Build a Netty HelloWorld Server in IntelliJ IDEA and Examine Core Components

What is Netty

Netty is a Java NIO‑based asynchronous event‑driven network application framework that provides an API for building TCP and UDP client/server applications while also exposing low‑level APIs. It is fully asynchronous and widely used in projects such as Dubbo and Elasticsearch.

Project setup

Create a new Gradle project in IntelliJ IDEA, configure the JDK, and add the Netty dependency in build.gradle:

dependencies {
    // https://mvnrepository.com/artifact/io.netty/netty-all
    compile group: 'io.netty', name: 'netty-all', version: '4.1.52.Final'
}

Gradle resolves the JAR after saving.

Server implementation

Create package com.badao.netty and class HelloWorldServer with a main method:

package com.badao.netty;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class HelloWorldServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workerGroup)
                           .channel(NioServerSocketChannel.class)
                           .childHandler(new HelloWorldServerInitializer());
            ChannelFuture channelFuture = serverBootstrap.bind(70).sync();
            channelFuture.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

The two EventLoopGroup instances follow Netty’s recommendation: bossGroup accepts incoming connections, workerGroup processes traffic.

Initializer

Create HelloWorldServerInitializer extending ChannelInitializer<SocketChannel> to configure the pipeline:

package com.badao.netty;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.http.HttpServerCodec;

public class HelloWorldServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast("httpServerCodec", new HttpServerCodec());
        pipeline.addLast("helloWorldServerHandler", new HelloWorldServerHandler());
    }
}

Handler

Implement HelloWorldServerHandler extending SimpleChannelInboundHandler<HttpObject> to respond to HTTP requests:

package com.badao.netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.*;
import io.netty.util.CharsetUtil;

public class HelloWorldServerHandler extends SimpleChannelInboundHandler<HttpObject> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, HttpObject msg) throws Exception {
        if (msg instanceof HttpRequest) {
            ByteBuf content = Unpooled.copiedBuffer("公众号:霸道的程序猿", CharsetUtil.UTF_8);
            FullHttpResponse response = new DefaultFullHttpResponse(
                    HttpVersion.HTTP_1_1, HttpResponseStatus.OK, content);
            response.headers().set(HttpHeaderNames.CONTENT_TYPE, "text/plain");
            response.headers().set(HttpHeaderNames.CONTENT_LENGTH, content.readableBytes());
            ctx.writeAndFlush(response);
        }
    }
}

Running and verification

In .idea/gradle.xml set the option delegatedBuild to false so that the main method runs as a regular Java application rather than a Gradle task.

Execute the main method; the server listens on port 70. Verify with:

curl http://localhost:70

The response body should be the plain‑text string “公众号:霸道的程序猿”, confirming that the Netty server is operational.

References

Netty version: 4.1.52.Final. Maven Central URL for the dependency: https://mvnrepository.com/artifact/io.netty/netty-all