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：）