关于jsp文件上传的，我作了些总结，代码已调试过，绝对正确，供菜鸟使用

Commons FileUpload，可以在http://jakarta.apache.org/commons/fileupload/下载，这个包需要Commons IO的支持，可以在http://jakarta.apache.org/commons/io/下载
Commons FileUpload提供三种文件上传处理方式，DiskFileUpload、ServletFileUpload和PortletFileUpload三种方式，其中DiskFileUpload已经在javadoc下已经被标记为过期的方法，建议用ServletFileUpload代替，而PortletFileUpload需要配合portlet-api来使用，这里我们只介绍前两种：
本人用jbuilder开发的，所以需要用工程引入外部jar包；若不是用ide则需把以上两个jar包放入开发目录的lib下以下是我的代码：
test.jsp:
<%@ page language="java" import="java.util.*" contentType="text/html;charset=gbk" pageEncoding="gbk"%>
<html>
  <body>
    <form action="/WebModule1/diskfileupload" enctype="multipart/form-data" method="post">
     <input type="text" name="username" /><br />
     <input type="file" name="myfile" /><br/>
     <input type="file" name="myfile" /><br/>
     <input type="submit" />
    </form>
    <br/><br/><br/><br/>
    <form action="/WebModule1/multiparttestservlet" enctype="multipart/form-data" method="post">
     <input type="text" name="username" /><br />
     <input type="file" name="myfile" /><br/>
     <input type="file" name="myfile" /><br/>
     <input type="submit" />
    </form>
    <br/><br/><br/><br/>
        <input type="submit" />
    </form>
  </body>
</html>DiskFileUpload:
package image;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import org.apache.commons.fileupload.*;
import org.apache.commons.beanutils.*;
public class DiskFileUpload
    extends HttpServlet {
  private static final String CONTENT_TYPE = "text/html; charset=GBK";  //Initialize global variables
  public void init() throws ServletException {  }  //Process the HTTP Get request
  public void doPost(HttpServletRequest request, HttpServletResponse response) throws
      ServletException, IOException {
     response.setContentType(CONTENT_TYPE);
  try{
      System.out.println("start----------------------");
    org.apache.commons.fileupload.DiskFileUpload fu=new org.apache.commons.fileupload.DiskFileUpload();
    fu.setSizeMax(1000000);
    fu.setSizeThreshold(1096);
    fu.setRepositoryPath("c:\\");
    if(request!=null)
   {
     List fileItems=fu.parseRequest(request);
     System.out.println("to here-----------------");
     Iterator i = fileItems.iterator();
     Hashtable ht = new Hashtable();
     InputStream in = null;
     int size = 0;
     while (i.hasNext()) {
       FileItem fi = (FileItem) i.next();
       if (fi.isFormField()) {
         ht.put(fi.getFieldName(), fi.getString());
         System.out.println("" + fi.getFieldName() + ":" + fi.getString());
       }
       else {
         in = fi.getInputStream();
         size = (int) fi.getSize();
         if (in != null && size > 0) {
           ht.put("filetype", fi.getContentType());
           System.out.println("filetype:" + fi.getContentType());
           ht.put("filename", fi.getName());
           System.out.println("filename:" + fi.getName());
         }
       }
     }
   }
  }catch(Exception e){
    e.printStackTrace(System.err);
  }
  }
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws
      ServletException, IOException {
    doPost(request,response);
  }
  //Clean up resources
  public void destroy() {
  }
}MultipartTestServlet.java:
package image;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUpload;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.RequestContext;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.fileupload.servlet.ServletRequestContext;public class MultipartTestServlet extends HttpServlet { public MultipartTestServlet() {
  super();
 } public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {  request.setCharacterEncoding("gbk");
  RequestContext requestContext = new ServletRequestContext(request);
  if(FileUpload.isMultipartContent(requestContext)){
   DiskFileItemFactory factory = new DiskFileItemFactory();
   factory.setRepository(new File("c:/tmp/"));
   ServletFileUpload upload = new ServletFileUpload(factory);
   //upload.setHeaderEncoding("gbk");
   upload.setSizeMax(2000000);
   List items = new ArrayList();
    try {
     items = upload.parseRequest(request);
    } catch (FileUploadException e1) {
     System.out.println("文件上传发生错误" + e1.getMessage());
    }   Iterator it = items.iterator();
   while(it.hasNext()){
    FileItem fileItem = (FileItem) it.next();
    if(fileItem.isFormField()){
     System.out.println(fileItem.getFieldName() + "   " + fileItem.getName() + "   " + new String(fileItem.getString().getBytes("iso8859-1"), "gbk"));
    }else{
     System.out.println(fileItem.getFieldName() + "   " +
        fileItem.getName() + "   " +
        fileItem.isInMemory() + "    " +
        fileItem.getContentType() + "   " +
        fileItem.getSize());     if(fileItem.getName()!=null && fileItem.getSize()!=0){
      File fullFile = new File(fileItem.getName());
      File newFile = new File("c:/temp/" + fullFile.getName());
      try {
       fileItem.write(newFile);
      } catch (Exception e) {
       e.printStackTrace();
      }
     }else{
      System.out.println("文件没有选择 或 文件内容为空");
     }
    }   }
  }
 }}web.xml:
<?xml version="1.0" encoding="UTF-8"?>
<web-app 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/j2ee/web-app_2_4.xsd" version="2.4">
  <display-name>WebModule1</display-name>
  <servlet>
    <servlet-name>multiparttestservlet</servlet-name>
    <servlet-class>image.MultipartTestServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>multiparttestservlet</servlet-name>
    <url-pattern>/multiparttestservlet</url-pattern>
  </servlet-mapping>
    <servlet>
    <servlet-name>diskfileupload</servlet-name>
    <servlet-class>image.DiskFileUpload</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>diskfileupload</servlet-name>
    <url-pattern>/diskfileupload</url-pattern>
  </servlet-mapping>
</web-app>
要注意的是，你必需先在c盘下建立temp和tmp文件夹，否则运行时会抛出例外