Spring MVC介紹(二)之 Spring MVC 執行流程解析
一、MVC組件執行流程
回顧一下MVC的體系結構與組件執行流程,如下圖:
dispatcherServlet -> handlermapping ->基於url查找handler -> handlerAdapter
-> 基於handler找到adapter -> 由adapter找到我們的 handler -> 執行業務處理返回 modelAndView
-> viewResolver -> 基於viweName找到view -> 執行視圖解析 -> 返回前端
再來看一個例子,基於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>
此時啓動容器,訪問 http://localhost:8080/spring_mvc/beanName ,可以看到顯示的是我們control返回的數據。
BeanName Control
我們在此之前未配置HandlerMapping、HandlerAdapter、InternalResourceViewResolver,爲何還是能找到呢?原因是因爲spring有個默認的配置:
路徑如下:
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
在這裏面可以看到:
BeanNameUrlHandlerMapping
HttpRequestHandlerAdapter
InternalResourceViewResolver
由此我們知道,spring有一套默認的mvc處理實現。
二、HandlerMapping
HandlerMapping爲mvc中url路徑與control對象的映射,dispatcherServlet就是基於handlerMapping組件來尋找對應的control,找不到時會拋出異常 noHandlerFound異常。
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;
}
其實現類,如下:
目前大部分使用其中三種:
1、org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping:
基於bean name查找,在xml以“/”開頭
<bean id="/beanName" class="com.demo.spring.mvc.control.BeanNameControl"></bean>
2、org.springframework.web.servlet.handler.SimpleUrlHandlerMapping
手動在xml中配置url與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
基於@RequestMapping 註解,配置對應映射
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/>
<!-- 視圖倉庫 -->
<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
當ioc中實例化這些類之後,dispatcherServlet就會通過org.springframework.web.servlet.DispatcherServlet#getHandler(HttpServletRequest request)方法基於request,查找對應的handler,這裏就會用到的HandlerAdapter,根據handler的不用採用不同的handlerAdapter(適配器模式)。
三、HandlerAdapter
Spring mvc採用適配器模式來適配調用指定的handler,根據handler的不同種類,採用不同的Adapter,其中handler與handlerAdapter對應關係如下:
Handler類別 | HandlerAdapter | 描述 |
---|---|---|
Control | SimpleControllerHandlerAdapter | 標準控制器,返回ModelAndView |
HttpRequestHandler | HttpRequestHandlerAdapter | 業務自行處理請求,不需要通過ModelAndView轉到視圖 |
Servlet | SimpleServletHandlerAdapter | 基於標準的Servlet處理 |
HandlerMethod | RequestMappingHandlerAdapter | 基於@RequestMapping對應方法處理 |
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);
}
其中xml配置,例如:
<bean class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter"></bean>
當ioc容器實例化配置的類之後,dispatcherServlet會通過org.springframework.web.servlet.DispatcherServlet#getHandlerAdapter來獲取HandlerAdapter,如果找不到則拋出異常 No adapter for handler。
四、ViewResolver 與 View
找到對應的Adapter之後,就會基於適配器調用業務處理,處理完成之後,業務方法會返回一個ModelAndView,接下來會去查找對應的視圖進行處理,dispatcherServlet會通過調用org.springframework.web.servlet.DispatcherServlet#resolveViewName,遍歷viewResolvers,然後根據viewName找到對應的View,如果找不到則拋出異常:
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;
}
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;
}
ViewResolver調用resolveViewName方法來獲取對應的view,然後解析生成對應的html,然後返回前臺。
五、HandlerExceptionResolver
當出現異常時,dispatcherServlet會調用org.springframework.web.servlet.DispatcherServlet#processHandlerException方法,遍歷handlerExceptionResolvers,然後進行異常處理,處理完成之後返回errorView跳轉到我們的異常視圖進行顯示。
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);
}
示例代碼:
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
<!-- 自定義異常處理器 -->
<bean class="com.demo.spring.mvc.control.SimpleExceptionHandler"/>
web.xml
classpath:/spring-mvc-interceptors.xml
六、HandlerInterceptor
除了異常處理之外,spring mvc還引入了攔截器interceptor機制,類似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;
}
示例代碼:
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映謝器-->
<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>
<!-- 執行適配器-->
<bean class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter"/>
<!--資源解析器 -->
<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>
<!-- 自定義異常處理器 -->
<bean class="com.demo.spring.mvc.control.SimpleExceptionHandler"/>
</beans>
其中調用過程是在HandlerExecutionChain中進行調用以下方法:
- preHandle :業務處理前執行
- postHandle :業務處理後執行(異常則不執行)
- afterCompletion : 視圖處理後執行
整個的MVC 的執行流程可以看下DispatcherServlet中的doDispatch方法。
org.springframework.web.servlet.DispatcherServlet#doDispatch
歡迎留言交流:)