ServerPinger.java

package sk.tomsik68.mclauncher.impl.servers;

import net.minidev.json.JSONObject;
import net.minidev.json.JSONValue;
import sk.tomsik68.mclauncher.api.servers.ServerInfo;

import javax.net.SocketFactory;
import java.io.DataInputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Inet4Address;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketImplFactory;
import java.util.concurrent.Callable;

final class ServerPinger implements Callable<ServerPingResult> {
    private final ServerPingPacketFactory pingPacketFactory;
    private final ServerInfo server;

    public ServerPinger(ServerInfo server, ServerPingPacketFactory pingPacketFactory) {
        this.server = server;
        this.pingPacketFactory = pingPacketFactory;
    }

    public ServerPingResult call() throws Exception {
        ServerPingResult result = null;
        // open a connection
        InetSocketAddress addr = InetSocketAddress.createUnresolved(server.getIP(), server.getPort());
        Socket socket = SocketFactory.getDefault().createSocket();
        socket.connect(addr);
        // get streams
        InputStream is = socket.getInputStream();
        DataInputStream dis = new DataInputStream(is);
        OutputStream os = socket.getOutputStream();


        // send data
        os.write(pingPacketFactory.createPingPacket(server));
        // wait for data
        while (is.available() == 0) {
            Thread.sleep(20l);
        }


        // receive data
        byte zero = dis.readByte();
        if (zero != 0) {
            return new ServerPingResult(new RuntimeException("Outdated protocol!"));
        }
        String jsonString = dis.readUTF();
        result = new ServerPingResult(new JSONPingedServerInfo47((JSONObject)JSONValue.parse(jsonString), server.getIP(), server.getName(), server.getPort()));
        socket.close();
        return null;
    }
}