给你一个servlet例子，JSP差不多

答案：来源水木清华

public class UploadServlet extends HttpServlet
{
  //default maximum allowable file size is 100k
  static final int MAX_SIZE = 102400;
  //instance variables to store root and success message
  String rootPath, successMessage;
  /**
   * init method is called when servlet is initialized.
   */
  public void init(ServletConfig config) throws ServletException
  {
    super.init(config);
    //get path in which to save file
    rootPath = config.getInitParameter("RootPath");
    if (rootPath == null)
    {
      rootPath = "/";
    }
    /*Get message to show when upload is complete. Used only if
      a success redirect page is not supplied.*/
    successMessage = config.getInitParameter("SuccessMessage");
    if (successMessage == null)
    {
      successMessage = "File upload complete!";
    }
  }
  /**
   * doPost reads the uploaded data from the request and writes
   * it to a file.
   */
  public void doPost(HttpServletRequest request,
    HttpServletResponse response)
  {
    ServletOutputStream out=null;
    DataInputStream in=null;
    FileOutputStream fileOut=null;
    try
    {
      /*set content type of response and get handle to output
        stream in case we are unable to redirect client*/
      response.setContentType("text/plain");
      out = response.getOutputStream();
    }
    catch (IOException e)
    {
      //print error message to standard out
      System.out.println("Error getting output stream.");
      System.out.println("Error description: " + e);
      return;
    }
    try
    {
      //get content type of client request
      String contentType = request.getContentType();
      //make sure content type is multipart/form-data
      if(contentType != null && contentType.indexOf(
        "multipart/form-data") != -1)
      {
        //open input stream from client to capture upload file
        in = new DataInputStream(request.getInputStream());
        //get length of content data
        int formDataLength = request.getContentLength();
        //allocate a byte array to store content data
        byte dataBytes[] = new byte[formDataLength];
        //read file into byte array
        int bytesRead = 0;
        int totalBytesRead = 0;
        int sizeCheck = 0;
        while (totalBytesRead < formDataLength)
        {
          //check for maximum file size violation
          sizeCheck = totalBytesRead + in.available();
          if (sizeCheck > MAX_SIZE)
          {
            out.println("Sorry, file is too large to upload.");
            return;
          }
          bytesRead = in.read(dataBytes, totalBytesRead,
            formDataLength);
          totalBytesRead += bytesRead;
        }
        //create string from byte array for easy manipulation
        String file = new String(dataBytes);
        //since byte array is stored in string, release memory
        dataBytes = null;
        /*get boundary value (boundary is a unique string that
          separates content data)*/
        int lastIndex = contentType.lastIndexOf("=");
        String boundary = contentType.substring(lastIndex+1,
          contentType.length());
        //get Directory web variable from request
        String directory="";
        if (file.indexOf("name=\"Directory\"") > 0)
        {
          directory = file.substring(
            file.indexOf("name=\"Directory\""));
          //remove carriage return
          directory = directory.substring(
            directory.indexOf("\n")+1);
          //remove carriage return
          directory = directory.substring(
            directory.indexOf("\n")+1);
          //get Directory
          directory = directory.substring(0,
            directory.indexOf("\n")-1);
          /*make sure user didn't select a directory higher in
            the directory tree*/
          if (directory.indexOf("..") > 0)
          {
       &n

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