要测试服务器套接字连接，如何直接向其发送一个或多个字节？

Question

Let's say I have this example Java code running which listens on port 1234:

ServerSocket socket = new ServerSocket(1234);

And switches on the first byte received:

Socket s = socket.accept();

byte[] buffer = new byte[1];
BufferedInputStream bis = new BufferedInputStream(s.getInputStream());
int read = bis.read(buffer, 0, 1);

switch (buffer[0]) {
case 0x01:
    System.out.println("One.");
    break;
case 0x02:
    System.out.println("Two.");
    break;
default:
    System.out.println("Other.");
    break;
}

Is there a way to test this code from an external source? For example, could I use something like Telnet or NetCat to accomplish this?

Answer 1

You can do it with NetCat like this:

echo -e '\x02' | nc 127.0.0.1 1234

This will cause "Two." to be output to the console of the Java application.

You can do it with Telnet like this (Telnet will just send each key you type as an ASCII byte. If you want to send bytes less than the typeable characters, you can hold Ctrl down to subtract 64 from the ASCII value):

telnet 127.0.0.1 1234

Then press Ctrl+B to send 0x02 (B is ASCII value 66, so holding Ctrl subtracts 64 from the value). This will cause "Two." to be output to the console of the Java application.