Reading socket one byte a time, how to change this, optimisation

Question

I need some help about optimisation. I am trying to improve this open-source game server made with JAVA. Each player has its own thread, and each thread goes something like this:

BufferedReader _in = new BufferedReader(new InputStreamReader(_socket.getInputStream()));

String packet = "";
char charCur[] = new char[1];

while(_in.read(charCur, 0, 1)!=-1)
{
    if (charCur[0] != '\u0000' && charCur[0] != '\n' && charCur[0] != '\r')
    {
        packet += charCur[0];

    }else if(!packet.isEmpty())
    {
        parsePlayerPacket(packet);
        packet = "";
    }
}

I have been told so many times that this code is stupid, and I agree because when profiling it I see that reading each byte and appending it using packet += "" is just stupid and slow.

I want to improve this but I don't know how.. I'm sure I can find something, but I'm afraid it will be even slower than this, because I have to split packets based on the '\u0000', '\n', or '\r' to parse them. And I know that splitting 3 times is verry slow.

Can someone give me an idea? Or a piece of code for this? It will make my day.

If you're going to explain, please, please use verry simple words, with code examples, I'm just a JAVA beginner. Thank's

Answer 1

Perhaps you should look into the readLine() method of BufferedReader. Looks like you're reading Strings, calling BufferedReader.readLine() gives you the next line (sans the newline/linefeed).

Something like this:

String packet = _in.readLine();
while(packet!=null) {
    parsePlayerPacket(packet);
    packet = _in.readLine();
}

Just like you're implementation, readLine() will block until either the stream is closed or there's a newline/linefeed.

EDIT: yeah, this isn't going to split '\0'. You're best bet is probably a PushbackReader, read in some buffer of chars (like David Oliván Ubieto suggests)

PushbackReader _in = new PushbackReader(new InputStreamReader(_socket.getInputStream()));
StringBuilder packet = new StringBuilder();
char[] buffer = new char[1024];
// read in as much as we can
int bytesRead = _in.read(buffer);

while(bytesRead > 0) {
    boolean process = false;
    int index = 0;
    // see if what we've read contains a delimiter
    for(index = 0;index<bytesRead;index++) {
        if(buffer[index]=='\n' ||
           buffer[index]=='\r' ||
           buffer[index]=='\u0000') {
            process = true;
            break;
        }
    }
    if(process) {
         // got a delimiter, process entire packet and push back the stuff we don't care about
         _in.unread(buffer,index+1,bytesRead-(index+1));  // we don't want to push back our delimiter
         packet.append(buffer,0,index);
         parsePlayerPacket(packet);
         packet = new StringBuilder();
    }
    else {
         // no delimiter, append to current packet and read some more
         packet.append(buffer,0,bytesRead);
    }
    bytesRead = _in.read(buffer);
}

I didn't debug that, but you get the idea.

Note that using String.split('\u0000') has the problem where a packet ending with '\u0000' won't get processed until a newline/linefeed is sent across the stream. Since you're writing some kind of game, I assume it's important to process an incoming packet as soon as you get it.