Tom 5 Tom 5 -4 years ago 99
Java Question

Java multiple file transfer over socket

Ok, trying to transfer a specified directory of files over a socket, remove the directory objects from the arraylist, so only files are left, and transfer them 1 by 1 over the same socket. The arraylist here is filled with ONLY files, no directories. Heres the receive and send code for the client and server respectively . The code runs fine without errors, except for ALL the data is being written to the first file. The subsequent files are created in the server folder, but they are 0 bytes. Any input would be greatly appreciated.

THIS IS THE SERVER CODE FOR RECEIVING THE FILES

public void receive(){


try {
DataInputStream dis = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
DataOutputStream dos = new DataOutputStream(new BufferedOutputStream(socket.getOutputStream()));
//read the number of files from the client
int number = dis.readInt();
ArrayList<File>files = new ArrayList<File>(number);
System.out.println("Number of Files to be received: " +number);
//read file names, add files to arraylist
for(int i = 0; i< number;i++){
File file = new File(dis.readUTF());
files.add(file);
}
int n = 0;
byte[]buf = new byte[4092];

//outer loop, executes one for each file
for(int i = 0; i < files.size();i++){

System.out.println("Receiving file: " + files.get(i).getName());
//create a new fileoutputstream for each new file
FileOutputStream fos = new FileOutputStream("C:\\users\\tom5\\desktop\\salestools\\" +files.get(i).getName());
//read file
while((n = dis.read(buf)) != -1){
fos.write(buf,0,n);
fos.flush();
}
fos.close();
}

} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();

}


}


THIS IS THE CLIENT CODE FOR SENDING THE FILES

public void send(ArrayList<File>files){

try {
DataInputStream dis = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
DataOutputStream dos = new DataOutputStream(new BufferedOutputStream(socket.getOutputStream()));
System.out.println(files.size());
//write the number of files to the server
dos.writeInt(files.size());
dos.flush();

//write file names
for(int i = 0 ; i < files.size();i++){
dos.writeUTF(files.get(i).getName());
dos.flush();
}

//buffer for file writing, to declare inside or outside loop?
int n = 0;
byte[]buf = new byte[4092];
//outer loop, executes one for each file
for(int i =0; i < files.size(); i++){

System.out.println(files.get(i).getName());
//create new fileinputstream for each file
FileInputStream fis = new FileInputStream(files.get(i));

//write file to dos
while((n =fis.read(buf)) != -1){
dos.write(buf,0,n);
dos.flush();

}
//should i close the dataoutputstream here and make a new one each time?
}
//or is this good?
dos.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}


}

Answer Source

You are reading the socket until read() returns -1. This is the end-of-stream condition (EOS). EOS happens when the peer closes the connection. Not when it finishes writing one file.

You need to send the file size ahead of each file. You're already doing a similar thing with the file count. Then make sure you read exactly that many bytes for that file:

String filename = dis.readUTF();
long fileSize = dis.readLong();
FileOutputStream fos = new FileOutputStream(filename);
while (fileSize > 0 && (n = dis.read(buf, 0, (int)Math.min(buf.length, fileSize))) != -1)
{
  fos.write(buf,0,n);
  fileSize -= n;
}
fos.close();

You can enclose all this in a loop that terminates when readUTF() throws EOFException. Conversely of course you have to call writeUTF(filename) and writeLong(filesize) at the sender, before sending the data.

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