Spring webmvc啓動流程
本文將從spring容器啓動過程去分析springmvc源碼，首先我們思考一個問題：
web容器在啓動的時候是怎麼將bean解析並加載到spring容器中的，像我們自己如果要啓動容器，那是不是要new ApplicationContext(),並且把xml配置文件路徑或者包掃描路徑傳進去。那麼webmvc是怎麼解決這個問題的呢？
以tomcat爲例，我們的web應用程序是部署在tomcat的容器中的，那麼tomcat就爲我們的應用提供了一個全局的上下文環境，也就是ServletContext,spring的applicationContext最終也是注入到ServletContext當中的。我們在springmvc的開發過程中，在web.xml中經常會有如下配置：
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:application.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<servlet>
<servlet-name>dispatcherServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:mvc.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcherServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
web容器在啓動的時候會加載三個組件：listener >> filter >> servlet
而我們在web.xml中配置的一個很重要的listener就是ContextLoaderListener，這個監聽器實現了ServletContextListener，ServletContextListener它能夠監聽ServletContext對象的生命週期，也就是web應用的生命週期。在web容器啓動或者終止時會觸發ServletContextEvent事件，ServletContextListener監聽的就是這個事件，分別調用contextInitialized和contextDestroyed
也就是說容器啓動的時候會調用ContextLoaderListener的contextInitialized方法，ContextLoaderListener同時還繼承了ContextLoader
// 初始化web容器上下文
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}
轉到父類ContextLoader中的initWebApplicationContext，spring容器的初始化入口
// ContextLoader：
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
// 這些都忽略，往下看重點
if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
throw new IllegalStateException(
"Cannot initialize context because there is already a root application context present - " +
"check whether you have multiple ContextLoader* definitions in your web.xml!");
}
Log logger = LogFactory.getLog(ContextLoader.class);
servletContext.log("Initializing Spring root WebApplicationContext");
if (logger.isInfoEnabled()) {
logger.info("Root WebApplicationContext: initialization started");
}
long startTime = System.currentTimeMillis();
try {
// Store context in local instance variable, to guarantee that
// it is available on ServletContext shutdown.
if (this.context == null) {
// 這裏就是重點了，創建applicationContext,默認爲xmlWebApplicationContext
this.context = createWebApplicationContext(servletContext);
}
if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent ->
// determine parent for root web application context, if any.
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
// 重點，就是在這一步加載的spring 配置，
configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
// 在這裏將applicationContext注入到servletContext當中 servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
ClassLoader ccl = Thread.currentThread().getContextClassLoader();
if (ccl == ContextLoader.class.getClassLoader()) {
currentContext = this.context;
}
else if (ccl != null) {
currentContextPerThread.put(ccl, this.context);
}
if (logger.isDebugEnabled()) {
logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" +
WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
}
if (logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
}
return this.context;
}
catch (RuntimeException ex) {
logger.error("Context initialization failed", ex);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
throw ex;
}
catch (Error err) {
logger.error("Context initialization failed", err);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);
throw err;
}
}
我們看一下創建spring容器的過程：createWebApplicationContext(servletContext)
// ContextLoader：
protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
// 很明顯這裏決定了spring容器的類型
Class<?> contextClass = determineContextClass(sc);
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
}
return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
}
往下看determineContextClass的源碼：
// ContextLoader：390
protected Class<?> determineContextClass(ServletContext servletContext) {
// 默認的contextClass的名稱
String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
if (contextClassName != null) {
try {
return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load custom context class [" + contextClassName + "]", ex);
}
}
else {
// 從properties中獲取類名，接着看這個defaultStrategies是什麼時候賦值的
contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
try {
return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load default context class [" + contextClassName + "]", ex);
}
}
}
static {
// Load default strategy implementations from properties file.
// This is currently strictly internal and not meant to be customized
// by application developers.
try {
// 從DEFAULT_STRATEGIES_PATH獲取到資源
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
// 就是在這裏對 defaultStrategies進行的初始化
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
}
}
我們可以看到是從DEFAULT_STRATEGIES_PATH這個路徑獲取到的類名配置
private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";
這個ContextLoader.properties其實就是在spring-web中org.springframework.web.context.ContextLoader的同級目錄下：
可以看到webmvc默認創建容器的實現類就是XmlWebApplicationContext，最後通過反射獲取實例
至此spring容器已創建，下面bean的初始化configureAndRefreshWebApplicationContext
// ContextLoader：413
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
wac.setServletContext(sc);
// 這一步得到了web.xml中設置的<param-name>：contextConfigLocation，即spring配置文件路徑
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
// contextConfigLocation賦值
wac.setConfigLocation(configLocationParam);
}
// The wac environment's #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
// 初始化spirng環境
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
}
customizeContext(sc, wac);
// 重點，spring的bean加載，實例化等相關操作都在這裏了
wac.refresh();
}
在這裏把web.xml中配置的contextConfigLocation參數傳給了applicationContext。最後是spring真正初始化的地方：wac.refresh();
// AbstractApplicationContext：509
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
這裏涉及spring初始化過程的代碼比較複雜，就不在此文中敘述了。下面開始探討DispatcherServlet
DispatcherServlet
在開始分析DispatcherServlet之前，我們看一下springmvc的整個流程
接着分析DispatcherServlet
<servlet>
<servlet-name>dispatcherServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:mvc.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcherServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
在web.xml中配置的DispatcherServlet是springmvc的核心組件，接收到的請求都交由DispatcherServlet來處理。web容器在加載完listener後filter之後，會根據load-on-startup指定的級別開始初始化servlet，並調用其init()方法
從上面的類圖我們可以看到，DispatcherServlet實現了Servlet接口，Servlet中提供了初始化方法：init()，其具體實現在DispatcherServlet繼承的HttpServletBean中
// servlet >> HttpServletBean
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
// 獲取servlet初始化配置參數
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}
// 重點是這裏，初始化servlet實例
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}
繼續看初始化servlet的過程：initServletBean，其具體實現在FrameworkServlet中
// FrameworkServlet
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
if (this.logger.isInfoEnabled()) {
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
}
long startTime = System.currentTimeMillis();
try {
// 重點，初始化webapplicationContext
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
......
}
這裏又看到了initWebApplicationContext，是不是很眼熟，我們進入到initWebApplicationContext中
// FrameworkServlet:522
protected WebApplicationContext initWebApplicationContext() {
// 由於我們配置了ContextLoaderListener，前面創建xmlWebApplicationContext的時候已經給
// rootContext注入了值，這裏就是從servletContext當中獲取之前的根上下文
// 如果沒有配置ContextLoaderListener，那麼此處的rootContext爲null，不過不影響springmvc，我們接着往下看
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
// dispatcher在初始化的時候會建立自己的IOC上下文，
// 用來存儲springmvc相關的bean，在創建之前，
// 要判斷一下servlet的上下文中是否已經存在webApplicationContext
// 這個時候dispatcher的webApplicationContext還是null，所以默認情況不會走這個分支
if (this.webApplicationContext != null) {
// 如果存在那就直接拿來用
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// 將之前的根上下文作爲自己的parent
cwac.setParent(rootContext);
}
// 初始化applicationContext
configureAndRefreshWebApplicationContext(cwac);
}
}
}
// 因爲wac還是null，所以會進入到這個分支
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context.
// 去servlet的上下文中找是否已經存在webApplicationContext
wac = findWebApplicationContext();
}
// 上述都找不到，所以會進到這裏
if (wac == null) {
// 重點，創建自己的WebApplicationContext
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
// refreshed -> trigger initial onRefresh manually here.
onRefresh(wac);
}
// 將dispatcher創建的WebApplicationContext注入到servletContext中
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}
return wac;
}
我們再轉到createWebApplicationContext，前面分析listener創建springioc容器時候，也有調用類似方法
// FrameworkServlet:614
protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
// 獲取class對象，這裏也是XmlWebApplicationContext
Class<?> contextClass = getContextClass();
if (this.logger.isDebugEnabled()) {
this.logger.debug("Servlet with name '" + getServletName() +
"' will try to create custom WebApplicationContext context of class '" +
contextClass.getName() + "'" + ", using parent context [" + parent + "]");
}
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException(
"Fatal initialization error in servlet with name '" + getServletName() +
"': custom WebApplicationContext class [" + contextClass.getName() +
"] is not of type ConfigurableWebApplicationContext");
}
// 通過反射實例化XmlWebApplicationContext
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
// 設置spring環境
wac.setEnvironment(getEnvironment());
// 將從servletContext中獲取的跟上下文作爲自己的parent
wac.setParent(parent);
// 設置我們在web.xml中dispatcherServlet節點下配置的<param-name>contextConfigLocation，本文中配置的是mvc.xml
wac.setConfigLocation(getContextConfigLocation());
// 這裏最終還是調用refresh，進行springmvc相關bean加載和初始化等工作，前面已經說過了，這裏不再說
configureAndRefreshWebApplicationContext(wac);
return wac;
}
這裏最終是調用configureAndRefreshWebApplicationContext，又到了這個熟悉的方法，繼續跟進
// FrameworkServlet：639
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
.......
postProcessWebApplicationContext(wac);
applyInitializers(wac);
// 在這裏初始化
wac.refresh();
}
// 接口
void refresh() throws BeansException, IllegalStateException;
接着追蹤wac.refresh()的具體實現
// AbstractApplicationContext：509
public void refresh() throws BeansException, IllegalStateException {
// 先來個鎖，不然容器還沒refresh，你又啓動個容器，那不得炸了，要知道是可以啓動多個容器的
synchronized (this.startupShutdownMonitor) {
// 記錄下容器啓動時間，標記爲“已啓動”
prepareRefresh();
// 這一步針對不同方式注入採取不同實現
// 如果是xml方式，是在這一步初始化beanfactory，解析xml配置文件得到bean定義，
// 掃描@component,@service,@repository，完成bean註冊
// 如果爲annotation方式，在執行refresh之前就已經完成了BeanFactory的初始化
// 和Bean容器註冊，此時裏面的邏輯是非常簡單的，我們進去看看
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 設置beanfactory的類加載器
prepareBeanFactory(beanFactory);
try {
// Bean如果實現了BeanFactoryPostProcessor，容器在初始化以後會調用postProcessBeanFactory方法，並且子類可以對這步進行擴展
postProcessBeanFactory(beanFactory);
// 調用BeanFactoryPostProcessor實現類的postProcessBeanFactory回調
invokeBeanFactoryPostProcessors(beanFactory);
// 註冊BeanPostProcessor實現類
registerBeanPostProcessors(beanFactory);
// 初始化MessageSource，國際化
initMessageSource();
// 初始化事件廣播器
initApplicationEventMulticaster();
// 模版方法，子類可以在這一步初始化一些bean
onRefresh();
// 註冊監聽器（實現ApplicationListener）
registerListeners();
// 實例化所有非懶加載的singleton benas
finishBeanFactoryInitialization(beanFactory);
// 初始化完成廣播事件
finishRefresh();
}
......
}
}
這裏又到了spring的最核心的方法：refresh()，這個方法裏有一個比較重要的步驟： obtainFreshBeanFactory()，我們在mvc相關的配置文件中配置的<context:component-scan>，就是一步通過解析xml拿到掃描路徑的。經過一系列的調用鏈路，會調用doScan，傳入包掃描路徑，將@component,@service,@repository這些註解標識的類註冊到spring ioc容器。
<context:component-scan base-package="com.cf.spring.code"></context:component-scan>
spring完成bean註冊後，會在finishBeanFactoryInitialization這一步統一完成bean的實例化。spring容器的bean初始化完成後最還有一個廣播事件：finishRefresh()：
經過一系列的調用鏈路
AbstractApplicationContext.finishRefresh()
>> AbstractApplicationContext.publishEvent(new ContextRefreshedEvent(this)) //向所有監聽者發佈容器刷新事件>> FrameworkServlet.onApplicationEvent(ContextRefreshedEvent event) //接收到容器刷新事件，調用DispatcherServlet的onRefresh
>> DispatcherServlet.onRefresh()
最終會調用DispatcherServlet的onRefresh()方法,而onRefresh()裏就一行代碼，真正幹實事的是initStrategies
// DispatcherServlet
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
// springmvc組件一系列初始化操作
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
// 初始化handlerMapping
initHandlerMappings(context);
// 初始化HandlerAdapters
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
// 初始化視圖解析器
initViewResolvers(context);
initFlashMapManager(context);
}
DispatcherServlet的initStrategies完成了springmvc組件的一系列初始化操作，也就是說springmvc組件在DispatcherServlet初始化自己的上下文（webApplicationContext）的時候就已經實例化完成了。
至此我們已經知道springmvc是怎麼加載bean並完成初始化的流程，接下來分析一波dispatcherServlet如何處理請求。
DispatcherServlet繼承了HttpServlet，servlet處理請求最核心的方法就是service()方法,但是在DispatcherServlet的父類FrameworkServlet中重寫了service方法：
// FrameworkServlet
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
// 判斷是不是patch的請求方式
if (HttpMethod.PATCH == httpMethod || httpMethod == null) {
processRequest(request, response);
}
// 如果不是patch的請求方式，調用父類的service方法，最終還是會調用本類中的doGet和doPost方法
else {
super.service(request, response);
}
}
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
protected final void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
不管是doPost還是doGet，都 會調用processRequest(request, response)方法
// FrameworkServlet
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
......
try {
// 這裏纔是重點，別的都略過，跟進去
doService(request, response);
}
catch (ServletException ex) {
failureCause = ex;
throw ex;
}
......
publishRequestHandledEvent(request, response, startTime, failureCause);
}
}
這裏的doService是abstract的，其實現是在DipatcherServlet中
// DipatcherServlet
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
......
try {
// 繼續，跟進
doDispatch(request, response);
}
......
}
終於到了SpringMvc最核心的代碼：doDispatch
// DipatcherServlet
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
// 請求對象
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;//定義ModelAndView
Exception dispatchException = null;
try {
// 判斷是否上傳文件請求
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 通過當前request對象獲取handler，handler是什麼？就是指處理器（像controller）
// 下面重點分析一下handler獲取的過程
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// 獲取對應的handlerAdapter.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 真正執行handle
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
// 如果沒有返回視圖，則使用默認的
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
// 處理返回結果
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
處理請求時首先會根據當前的request獲取一個handler
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// 遍歷handlerMappings
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
// 找到具體handler
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// 真正獲取handler
Object handler = getHandlerInternal(request);
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
// 獲取handler執行鏈
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
spring會遍歷handlerMappings，詢問每一個HandlerMapping，有沒有我要的控制器，最終返回了HandlerExecutionChain
接着追蹤下getHandlerInternal，以AbstractUrlHandlerMapping爲例，分析一下根據url獲取handler
// AbstractUrlHandlerMapping
protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
// url路徑
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
// 尋找handler，就是這裏了，我們接着往下看
Object handler = lookupHandler(lookupPath, request);
......
return handler;
}
protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
// handlerMap這是一個LinkedHashMap<String, Object>，鍵值爲url，value爲controller實例
// 這裏通過url從map中 獲取到真正執行業務的controller的實例（handler）
Object handler = this.handlerMap.get(urlPath);
if (handler != null) {
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
validateHandler(handler, request);
return buildPathExposingHandler(handler, urlPath, urlPath, null);
}
return buildPathExposingHandler(handler, urlPath, urlPath, null);
......
}
我們繼續看下一個關鍵步驟getHandlerAdapter(mappedHandler.getHandler()
// DipatcherServlet
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
......
// 獲取適配器
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
......
}
接着看獲取適配器的步驟
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
for (HandlerAdapter ha : this.handlerAdapters) {
if (logger.isTraceEnabled()) {
logger.trace("Testing handler adapter [" + ha + "]");
}
if (ha.supports(handler)) {
return ha;
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
在這裏根據handler匹配合適的適配器，接着往下看.applyPreHandle(processedRequest, response)
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
......
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
......
}
}
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
在applyPreHandle這一步調用了一系列攔截器的preHandle方法，接下來就是去執行handle
// 正在的執行handle
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
找到handle方法的具體實現
// AnnotationMethodHandlerAdapter
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
// 獲取controller的class對象
Class<?> clazz = ClassUtils.getUserClass(handler);
Boolean annotatedWithSessionAttributes = this.sessionAnnotatedClassesCache.get(clazz);
if (annotatedWithSessionAttributes == null) {
annotatedWithSessionAttributes = (AnnotationUtils.findAnnotation(clazz, SessionAttributes.class) != null);
this.sessionAnnotatedClassesCache.put(clazz, annotatedWithSessionAttributes);
}
if (annotatedWithSessionAttributes) {
checkAndPrepare(request, response, this.cacheSecondsForSessionAttributeHandlers, true);
}
else {
checkAndPrepare(request, response, true);
}
// Execute invokeHandlerMethod in synchronized block if required.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
return invokeHandlerMethod(request, response, handler);
}
}
}
// 這裏纔是執行controller對應方法的地方，繼續看
return invokeHandlerMethod(request, response, handler);
}
protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
ServletHandlerMethodResolver methodResolver = getMethodResolver(handler);
// 獲取到要執行的方法對象
Method handlerMethod = methodResolver.resolveHandlerMethod(request);
ServletHandlerMethodInvoker methodInvoker = new ServletHandlerMethodInvoker(methodResolver);
ServletWebRequest webRequest = new ServletWebRequest(request, response);
ExtendedModelMap implicitModel = new BindingAwareModelMap();
// 通過反射執行url對應controller中的方法
Object result = methodInvoker.invokeHandlerMethod(handlerMethod, handler, webRequest, implicitModel);
// 獲取modelAndView
ModelAndView mav =
methodInvoker.getModelAndView(handlerMethod, handler.getClass(), result, implicitModel, webRequest);
methodInvoker.updateModelAttributes(handler, (mav != null ? mav.getModel() : null), implicitModel, webRequest);
return mav;
}
到這裏已經執行完url對應controller方法中的業務邏輯，並且返回了modelAndView