syshlangSpringMvc配置详解及源码分析 | 浪迹一生

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SpringMvc配置详解及源码分析

SpringMVC配置详解

配置前端控制器DispatcherServlet

     SpringMVC是一个基于DispatcherServlet的MVC框架,每一个请求最先访问的都是DispatcherServlet,DispatcherServlet是继承自HttpServlet的,DispatcherServlet负责转发每一个Request请求给相应的Handler,Handler处理以后再返回相应的视图(View)和模型(Model),返回的视图和模型都可以不指定,即可以只返回Model或只返回View或都不返回。

     首先,在web.xml文件中声明DispatcherServlet:

web.xml
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<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.1">
<!--<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
/WEB-INF/applicationContext.xml,
classpath:springmvc.xml,
</param-value>
</context-param>-->
<!--<context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>log4j.properties</param-value>
</context-param>-->
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<!--SpringMVC前端控制器-->
<servlet>
<servlet-name>dispatcher</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<!--
contextConfigLocation 配置SpringMVC加载的配置文件(配置处理器映射器、适配器等)
如果不配置,默认加载的是/WEB_INF/servlet名称-servlet.xml(dispatcher-servlet.xml)
-->
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:spring/spring-mvc.xml</param-value>
</init-param>
<!--
1)load-on-startup元素标记容器是否在启动的时候就加载这个servlet(实例化并调用其
init()方法)。
2)它的值必须是一个整数,表示servlet应该被载入的顺序
2)当值为0或者大于0时,表示容器在应用启动时就加载并初始化这个servlet;
3)当值小于0或者没有指定时,则表示容器在该servlet被选择时才会去加载。
4)正数的值越小,该servlet的优先级越高,应用启动时就越先加载
5)当值相同时,容器就会自己选择顺序来加载。
所以,<load-on-startup>x</load-on-startup>,
中x的取值1,2,3,4,5代表的是优先级,而非启动延迟时间。
-->
<load-on-startup>1</load-on-startup>
<!--
<async-supported>子标签,该标签的默认取值为false,
要启用异步处理支持,则将其设为true即可
-->
<async-supported>true</async-supported>
</servlet>

<servlet-mapping>
<servlet-name>dispatcher</servlet-name>
<!--
① *.action,访问以.action结尾的由DispatcherServlet进行解析;
② /,所有/的地址都由DispatcherServlet进行解析,
对于静态的文件的解析需要配置不让DispatcherServlet进行解析,
使用此种风格可以实现RESTFull风格的url解析;
③ /*,这样配置错误,使用这种配置时,最终要转发到jsp页面时,
仍然会由DsipatcherServlet解析jsp地址,不能根据jsp页面找到handler,会报错
-->
<url-pattern>*.action</url-pattern>
</servlet-mapping>

<!--welcome pages-->
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

配置处理器适配器、映射器、视图解析器等

     然后,在classpath下的spring-mvc.xml中配置处理器适配器:

spring-mvc.xml
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<?xml version="1.0" encoding="UTF-8"?>
<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"
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">
<!--
说明:前端控制器加载处理映射器、适配器、视图解析器等组件,如果不在spring-mvc.xml中配置,则会自动使用spring-webmvc-4.3.1.RELEASE.jar包中org\springframework.web.servlet中DispatcherSerlvet.properties配置文件中的默认配置。
-->


<!--启用spring的一些annotation -->
<!--<context:annotation-config/>-->

<!-- ****************配置Handler 开始*********************-->
<bean id="queryController" name="/query.action" class="com.syshlang.smm.controller.QueryController"></bean>
<bean id="queryHttpController" name="/httpquery.action"
class="com.syshlang.smm.controller.QueryHttpController">
</bean>
<!--
对于注解的Handler可以单个配置,实际开发中建议使用组件扫描
可以扫描controller、service、...这里让扫描controller,指定controller的包
-->
<!--<bean class="com.syshlang.smm.controller.QueryAnnotationController" />-->
<context:component-scan base-package="com.syshlang.smm.controller">
</context:component-scan>


<!-- ****************配置Handler 结束*********************-->


<!-- *********************配置处理器映射器 开始*************************************** -->
<!--
所有的适配器都实现了HandlerMapping接口
-->
<!--第一种方式:最简单的,一个class对应一个handler(非注解)
将bean的name当作url来查找,需要在配置Handler时配置bean的name(就是url),如上
-->
<bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping">
</bean>
<!--第二种方式 集中映射配置 (非注解)
SimpleUrlHandlerMapping是BeanNameUrlHandlerMapping的增强版本,
它可以将url和处理器的bean的id进行统一的映射配置
-->
<bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">
<props>
<prop key="/query0.action">queryController</prop>
<prop key="/query1.action">queryController</prop>
<prop key="/httpquery0.action">queryHttpController</prop>
<prop key="/httpquery1.action">queryHttpController</prop>
<!--<prop key="url地址">Controller的bean的id</prop>-->
</props>
</property>
</bean>

<!-- 第三种方式 注解映射器
在spring3.1之前使用org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping注解映射器。

在spring3.1之后使用org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping注解映射器
-->
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"></bean>

<!--
结论:① 多个映射器可以并存;
② 一个bean可以对应多个url;
③HandlerMapping 无需配置,springmvc可以默认启动;
④使用注解的映射器和注解的适配器。(注解的映射器和注解的适配器必须配对使用)。
-->

<!-- ********************************配置处理器映射器 结束************************** -->

<!-- *********************配置处理器适配器 开始*************************************** -->
<!--
所有的处理器适配器都实现HandlerAdapter接口
-->
<!--①配置处理器适配器 (非注解)
public boolean supports(Object handler) {
return handler instanceof Controller;
}

SimpleControllerHandlerAdapter中的support方法可以看出:
编写的handler需要实现Controller接口
public interface Controller {
ModelAndView handleRequest(HttpServletRequest var1, HttpServletResponse var2) throws Exception;
}
由此,开发Handler时需要实现Controller接口才能由org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter来执行
-->
<bean class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter">
</bean>
<!--
②HttpRequestHandlerAdapter 是http请求处理适配器, (非注解)
所有实现了HttpRequestHandler接口的bean通过此适配器进行适配、执行
public boolean supports(Object handler) {
return handler instanceof HttpRequestHandler;
}

由HttpRequestHandlerAdapter中的support方法可以看出:
编写的handler需要实现HttpRequestHandler接口
public interface HttpRequestHandler {
void handleRequest(HttpServletRequest var1, HttpServletResponse var2) throws ServletException, IOException;
}
-->
<bean class="org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter"></bean>

<!--③注解适配器
在spring3.1之前使用org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter注解适配器。

在spring3.1之后使用org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter注解适配器。

-->
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"></bean>
<!-- *********************配置处理器适配器 结束*************************************** -->

<!-- 使用 mvc:annotation-driven代替上边注解映射器和注解适配器配置
mvc:annotation-driven默认加载很多的参数绑定方法,
比如json转换解析器就默认加载了,如果使用mvc:annotation-driven不用配置上边的RequestMappingHandlerMapping和RequestMappingHandlerAdapter
实际开发时使用mvc:annotation-driven
-->
<!-- <mvc:annotation-driven></mvc:annotation-driven> -->


<!-- *********************配置视图解析器 开始*************************************** -->
<!--视图解析器
解析jsp文件,默认使用jstl的标签
classpatch下要有jstl的jar包
-->
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"></bean>
<!-- *********************配置视图解析器 结束*************************************** -->

<bean id="log4jInitialization"
class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
<property name="targetClass" value="org.springframework.util.Log4jConfigurer" />
<property name="targetMethod" value="initLogging" />
<property name="arguments">
<list>
<value>classpath:log4j.properties</value>
</list>
</property>
</bean>

</beans>

开发Handler

     在此处只举一例,如下:
     通过实现 controller接口,由org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter适配器执行的情况。

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package com.syshlang.smm.controller;

import com.syshlang.smm.pojo.QueryPojo;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.ArrayList;
import java.util.List;

/**
* Created by sunys on 2017/7/1 2:44.
* Description: 使用SimpleControllerHandlerAdapter处理器适配器实现Controller接口的处理器
*/
public class QueryController implements Controller{

//添加一个日志器
private static final Logger logger = LoggerFactory.getLogger(QueryController.class);

@Override
public ModelAndView handleRequest(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
//调用service层,查询数据库
List<QueryPojo> list = new ArrayList<QueryPojo>();
QueryPojo pojo = new QueryPojo();
pojo.setId("1");
pojo.setName("aaaaaa");
list.add(pojo);
//返回ModelAndView
ModelAndView modelAndView = new ModelAndView();
//相当于request的setAttribut,在jsp页面通过list取值
modelAndView.addObject("listpojo",list);
modelAndView.addObject("des","使用SimpleControllerHandlerAdapter处理器适配器实现Controller接口的处理器");
//指定视图View
modelAndView.setViewName("/view/query.jsp");
//输出日志文件
logger.info("the first jsp pages");
return modelAndView;
}
}

源码分析

源码分析

     根据配置过程,通过前端控制器源码分析SpringMVC的执行过程。

第一步:前端控制器接收请求

     在org.springframework.web.servlet.DispatcherServlet中可以看到doDispatch方法。前端控制器接收请求,.action类型的URL通过过滤器进入DispatcherServlet类,doDispatch()方法

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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;
mappedHandler = this.getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
this.noHandlerFound(processedRequest, response);
return;
}

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;
}

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);
}

}
}

第二步:前端控制器调用处理器映射器查找 Handler

     在doDispatch()方法中调用了DispatcherServlet类的getHandler方法。映射器根据request当中的URL,找到了Handler,最终返回一个执行器的链(HandlerExecutionChain)。这个链里面有Handler。

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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;
}

第三步:调用处理器适配器执行Handler,得到执行结果ModelAndView

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...
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
...

第四步:视图渲染,将model数据填充到request域。

     视图解析,得到view:
在doDispatch()方法中

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this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
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private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
boolean errorView = false;
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
this.logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException)exception).getModelAndView();
} else {
Object handler = mappedHandler != null ? mappedHandler.getHandler() : null;
mv = this.processHandlerException(request, response, handler, exception);
errorView = mv != null;
}
}

if (mv != null && !mv.wasCleared()) {
this.render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
} else if (this.logger.isDebugEnabled()) {
this.logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + this.getServletName() + "': assuming HandlerAdapter completed request handling");
}

if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
if (mappedHandler != null) {
mappedHandler.triggerAfterCompletion(request, response, (Exception)null);
}

}
}

在processDispatchResulth()方法中

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this.render(mv, request, response);
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protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
Locale locale = this.localeResolver.resolveLocale(request);
response.setLocale(locale);
View view;
if (mv.isReference()) {
view = this.resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
if (view == null) {
throw new ServletException("Could not resolve view with name '" + mv.getViewName() + "' in servlet with name '" + this.getServletName() + "'");
}
} else {
view = mv.getView();
if (view == null) {
throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " + "View object in servlet with name '" + this.getServletName() + "'");
}
}

if (this.logger.isDebugEnabled()) {
this.logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + this.getServletName() + "'");
}

try {
if (mv.getStatus() != null) {
response.setStatus(mv.getStatus().value());
}

view.render(mv.getModelInternal(), request, response);
} catch (Exception var7) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" + this.getServletName() + "'", var7);
}

throw var7;
}
}

在render()方法中

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view = this.resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);

调用view的渲染方法,将model数据填充到request域

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view.render(mv.getModelInternal(), request, response);

根据InternalResourceView的继承关系:org.springframework.web.servlet.view.AbstractView ,org.springframework.web.servlet.view.AbstractUrlBasedView,org.springframework.web.servlet.view.InternalResourceView 最终找到render方法在AbstractView中,如下代码所示:

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public void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
if (this.logger.isTraceEnabled()) {
this.logger.trace("Rendering view with name '" + this.beanName + "' with model " + model + " and static attributes " + this.staticAttributes);
}

Map<String, Object> mergedModel = this.createMergedOutputModel(model, request, response);
this.prepareResponse(request, response);
this.renderMergedOutputModel(mergedModel, this.getRequestToExpose(request), response);
}
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protected void exposeModelAsRequestAttributes(Map<String, Object> model, HttpServletRequest request) throws Exception {
Iterator var3 = model.entrySet().iterator();

while(var3.hasNext()) {
Entry<String, Object> entry = (Entry)var3.next();
String modelName = (String)entry.getKey();
Object modelValue = entry.getValue();
if (modelValue != null) {
request.setAttribute(modelName, modelValue);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Added model object '" + modelName + "' of type [" + modelValue.getClass().getName() + "] to request in view with name '" + this.getBeanName() + "'");
}
} else {
request.removeAttribute(modelName);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Removed model object '" + modelName + "' from request in view with name '" + this.getBeanName() + "'");
}
}
}

}

------------- The End -------------
  • 本文作者: 浪迹一生
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