实例详解Spring MVC入门使用

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2019-07-01

MVC模式(Model-View-Controller)是软件工程中的一种软件架构模式,把软件系统分为三个基本部分：模型(Model),视图(View)和控制器(Controller).通过分层使开发的软件结构更清晰,从而达到开发效率的提高,可维护性和扩展性得到提高.Spring提供的MVC框架是在J2EE Web开发中对MVC模式的一个实现,本文通过实例讲解一下Spring MVC 的使用.

先来看一个HTTP request在Spring的MVC框架是怎么被处理的:(图片来源于Spring in Action)
实例详解Spring MVC入门使用

1,DispatcherServlet是Spring MVC的核心,它的本质是一个实现了J2EE标准中定义的HttpServlet,通过在web.xml配置<servlet-mapping>,来实现对request的监听.

<servlet>         <servlet-name>springTestServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>2</load-on-startup>     </servlet>     <servlet-mapping>
    <servlet-name>springTestServlet</servlet-name>
    <url-pattern>*.do</url-pattern>     </servlet-mapping>
** 以.do结尾的request都会由springTestServlet来处理.
2,3,当接受到request的时候,DispatcherServlet根据HandlerMapping的配置(HandlerMapping的配置文件默认根据<servlet-name>的值来决定,这里会读取springTestServlet-servlet.xml来获得HandlerMapping的配置信息),调用相应的Controller来对request进行业务处理.
<bean id="simpleUrlMapping"
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">             <props>
            <prop key="/login.do">loginController</prop>             </props>         </property>     </bean>     <bean id="loginController"
class="com.test.spring.mvc.contoller.LoginController"> <property
name="sessionForm"> <value>true</value> </property> <property
name="commandName"> <value>loginCommand</value> </property>
<property name="commandClass">
        <value>com.test.spring.mvc.commands.LoginCommand</value>
    </property>         <property name="authenticationService">             <ref
bean="authenticationService"/> </property> <property
name="formView"> <value>login</value> </property> <property
name="successView"> <value>loginDetail</value> </property>
</bean>
** 以login.do结尾的request由loginController来处理.<property name="formView">配置的是Controller接收到HTTP GET请求的时候需要显示的逻辑视图名,本例是显示login.jsp,<property name="successView">配置的是在接收到HTTP POST请求的时候需要显示的逻辑视图名,在本例中即login.jsp提交的时候需要显示名为loginDetail的逻辑视图.
4,Controller进行业务处理之后,返回一个ModelAndView对象.
return new ModelAndView(getSuccessView(),"loginDetail",loginDetail);
5,6,DispatcherServlet根据ViewResolver的配置(本例是在springTestServlet-servlet.xml文件中配置)将逻辑view转换到真正要显示的View,如JSP等.
<bean id="viewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="viewClass">
        <value>org.springframework.web.servlet.view.JstlView</value>
    </property>         <property name="prefix">             <value>/jsp/</value>
    </property>         <property name="suffix">             <value>.jsp</value>
    </property>     </bean>

**其作用是将Controller中返回的ModleAndView解析到具体的资源(JSP文件),如上例中的return new ModelAndView(getSuccessView();按照上面ViewResolver配置,会解析成/jsp/loginDetail.jsp.规则为prefix+ModelAndView的第二个参数+suffix.
示例的完整代码如下:

1web.xml:

<?xml version="1.0" encoding="UTF-8"?> <web-app id="WebApp_ID"
version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2...d"> <display-name>

prjSpring3</display-name>     <servlet>
    <servlet-name>springTestServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>2</load-on-startup>     </servlet>     <servlet-mapping>
    <servlet-name>springTestServlet</servlet-name>
    <url-pattern>*.do</url-pattern>     </servlet-mapping>     <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>     <listener>
    <listener-class>org.springframework.web.context.request.RequestContextListener</listener-class>
</listener>     <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/springTest-services.xml</param-value>
</context-param>     <jsp-config>         <taglib>
        <taglib-uri>/spring</taglib-uri>
        <taglib-location>/WEB-INF/spring.tld</taglib-location>         </taglib>
</jsp-config> </web-app>

2,springTestServlet-servlet.xml的内容如下:

<?xml version="1.0" encoding="UTF-8"?> <beans
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.or...d">
<bean id="simpleUrlMapping"
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">             <props>
            <prop key="/login.do">loginController</prop>             </props>         </property>     </bean>     <bean id="loginController"
class="com.test.spring.mvc.contoller.LoginController"> <property
name="sessionForm"> <value>true</value> </property> <property
name="commandName"> <value>loginCommand</value> </property>
<property name="commandClass">
        <value>com.test.spring.mvc.commands.LoginCommand</value>
    </property>         <property name="authenticationService">             <ref
bean="authenticationService"/> </property> <property
name="formView"> <value>login</value> </property> <property
name="successView"> <value>loginDetail</value> </property>
</bean>     <bean id="viewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="viewClass">
        <value>org.springframework.web.servlet.view.JstlView</value>
    </property>         <property name="prefix">             <value>/jsp/</value>
    </property>         <property name="suffix">             <value>.jsp</value>
    </property>     </bean> </beans>
3,springTest-services.xml的内容:
<bean id="authenticationService" class="com.test.spring.mvc.services.AuthenticationService"/>

4,Java代码:

public class LoginController extends SimpleFormController {
org.springframework.web.servlet.DispatcherServlet t;     protected
ModelAndView onSubmit(Object command) throws Exception{
LoginCommand loginCommand = (LoginCommand) command;
    authenticationService.authenticate(loginCommand);         LoginDetail
loginDetail =
authenticationService.getLoginDetail(loginCommand.getUserId());
return new ModelAndView(getSuccessView(),"loginDetail",loginDetail);
}         private AuthenticationService authenticationService;     public
AuthenticationService getAuthenticationService() { return
authenticationService; } public void setAuthenticationService(
AuthenticationService authenticationService) {
    this.authenticationService = authenticationService;     }     .... public
class LoginCommand { private String userId; private String password;
.... public class LoginDetail {     private String userName; public
class AuthenticationService { public void authenticate(LoginCommand
command) throws Exception{ if(command.getUserId()!= null &&
command.getUserId().equalsIgnoreCase("test")
&& command.getPassword()!= null && command.getPassword().equalsIgnoreCase("test")){             }else{             throw
new Exception("User id is not authenticated"); } } public
LoginDetail getLoginDetail(String userId){ return new
LoginDetail(userId); } }

5,JSP文件:放在web-inf的jsp文件夹内

login.jsp: <html><head> <title>Login to Spring Test</title></head>
<body> <h1>Please enter your userid and password.</h1> <form
method="post" action="login.do"> <table width="95%" bgcolor="f8f8ff"
border="0" cellspacing="0" cellpadding="5"> <tr> <td alignment="right"
width="20%">User id:</td> <td width="20%"><input type="text"
name="userId" value="test"></td> <td width="60%"> </tr> <tr> <td
alignment="right" width="20%">Password:</td> <td width="20%"><input
type="password" name="password" value="test"></td> <td width="60%">
</tr> </table>
<input type="submit" alignment="center"
value="login"> </form> </body> </html> loginDetail.jsp: <%@ taglib
uri="http://java.sun.com/jstl/core_rt" prefix="c"%> <html><head>
<title>Login to Spring Test</title></head> <body> <h1>Login
Details:</h1> <br/> Login as: <c:out value
="${loginDetail.userName}"/> <br/> logout </body> </html>

在浏览器的地址栏输入http://localhost:8080/XXX/login.do进入login.jsp页面.

对配置的一些扩充点:

1为HandlerMapping和Controller的配置指定文件名称.

<servlet>
<servlet-name>springTestServlet</servlet-name>  
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

<init-param>  
    <param-name>contextConfigLocation</param-name>  
    <param-value>classpath*:/xxx.xml</param-value>  
</init-param>  
<load-on-startup>1</load-on-startup>   </servlet>
2,加入对MVC注解的支持:
<?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"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.or...
http://www.springframework.org/schema/context
http://www.springframework.or...
http://www.springframework.org/schema/mvc
http://www.springframework.or...d">
<context:annotation-config />     <context:component-scan
base-package="com.test.spring.mvc.contoller" />
<mvc:annotation-driven />   @Controller public class
AnnotationController {
   @RequestMapping("annotation.do")
   protected void test(HttpServletRequest request,
           HttpServletResponse response) throws Exception{
       response.getWriter().println("test Spring MVC annotation");
   }

3,注解和SimpleFormController同时使用需要在DispatcherServlet对应的servlet配置文件(本例是springTestServlet-servlet.xml)里面配置:

<bean
class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter"/>
否则会发生下面的异常: javax.servlet.ServletException: No adapter for handler

handler implement a supported interface like Controller?

org.springframework.web.servlet.DispatcherServlet.getHandlerAdapter(DispatcherServlet.java:982)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:770)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:716)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:647)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:552)
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

在WEB应用中的context配置文件通过下面的方式load,ContextLoaderListener是一个实现了ServletContextListener的listener,
它能够访问<context-param>而得到配置文件的路径,加载后初始化了一个WebApplicationContext,并且将其作为Attribute放在了servletContext中,
所有可以访问servletContext的地方则可以访问WebApplicationContext.

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>     <context-param>
    <param-name>contextConfigLocation</param-name>         <param-value>
        /WEB-INF/springTest-services.xml,
        classpath:conf/jndiDSAppcontext.xml         </param-value>
</context-param>

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实例详解Spring MVC入门使用

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