Sending file through ObjectOutputStream and then saving it in Java?

Question

I have this simple Server/Client application. I'm trying to get the Server to send a file through an OutputStream (FileOutputStream, OutputStream, ObjectOutputStream, etc) and receive it at the client side before saving it into an actual file. The problem is, I've tried doing this but it keeps failing. Whenever I create the file and write the object I received from the server into it, I get a broken image (I just save it as a jpg, but that shouldn't matter). Here are the parts of the code which are most likely to be malfunctioning (all the seemingly un-declared objects you see here have already been declared beforehand):

Server:

                ObjectOutputStream outToClient = new ObjectOutputStream(
                        connSocket.getOutputStream());
                File imgFile = new File(dir + children[0]);
                outToClient.writeObject(imgFile);
                outToClient.flush();

Client:

ObjectInputStream inFromServer = new ObjectInputStream(
                clientSocket.getInputStream());
        ObjectOutputStream saveImage = new ObjectOutputStream(
                new FileOutputStream("D:/ServerMapCopy/gday.jpg"));
        saveImage.writeObject(inFromServer.readObject());

So, my problem would be that I can't get the object through the stream correctly without getting a broken file.

Jeffrey · Accepted Answer · 2012-07-21 16:08:30Z

11

A File object represents the path to that file, not its actual content. What you should do is read the bytes from that file and send those over your ObjectOutputStream.

File f = ...
ObjectOutputStream oos = ...

byte[] content = Files.readAllBytes(f.toPath);
oos.writeObject(content);

File f=...
ObjectInputStream ois = ...

byte[] content = (byte[]) ois.readObject();
Files.write(f.toPath(), content);

answered Jul 21, 2012 at 16:08

Jeffrey

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5 Comments

ZimZim Over a year ago

I knew I was missing a step. I figured I had to do something before sending the file because that file object was incomplete.

sarcan Over a year ago

Though with this approach you'll read the entire file into memory before actually writing the bytes to the socket.

Jeffrey Over a year ago

@sarcan I used the Files.read / Files.write methods for the sake of brevity. The OP could always use a loop to write the bytes incrementally

sarcan Over a year ago

@Jeffrey I got that and didn't mean to criticize you, my comment was simply meant as an additional remark for the OP.

sapy Over a year ago

f.toPath() undefined

sarcan · Accepted Answer · 2012-07-21 16:11:50Z

1

You are not actually transferring the file, but the File instance from Java. Think of your File object as a (server-)local handle to the file, but not its contents. For transferring the image, you'd actually have to read it on the server first.

However, if you're just going to save the bytes on the client anyway, you can forget about the ObjectOutputStream to begin with. You can just transfer the bytes stored in the File. Take a look at the FileChannel class and its transferTo and transferFrom methods as a start.

answered Jul 21, 2012 at 16:11

sarcan

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1 Comment

user207421 Over a year ago

It's not even a handle, just a filename, otherwise +1.

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