Java套接字非阻塞读取

Question

I'm using a DataInputStream to read characters/data from a socket.

I want to use .readUnsignedShort(); and have it throw an exception if there isn't 2 bytes to read. Should I subclass the DataInputStream and override the methods adding the exceptions, or is there an easier way?

Answer 1

If you want something quick and dirty, try inputStream.available() .

if (stream.available() < 2) {
    // throw it
}

If you want true non blocking reads and callbacks when data is available, I think Pablo's answer is better.

Answer 2

I think Java NIO non-blocking classes are your best choice. Check SocketChannel class and its related code samples.

But be careful, when you issue your read command, it might be the case that bytes are not available yet, but that doesn't mean that the will never arrive to your socket...

Answer 3

void readButDoNotBlockForALongTime(java.net.Socket socket) {
    int someTimeout = 1000;
    socket.setSoTimeout(someTimeout);
    try {
        // read as much as you want - blocks until timeout elapses
    } catch (java.net.SocketTimeoutException e) {
        // read timed out - you may throw an exception of your choice
    }
}

This is a simple way to block for only as long as you want.

setSoTimeout(int timeout): Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, a read() call on the InputStream associated with this Socket will block for only this amount of time. If the timeout expires, a java.net.SocketTimeoutException is raised, though the Socket is still valid. The option must be enabled prior to entering the blocking operation to have effect. The timeout must be > 0. A timeout of zero is interpreted as an infinite timeout.

For a more elegant solution, you may consider using NIO.

Answer 4

If the input ends before supplying two bytes it will throw EOFException. If there is no input available() will return zero, although it can also return zero if there is input in some circumstances (eg SSL).