如何在Web页上实现文件上传-JSP教程,Jsp/Servlet:站长天空｜虚拟主机资讯|虚拟主机新闻|虚拟主机动态

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 didnt select a directory higher in 
            the directory tree*/ 
          if (directory.indexof("..") > 0) 
          { 
            out.println("security error: you cant 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 doesnt 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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