Spring MVC介绍（二）之 Spring MVC 执行流程解析

spring.png

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

web.xml

    spring-mvc
    
        dispatcherServlet
        org.springframework.web.servlet.DispatcherServlet
        
            contextConfigLocation
            
                classpath:/spring-mvc_beanName.xml
            
        
    
    
        dispatcherServlet
        /
    

    
        /index.jsp
    

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

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

手动在xml中配置url与control映射

    
        
            simple
        
    

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

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：

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 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

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

    
    
    
    
    
        
            
                simpleControl
            
        
        
    

    
    

    
    
        
        
        
    

    
    

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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