Java - Socket read from datainputstream and not get stuck in it

Question

I've been trying to do communication from another language to Java, but when I try read data from DataInputStream in a while loop...

static String getData(DataInputStream stream){

    int charbyte;
    StringBuilder strbuilder = new StringBuilder();
    try {
        while ((charbyte = stream.read()) != -1){
            strbuilder.append(Character.toChars(charbyte));
        }
        stream.close();

        return new String(strbuilder);

    } catch (Exception e) {
        return null;
    }
}

The problem is stream.read() is not returning -1 because it just keeps waiting for new data to be sent. How can I just get the data that was just sent?

How do you create the DataInputStream? Do you get any bytes at all? Is the "other side" actually sending? — laune, Jan 25 '15 at 13:06
Oh so, I get the Input stream with .getInputStream() on the socket obj and use that for a new DataInputStream — user3818650, Jan 25 '15 at 13:08
How do you know the other side is really sending? Does the other side close the connection so you sense EOF on the Java side? — laune, Jan 25 '15 at 13:10
I make a connection, because this script is actually in a java server and then I send. In the while loop I put test data to print charbyte and ints were printed — user3818650, Jan 25 '15 at 13:14
**Question:** Does the other side close the connection so you sense EOF on the Java side? — laune, Jan 25 '15 at 13:17
No, the other side doesn't close the connection because that's not the only communication I want to happen — user3818650, Jan 25 '15 at 13:20
"Not the only communication" - between the server and this client? Or the server and any other client? — laune, Jan 25 '15 at 13:24
Mainly the client is sending the data to the server, but from sending server to client is no problem for me — user3818650, Jan 25 '15 at 13:30

laune · Accepted Answer · 2015-01-25T13:44:19.743

The method never returns because the while loop never ends, and this is caused by the connection or the DataInputStream remaining open.

To send a variable number of bytes over a network connection where the reader reads a stream of characters you have three options:

Send the number of bytes to follow, as an int in network order, followed by as many bytes.
If the bytes are printable characters, send a null byte to indicate the end.
Close the stream after sending the bytes.

For #1, change the loop to

try {
    int count = stream.readInt();
    for( int i = 0; i < count; ++i ){
        strbuilder.append(Character.toChars(stream.read()));
    }
    return strbuilder.toString();
}

For #2, use

try {
    while ((charbyte = stream.read()) != 0){
        strbuilder.append(Character.toChars(charbyte));
    }
    return strbuilder.toString();
}

The code you have now is for #3.

The receiving side? The sending side? – laune Jan 25 '15 at 13:40 — laune, Jan 25 '15 at 13:40
Receiving in the while loop on the server – user3818650 Jan 25 '15 at 13:41 — user3818650, Jan 25 '15 at 13:41

Java - Socket read from datainputstream and not get stuck in it

1 Answers1