Netty Http客户端：如何将客户端启动，发送请求和客户端关闭分为不同的方法

Question

I found most of the http client examples using Netty seem to be following this code structure:

public void run() {
    EventLoopGroup group = new NioEventLoopGroup();
    try {
        Bootstrap b = new Bootstrap();
        b.group(group)
         .channel(NioSocketChannel.class)
         .handler(new HttpSnoopClientInitializer(sslCtx));

        // Make the connection attempt.
        Channel ch = b.connect(host, port).sync().channel();
        // send something
        ch.writeAndFlush(XXXX);
        // Wait for the server to close the connection.
        ch.closeFuture().sync();
    } finally {
        // Shut down executor threads to exit.
        group.shutdownGracefully();
    }
}

So if I understand it correctly, each time I send a request, I need to create a client, and call client.run() on it. That said, it seems I can only make one "fixed" request at a time.

I need a long-standing client that can send multiple requests. More specifically, there will be another thread sending instruction to the client, and each time the client gets the instruction, it will send a request. Something like this:

Client client = new Client();
client.start();

client.sendRequest(request1);
client.sendRequest(request2);
...
client.shutDownGracefully(); // not sure if this shutdown is necessary or not
// because I need a long-standing client to wait for instructions to send requests
// in this sense it's kinda like a server.

I have tried something like this: from this link

public MyClient(String host, int port) {
    System.out.println("Initializing client and connecting to server..");
    EventLoopGroup workerGroup = new NioEventLoopGroup();

    Bootstrap b = new Bootstrap();
    b.group(workerGroup)
        .channel(NioSocketChannel.class)
        .option(ChannelOption.SO_KEEPALIVE, true)
        .handler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel channel) throws Exception {
                channel.pipeline().addLast(new StringDecoder());
                channel.pipeline().addLast(new StringEncoder());
                channel.pipeline().addLast(new MyAppClientHandler());
            }
        });

    channelFuture = b.connect(host, port);
}

public ResponseFuture send(final String msg) {
    final ResponseFuture responseFuture = new ResponseFuture();

    channelFuture.addListener(new GenericFutureListener<ChannelFuture>() {
        @Override
        public void operationComplete(ChannelFuture future)
                throws Exception {
            channelFuture.channel().pipeline().get(MyAppClientHandler.class).setResponseFuture(responseFuture);
            channelFuture.channel().writeAndFlush(msg);                             
        }
    });

    return responseFuture;
}

public void close() {
    channelFuture.channel().close();        
}

The problem is that it seems this code didn't call workerGroup.shutDownGracefully() , so I'm guessing this can have problems. Is there a way to split the "start client", "send request", "shutdown client" into separate methods? Thanks in advance!

Answer 1

The easiest solution will be to use a ChannelPool provided by netty: https://netty.io/news/2015/05/07/4-0-28-Final.html

It provides gracefulshutdown , maxconnections , etc out-of-the-box.