client.java

package test;
import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import java.nio.charset.Charset;
public class NettyTest {
    public static void main(String[] args) throws Exception {
        String host = args[0];
        int port = Integer.parseInt(args[1]);
        int sleepMillis = Integer.parseInt(args[2]);
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap()
                    .group(workerGroup)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                                @Override
                                public void channelActive(final ChannelHandlerContext ctx) {
                                    System.out.println("channelActive");
                                    try {
                                        System.out.println("Sleeping...");
                                        Thread.sleep(sleepMillis);
                                    } catch (InterruptedException e) {
                                        e.printStackTrace();
                                    }
                                }
                                @Override
                                public void channelRead(ChannelHandlerContext ctx, Object msg) {
                                    System.out.println("channelRead");
                                    ByteBuf m = (ByteBuf) msg;
                                    try {
                                        int bytesAvaliable = m.readableBytes();
                                        System.out.println(bytesAvaliable + " readable bytes in response buffer");
                                        m.readBytes(bytesAvaliable);
                                        System.out.println(m.getCharSequence(0, bytesAvaliable, Charset.defaultCharset()));
                                        ctx.close();
                                    } finally {
                                        m.release();
                                    }
                                }
                                @Override
                                public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
                                    cause.printStackTrace();
                                    ctx.close();
                                }
                            });
                        }
                    });
            // Start the client.
            ChannelFuture f = b.connect(host, port).sync();
            // Wait until the connection is closed.
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }
}

Output

$ gradle shadowJar && java -jar build/libs/async-java-all.jar localhost 6379 10000
:compileJava UP-TO-DATE
:processResources NO-SOURCE
:classes UP-TO-DATE
:shadowJar UP-TO-DATE

BUILD SUCCESSFUL

Total time: 0.999 secs
log4j:WARN No appenders could be found for logger (io.netty.util.internal.logging.InternalLoggerFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
channelActive
Sleeping...
channelRead
36 readable bytes in response buffer
-ERR max number of clients reached```