如何在Web页上实现文件上传_JSP教程 - 开发实例_JSP教程

如何在Web页上实现文件上传

日期：2005-8-19 19:07:37　作者：佚名　人气：　　来源：网络

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) 
          { 
            out.println("Security Error: You can't upload " + 
              "to a directory higher in the directory tree."); 
            return; 
          } 
        } 
        //get SuccessPage web variable from request 
        String successPage=""; 
        if (file.indexOf("name=\"SuccessPage\"") > 0) 
        { 
          successPage = file.substring( 
            file.indexOf("name=\"SuccessPage\"")); 
          //remove carriage return 
          successPage = successPage.substring( 
            successPage.indexOf("\n")+1); 
          //remove carriage return 
          successPage = successPage.substring( 
            successPage.indexOf("\n")+1); 
          //get success page 
          successPage = successPage.substring(0, 
            successPage.indexOf("\n")-1); 
        } 
        //get OverWrite flag web variable from request 
        String overWrite; 
        if (file.indexOf("name=\"OverWrite\"") > 0) 
        { 
          overWrite = file.substring( 
            file.indexOf("name=\"OverWrite\"")); 
          //remove carriage return 
          overWrite = overWrite.substring( 
            overWrite.indexOf("\n")+1); 
          //remove carriage return 
          overWrite = overWrite.substring( 
            overWrite.indexOf("\n")+1); 
          //get overwrite flag 
          overWrite = overWrite.substring(0, 
            overWrite.indexOf("\n")-1); 
        } 
        else 
        { 
          overWrite = "false"; 
        } 
        //get OverWritePage web variable from request 
        String overWritePage=""; 
        if (file.indexOf("name=\"OverWritePage\"") > 0) 
        { 
          overWritePage = file.substring( 
            file.indexOf("name=\"OverWritePage\"")); 
          //remove carriage return 
          overWritePage = overWritePage.substring( 
            overWritePage.indexOf("\n")+1); 
          //remove carriage return 
          overWritePage = overWritePage.substring( 
            overWritePage.indexOf("\n")+1); 
          //get overwrite page 
          overWritePage = overWritePage.substring(0, 
            overWritePage.indexOf("\n")-1); 
        } 
        //get filename of upload file 
        String saveFile = file.substring( 
          file.indexOf("filename=\"")+10); 
        saveFile = saveFile.substring(0, 
          saveFile.indexOf("\n")); 
        saveFile = saveFile.substring( 
          saveFile.lastIndexOf("\\")+1, 
          saveFile.indexOf("\"")); 
        /*remove boundary markers and other multipart/form-data 
          tags from beginning of upload file section*/ 
        int pos; //position in upload file 
        //find position of upload file section of request 
        pos = file.indexOf("filename=\""); 
        //find position of content-disposition line 
        pos = file.indexOf("\n",pos)+1; 
        //find position of content-type line 
        pos = file.indexOf("\n",pos)+1; 
        //find position of blank line 
        pos = file.indexOf("\n",pos)+1; 
        /*find the location of the next boundary marker 
          (marking the end of the upload file data)*/ 
        int boundaryLocation = file.indexOf(boundary,pos)-4; 
        //upload file lies between pos and boundaryLocation 
        file = file.substring(pos,boundaryLocation); 
        //build the full path of the upload file 
        String fileName = new String(rootPath + directory + 
          saveFile); 
        //create File object to check for existence of file 
        File checkFile = new File(fileName); 
        if (checkFile.exists()) 
        { 
          /*file exists, if OverWrite flag is off, give 
            message and abort*/ 
          if (!overWrite.toLowerCase().equals("true")) 
          { 
            if (overWritePage.equals("")) 
            { 
              /*OverWrite HTML page URL not received, respond 
                with generic message*/ 
              out.println("Sorry, file already exists."); 
            } 
            else 
            { 
              //redirect client to OverWrite HTML page 
              response.sendRedirect(overWritePage); 
            } 
            return; 
          } 
        } 
        /*create File object to check for existence of 
          Directory*/ 
        File fileDir = new File(rootPath + directory); 
        if (!fileDir.exists()) 
        { 
          //Directory doesn't exist, create it 
          fileDir.mkdirs(); 
        } 
        //instantiate file output stream 
        fileOut = new FileOutputStream(fileName); 
        //write the string to the file as a byte array 
        fileOut.write(file.getBytes(),0,file.length()); 
        if (successPage.equals("")) 
        { 
          /*success HTML page URL not received, respond with 
            generic success message*/ 
          out.println(successMessage); 
          out.println("File written to: " + fileName); 
        } 
        else 
        { 
          //redirect client to success HTML page 
          response.sendRedirect(successPage); 
        } 
      } 
      else //request is not multipart/form-data 
      { 
        //send error message to client 
        out.println("Request not multipart/form-data."); 
      } 
    } 
    catch(Exception e) 
    { 
      try 
      { 
        //print error message to standard out 
        System.out.println("Error in doPost: " + e); 
        //send error message to client 
        out.println("An unexpected error has occurred."); 
        out.println("Error description: " + e); 
      } 
      catch (Exception f) {} 
    } 
    finally 
    { 
      try 
      { 
        fileOut.close(); //close file output stream 
      } 
      catch (Exception f) {} 
      try 
      { 
        in.close(); //close input stream from client 
      } 
      catch (Exception f) {} 
      try 
      { 
        out.close(); //close output stream to client 
      } 
      catch (Exception f) {} 
    } 
  } 
}

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