In Java, what's the fastest way to "build" and use a string, character by character?

Question

I have a Java socket connection that is receiving data intermittently. The number of bytes of data received with each burst varies. The data may or may not be terminated by a well-known character (such as CR or LF). The length of each burst of data is variable.

I'm attempting to build a string out of each burst of data. What is the fastest way (speed, not memory), to build a string that would later need to be parsed?

I began by using a byte array to store the incoming bytes, then converting them to a String with each burst, like so:

byte[] message = new byte[1024];
...
message[i] = //byte from socket
i++;
...
String messageStr = new String(message);
...
//parse the string here

The obvious disadvantage of this is that some bursts may be longer than 1024. I don't want to arbitrarily create a larger byte array (what if my burst is larger?).

What is the best way of doing this? Should I create a StringBuilder object and append() to it? That way I don't have to convert from StringBuilder to String (since the former has most of the methods I need).

Again, speed of execution is my biggest concern.

TIA.

Answer 1

I would probably use an InputStreamReader wrapped around a BufferedInputStream, which in turn wraps the socket. And write code that processes a message at a time, potentially blocking for input. If the input is bursty, I might run on a background thread and use a concurrent queue to hold the messages.

Reading a buffer at a time and trying to convert it to characters is exactly what BufferedInputStream/InputStreamReader does. And it does so while paying attention to encoding, something that (as other people have noted) your solution does not.

I don't know why you're focused on speed, but you'll find that the time to process data coming off a socket is far less than the time it takes to transmit over that socket.

Answer 2

Note that as you're transmitting across network layers, your speed of conversion may not be the bottleneck. It would be worth measuring, if you believe this to be important.

Note (also) that you're not specifying a character encoding in your conversion from bytes to String (via characters). I would enforce that somehow, otherwise your client/server communication can become corrupted if/when your client/server run in different environments. You can enforce that via JVM runtime args, but it's not a particularly safe option.

Given the above, you may want to consider StringBuilder(int capacity) to configure it in advance with an appropriate size, such that it doesn't have to reallocate on the fly.