2-way file upload/download b/w client/server

Question

I need help for a good design strategy for 2-way file upload/download betweeen client and server.
I have to upload a set of files to the server (which is a servlet)
and again the servlet downloads another set of files to the client (which is an applet)
I could find a solution to this problem only to a certain extent (i.e) I can upload any no.of files to the servlet from applet but the servlet can download only a single file to the applet.
But now the requirement needs the servlet to be able to send more than one file. I am not going anywhere ahead from this point since last 2 days.
I have used ObjectOutputStream-ObjectInputStream objects at both ends for communcation and sending the files as bufferes of 128 size. But this is becoming more complicated to manage the streams!!
if anyone of you have done this before please help with this!
Thaks
sri

Answer 1

Give this a try.
1) construct
2) call ZipDocVO.add(Serializable) for each obj that you wish to send.
3) call ZipDocVO.zip() to zip it up when you are finished adding objects.
4) send the ZipDocVO, using ObjectOuputStream or whatever
5) call ZipDocVO.unzip()
6) call ZipDocVO.getDocuments() to access your objects
import java.io.*;
import java.util.zip.*;
import java.util.*;
public class ZipDocVO implements Serializable {
     private List     vos;
     private byte[]     rawData;
     private boolean     isZipped;
     public ZipDocVO( byte botype, int key )
          vos = new ArrayList();
     public List getDocuments() { return vos; }
     public void add( Serializable doc ) { vos.add( doc ); }
     private boolean isZipped() { return isZipped; }
     public void zip() {
          if( isZipped() ) {
               System.out.println( "Already zipped!" );
          else {
               try {
                    // First zip our documents
                    ByteArrayOutputStream baos = new ByteArrayOutputStream();
                    GZIPOutputStream gzos = new GZIPOutputStream( baos );
                    ObjectOutputStream oos = new ObjectOutputStream( gzos );
                    oos.writeObject( vos );
                    oos.close();
                    // Then get rid of the unzipped versions
                    rawData = baos.toByteArray();
                    vos = null;
                    isZipped = true;
               catch( IOException ioe ) {
                    System.out.println( "Unable to zip : " +ioe.getMessage());
     public void unzip() {
          if( !isZipped() ) {
               System.out.println( "Not zipped!" );
          else {
               try {
                    // First unzip our documents
                    ByteArrayInputStream bais = new ByteArrayInputStream( rawData );
                    GZIPInputStream gzis = new GZIPInputStream( bais );
                    ObjectInputStream ois = new ObjectInputStream( gzis );
                    vos = (ArrayList)ois.readObject();
                    ois.close();
                    // Then get rid of the zipped versions
                    rawData = null;
                    isZipped = false;
               catch( Exception e ) {
                    System.out.println( "Unable to unzip : " +e.getMessage());
}