Detailed explanation of file upload code examples in SpringMVC

<?xml version="1.0" encoding="UTF-8"?>  
<web-app version="2.5"   
    xmlns="http://java.sun.com/xml/ns/javaee"   
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee   
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  
  <servlet>  
        <servlet-name>upload</servlet-name>  
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>  
        <load-on-startup>1</load-on-startup>  
    </servlet>  
    <servlet-mapping>  
        <servlet-name>upload</servlet-name>  
        <url-pattern>/</url-pattern>  
    </servlet-mapping>  
  
    <filter>  
        <filter-name>SpringCharacterEncodingFilter</filter-name>  
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>  
        <init-param>  
            <param-name>encoding</param-name>  
            <param-value>UTF-8</param-value>  
        </init-param>  
    </filter>  
    <filter-mapping>  
        <filter-name>SpringCharacterEncodingFilter</filter-name>  
        <url-pattern>/*</url-pattern>  
    </filter-mapping>  
      
    <welcome-file-list>  
        <welcome-file>/WEB-INF/jsp/user/add.jsp</welcome-file>  
    </welcome-file-list>  
</web-app>

<?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:mvc="http://www.springframework.org/schema/mvc"  
    xmlns:context="http://www.springframework.org/schema/context"  
    xsi:schemaLocation="http://www.springframework.org/schema/beans   
                        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd  
                        http://www.springframework.org/schema/mvc  
                        http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd  
                        http://www.springframework.org/schema/context   
                        http://www.springframework.org/schema/context/spring-context-3.0.xsd">  
    <context:component-scan base-package="com.jadyer"/>  
      
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">  
        <property name="prefix" value="/WEB-INF/jsp/"/>  
        <property name="suffix" value=".jsp"/>  
    </bean>  
      
    <!-- SpringMVC上传文件时，需要配置MultipartResolver处理器 -->  
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">  
        <property name="defaultEncoding" value="UTF-8"/>  
        <!-- 指定所上传文件的总大小不能超过200KB。注意maxUploadSize属性的限制不是针对单个文件，而是所有文件的容量之和 -->  
        <property name="maxUploadSize" value="200000"/>  
    </bean>  
      
    <!-- SpringMVC在超出上传文件限制时，会抛出org.springframework.web.multipart.MaxUploadSizeExceededException -->  
    <!-- 该异常是SpringMVC在检查上传的文件信息时抛出来的，而且此时还没有进入到Controller方法中 -->  
    <bean id="exceptionResolver" class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">  
        <property name="exceptionMappings">  
            <props>  
                <!-- 遇到MaxUploadSizeExceededException异常时，自动跳转到/WEB-INF/jsp/error_fileupload.jsp页面 -->  
                <prop key="org.springframework.web.multipart.MaxUploadSizeExceededException">error_fileupload</prop>  
            </props>  
        </property>  
    </bean>  
</beans>

<%@ page language="java" pageEncoding="UTF-8"%>  
<form action="<%=request.getContextPath()%>/user/add" method="POST" enctype="multipart/form-data">  
    username: <input type="text" name="username"/><br/>  
    nickname: <input type="text" name="nickname"/><br/>  
    password: <input type="password" name="password"/><br/>  
    yourmail: <input type="text" name="email"/><br/>  
    yourfile: <input type="file" name="myfiles"/><br/>  
    yourfile: <input type="file" name="myfiles"/><br/>  
    yourfile: <input type="file" name="myfiles"/><br/>  
    <input type="submit" value="添加新用户"/>  
</form>

<%@ page language="java" pageEncoding="UTF-8"%>  
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>  
<c:forEach items="${users}" var="user">  
    ${user.value.username}----${user.value.nickname}----${user.value.password}----${user.value.email}  
        <a href="<%=request.getContextPath()%>/user/${user.value.username}">查看</a>  
        <a href="<%=request.getContextPath()%>/user/${user.value.username}/update">编辑</a>  
        <a href="<%=request.getContextPath()%>/user/${user.value.username}/delete">删除</a>  
    <br/>  
</c:forEach>  
<br/>  
<a href="<%=request.getContextPath()%>/user/add">继续添加用户</a>

<%@ page language="java" pageEncoding="UTF-8"%>  
<h1>文件过大，请重新选择</h1>

package com.jadyer.model;  
  
/** 
 * User 
 * @author 宏宇 
 * @create May 12, 2012 1:24:43 AM 
 */  
public class User {  
    private String username;  
    private String nickname;  
    private String password;  
    private String email;  
    /*==四个属性的getter()、setter()略==*/  
    public User() {}  
    public User(String username, String nickname, String password, String email) {  
        this.username = username;  
        this.nickname = nickname;  
        this.password = password;  
        this.email = email;  
    }  
}

package com.jadyer.controller;  
  
import java.io.File;  
import java.io.IOException;  
import java.util.HashMap;  
import java.util.Map;  
  
import javax.servlet.http.HttpServletRequest;  
  
import org.apache.commons.io.FileUtils;  
import org.springframework.stereotype.Controller;  
import org.springframework.ui.Model;  
import org.springframework.web.bind.annotation.RequestMapping;  
import org.springframework.web.bind.annotation.RequestMethod;  
import org.springframework.web.bind.annotation.RequestParam;  
import org.springframework.web.multipart.MultipartFile;  
  
import com.jadyer.model.User;  
  
/** 
 * SpringMVC中的文件上传 
 * @see 第一步：由于SpringMVC使用的是commons-fileupload实现，故将其组件引入项目中 
 * @see       这里用到的是commons-fileupload-1.2.2.jar和commons-io-2.0.1.jar 
 * @see 第二步：在####-servlet.xml中配置MultipartResolver处理器。可在此加入对上传文件的属性限制 
 * @see 第三步：在Controller的方法中添加MultipartFile参数。该参数用于接收表单中file组件的内容 
 * @see 第四步：编写前台表单。注意enctype="multipart/form-data"以及<input type="file" name="****"/> 
 * @author 宏宇 
 * @create May 12, 2012 1:26:21 AM 
 */  
@Controller  
@RequestMapping("/user")  
public class UserController {  
    private final static Map<String,User> users = new HashMap<String,User>();  
      
    //模拟数据源,构造初始数据  
    public UserController(){  
        users.put("张起灵", new User("张起灵", "闷油瓶", "02200059", "menyouping@yeah.net"));  
        users.put("李寻欢", new User("李寻欢", "李探花", "08866659", "lixunhuan@gulong.cn"));  
        users.put("拓拔野", new User("拓拔野", "搜神记", "05577759", "tuobaye@manhuang.cc"));  
        users.put("孙悟空", new User("孙悟空", "美猴王", "03311159", "sunhouzi@xiyouji.zh"));  
    }  
      
    @RequestMapping("/list")  
    public String list(Model model){  
        model.addAttribute("users", users);  
        return "user/list";  
    }  
      
    @RequestMapping(value="/add", method=RequestMethod.GET)  
    public String addUser(){  
        return "user/add";  
    }  
    @RequestMapping(value="/add", method=RequestMethod.POST)  
    public String addUser(User user, @RequestParam MultipartFile[] myfiles, HttpServletRequest request) throws IOException{  
        //如果只是上传一个文件，则只需要MultipartFile类型接收文件即可，而且无需显式指定@RequestParam注解  
        //如果想上传多个文件，那么这里就要用MultipartFile[]类型来接收文件，并且还要指定@RequestParam注解  
        //并且上传多个文件时，前台表单中的所有<input type="file"/>的name都应该是myfiles，否则参数里的myfiles无法获取到所有上传的文件  
        for(MultipartFile myfile : myfiles){  
            if(myfile.isEmpty()){  
                System.out.println("文件未上传");  
            }else{  
                System.out.println("文件长度: " + myfile.getSize());  
                System.out.println("文件类型: " + myfile.getContentType());  
                System.out.println("文件名称: " + myfile.getName());  
                System.out.println("文件原名: " + myfile.getOriginalFilename());  
                System.out.println("========================================");  
                //如果用的是Tomcat服务器，则文件会上传到\\%TOMCAT_HOME%\\webapps\\YourWebProject\\WEB-INF\\upload\\文件夹中  
                String realPath = request.getSession().getServletContext().getRealPath("/WEB-INF/upload");  
                //这里不必处理IO流关闭的问题，因为FileUtils.copyInputStreamToFile()方法内部会自动把用到的IO流关掉，我是看它的源码才知道的  
                FileUtils.copyInputStreamToFile(myfile.getInputStream(), new File(realPath, myfile.getOriginalFilename()));  
            }  
        }  
        users.put(user.getUsername(), user);  
        return "redirect:/user/list";  
    }  
}