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执行流程.png
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<String, ?> 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
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
id="WebApp_ID" version="3.0">
<display-name>spring-mvc</display-name>
<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:/spring-mvc.xml
</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>dispatcherServlet</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>/index.jsp</welcome-file>
</welcome-file-list>
</web-app>
spring-mvc.xml
<?xml version="1.0" encoding="GBK"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd">
<bean id="simple" class="com.demo.spring.mvc.control.SimpleControl"></bean>
<bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="urlMap">
<props>
<prop key="/hello.do">simple</prop>
</props>
</property>
</bean>
<bean class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter"></bean>
<!-- 视图仓库 -->
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/page/"/>
<property name="suffix" value=".jsp"/>
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
</bean>
</beans>
userView.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>userView</title>
</head>
<body>
${name}
</body>
</html>
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
Spirng MVC 体系结构UML.png
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<String, Object> 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：）