SpringMVC是一个基于MVC的Web框架,是spring框架的一个模块,使用了MVC架构模式的思想,将web层进行职责解耦。首先让我们整体看一下SpringMVC处理请求的流程:
- 发起请求到前端控制器(DispatcherServlet)
- 前端控制器请求HandlerMapping查找Handler,可以根据xml配置、注解进行查找
- 处理器映射器HandlerMapping向前端控制器返回Handler
- 前端控制器调用处理器适配器去执行Handler
- 处理器适配器去执行Handler
- Handler执行完成给适配器返回ModelAndView
- 处理器适配器向前端控制器返回ModelAndView(springmvc框架的一个底层对象,包括Model和view)
- 前端控制器请求视图解析器去进行视图解析,根据逻辑视图名解析成真正的视图(jsp)
- 视图解析器向前端控制器返回View
- 前端控制器进行视图渲染,视图渲染将模型数据(在ModelAndView对象中)填充到request域
- 前端控制器向用户响应结果
【源码分析】
首先是SpringMVC的入口类DispatcherServlet,该类其实是一个servlet类,(可以从web.xml文件的配置中直接点击进去查看类源码),前端控制器接收到请求之后,会调用它的doService方法,然后调用doDispatch方法,重点就是doDispatch方法,源码如下:
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
// 如果请求方式为multipart,则通过multipart进行解析
multipartRequestParsed = processedRequest != request;
// Determine handler for the current request.(上图中的步骤2:通过调用getHandler方法,调用处理器映射器HandlerMapping查找Handler,详见方法二)
mappedHandler = getHandler(processedRequest, false);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.(根据处理器得到相应的适配器)
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
String requestUri = urlPathHelper.getRequestUri(request);
logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
//执行预处理
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
try {
// Actually invoke the handler.(上图中步骤4:请求处理器适配器HandlerAdapter执行Handler)
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
}
applyDefaultViewName(request, mv);
// 执行相应的后处理
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
//该方法详情见方法三(上图中的步骤8、9、10)
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Error err) {
triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
return;
}
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
②方法二(getHandler方法源码)
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}
③方法三(processDispatchResult方法源码)
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) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// Did the handler return a view to render?(上图中的步骤8:通过render方法,请求视图解析器view Resolver解析视图,具体源码如方法四)
if (mv != null && !mv.wasCleared()) {
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
"': assuming HandlerAdapter completed request handling");
}
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
if (mappedHandler != null) {
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
④方法四(render方法源码)
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
// Determine locale for request and apply it to the response.
Locale locale = this.localeResolver.resolveLocale(request);
response.setLocale(locale);
View view;
if (mv.isReference()) {
// We need to resolve the view name.
view = 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 '" +
getServletName() + "'");
}
}
else {
// No need to lookup: the ModelAndView object contains the actual View object.
view = mv.getView();
if (view == null) {
throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
"View object in servlet with name '" + getServletName() + "'");
}
}
// Delegate to the View object for rendering.
if (logger.isDebugEnabled()) {
logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
}
view.render(mv.getModelInternal(), request, response);
}
【优点】
1、清晰的角色划分:前端控制器(DispatcherServlet)、请求到处理器映射(HandlerMapping)、处理器适配器(HandlerAdapter)、视图解析器(ViewResolver)、处理器或页面控制器(Controller)、验证器( Validator)、命令对象(Command 请求参数绑定到的对象就叫命令对象)、表单对象(Form Object提供给表单展示和提交到的对象就叫表单对象)。
2、和Spring其他框架无缝集成,是其它Web框架所不具备的;
3、可适配,通过HandlerAdapter可以支持任意的类作为处理器;
4、可定制性,HandlerMapping、ViewResolver等能够非常简单的定制;
5、功能强大的数据验证、格式化、绑定机制;
6、强大的JSP标签库,使JSP编写更容易。
【缺点】
1.SpringMVC与servlet API耦合,难以脱离servlet容器独立运行,降低了SpringMVC框架的可扩展性。
2.太过细化的角色划分,太过繁琐,降低了应用的开发效率。
【入门小程序】
开发环境:eclipse、MySQL、JDK、tomcat、引入如下图所示jar包(点击链接下载jar包)
程序结构如下:
①Items类:
package cn.itcast.ssm.po;
import java.util.Date;
public class Items {
private Integer id;
private String name;
private Float price;
private String pic;
private Date createtime;
private String detail;
// get和set方法略
}
②Web.xml代码:
<?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"
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>mySpringMVC</display-name>
<!-- springmvc前端控制器 -->
<servlet>
<servlet-name>springmvc</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、适配器等等)如果不配置,默认加载的是WEB-INF/servlet名称-servlet.xml -->
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:springmvc.xml</param-value>
</init-param>
</servlet>
<!-- 第一种:*.action,访问以.action结尾 由DispatcherServlet进行解析 第二种:/,所以访问的地址都由DispatcherServlet进行解析,对于静态文件的解析需要配置不让DispatcherServlet进行解析
使用此种方式可以实现 RESTful风格的url 第三种:/*,这样配置不对,使用这种配置,最终要转发到一个jsp页面时, 仍然会由DispatcherServlet解析jsp地址,不能根据jsp页面找到handler,会报错。 -->
<servlet-mapping>
<servlet-name>springmvc</servlet-name>
<url-pattern>*.action</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
</web-app>
③Springmvc.xml代码:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.2.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-3.2.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.2.xsd ">
<!-- **************************************************************************************** -->
<!-- 配置Handler -->
<bean name="/queryItems.action" class="cn.itcast.ssm.controller.ItemsController1" />
<!-- **************************************************************************************** -->
<!-- **************************************************************************************** -->
<!-- 处理器映射器 -->
<!-- 将bean的name作为 URL进行查询,需要在配置Handler时指定beanname(就是url) -->
<bean
class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping" />
<!-- **************************************************************************************** -->
<!-- **************************************************************************************** -->
<!-- 处理器适配器 -->
<!-- 所有的处理器适配器都实现HandlerAdapter接口,该接口中有boolean supports(Object handler);
方法,通过这个supports方法来判断寻找相应的Handler -->
<bean
class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter" />
<!-- **************************************************************************************** -->
<!-- **************************************************************************************** -->
<!-- 视图解析器 -->
<!--解析jsp解析,默认使用jstl标签,classpath下的得有jstl的包 -->
<bean
class="org.springframework.web.servlet.view.InternalResourceViewResolver">
</bean>
<!-- **************************************************************************************** -->
</beans>
④controller代码:
package cn.itcast.ssm.controller;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;
import cn.itcast.ssm.po.Items;
/**
* 实现controller接口的处理器
*
* @author happy
*
*/
public class ItemsController1 implements Controller {
@Override
public ModelAndView handleRequest(HttpServletRequest request,
HttpServletResponse response) throws Exception {
// 调用Services查找数据库,查询商品列表,这里使用静态数据模拟
List<Items> itemsList = new ArrayList<Items>();
// 想List中填充静态数据
Items items_1 = new Items();
items_1.setName("联想笔记本");
items_1.setPrice(6000f);
items_1.setDetail("ThinkPad T430 联想笔记本电脑!");
Items items_2 = new Items();
items_2.setName("苹果手机");
items_2.setPrice(5000f);
items_2.setDetail("iphone6苹果手机!");
itemsList.add(items_1);
itemsList.add(items_2);
// 返回ModelAndView
ModelAndView modelAndView = new ModelAndView();
// 相当于request的setAttribute,在jsp页面中通过itemsList取数据
modelAndView.addObject("itemsList", itemsList);
// 指定视图
modelAndView.setViewName("/WEB-INF/jsp/items/itemsList.jsp");
return modelAndView;
}
}
⑤itemsList.jsp代码:
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
<!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>查询商品列表</title>
</head>
<body>
<form action="${pageContext.request.contextPath }/item/queryItem.action" method="post">
查询条件:
<table width="100%" border=1>
<tr>
<td><input type="submit" value="查询"/></td>
</tr>
</table>
商品列表:
<table width="100%" border=1>
<tr>
<td>商品名称</td>
<td>商品价格</td>
<td>生产日期</td>
<td>商品描述</td>
<td>操作</td>
</tr>
<c:forEach items="${itemsList }" var="item">
<tr>
<td>${item.name }</td>
<td>${item.price }</td>
<td><fmt:formatDate value="${item.createtime}" pattern="yyyy-MM-dd HH:mm:ss"/></td>
<td>${item.detail }</td>
<td><a href="${pageContext.request.contextPath }/item/editItem.action?id=${item.id}">修改</a></td>
</tr>
</c:forEach>
</table>
</form>
</body>
</html>