netty使用tcp/ip协议传输数据。而tcp/ip协议是类似水流一样的数据传输方式。多次访问的时候有可能出现数据粘包的问题。客户端和服务器，协商定义一个特殊的分隔符号，分隔符号长度自定义。如：‘#’、‘$_$’、‘AA@’。在通讯的时候，只要没有发送分隔符号，则代表一条数据没有结束。
大致内容同前一篇博客相似，不同之处在于bootstrap.childHandler()方法，在该方法中，定义了一个ChannelHandler[] acceptorHandlers = new ChannelHandler[3];数组的三个元素分别对应：自定义结束符、自定义编码、自定义处理器。最后，将这个数组作为参数进行传递。
服务端代码如下：
public class Server4Delimiter {
// 监听线程组，监听客户端请求
private EventLoopGroup acceptorGroup = null;
// 处理客户端相关操作线程组，负责处理与客户端的数据通讯
private EventLoopGroup clientGroup = null;
// 服务启动相关配置信息
private ServerBootstrap bootstrap = null;
public Server4Delimiter(){
init();
}
private void init(){
acceptorGroup = new NioEventLoopGroup();
clientGroup = new NioEventLoopGroup();
bootstrap = new ServerBootstrap();
// 绑定线程组
bootstrap.group(acceptorGroup, clientGroup);
// 设定通讯模式为NIO
bootstrap.channel(NioServerSocketChannel.class);
// 设定缓冲区大小
bootstrap.option(ChannelOption.SO_BACKLOG, 1024);
// SO_SNDBUF发送缓冲区，SO_RCVBUF接收缓冲区，SO_KEEPALIVE开启心跳监测（保证连接有效）
bootstrap.option(ChannelOption.SO_SNDBUF, 16*1024)
.option(ChannelOption.SO_RCVBUF, 16*1024)
.option(ChannelOption.SO_KEEPALIVE, true);
}
public ChannelFuture doAccept(int port) throws InterruptedException{
bootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
// 数据分隔符, 定义的数据分隔符一定是一个ByteBuf类型的数据对象。
ByteBuf delimiter = Unpooled.copiedBuffer("$E$".getBytes());
ChannelHandler[] acceptorHandlers = new ChannelHandler[3];
// 处理固定结束标记符号的Handler。这个Handler没有@Sharable注解修饰，
// 必须每次初始化通道时创建一个新对象
// 使用特殊符号分隔处理数据粘包问题，也要定义每个数据包最大长度。netty建议数据有最大长度。
acceptorHandlers[0] = new DelimiterBasedFrameDecoder(1024, delimiter);
// 字符串解码器Handler，会自动处理channelRead方法的msg参数，将ByteBuf类型的数据转换为字符串对象
acceptorHandlers[1] = new StringDecoder(Charset.forName("UTF-8"));
acceptorHandlers[2] = new Server4DelimiterHandler();
ch.pipeline().addLast(acceptorHandlers);
}
});
ChannelFuture future = bootstrap.bind(port).sync();
return future;
}
public void release(){
this.acceptorGroup.shutdownGracefully();
this.clientGroup.shutdownGracefully();
}
public static void main(String[] args){
ChannelFuture future = null;
Server4Delimiter server = null;
try{
server = new Server4Delimiter();
future = server.doAccept(9999);
System.out.println("server started.");
future.channel().closeFuture().sync();
}catch(InterruptedException e){
e.printStackTrace();
}finally{
if(null != future){
try {
future.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
if(null != server){
server.release();
}
}
}
}
public class Server4DelimiterHandler extends ChannelHandlerAdapter {
// 业务处理逻辑
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
String message = msg.toString();
System.out.println("from client : " + message);
String line = "server message $E$ test delimiter handler!! $E$ second message $E$";
ctx.writeAndFlush(Unpooled.copiedBuffer(line.getBytes("UTF-8")));
}
// 异常处理逻辑
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
System.out.println("server exceptionCaught method run...");
// cause.printStackTrace();
ctx.close();
}
}
客户端代码如下：
public class Client4Delimiter {
// 处理请求和处理服务端响应的线程组
private EventLoopGroup group = null;
// 服务启动相关配置信息
private Bootstrap bootstrap = null;
public Client4Delimiter(){
init();
}
private void init(){
group = new NioEventLoopGroup();
bootstrap = new Bootstrap();
// 绑定线程组
bootstrap.group(group);
// 设定通讯模式为NIO
bootstrap.channel(NioSocketChannel.class);
}
public ChannelFuture doRequest(String host, int port) throws InterruptedException{
this.bootstrap.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
// 数据分隔符
ByteBuf delimiter = Unpooled.copiedBuffer("$E$".getBytes());
ChannelHandler[] handlers = new ChannelHandler[3];
handlers[0] = new DelimiterBasedFrameDecoder(1024, delimiter);
// 字符串解码器Handler，会自动处理channelRead方法的msg参数，将ByteBuf类型的数据转换为字符串对象
handlers[1] = new StringDecoder(Charset.forName("UTF-8"));
handlers[2] = new Client4DelimiterHandler();
ch.pipeline().addLast(handlers);
}
});
ChannelFuture future = this.bootstrap.connect(host, port).sync();
return future;
}
public void release(){
this.group.shutdownGracefully();
}
public static void main(String[] args) {
Client4Delimiter client = null;
ChannelFuture future = null;
try{
client = new Client4Delimiter();
future = client.doRequest("localhost", 9999);
Scanner s = null;
while(true){
s = new Scanner(System.in);
System.out.print("enter message send to server > ");
String line = s.nextLine();
future.channel().writeAndFlush(Unpooled.copiedBuffer(line.getBytes("UTF-8")));
TimeUnit.SECONDS.sleep(1);
}
}catch(Exception e){
e.printStackTrace();
}finally{
if(null != future){
try {
future.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
if(null != client){
client.release();
}
}
}
}
public class Client4DelimiterHandler extends ChannelHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
try{
String message = msg.toString();
System.out.println("from server : " + message);
}finally{
// 用于释放缓存。避免内存溢出
ReferenceCountUtil.release(msg);
}
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
System.out.println("client exceptionCaught method run...");
// cause.printStackTrace();
ctx.close();
}
}