一、我出现错误的原因

是在前端的表单属性里没有加入这一属性enctype="multipart/form-data"，然后继续运行Tomcat，
上传还是报一样的错误，继续认真观看，发现我使用表单的默认提交方式，所以把提交方式改为method="post"，
再次运行Tomcat上传文件就没有报错了，还有要记springMVC的配置文件上传相关的也必不可少。如果你跟我的错误一样的话，
希望我的解析能够给你提供一点点的帮助。

二、正确的代码

1、后台

@Controller
@RequestMapping("user")
public class UserAction
{
  @RequestMapping("upload1")
  public String upload1(
      @RequestParam(value = "myfile", required = false) MultipartFile file,
      HttpServletRequest request, Model model)
      throws IllegalStateException, IOException
  {
    String path = request.getSession().getServletContext()
        .getRealPath("upload");
    String fileName = file.getOriginalFilename();// "1.png"
    fileName = UUID.randomUUID().toString().replace("-", "")
        + fileName.substring(fileName.lastIndexOf("."));// XXXX.png
 
    File targetFile = new File(path, fileName);// "C:///.../upload/XXX.png"
    if (!targetFile.exists())
    {
      targetFile.mkdirs();
    }
 
    file.transferTo(targetFile);
    // 到这里，文件上传已经结束！
    model.addAttribute("newfile", fileName);// XXX.png
 
    return "index";// index.jsp
  }
}

2、前台

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'index.jsp' starting page</title>
  <meta http-equiv="pragma" content="no-cache">
  <meta http-equiv="cache-control" content="no-cache">
  <meta http-equiv="expires" content="0">    
  <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
  <meta http-equiv="description" content="This is my page">
  <!--
  <link rel="stylesheet" type="text/css" href="styles.css">
  -->
  </head>
  
  <body>
    <form action="user/upload1.do" method="post" enctype="multipart/form-data">
      单文件上传:<input type="file" name="myfile">
      <input type="submit" value="上传">
      <hr>
      
      <img src="upload/${newfile}"/>
    </form>
  </body>
</html>

3.配置

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'index.jsp' starting page</title>
  <meta http-equiv="pragma" content="no-cache">
  <meta http-equiv="cache-control" content="no-cache">
  <meta http-equiv="expires" content="0">    
  <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
  <meta http-equiv="description" content="This is my page">
  <!--
  <link rel="stylesheet" type="text/css" href="styles.css">
  -->
  </head>
  
  <body>
    <form action="user/upload1.do" method="post" enctype="multipart/form-data">
      单文件上传:<input type="file" name="myfile">
      <input type="submit" value="上传">
      <hr>
      
      <img src="upload/${newfile}"/>
    </form>
  </body>
</html>