public static Object[] call(Method method,
    Object[][] params,
    InetSocketAddress[] addrs,
    Configuration conf) throws IOException 
{
    Invocation[] invocations = new Invocation[params.length];
    for (int i = 0; i <  params.length; i++)
      invocations[i] = new Invocation(method, params[i]);
    Writable[] wrappedValues = getClient(conf).call(invocations, addrs);
    if (method.getReturnType() == Void.TYPE) {
      return null;
    }
    Object[] values =
      (Object[])Array.newInstance(method.getReturnType(), wrappedValues.length);
    for (int i = 0; i <  values.length; i++)
      if (wrappedValues[i] != null)
        values[i] = ((ObjectWritable)wrappedValues[i]).get();
    return values;
}

Expert: Make multiple, parallel calls to a set of servers.

 public static VersionedProtocol getProxy(Class protocol,
    long clientVersion,
    InetSocketAddress addr,
    Configuration conf) throws IOException 
{
    VersionedProtocol proxy = (VersionedProtocol) Proxy.newProxyInstance(
                                                                         protocol.getClassLoader(),
                                                                         new Class[] { protocol },
                                                                         new Invoker(addr, conf));
    long serverVersion = proxy.getProtocolVersion(protocol.getName(), 
                                                  clientVersion);
    if (serverVersion == clientVersion) {
      return proxy;
    } else {
      throw new VersionMismatch(protocol.getName(), clientVersion, 
                                serverVersion);
    }
}

Construct a client-side proxy object that implements the named protocol, talking to a server at the named address.

 public static RPC.Server getServer(Object instance,
    String bindAddress,
    int port,
    Configuration conf) throws IOException 
{
    return getServer(instance, bindAddress, port, 1, false, conf);
}

Construct a server for a protocol implementation instance listening on a port and address.

 public static RPC.Server getServer(Object instance,
    String bindAddress,
    int port,
    int numHandlers,
    boolean verbose,
    Configuration conf) throws IOException 
{
    return new Server(instance, conf, bindAddress, port, numHandlers, verbose);
}

Construct a server for a protocol implementation instance listening on a port and address.

 public static synchronized  void stopClient() 
{
    if (CLIENT != null) {
      CLIENT.stop();
      CLIENT = null;
    }
}

Stop all RPC client connections

 public static VersionedProtocol waitForProxy(Class protocol,
    long clientVersion,
    InetSocketAddress addr,
    Configuration conf) throws IOException 
{
    while (true) {
      try {
        return getProxy(protocol, clientVersion, addr, conf);
      } catch(ConnectException se) {  // namenode has not been started
        LOG.info("Server at " + addr + " not available yet, Zzzzz...");
      } catch(SocketTimeoutException te) {  // namenode is busy
        LOG.info("Problem connecting to server: " + addr);
      }
      try {
        Thread.sleep(1000);
      } catch (InterruptedException ie) {
        // IGNORE
      }
    }
}