深入探讨 Spring MVC 的执行流程

Spring MVC介绍（二）之 Spring MVC 执行流程解析

一、MVC组件执行流程

回顾一下MVC的体系结构与组件执行流程，如下图：

Spring MVC组件执行流程.png

    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

再来看一个例子，基于beanNameHandlerMapper的示例：

BeanNameControl.java

    package com.demo.spring.mvc.control;
    
    import org.springframework.web.HttpRequestHandler;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    /**
     * com.demo.spring.mvc.control
     *
     * @author Zyy
     * @date 2019/2/24 15:34
     */
    public class BeanNameControl implements HttpRequestHandler {
        @Override
        public void handleRequest(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws ServletException, IOException {
            httpServletResponse.getWriter().println("BeanName Control");
        }
    }

spring-mvc_beanName.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="/beanName" class="com.demo.spring.mvc.control.BeanNameControl"></bean>
    
    
    </beans>

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_beanName.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>

此时启动容器，访问 http://localhost:8080/spring_mvc/beanName ，可以看到显示的是我们control返回的数据。

    BeanName Control

我们在此之前未配置 HandlerMapping、HandlerAdapter、InternalResourceViewResolver ，为何还是能找到呢？原因是因为spring有个默认的配置：

路径如下：

    org\springframework\spring-webmvc\4.3.8.RELEASE\spring-webmvc-4.3.8.RELEASE.jar!\org\springframework\web\servlet\DispatcherServlet.properties

DispatcherServlet.properties

    # Default implementation classes for DispatcherServlet's strategy interfaces.
    # Used as fallback when no matching beans are found in the DispatcherServlet context.
    # Not meant to be customized by application developers.
    
    org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver
    
    org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver
    
    org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
        org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping
    
    org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
        org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
        org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter
    
    org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\
        org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
        org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver
    
    org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator
    
    org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver
    
    org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

在这里面可以看到：

    BeanNameUrlHandlerMapping
    HttpRequestHandlerAdapter
    InternalResourceViewResolver

由此我们知道，spring有一套默认的mvc处理实现。

二、HandlerMapping

HandlerMapping为mvc中url路径与control对象的映射，dispatcherServlet就是基于handlerMapping组件来寻找对应的control，找不到时会抛出异常 noHandlerFound异常。

HandlerMapping.java

    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;
    }

其实现类，如下：

handlerMapping实现类.png

目前大部分使用其中三种：

1、 org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping ：

基于bean name查找，在xml以“/”开头

    <bean id="/beanName" class="com.demo.spring.mvc.control.BeanNameControl"></bean>

2、 org.springframework.web.servlet.handler.SimpleUrlHandlerMapping

手动在xml中配置url与control映射

    <bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
        <property name="urlMap">
            <props>
                <prop key="/hello.do">simple</prop>
            </props>
        </property>
    </bean>

3、 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping

基于@RequestMapping 注解，配置对应映射

AnnotationControl.java

    package com.demo.spring.mvc.control;
    
    import org.springframework.stereotype.Controller;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.servlet.ModelAndView;
    
    /**
     * com.demo.spring.mvc.control
     *
     * @author Zyy
     * @date 2019/2/24 16:35
     */
    @Controller
    @RequestMapping("/annotation")
    public class AnnotationControl {
    
        @RequestMapping("/")
        public ModelAndView get() {
            //mapped to localhost:8080/spring_mvc/annotation/
            ModelAndView modelAndView = new ModelAndView("userView");
            modelAndView.addObject("name","this is /annotation/");
            return modelAndView;
        }
        @RequestMapping("/index")
        public ModelAndView index() {
            //mapped to localhost:8080/spring_mvc/annotation/index/
            ModelAndView modelAndView = new ModelAndView("userView");
            modelAndView.addObject("name","this is /annotation/index");
            return modelAndView;
        }
    }

spring-mvc-annotation.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">
    
        <context:component-scan base-package="com.demo.spring.mvc.control" />
    
        <mvc:annotation-driven/>
    
        <!-- 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>

web.xml

    classpath:/spring-mvc-annotation.xml

当ioc中实例化这些类之后，dispatcherServlet就会通过org.springframework.web.servlet.DispatcherServlet#getHandler(HttpServletRequest request)方法基于request，查找对应的handler，这里就会用到的HandlerAdapter，根据handler的不用采用不同的handlerAdapter（适配器模式）。

三、HandlerAdapter

Spring mvc采用适配器模式来适配调用指定的handler，根据handler的不同种类，采用不同的Adapter，其中handler与handlerAdapter对应关系如下：

Handler类别	HandlerAdapter	描述
Control	SimpleControllerHandlerAdapter	标准控制器，返回ModelAndView
HttpRequestHandler	HttpRequestHandlerAdapter	业务自行处理请求，不需要通过ModelAndView转到视图
Servlet	SimpleServletHandlerAdapter	基于标准的Servlet处理
HandlerMethod	RequestMappingHandlerAdapter	基于@RequestMapping对应方法处理

HandlerAdapter.java

    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);
    }

HandlerAdapter 接口结构图.png

其中xml配置，例如：

    <bean class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter"></bean>

当ioc容器实例化配置的类之后，dispatcherServlet会通过 org.springframework.web.servlet.DispatcherServlet#getHandlerAdapter 来获取HandlerAdapter，如果找不到则抛出异常 No adapter for handler。

四、ViewResolver 与 View

找到对应的Adapter之后，就会基于适配器调用业务处理，处理完成之后，业务方法会返回一个ModelAndView，接下来会去查找对应的视图进行处理，dispatcherServlet会通过调用 org.springframework.web.servlet.DispatcherServlet#resolveViewName ，遍历 viewResolvers ，然后根据viewName找到对应的View，如果找不到则抛出异常： Could not resolve view with name。

    ViewResolver viewResolver = (ViewResolver)var5.next();
    view = viewResolver.resolveViewName(viewName, locale

ViewResolver.java

    package org.springframework.web.servlet;
    
    import java.util.Locale;
    
    public interface ViewResolver {
        View resolveViewName(String var1, Locale var2) throws Exception;
    }

ViewResolver 接口结构.png

View.java

    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;
    }

View 接口结构图.png

ViewResolver调用resolveViewName方法来获取对应的view，然后解析生成对应的html，然后返回前台。

五、HandlerExceptionResolver

当出现异常时，dispatcherServlet会调用 org.springframework.web.servlet.DispatcherServlet#processHandlerException 方法，遍历 handlerExceptionResolvers ，然后进行异常处理，处理完成之后返回errorView跳转到我们的异常视图进行显示。

HandlerExceptionResolver.java

    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);
    }

HandlerExceptionResovler 接口结构图.png

示例代码：

SimpleExceptionHandler.java

    package com.demo.spring.mvc.control;
    
    import org.springframework.web.servlet.HandlerExceptionResolver;
    import org.springframework.web.servlet.ModelAndView;
    
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    /**
     * com.demo.spring.mvc.control
     *
     * @author Zyy
     * @date 2019/2/24 17:41
     */
    public class SimpleExceptionHandler implements HandlerExceptionResolver {
        @Override
        public ModelAndView resolveException(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) {
            return new ModelAndView("error");
        }
    }

spring-mvc.xml

    <!-- 自定义异常处理器 -->
    <bean class="com.demo.spring.mvc.control.SimpleExceptionHandler"/>

web.xml

    classpath:/spring-mvc-interceptors.xml

六、HandlerInterceptor

除了异常处理之外，spring mvc还引入了拦截器interceptor机制，类似Filter。

HandlerInterceptor.java

    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;
    }

HandlerInterceptor 接口结构图.png

示例代码：

SimpleHandlerInterceptor.java

    package com.demo.spring.mvc.control;
    
    import org.springframework.web.servlet.HandlerInterceptor;
    import org.springframework.web.servlet.ModelAndView;
    
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    /**
     * com.demo.spring.mvc.control
     *
     * @author Zyy
     * @date 2019/2/19 22:59
     */
    public class SimpleHandlerInterceptor implements HandlerInterceptor {
        @Override
        public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
            System.out.println("preHandle...");
            return true;
        }
    
        @Override
        public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
            System.out.println("postHandle...");
        }
    
        @Override
        public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
            System.out.println("afterCompletion...");
        }
    }

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">
        <!--控制器-->
        <bean id="simpleControl" class="com.demo.spring.mvc.control.SimpleControl"/>
        <bean id="handlerInterceptor" class="com.demo.spring.mvc.control.SimpleHandlerInterceptor"></bean>
        <!-- url映谢器-->
        <bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
            <property name="urlMap">
                <props>
                    <prop key="/hello.do">simpleControl</prop>
                </props>
            </property>
            <property name="interceptors" ref="handlerInterceptor"/>
        </bean>
    
        <!-- 执行适配器-->
        <bean class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter"/>
    
        <!--资源解析器 -->
        <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>
    
        <!-- 自定义异常处理器 -->
        <bean class="com.demo.spring.mvc.control.SimpleExceptionHandler"/>
    </beans>

其中调用过程是在 HandlerExecutionChain 中进行调用以下方法：

• preHandle ：业务处理前执行
• postHandle ：业务处理后执行（异常则不执行）
• afterCompletion : 视图处理后执行

整个的MVC 的执行流程可以看下DispatcherServlet中的doDispatch方法。

    org.springframework.web.servlet.DispatcherServlet#doDispatch

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