SpringMVC如何从请求中分发解析视图
首先了解SpringMVC的9大组件
// 文件解析
/** MultipartResolver used by this servlet. */
@Nullable
private MultipartResolver multipartResolver;
// 国际化解析
/** LocaleResolver used by this servlet. */
@Nullable
private LocaleResolver localeResolver;
// 主题解析器
/** ThemeResolver used by this servlet. */
@Nullable
private ThemeResolver themeResolver;
// 映射表
/** List of HandlerMappings used by this servlet. */
@Nullable
private List<HandlerMapping> handlerMappings;
// 适配器表
/** List of HandlerAdapters used by this servlet. */
@Nullable
private List<HandlerAdapter> handlerAdapters;
// 异常处理
/** List of HandlerExceptionResolvers used by this servlet. */
@Nullable
private List<HandlerExceptionResolver> handlerExceptionResolvers;
//请求转视图名
/** RequestToViewNameTranslator used by this servlet. */
@Nullable
private RequestToViewNameTranslator viewNameTranslator;
// 重定向数据
/** FlashMapManager used by this servlet. */
@Nullable
private FlashMapManager flashMapManager;
// 视图解析器
/** List of ViewResolvers used by this servlet. */
@Nullable
private List<ViewResolver> viewResolvers;
1. 收到htttp请求
2. 过滤请求 包含一系列的过滤 一般都是dofilter方法
3. 通过DispatchSerlet.class来处理请求(核心类)
4. 根据请求利用handleMappings找到应该处理的Controller以及目标方法
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
如何找到的呢?
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
for (HandlerMapping mapping : this.handlerMappings) {
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
很简单的遍历所有的HandlerMapping
在初始化HandlerMapping的过程中,至少有一个handlerMapping
// handlerMappings的初始化
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
if (this.detectAllHandlerMappings) {
// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList<>(matchingBeans.values());
// We keep HandlerMappings in sorted order.
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.
}
}
// Ensure we have at least one HandlerMapping, by registering
// a default HandlerMapping if no other mappings are found.
if (this.handlerMappings == null) {
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}
5. 根据handler选择合适的handlerAdapter
// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
6. 执行目标方法并生成ModelAndView
适配器
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
测试对于POJO,String 类型实际上只有返回值那么 此时的mav = null;
7.根据ModelAndView返回结果
有视图render视图,没有就跳过装载视图
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
流程图如下
DispatcherServlet核心方法dodispatch:
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
// 是否为文件上传
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 找到处理这个请求的Controller
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
// 没有找到处理的Controller准备返回
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// 处理适配器
// Determine handler adapter for the current request.
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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 生成ModelAndView (最最最核心的部分)
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
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);
}
// 渲染ModelAndView 到页面
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);
}
}
}
}
结果
显然SpringMVC 使用了适配器模式
根据不同的方法执行选择不同的类