获取ServletWebServerFactory类型的bean，然后实例化

protected ServletWebServerFactory getWebServerFactory() {// Use bean names so that we don't consider the hierarchyString[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);//只有一个元素：tomcatServletWebServerFactoryif (beanNames.length == 0) {throw new MissingWebServerFactoryBeanException(getClass(), ServletWebServerFactory.class,WebApplicationType.SERVLET);}if (beanNames.length > 1) {throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "+ "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));}//createBean并返回 factory = {TomcatServletWebServerFactory@6532} return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}

1.2. 实例化webServer服务factory.getWebServer(getSelfInitializer())

getSelfInitializer()是一个Lambda方法引用。

private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {return this::selfInitialize;
}
//context初始化的时候执行
private void selfInitialize(ServletContext servletContext) throws ServletException {for (ServletContextInitializer beans : getServletContextInitializerBeans()) {beans.onStartup(servletContext);}
}

继续看getWebServer方法。这一步就是模仿了原生的tomcat启动流程，创建server、service、connector、egine、host、context
值得注意的是内嵌的tomcat是直接创建了一个context。而不是扫描webapps目录

//默认的连接协议，nio
public static final String protocol = "org.apache.coyote.http11.Http11NioProtocol";public WebServer getWebServer(ServletContextInitializer... initializers) {if (this.disableMBeanRegistry) {//trueRegistry.disableRegistry();//禁用tomcat注册对象到MBean}Tomcat tomcat = new Tomcat();//这个Tomcat类里面是一些基本的操作，基本的属性，我认为这就是一个配置上下文类，如下// protected Server server;// protected int port = 8080;// protected String hostname = "localhost";File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");//C:\Users\SHENSH~1\AppData\Local\Temp\tomcat.8080.1801441663765902424tomcat.setBaseDir(baseDir.getAbsolutePath());//创建Connector，构造方法中创建了Http11NioProtocolConnector connector = new Connector(this.protocol);connector.setThrowOnFailure(true);//创建Server和Servicetomcat.getService().addConnector(connector);customizeConnector(connector);tomcat.setConnector(connector);registerConnectorExecutor(tomcat, connector);//创建Host和Enginetomcat.getHost().setAutoDeploy(false);//禁用自动部署，不扫描webApps目录//创建contextprepareContext(tomcat.getHost(), initializers);//创建tomcatWebServer，返回给springboot，用于后续操作return getTomcatWebServer(tomcat);
}

1.2.1. 创建Connector

new Connector("org.apache.coyote.http11.Http11NioProtocol");public Connector(String protocol) {configuredProtocol = protocol;ProtocolHandler p = null;try {p = ProtocolHandler.create(protocol);} catch (Exception e) {log.error(sm.getString("coyoteConnector.protocolHandlerInstantiationFailed"), e);}
}

1.2.2. 创建Server和Service

public Service getService() {return getServer().findServices()[0];
}
public Server getServer() {if (server != null) {return server;}System.setProperty("catalina.useNaming", "false");server = new StandardServer();//创建StandardServerinitBaseDir();// Set configuration sourceConfigFileLoader.setSource(new CatalinaBaseConfigurationSource(new File(basedir), null));server.setPort(-1);Service service = new StandardService();//创建StandardServiceservice.setName("Tomcat");server.addService(service);return server;
}

1.2.3. 创建Host和Engine

public Host getHost() {Engine engine = getEngine();if (engine.findChildren().length > 0) {//获取hostreturn (Host) engine.findChildren()[0];}Host host = new StandardHost();//创建StandardHosthost.setName(hostname);getEngine().addChild(host);return host;
}public Engine getEngine() {Service service = getServer().findServices()[0];if (service.getContainer() != null) {//获取enginereturn service.getContainer();}Engine engine = new StandardEngine();//创建StandardEngineengine.setName("Tomcat");engine.setDefaultHost(hostname);engine.setRealm(createDefaultRealm());service.setContainer(engine);return engine;
}

1.2.4. 创建Context

protected void prepareContext(Host host, ServletContextInitializer[] initializers) {TomcatEmbeddedContext context = new TomcatEmbeddedContext();//创建TomcatEmbeddedContext，这个是内嵌的tomcat上下文ServletContextInitializer[] initializersToUse = mergeInitializers(initializers);host.addChild(context);configureContext(context, initializersToUse);//配置context。没有重要逻辑
}

1.2.5. 创建tomcatWebServer封装对象

实例化TomcatWebServer、执行server的init方法

public TomcatWebServer(Tomcat tomcat, boolean autoStart, Shutdown shutdown) {Assert.notNull(tomcat, "Tomcat Server must not be null");this.tomcat = tomcat;this.autoStart = autoStart;this.gracefulShutdown = (shutdown == Shutdown.GRACEFUL) ? new GracefulShutdown(tomcat) : null;initialize();//启动server，执行start方法
}

1.2.5.1. 启动server，执行start方法

initialize();
//启动server，执行start方法
//这个初始化方法和原生tomcat的start方法一样
//值得注意的是，这里disableBindOnInit禁用了初始化时候绑定8080端口

//StandardEngine[Tomcat].StandardHost[localhost].TomcatEmbeddedContext[]
Context context = findContext();
context.addLifecycleListener((event) -> {if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {// Remove service connectors so that protocol binding doesn't// happen when the service is started.//当执行start context时候，会删除service中的connector，放到TomcatWebServer中removeServiceConnectors();}
});
//t禁用了初始化时候绑定8080端口
disableBindOnInit();// Start the server to trigger initialization listeners
this.tomcat.start();

我们重点看下TomcatEmbeddedContext的启动代码

// Call ServletContainerInitializers
for (Map.Entry<ServletContainerInitializer,Set<Class<?>>> entry : initializers.entrySet()) {try {//entry.getKey()，key = {TomcatStarter@6708}entry.getKey().onStartup(entry.getValue(), getServletContext());} catch (ServletException e) {log.error(sm.getString("standardContext.sciFail"), e);ok = false;break;}
}@Override
public void onStartup(Set<Class<?>> classes, ServletContext servletContext) throws ServletException {try {for (ServletContextInitializer initializer : this.initializers) {//initializer = {ServletWebServerApplicationContext$lambda@6808} initializer.onStartup(servletContext);}}catch (Exception ex) {}
}
//这个onStartup方法，正是context初始化的时候执行的，参考【## 1.2. 实例化webServer服务】标题
private void selfInitialize(ServletContext servletContext) throws ServletException {for (ServletContextInitializer beans : getServletContextInitializerBeans()) {//在beanFactory中匹配ServletContextInitializer类型的//beans = {DispatcherServletRegistrationBean@6931} "dispatcherServlet urls=[/]"beans.onStartup(servletContext);}
}//最终是创建了StandardWrapper并添加到context中
//servlet = {DispatcherServlet@6943}  这个就是最重要的DispatcherServlet，是在DispatcherServletAutoConfiguration类中创建的
wrapper = new StandardWrapper();
wrapper.setServletClass(servlet.getClass().getName());
wrapper.setServlet(servlet);

1.3. 注册tomcat bean生命周期WebServerStartStopLifecycle

getBeanFactory().registerSingleton("webServerStartStop", new WebServerStartStopLifecycle(this, this.webServer));
这个类WebServerStartStopLifecycle继承了Lifecycle

2. connector启动

上面分析过，执行context的启动时候，移除了connector，那么又是在哪一步启动的connector呢？

在springApplication.run.refreshContext.refresh.finishRefresh这一步中，connector启动。

// Propagate refresh to lifecycle processor first.
getLifecycleProcessor().onRefresh();
//onRefresh调用了startBeans
try {startBeans(true);
}private void startBeans(boolean autoStartupOnly) {Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();//beanFactory中匹配Lifecycle类型的bean//包含WebServerStartStopLifecyclelifecycleBeans.values().forEach(LifecycleGroup::start);
}//this = {TomcatWebServer@5764} 
public void start() throws WebServerException {addPreviouslyRemovedConnectors();
}private void addPreviouslyRemovedConnectors() {Service[] services = this.tomcat.getServer().findServices();for (Service service : services) {//service = {StandardService@6979} "StandardService[Tomcat]"Connector[] connectors = this.serviceConnectors.get(service);if (connectors != null) {for (Connector connector : connectors) {//connector = {Connector@7663} "Connector["http-nio-8080"]" 添加connector到serviceservice.addConnector(connector);}this.serviceConnectors.remove(service);}}
}//启动connector
public void addConnector(Connector connector) {connector.setService(this);connector.start();
}//绑定8080端口
bindWithCleanup();// Start poller thread
poller = new Poller();
Thread pollerThread = new Thread(poller, getName() + "-Poller");
pollerThread.setPriority(threadPriority);
pollerThread.setDaemon(true);
pollerThread.start();// Start acceptor thread
acceptor = new Acceptor<>(this);
String threadName = getName() + "-Acceptor";
acceptor.setThreadName(threadName);
Thread t = new Thread(acceptor, threadName);
t.setPriority(getAcceptorThreadPriority());
t.setDaemon(getDaemon());
t.start();

这里启动了2个线程执行nio模式。acceptor线程用于阻塞监听8080端口，获取到新连接socketChannel，存到tomcat的events事件队列；
poller线程用于循环读取events事件队列，获取新新连接socketChannel，最终通过Selector获取已准备好的channel，执行具体的controller逻辑。
详情请参考另一篇tomcat源码分析文章。

3. 内嵌tomcatEmbedded请求流程

到此内嵌tomcatEmbedded已经启动成功，接下来我们请求GET http://localhost:8080/test来分析一下执行流程。也和原生tomcat差不多。
我们从阻塞监听8080端口开始分析流程。

3.1. Acceptor获取新连接socketChannel

下面这个方法是sun.nio.ch.ServerSocketChannelImpl#implAccept源码java中的。

private int implAccept(FileDescriptor fd, FileDescriptor newfd, SocketAddress[] saa)throws IOException
{//此类实现 IP 套接字地址 （IP 地址 + 端口号）InetSocketAddress[] issa = new InetSocketAddress[1];//阻塞方法，是native方法，监听8080端口，直到有新连接请求int n = Net.accept(fd, newfd, issa);//我们调用[GET http://localhost:8080/test]后，代码继续执行if (n > 0) //n = 1saa[0] = issa[0];return n;
}//最终返回SocketChannelImpl对象
return new SocketChannelImpl(provider(), family, newfd, sa);//然后进入到NioEndpoint
endpoint.setSocketOptions(socket);//注册socketChannel到events
protected boolean setSocketOptions(SocketChannel socket) {NioChannel channel = new NioChannel();NioSocketWrapper newWrapper = new NioSocketWrapper(channel, this);channel.reset(socket, newWrapper);//注册poller.register(newWrapper);return true;
}public void register(final NioSocketWrapper socketWrapper) {socketWrapper.interestOps(SelectionKey.OP_READ);//读事件PollerEvent pollerEvent = createPollerEvent(socketWrapper, OP_REGISTER);//events = new SynchronizedQueue<>()events.offer(pollerEvent);
}

3.2. Poller消费SocketChannel

poller线程一直是死循环读取events，然后调用Processor协议的处理器

@Override
public void run() {while (true) {//读取eventsevents();Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();while (iterator != null && iterator.hasNext()) {SelectionKey sk = iterator.next();NioSocketWrapper socketWrapper = (NioSocketWrapper) sk.attachment();//调用协议的处理器processKey(sk, socketWrapper);}}
}//读取events
public boolean events() {PollerEvent pe = null;//遍历eventsfor (int i = 0, size = events.size(); i < size && (pe = events.poll()) != null; i++ ) {result = true;SocketChannel sc = socketWrapper.getSocket().getIOChannel();final SelectionKey key = sc.keyFor(getSelector());final NioSocketWrapper attachment = (NioSocketWrapper) key.attachment();//设置socketChannel为读或写事件int ops = key.interestOps() | interestOps;attachment.interestOps(ops);key.interestOps(ops);}
}//调用协议的处理器 {NioEndpoint$Poller@6539}
protected void processKey(SelectionKey sk, NioSocketWrapper socketWrapper) {if (sk.isReadable()) {//读，我们这里的[GET http://localhost:8080/test]请求是读事件processSocket(socketWrapper, SocketEvent.OPEN_READ, true)}if (sk.isWritable()) {processSocket(socketWrapper, SocketEvent.OPEN_WRITE, true)}
}//封装Runnable接口，异步处理socket请求
public boolean processSocket(SocketWrapperBase<S> socketWrapper, SocketEvent event, boolean dispatch) {SocketProcessorBase<S> sc = new SocketProcessor(socketWrapper, event);//Runnable接口实现类Executor executor = getExecutor();//异步执行executor.execute(sc);    
}@Override
public void run() {//getHandler() = {AbstractProtocol$ConnectionHandler@6630} getHandler().process(socketWrapper, event);
}//Http11Processor继续处理socket
if (status == SocketEvent.OPEN_READ) {state = service(socketWrapper);
}//下面这几个方法，看之前先了解一下tomcat组件的关系图
//【servlet封装成wrapper，wrapper添加到context，context是host的子容器，host属于engine，engine在service中，service是顶级容器server的子容器。】//getAdapter() = {CoyoteAdapter@8348} 
getAdapter().service(request, response);
//通过请求路径匹配对应的wrapper,根据[localhost:8080/test]匹配
//因为这里是内嵌的tomcat，匹配到了默认的StandardEngine[Tomcat].StandardHost[localhost].TomcatEmbeddedContext[].StandardWrapper[dispatcherServlet]
postParseSuccess = postParseRequest(req, request, res, response);
//engine
connector.getService().getContainer().getPipeline().getFirst().invoke(request, response);
//host
host.getPipeline().getFirst().invoke(request, response);
//context = {TomcatEmbeddedContext@8433}
context.getPipeline().getFirst().invoke(request, response);
//wrapper
wrapper.getPipeline().getFirst().invoke(request, response);
//过滤器，StandardWrapperValve里面调用了过滤器链
filterChain.doFilter(request.getRequest(), response.getResponse());
//filterChain = {ApplicationFilterChain@8496}//执行到最后一个过滤器后，再调用service，这里的servlet是 {DispatcherServlet@8470} 
servlet.service(request, response);//调用doGet方法
if (method.equals(METHOD_GET))doGet(req, resp);doService(request, response);
//所有的请求最终都走到了DispatcherServlet的doDispatch
doDispatch(request, response);

3.3. DispatcherServlet的doDispatch

这里会DispatcherServlet通过请求路径匹配对应的mappedHandler，然后调用Controller层逻辑并获取返回值，再把返回值封装到ModelAndView

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {//通过请求路径匹配对应的mappedHandlermappedHandler = getHandler(request);//mappedHandler = [cn.xxx.updownloadfile.contr.Controller#test()] 这个是我项目中自己的Controller层的类//再通过反射调用cn.xxx.updownloadfile.contr.Controller#test()方法，获取mv//如果是@ResponseBody修饰的，这个mv返回是空，如果没有这个注解，则返回对应的文件名称，例如返回"t.html"ModelAndView mv = mappedHandler.handle(processedRequest, response); //method.invoke(getBean(), args)//处理程序选择和处理程序调用的结果，即 ModelAndView//如果mv不是null，则会匹配项目中的对应文件，读取文件内容然后返回给前端，例如读取文件t.htmlprocessDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}