Stumped on applet to servlet comminication

Guys and Gals
I am stumped, hope someone can help out.
I have an applet talking to a servlet using some options sent through the URL (= doGet). The servlet queries a database, creates a vector with the results and serializes it back to the applet. No problem, works like a charm.
Now I want to expand on this:
- call the servlet using some parameters to determine what it should do (= doGet)
- write a serialized vector of information from the applet to the servlet
- the servlet queries a database based on what is in the vector
- the servlet creates a HashMap with the results of the queries and sends the serialized HashMap back to the applet
What happens is that I am getting an EOFException when the servlet attempts to read the Vector. The Vector is not empty.
Am I missing something fundamental here, because it really has me stumped? I have not read anything prohibiting me to write a Vector and receive a HashTable but I am getting the impression that writing and then reading on the same servlet connection is screwing things up.
Thanks
Ben

as far as I think, you should use doPost() as doGet() has restrictions over the amount of data sent. and use ObjectOutput/Input Streams to send and recieve Vector objects...

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Probem with applet and servlets

subject "not able to invoke applet from servlets"
i have attached files also..
Respected sir,
I am thomas from prateek techologies ,referred by madam Pratibha.
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WEB-INF/classes.
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tolgatanriverdi wrote:
I'm devoloping a server side java software(on netbeans 6) and I want my gui classes(Designed as swing japplet application) to be executed on server side.Call a company named Citrix, they do stuff like that using a special client.
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Message was edited by:
AntonVatchenko

The 2 apps (applet versus servlet) are likely using different versions of the Java runtime (and / or security extensions to them). And on one version that security algorithm exists (is built-in, or added as an extension in your JRE's lib/ext folder or something like that); while on the other the algorithm does not exist.
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thanks
Edited by: san_4u on Nov 24, 2007 1:00 PM

BalusC wrote:
san_4u wrote:
how can i made a HttpClient PostMethod using java applets? as i have experience making request using HttpURLConnection.POST method. ok first of all i am going make a search of this only after i will tell. please be onlineOnce again, see link [3] in my first reply of your former topic.
yeah! i got the related topic at http://www.theserverside.com/tt/articles/article.tss?l=HttpClient_FileUpload. please look it, i am reading it right now and expecting to be reliable for me.
well what i got, when request made by html code(stated above) then all the form fields and file data mixed as binary data and available in HttpServletRequest.getinputstream. and at servlet side we have to use a mutipart parser of DiskFileItemFactory class that automatically parse the file data and return a FileItem object cotaing the actual file data,right?.You can also setup the MultipartFilter in your environment and don't >care about it further. Uploaded files will be available as request attributes in the servlet.is the multipartfilter class file available in jar files(that u suggested to add in yours article) so that i can use it directly? one more thing the import org.apache.commons.httpclient package is not available in these jar files, so where can got it from?
one mere question..
i looked somewhere that when we request for a file from webserver using web browser then there is a server that process our request and after retrieving that file from database it sends back as response.
now i confused that, wheather these webservers are like apache tomcat, IBM's webspher etc those processes these request or there is a unique server that always turned on and process all the request?
because, suppose in an orgnisation made it's website using its own server then, in fact, all the time it will not turned on its server or yes it will? and a user can make a search for kind of information about this orgnisation at any time.
hopes, you will have understand my quary, then please let me know the actual process
thanks
Edited by: san_4u on Nov 25, 2007 11:25 AM

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String line;
while ((line = reader.readLine()) != null)
if (webadminApplet.DEBUG) System.out.println(line);
finally
// close the reader stream from servlet.
reader.close();
} // end of the big try block.
catch (Exception e)
System.out.println("Exception during file transfer:\n" + e);
e.printStackTrace();
return("FTP failed. See Java Console for Errors.");
} // end of catch block.
return("File: " + fname + " successfully transferred.");
} // end of method transferFile().
} // end of class fileTransferClient
Server side code:
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
import java.net.*;
// This servlet class acts as an FTP server to enable transfer of
files
// from client side.
public class FtpServerServlet extends HttpServlet
String ftpDir = "D:\\pub\\FTP\\";
private static final String FILENAME_HEADER = "fileName";
private static final String FILELASTMOD_HEADER = "fileLastMod";
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException,
IOException
doPost(req, resp);
public void doPost(HttpServletRequest req, HttpServletResponse
resp)
throws ServletException,
IOException
// ### for now enable overwrite by default.
boolean overwrite = true;
// get the fileName for this transmission.
String fileName = req.getHeader(FILENAME_HEADER);
// also get the last mod of this file.
String strLastMod = req.getHeader(FILELASTMOD_HEADER);
String message = "Filename: " + fileName + " saved
successfully.";
int status = HttpServletResponse.SC_OK;
System.out.println("fileName from client: " + fileName);
// if filename is not specified, complain.
if (fileName == null)
message = "Filename not specified";
status = HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
else
// open the file stream for the file about to be transferred.
File uploadedFile = new File(fileName);
// check if file already exists - and overwrite if necessary.
if (uploadedFile.exists())
if (overwrite)
// delete the file.
uploadedFile.delete();
// ensure the directory is writable - and a new file may be
created.
if (!uploadedFile.createNewFile())
message = "Unable to create file on server. FTP failed.";
status = HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
else
// get the necessary streams for file creation.
FileOutputStream fos = new FileOutputStream(uploadedFile);
InputStream is = req.getInputStream();
try
// create a buffer. 4K!
byte[] buffer = new byte[4096];
// read from input stream and write to file stream.
int byteCnt = 0;
while (true)
int bytes = is.read(buffer);
if (bytes < 0) break;
byteCnt += bytes;
// System.out.println(buffer);
fos.write(buffer, 0, bytes);
// flush the stream.
fos.flush();
} // end of try block.
finally
is.close();
fos.close();
// set last mod date for this file.
uploadedFile.setLastModified((new
Long(strLastMod)).longValue());
} // end of finally block.
} // end - the new file may be created on server.
} // end - we have a valid filename.
// set response headers.
resp.setContentType("text/plain");
resp.setStatus(status);
if (status != HttpServletResponse.SC_OK)
getServletContext().log("ERROR: " + message);
// get output stream.
PrintWriter out = resp.getWriter();
out.println(message);
} // end of doPost().
} // end of class FtpServerServlet

OK - the problem you describe is definitely what's giving you grief.
The workaround is to use a socket connection and send your own request headers, with the content length filled in. You may have to multi-part mime encode the stream on its way out as well (I'm not about that...).
You can use the following:
http://porsche.cis.udel.edu:8080/cis479/lectures/slides-04/slide-02.html
on your server to get a feel for the format that the request headers need to take.
- Kevin
I get the out of Memory Error on the client side. I
was told that this might be a bug in the URLConnection
class implementation that basically it wont know the
content length until all the data has been written to
the output stream, so it uses an in memory buffer to
store the data which basically causes memory issues..
do you think there might be a workaround of any kind..
or maybe a way that the buffer might be flushed after
a certain size of file has been uploaded.. ?? do you
have any ideas?

Writing Image files from Applet to Servlet

How to write ImageFiles from an Applet to a Servlet?
I draw a image on a JComponent in Applet and wanted to save the image file in the server.
I am unable to write an Image Object to the Servlet as the BufferedImage class is not serialized.
I tried writing the image to the Servlet output stream and tried reading the data in the servlet and writing the data to a jpg file.
But the files is not being written as proper jpeg file.
Any help would be great.
Thanks,
Sridhar.

I get the following exception below when i try to write a Serialized object from an applet to the servlet.
I copied the serialized class jar file to the tomcat webserver lib folder.
The serialized class has a BufferedImage object.
Serialized Class Code
public class SerializedImage implements Serializable{
     private BufferedImage im = null;
     public SerializedImage() {
          super();
     public BufferedImage getSerializedObject() {
          return im;
     public void setSerializedObject((BufferedImage im) {
          this.im = im;
     private BufferedImage fromByteArray(byte[] imagebytes) {
          try {
               if (imagebytes != null && (imagebytes.length > 0)) {
                    BufferedImage im = ImageIO.read(new ByteArrayInputStream(imagebytes));
                    return im;
               return null;
          } catch (IOException e) {
               throw new IllegalArgumentException(e.toString());
     private byte[] toByteArray(BufferedImage o) {
          if(o != null) {
               BufferedImage image = (BufferedImage)o;
               ByteArrayOutputStream baos = new ByteArrayOutputStream(1024);
               try {
                    ImageIO.write(image, "jpg", baos);
               } catch (IOException e) {
                    throw new IllegalStateException(e.toString());
               byte[] b = baos.toByteArray();
               return b;
          return new byte[0];
     private void writeObject(java.io.ObjectOutputStream out)
     throws IOException {
          byte[] b = toByteArray(im);
          out.writeInt(b.length);
          out.write(b);
     private void readObject(java.io.ObjectInputStream in)
     throws IOException, ClassNotFoundException {
          int length = in.readInt();
          byte[] b = new byte[length];
          in.read(b);
          im = fromByteArray(b);
Exception :
java.io.StreamCorruptedException: unexpected block data
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1288)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:18
45)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1769)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1
646)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1274)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:324)
Is there any thing that i am missing or doing wrong?
Thanks,
Sridhar.

Stumped on applet to servlet comminication

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