利用Netty构建自定义协议的通信

在复杂的网络世界中，各种应用之间通信需要依赖各种各样的协议，比如：​​HTTP​​​,​​Telnet​​​,​​FTP​​​,​​SMTP​​等等。

在开发过程中，有时候我们需要构建一些适应自己业务的应用层协议，​​Netty​​作为一个非常优秀的网络通信框架，可以帮助我们完成自定义协议的通信。

一般而言，我们制定的协议需要两个部分：

• Header : 协议头部，放置一些Meta信息。
• Content : 应用之间交互的信息主体。

例如：

| Version | Content-Length | SessionId | Content |
| Version | Content-Length | SessionId | Content |

其中​​Version​​​,​​Content-Length​​​,​​SessionId​​​就是Header信息，​​Content​​​就是交互的主体。给这个协议起一个名字叫做​​luck​​​,依照​​luck​​协议，我们构建一个类。

// 消息的头部
public class LuckHeader {

    // 协议版本
    private int version;
    // 消息内容长度
    private int contentLength;
    // 服务名称
    private String sessionId;

    public LuckHeader(int version, int contentLength, String sessionId) {
        this.version = version;
        this.contentLength = contentLength;
        this.sessionId = sessionId;
    }

    public int getVersion() {
        return version;
    }

    public void setVersion(int version) {
        this.version = version;
    }

    public int getContentLength() {
        return contentLength;
    }

    public void setContentLength(int contentLength) {
        this.contentLength = contentLength;
    }

    public String getSessionId() {
        return sessionId;
    }

    public void setSessionId(String sessionId) {
        this.sessionId = sessionId;
    }
}

// 消息的主体
public class LuckMessage {

    private LuckHeader luckHeader;
    private String content;

    public LuckMessage(LuckHeader luckHeader, String content) {
        this.luckHeader = luckHeader;
        this.content = content;
    }

    public LuckHeader getLuckHeader() {
        return luckHeader;
    }

    public void setLuckHeader(LuckHeader luckHeader) {
        this.luckHeader = luckHeader;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    @Override
    public String toString() {
        return String.format("[version=%d,contentLength=%d,sessionId=%s,content=%s]",
                luckHeader.getVersion(),
                luckHeader.getContentLength(),
                luckHeader.getSessionId(),
                content);
    }
}
// 消息的头部
public class LuckHeader {

    // 协议版本
    private int version;
    // 消息内容长度
    private int contentLength;
    // 服务名称
    private String sessionId;

    public LuckHeader(int version, int contentLength, String sessionId) {
        this.version = version;
        this.contentLength = contentLength;
        this.sessionId = sessionId;
    }

    public int getVersion() {
        return version;
    }

    public void setVersion(int version) {
        this.version = version;
    }

    public int getContentLength() {
        return contentLength;
    }

    public void setContentLength(int contentLength) {
        this.contentLength = contentLength;
    }

    public String getSessionId() {
        return sessionId;
    }

    public void setSessionId(String sessionId) {
        this.sessionId = sessionId;
    }
}

// 消息的主体
public class LuckMessage {

    private LuckHeader luckHeader;
    private String content;

    public LuckMessage(LuckHeader luckHeader, String content) {
        this.luckHeader = luckHeader;
        this.content = content;
    }

    public LuckHeader getLuckHeader() {
        return luckHeader;
    }

    public void setLuckHeader(LuckHeader luckHeader) {
        this.luckHeader = luckHeader;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    @Override
    public String toString() {
        return String.format("[version=%d,contentLength=%d,sessionId=%s,content=%s]",
                luckHeader.getVersion(),
                luckHeader.getContentLength(),
                luckHeader.getSessionId(),
                content);
    }
}

那么我们在​​Netty​​中如何去对这种自定义的协议编码(Encode)呢?

在​​Netty​​​中对数据进行编码解码需要利用​​Codec​​​组件，​​Codec​​组件中分为：

• Encoder : 编码器，将出站的数据从一种格式转换成另外一种格式。
• Decoder : 解码器，将入站的数据从一种格式转换成另外一种格式。

​​LuckDecoder.java​​

public class LuckDecoder extends ByteToMessageDecoder {

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {

        // 获取协议的版本
        int version = in.readInt();
        // 获取消息长度
        int contentLength = in.readInt();
        // 获取SessionId
        byte[] sessionByte = new byte[36];
        in.readBytes(sessionByte);
        String sessionId = new String(sessionByte);

        // 组装协议头
        LuckHeader header = new LuckHeader(version, contentLength, sessionId);

        // 读取消息内容
        byte[] content = in.readBytes(in.readableBytes()).array();

        LuckMessage message = new LuckMessage(header, new String(content));

        out.add(message);
    }
}
public class LuckDecoder extends ByteToMessageDecoder {

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {

        // 获取协议的版本
        int version = in.readInt();
        // 获取消息长度
        int contentLength = in.readInt();
        // 获取SessionId
        byte[] sessionByte = new byte[36];
        in.readBytes(sessionByte);
        String sessionId = new String(sessionByte);

        // 组装协议头
        LuckHeader header = new LuckHeader(version, contentLength, sessionId);

        // 读取消息内容
        byte[] content = in.readBytes(in.readableBytes()).array();

        LuckMessage message = new LuckMessage(header, new String(content));

        out.add(message);
    }
}

​​LuckEncoder.java​​

@ChannelHandler.Sharable
public class LuckEncoder extends MessageToByteEncoder<LuckMessage> {

    @Override
    protected void encode(ChannelHandlerContext ctx, LuckMessage message, ByteBuf out) throws Exception {

        // 将Message转换成二进制数据
        LuckHeader header = message.getLuckHeader();

        // 这里写入的顺序就是协议的顺序.

        // 写入Header信息
        out.writeInt(header.getVersion());
        out.writeInt(message.getContent().length());
        out.writeBytes(header.getSessionId().getBytes());

        // 写入消息主体信息
        out.writeBytes(message.getContent().getBytes());
    }
}
@ChannelHandler.Sharable
public class LuckEncoder extends MessageToByteEncoder<LuckMessage> {

    @Override
    protected void encode(ChannelHandlerContext ctx, LuckMessage message, ByteBuf out) throws Exception {

        // 将Message转换成二进制数据
        LuckHeader header = message.getLuckHeader();

        // 这里写入的顺序就是协议的顺序.

        // 写入Header信息
        out.writeInt(header.getVersion());
        out.writeInt(message.getContent().length());
        out.writeBytes(header.getSessionId().getBytes());

        // 写入消息主体信息
        out.writeBytes(message.getContent().getBytes());
    }
}

编写一个逻辑控制层，展现server接收到的协议信息：

public class NettyLuckHandler extends SimpleChannelInboundHandler<Message> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Message msg) throws Exception {
        // 简单地打印出server接收到的消息
        System.out.println(msg.toString());
    }
}
public class NettyLuckHandler extends SimpleChannelInboundHandler<Message> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Message msg) throws Exception {
        // 简单地打印出server接收到的消息
        System.out.println(msg.toString());
    }
}

编写完成之后，把​​编解码器​​​和​​逻辑控制器​​放入初始化组件中:

public class NettyLuckInitializer extends ChannelInitializer<SocketChannel> {

    private static final LuckEncoder ENCODER = new LuckEncoder();

    @Override
    protected void initChannel(SocketChannel channel) throws Exception {

        ChannelPipeline pipeline = channel.pipeline();

        // 添加编解码器, 由于ByteToMessageDecoder的子类无法使用@Sharable注解,
        // 这里必须给每个Handler都添加一个独立的Decoder.
        pipeline.addLast(ENCODER);
        pipeline.addLast(new LuckDecoder());

        // 添加逻辑控制层
        pipeline.addLast(new NettyLuckHandler());

    }
}
public class NettyLuckInitializer extends ChannelInitializer<SocketChannel> {

    private static final LuckEncoder ENCODER = new LuckEncoder();

    @Override
    protected void initChannel(SocketChannel channel) throws Exception {

        ChannelPipeline pipeline = channel.pipeline();

        // 添加编解码器, 由于ByteToMessageDecoder的子类无法使用@Sharable注解,
        // 这里必须给每个Handler都添加一个独立的Decoder.
        pipeline.addLast(ENCODER);
        pipeline.addLast(new LuckDecoder());

        // 添加逻辑控制层
        pipeline.addLast(new NettyLuckHandler());

    }
}

编写一个服务端启动类:

public class NettyLuckServer {

    // 指定端口号
    private static final int PORT = 8888;

    public static void main(String args[]) throws InterruptedException {

        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {

            ServerBootstrap serverBootstrap = new ServerBootstrap();
            // 指定socket的一些属性
            serverBootstrap.option(ChannelOption.SO_BACKLOG, 1024);
            serverBootstrap.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)  // 指定是一个NIO连接通道
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new NettyLuckInitializer());

            // 绑定对应的端口号,并启动开始监听端口上的连接
            Channel ch = serverBootstrap.bind(PORT).sync().channel();

            System.out.printf("luck协议启动地址：127.0.0.1:%d/\n", PORT);

            // 等待关闭,同步端口
            ch.closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}
public class NettyLuckServer {

    // 指定端口号
    private static final int PORT = 8888;

    public static void main(String args[]) throws InterruptedException {

        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {

            ServerBootstrap serverBootstrap = new ServerBootstrap();
            // 指定socket的一些属性
            serverBootstrap.option(ChannelOption.SO_BACKLOG, 1024);
            serverBootstrap.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)  // 指定是一个NIO连接通道
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new NettyLuckInitializer());

            // 绑定对应的端口号,并启动开始监听端口上的连接
            Channel ch = serverBootstrap.bind(PORT).sync().channel();

            System.out.printf("luck协议启动地址：127.0.0.1:%d/\n", PORT);

            // 等待关闭,同步端口
            ch.closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

光有服务端并不行，没法测试我们的server是不是成功了。所以我们还需要编写一个客户端程序。

​​LuckClientInitializer.java​​

public class LuckClientInitializer extends ChannelInitializer<SocketChannel> {

    private static final LuckEncoder ENCODER = new LuckEncoder();

    @Override
    protected void initChannel(SocketChannel channel) throws Exception {

        ChannelPipeline pipeline = channel.pipeline();

        // 添加编解码器, 由于ByteToMessageDecoder的子类无法使用@Sharable注解,
        // 这里必须给每个Handler都添加一个独立的Decoder.
        pipeline.addLast(ENCODER);
        pipeline.addLast(new LuckDecoder());

        // and then business logic.
        pipeline.addLast(new NettyLuckClientHandler());

    }
}
public class LuckClientInitializer extends ChannelInitializer<SocketChannel> {

    private static final LuckEncoder ENCODER = new LuckEncoder();

    @Override
    protected void initChannel(SocketChannel channel) throws Exception {

        ChannelPipeline pipeline = channel.pipeline();

        // 添加编解码器, 由于ByteToMessageDecoder的子类无法使用@Sharable注解,
        // 这里必须给每个Handler都添加一个独立的Decoder.
        pipeline.addLast(ENCODER);
        pipeline.addLast(new LuckDecoder());

        // and then business logic.
        pipeline.addLast(new NettyLuckClientHandler());

    }
}

​​LuckClientHandler.java​​

public class LuckClientHandler extends SimpleChannelInboundHandler<LuckMessage> {

    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, LuckMessage message) throws Exception {
        System.out.println(message);
    }
}
public class LuckClientHandler extends SimpleChannelInboundHandler<LuckMessage> {

    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, LuckMessage message) throws Exception {
        System.out.println(message);
    }
}

​​LuckClient.java​​

public class LuckClient {

    public static void main(String args[]) throws InterruptedException {

        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new NettyLuckInitializer());

            // Start the connection attempt.
            Channel ch = b.connect("127.0.0.1", 8888).sync().channel();

            int version = 1;
            String sessionId = UUID.randomUUID().toString();
            String content = "I'm the luck protocol!";

            LuckHeader header = new LuckHeader(version, content.length(), sessionId);
            LuckMessage message = new LuckMessage(header, content);
            ch.writeAndFlush(message);

            ch.close();

        } finally {
            group.shutdownGracefully();
        }
    }
}
public class LuckClient {

    public static void main(String args[]) throws InterruptedException {

        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new NettyLuckInitializer());

            // Start the connection attempt.
            Channel ch = b.connect("127.0.0.1", 8888).sync().channel();

            int version = 1;
            String sessionId = UUID.randomUUID().toString();
            String content = "I'm the luck protocol!";

            LuckHeader header = new LuckHeader(version, content.length(), sessionId);
            LuckMessage message = new LuckMessage(header, content);
            ch.writeAndFlush(message);

            ch.close();

        } finally {
            group.shutdownGracefully();
        }
    }
}

先运行​​NettyLuckServer.java​​​，然后再去运行​​LuckClient.java​​可以看到控制的输出

四月 15, 2016 11:31:34 下午 io.netty.handler.logging.LoggingHandler channelRegistered
信息: [id: 0x92534c29] REGISTERED
四月 15, 2016 11:31:34 下午 io.netty.handler.logging.LoggingHandler bind
信息: [id: 0x92534c29] BIND(0.0.0.0/0.0.0.0:8888)
luck协议启动地址：127.0.0.1:8888 
四月 15, 2016 11:31:34 下午 io.netty.handler.logging.LoggingHandler channelActive
信息: [id: 0x92534c29, L:/0:0:0:0:0:0:0:0:8888] ACTIVE
四月 15, 2016 11:31:54 下午 io.netty.handler.logging.LoggingHandler logMessage
信息: [id: 0x92534c29, L:/0:0:0:0:0:0:0:0:8888] RECEIVED: [id: 0x67a91c6b, L:/127.0.0.1:8888 - R:/127.0.0.1:53585]
[version=1,contentLength=22,sessionId=cff7b3ea-1188-4314-abaa-de04db32d39f,content=I'm the luck protocol!]

服务端顺利解析出了我们自定义的​​luck​​协议。