利用servlet实现上传

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
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.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class UploadServlet extends HttpServlet {

 /**
  * Destruction of the servlet. <br>
  */
 public void destroy() {
  super.destroy(); // Just puts "destroy" string in log
  // Put your code here
 }

 /**
  * The doPost method of the servlet. <br>
  *
  * This method is called when a form has its tag value method equals to post.
  *
  * @param request the request send by the client to the server
  * @param response the response send by the server to the client
  * @throws ServletException if an error occurred
  * @throws IOException if an error occurred
  */
 
 @SuppressWarnings("unchecked")
 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {

  System.out.println("hello");
  
  DiskFileItemFactory factory = new DiskFileItemFactory(); //磁盘文件工厂
  
  String path = request.getRealPath("/upload");//上传路径
  
  factory.setRepository(new File(path));
  factory.setSizeThreshold(1024*1024);//如果所上传文件大于这个范围则存储在磁盘上，否则放到内存中
  
  ServletFileUpload upload = new ServletFileUpload(factory);
  
  List<FileItem> list = null;
  try {
   list = upload.parseRequest(request);
  } catch (FileUploadException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
  for(FileItem item : list){
   if(item.isFormField()){
    
    String name = item.getFieldName();
    String value = item.getString("gbk");
    
    request.setAttribute(name, value);
   }else{
    
    String name = item.getFieldName();
    String value = item.getName();
    
    int start = value.lastIndexOf("//");
    
    String fileName = value.substring(start+1);
    
    request.setAttribute(name, fileName);
    
    
    try {
     item.write(new File(path,fileName));//下面的所有东西用这一句话也可以实现
    } catch (Exception e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
    }
    
    
//    OutputStream os = new FileOutputStream(new File(path,fileName));
//    InputStream is = item.getInputStream();
//    
//    byte[] buffer = new byte[400];
//    
//    int length = 0;
//    
//    while((length=is.read(buffer))>0){
//     
//     os.write(buffer,0,length);
//     
//    }
//   
//    os.close();
//    is.close();
    
   }
   
  }
  request.getRequestDispatcher("/upload/result2.jsp").forward(request, response);
 }

 /**
  * Initialization of the servlet. <br>
  *
  * @throws ServletException if an error occurs
  */
 public void init() throws ServletException {
  // Put your code here
 }

}