Spring MVC介绍(一)之 Spring MVC体系结构与执行流程
Spring MVC是Spring的一个模块,包含Web MVC、Framework,Web Views,JSP等等。
其中MVC分别对应:Model,View,Controller,本质上SpirngMVC还是使用Servlet进行处理,并在其基础上进行了封装,简化了开发流程,提高易用性,并使得逻辑结构变得非常清晰。
Spring MVC对比Servlet简化开发流程的方面有:
- 基于注解的url映射
- http表单参数转换
- 全局统一异常处理
- 拦截器的实现
等等。
Spring MVC 体系结构
HandlerMapping : url与控制器的映射
package org.springframework.web.servlet;
import javax.servlet.http.HttpServletRequest;
public interface HandlerMapping {
String PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE = HandlerMapping.class.getName() + ".pathWithinHandlerMapping";
String BEST_MATCHING_PATTERN_ATTRIBUTE = HandlerMapping.class.getName() + ".bestMatchingPattern";
String INTROSPECT_TYPE_LEVEL_MAPPING = HandlerMapping.class.getName() + ".introspectTypeLevelMapping";
String URI_TEMPLATE_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".uriTemplateVariables";
String MATRIX_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".matrixVariables";
String PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE = HandlerMapping.class.getName() + ".producibleMediaTypes";
HandlerExecutionChain getHandler(HttpServletRequest var1) throws Exception;
}
HandlerAdapter : 控制器与执行适配器
package org.springframework.web.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public interface HandlerAdapter {
boolean supports(Object var1);
ModelAndView handle(HttpServletRequest var1, HttpServletResponse var2, Object var3) throws Exception;
long getLastModified(HttpServletRequest var1, Object var2);
}
ViewResolver : 视图仓库
package org.springframework.web.servlet;
import java.util.Locale;
public interface ViewResolver {
View resolveViewName(String var1, Locale var2) throws Exception;
}
View : 视图
package org.springframework.web.servlet;
import java.util.Map;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public interface View {
String RESPONSE_STATUS_ATTRIBUTE = View.class.getName() + ".responseStatus";
String PATH_VARIABLES = View.class.getName() + ".pathVariables";
String SELECTED_CONTENT_TYPE = View.class.getName() + ".selectedContentType";
String getContentType();
void render(Map var1, HttpServletRequest var2, HttpServletResponse var3) throws Exception;
}
HandlerExceptionResolver : 异常捕捉器
package org.springframework.web.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public interface HandlerExceptionResolver {
ModelAndView resolveException(HttpServletRequest var1, HttpServletResponse var2, Object var3, Exception var4);
}
HandlerInterceptor : 拦截器
package org.springframework.web.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public interface HandlerInterceptor {
boolean preHandle(HttpServletRequest var1, HttpServletResponse var2, Object var3) throws Exception;
void postHandle(HttpServletRequest var1, HttpServletResponse var2, Object var3, ModelAndView var4) throws Exception;
void afterCompletion(HttpServletRequest var1, HttpServletResponse var2, Object var3, Exception var4) throws Exception;
}
Spring MVC 执行流程
先看个简单的demo
web.xml
spring-mvc
dispatcherServlet
org.springframework.web.servlet.DispatcherServlet
contextConfigLocation
classpath:/spring-mvc.xml
dispatcherServlet
/
/index.jsp
spring-mvc.xml
simple
userView.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
userView
${name}
SimpleControl.java
package com.demo.spring.mvc.control;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* com.demo.spring.mvc.control
*
* @author Zyy
* @date 2019/2/20 22:47
*/
public class SimpleControl implements Controller {
@Override
public ModelAndView handleRequest(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
ModelAndView modelAndView = new ModelAndView("userView");
modelAndView.addObject("name","ayang");
return modelAndView;
}
}
启动后访问localhost:8080/hello.do 就可以显示我们jsp中我们返回的name了。
整个mvc流程如下:
浏览器访问/hello.do -> 请求dispatcher servlet -> 然后找到SimpleUrlHandlerMapping
-> 然后根据配置找到/hello.do对应simple ref -> 然后根据simple ref找到
simple这个control bean -> 然后根据control会找到对应的适配器SimpleControllerHandlerAdapter
-> 基于适配器执行业务处理 -> 然后返回给dispatcher Servlet -> 然后找到视图仓库InternalResourceViewResolver ->
然后视图仓库根据viewName找到对应的视图解析JstlView ->然后返回给view
Spring MVC 体系结构UML
从上图可以看出,其中最主要的就是DispatcherServlet,看一下相关的源码。
org.springframework.web.servlet.DispatcherServlet
核心的方法:
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
try {
ModelAndView mv = null;
Object dispatchException = null;
try {
processedRequest = this.checkMultipart(request);
multipartRequestParsed = processedRequest != request;
//获取mappedHandler
mappedHandler = this.getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
this.noHandlerFound(processedRequest, response);
return;
}
//根据handler获取HandlerAdapter
HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (this.logger.isDebugEnabled()) {
this.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;
}
//HandlerAdapter找到我们配置的SimpleControllerHandlerAdapter,
//然后由此找到我们自己的SimpleControl
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
this.applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
} catch (Exception var20) {
dispatchException = var20;
} catch (Throwable var21) {
dispatchException = new NestedServletException("Handler dispatch failed", var21);
}
this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
} catch (Exception var22) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22);
} catch (Throwable var23) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23));
}
} finally {
if (asyncManager.isConcurrentHandlingStarted()) {
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
} else if (multipartRequestParsed) {
this.cleanupMultipart(processedRequest);
}
}
}
其中首先根据request进行getHandler(HttpServletRequest request) 方法,返回一个HandlerExecutionChain ,方法是遍历 handlerMappings,然后从handlerMappings中获取HandlerExecutionChain,相关代码如下:
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Iterator var2 = this.handlerMappings.iterator();
HandlerExecutionChain handler;
do {
if (!var2.hasNext()) {
return null;
}
HandlerMapping hm = (HandlerMapping)var2.next();
if (this.logger.isTraceEnabled()) {
this.logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name '" + this.getServletName() + "'");
}
handler = hm.getHandler(request);
} while(handler == null);
return handler;
}
上面方法中 HandlerMapping.getHandler(request) 源码如下:
org.springframework.web.servlet.handler.AbstractHandlerMapping#getHandler
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Object handler = this.getHandlerInternal(request);
if (handler == null) {
handler = this.getDefaultHandler();
}
if (handler == null) {
return null;
} else {
if (handler instanceof String) {
String handlerName = (String)handler;
handler = this.getApplicationContext().getBean(handlerName);
}
HandlerExecutionChain executionChain = this.getHandlerExecutionChain(handler, request);
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = this.getCorsConfiguration(handler, request);
CorsConfiguration config = globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig;
executionChain = this.getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
}
上面方法中 getHandlerExecutionChain(handler, request) 源码如下:
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
HandlerExecutionChain chain = handler instanceof HandlerExecutionChain ? (HandlerExecutionChain)handler : new HandlerExecutionChain(handler);
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
Iterator var5 = this.adaptedInterceptors.iterator();
while(var5.hasNext()) {
HandlerInterceptor interceptor = (HandlerInterceptor)var5.next();
if (interceptor instanceof MappedInterceptor) {
MappedInterceptor mappedInterceptor = (MappedInterceptor)interceptor;
if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
} else {
chain.addInterceptor(interceptor);
}
}
return chain;
}
继续回到doDispatch,根据获取到的handler进行继续获取适配器,方法:getHandlerAdapter 相关源码如下:
org.springframework.web.servlet.DispatcherServlet#getHandlerAdapter
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
Iterator var2 = this.handlerAdapters.iterator();
HandlerAdapter ha;
do {
if (!var2.hasNext()) {
throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
ha = (HandlerAdapter)var2.next();
if (this.logger.isTraceEnabled()) {
this.logger.trace("Testing handler adapter [" + ha + "]");
}
} while(!ha.supports(handler));
return ha;
}
回去到适配器之后,做handle处理,相关方法:
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter#handle
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
return ((Controller)handler).handleRequest(request, response);
}
其中 handleRequest(request, response) 的实现方法就是我们自己写的SimpleControl中的handleRequest方法:
@Override
public ModelAndView handleRequest(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
ModelAndView modelAndView = new ModelAndView("userView");
modelAndView.addObject("name","ayang");
return modelAndView;
}
handleRequest 处理完成之后,就会返回一个ModelAndView,接下来会用到resolveViewName,由viewName来获取到view,然后 view 再进行解析,相关源码如下:
org.springframework.web.servlet.DispatcherServlet#resolveViewName
protected View resolveViewName(String viewName, Map model, Locale locale, HttpServletRequest request) throws Exception {
Iterator var5 = this.viewResolvers.iterator();
View view;
do {
if (!var5.hasNext()) {
return null;
}
ViewResolver viewResolver = (ViewResolver)var5.next();
view = viewResolver.resolveViewName(viewName, locale);
} while(view == null);
return view;
}
整个 mvc 执行流程如下:
dispatcherServlet -> handlermapping ->基于url查找handler -> handlerAdapter
-> 基于handler找到adapter -> 由adapter找到我们的 handler -> 执行业务处理返回 modelAndView
-> viewResolver -> 基于viweName找到view -> 执行视图解析 -> 返回前端
欢迎留言交流:)