关于springmvc核心控制器DispatcherServlet的个人心得
一、DispatcherServlet的源码分析
从继承树关系可以看出DispatcherServlet继承自HttpServlet,所以这个类也满足init-service-destroy三阶段，下面就进入源码分析
1.1、关于init()源码的分析，因为DispatcherServlet继承自FrameWorkServlet;FrameWorkServlet又继承自HttpServletBean,而DispatcherServlet和FrameWorkServlet并没有覆写init()方法，所以直接调用基类HttpServletBean中的init()方法，源码如下
@Override
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
// 使用ServletConfig获取web.xml中的配置信息，然后使用静态内部类进行封装，getServletConfig()此方法来自GenericServlet
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
//利用BeanWrapper 完成DispatcherServlet的构造，forBeanPropertyAccess()会对this进行充分判定然后创建BeanWrapper
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
//获取servletContext后创建ResourceLoader
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
//用linkedMap以Resource.class为key,ResourceEditor为value存储后注册到BeanWrapper 中
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;
}
}
// 初始化ServletBean,此方法被FrameWorkSerlvet覆写
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}
1.2、FrameWorkServlet中的initServletBean()方法源码
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
try {
//初始化SpringMvc中的Ioc容器
this.webApplicationContext = initWebApplicationContext();
//此方法还未实现内容
initFrameworkServlet();
}
catch (ServletException ex) {
}
catch (RuntimeException ex) {
}
}
1.3、初始化springMvc ioc容器的源码initWebApplicationContext()
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// 此时ServletContext还未刷新，设置上下文全局设置等等
if (cwac.getParent() == null) {
cwac.setParent(rootContext);
}
//配置此ioc容器的各种配置，比如Servletcontext,Servletconfig...
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
//不存在时去到ServletContext中寻找已存在的容器
wac = findWebApplicationContext();
}
if (wac == null) {
// 没有找到就创建
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
//刷新上下文
onRefresh(wac);
}
if (this.publishContext) {
//发布此容器到ServletContext中
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;
}
1.4、DispatcherServlet已覆写的onRefresh()源码
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);//初始化handlerMapping
initHandlerAdapters(context);//初始化handlerAdapter
initHandlerExceptionResolvers(context);//和handlermapping流程相似
initRequestToViewNameTranslator(context);
initViewResolvers(context);//和handlermapping流程相似
initFlashMapManager(context);
}
1.5、初始化handlerMapping源码
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
if (this.detectAllHandlerMappings) {
// 从全局上下文中获取所有的handlermapping
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
// 按照特定顺序存放HanderMapping
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
else {
try {
HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
this.handlerMappings = Collections.singletonList(hm);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, we'll add a default HandlerMapping later.
}
}
if (this.handlerMappings == null) {
//使用默认handlerMapping
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isDebugEnabled()) {
logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
}
}
}
1.6、初始化handlerAdapter源码
private void initHandlerAdapters(ApplicationContext context) {
this.handlerAdapters = null;
if (this.detectAllHandlerAdapters) {
// 全局获取handlerAdapter
Map<String, HandlerAdapter> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerAdapters = new ArrayList<HandlerAdapter>(matchingBeans.values());
// 按照特定顺序排序
AnnotationAwareOrderComparator.sort(this.handlerAdapters);
}
}
else {
try {
HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
this.handlerAdapters = Collections.singletonList(ha);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, we'll add a default HandlerAdapter later.
}
}
if (this.handlerAdapters == null) {
//使用默认handlerAdapter
this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
if (logger.isDebugEnabled()) {
logger.debug("No HandlerAdapters found in servlet '" + getServletName() + "': using default");
}
}
}
二 、springMvc处理请求
2.1、这也是面试时很容易被问到的问题，首先最常用的是doGet和doPost方法，而这两个方法DispatcherServlet并没有覆写，而是执行父类FrameWorkServlet的这两个方法，因为doGet和doPost类似所以只展示doGet以下是源码
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
//获取本次请求的相应配置
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
LocaleContext localeContext = buildLocaleContext(request);
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
initContextHolders(request, localeContext, requestAttributes);
try {
doService(request, response);//核心方法，调用DispatcherServlet中的doService()方法
}
catch (ServletException ex) {
failureCause = ex;
throw ex;
}
catch (IOException ex) {
failureCause = ex;
throw ex;
}
catch (Throwable ex) {
failureCause = ex;
throw new NestedServletException("Request processing failed", ex);
}
finally {
resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}
if (logger.isDebugEnabled()) {
if (failureCause != null) {
this.logger.debug("Could not complete request", failureCause);
}
else {
if (asyncManager.isConcurrentHandlingStarted()) {
logger.debug("Leaving response open for concurrent processing");
}
else {
this.logger.debug("Successfully completed request");
}
}
}
publishRequestHandledEvent(request, response, startTime, failureCause);
}
}
2.2、doService源码
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (logger.isDebugEnabled()) {
String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
" processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
}
//保存request中的原始属性，防止有包含的信息丢失
Map<String, Object> attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
attributesSnapshot = new HashMap<String, Object>();
Enumeration<?> attrNames = request.getAttributeNames();
while (attrNames.hasMoreElements()) {
String attrName = (String) attrNames.nextElement();
if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
}
// 放置本次请求所需要的资源
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
if (inputFlashMap != null) {
request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
}
request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
try {
doDispatch(request, response);//DispatcherServlet的核心方法
}
finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);//重新把快照属性存储进request
}
}
}
}
2.3、Dispatcherservlet中doDispatch()方法的源码
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
// 获取当前请求的WebAsyncManager，底层中若未找到就会创建
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);//检查是否是Multipart请求，如果是就转换为Multipart请求类型
multipartRequestParsed = (processedRequest != request);
// 根据当前请求获取对应的HandlerMapping,找到与当前request对应的handler,并一起和拦截器封装到HandlerExecutionChain 对象中
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// 遍历所有handlerAdapter.找到可以执行当前求情的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;
}
}
//遍历拦截器，执行它们的 preHandle() 方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
//处理实际的业务
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
// 遍历拦截器，执行它们的 postHandle() 方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
dispatchException = new NestedServletException("Handler dispatch failed", err);
}//清空请求属性，对处理结果进行渲染
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) {// 遍历拦截器，执行它们的 afterConcurrentHandlingStarted() 方法
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
三、总结
大致流程就可以按此代码流程进行说明啦，当然感兴趣的小伙伴还阔以针对其他方法进行深入的学习，对了，此源码来源spring-webmvc-4.3.12;
虽然早早建了账号，但是今天终于下决心开始写我的第一篇博客啦，记录一些日常心得和不足之处，写的不好，望请伙伴多多指教，谢谢大家。