本文同步至 http://www.waylau.com/netty-time-out-and-heartbeat/
本文介绍了 Netty 超时机制的原理,以及如何在连接闲置时发送一个心跳来维持连接。
Netty 超时机制的介绍
Netty 的超时类型 IdleState 主要分为:
- ALL_IDLE : 一段时间内没有数据接收或者发送
- READER_IDLE : 一段时间内没有数据接收
- WRITER_IDLE : 一段时间内没有数据发送
在 Netty 的 timeout 包下,主要类有:
- IdleStateEvent : 超时的事件
- IdleStateHandler : 超时状态处理
- ReadTimeoutHandler : 读超时状态处理
- WriteTimeoutHandler : 写超时状态处理
其中 IdleStateHandler 包含了读\写超时状态处理,比如
private static final int READ_IDEL_TIME_OUT = 4; // 读超时
private static final int WRITE_IDEL_TIME_OUT = 5;// 写超时
private static final int ALL_IDEL_TIME_OUT = 7; // 所有超时
new IdleStateHandler(READ_IDEL_TIME_OUT,
WRITE_IDEL_TIME_OUT, ALL_IDEL_TIME_OUT, TimeUnit.SECONDS));
上述例子,在 IdleStateHandler 中定义了读超时的时间是 4 秒, 写超时的时间是 5 秒,其他所有的超时时间是 7 秒。
应用 IdleStateHandler
既然 IdleStateHandler 包括了读\写超时状态处理,那么很多时候 ReadTimeoutHandler 、 WriteTimeoutHandler 都可以不用使用。定义另一个名为 HeartbeatHandlerInitializer 的 ChannelInitializer :
public class HeartbeatHandlerInitializer extends ChannelInitializer<Channel> {
private static final int READ_IDEL_TIME_OUT = 4; // 读超时
private static final int WRITE_IDEL_TIME_OUT = 5;// 写超时
private static final int ALL_IDEL_TIME_OUT = 7; // 所有超时
@Override
protected void initChannel(Channel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new IdleStateHandler(READ_IDEL_TIME_OUT,
WRITE_IDEL_TIME_OUT, ALL_IDEL_TIME_OUT, TimeUnit.SECONDS)); // 1
pipeline.addLast(new HeartbeatServerHandler()); // 2
}
}
- 使用了 IdleStateHandler ,分别设置了读、写超时的时间
- 定义了一个 HeartbeatServerHandler 处理器,用来处理超时时,发送心跳
定义了一个心跳处理器
public class HeartbeatServerHandler extends ChannelInboundHandlerAdapter {
// Return a unreleasable view on the given ByteBuf
// which will just ignore release and retain calls.
private static final ByteBuf HEARTBEAT_SEQUENCE = Unpooled
.unreleasableBuffer(Unpooled.copiedBuffer("Heartbeat",
CharsetUtil.UTF_8)); // 1
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt)
throws Exception {
if (evt instanceof IdleStateEvent) { // 2
IdleStateEvent event = (IdleStateEvent) evt;
String type = "";
if (event.state() == IdleState.READER_IDLE) {
type = "read idle";
} else if (event.state() == IdleState.WRITER_IDLE) {
type = "write idle";
} else if (event.state() == IdleState.ALL_IDLE) {
type = "all idle";
}
ctx.writeAndFlush(HEARTBEAT_SEQUENCE.duplicate()).addListener(
ChannelFutureListener.CLOSE_ON_FAILURE); // 3
System.out.println( ctx.channel().remoteAddress()+"超时类型:" + type);
} else {
super.userEventTriggered(ctx, evt);
}
}
}
- 定义了心跳时,要发送的内容
- 判断是否是 IdleStateEvent 事件,是则处理
- 将心跳内容发送给客户端
服务器
服务器代码比较简单,启动后侦听 8082 端口
public final class HeartbeatServer {
static final int PORT = 8082;
public static void main(String[] args) throws Exception {
// Configure the server.
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG, 100)
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new HeartbeatHandlerInitializer());
// Start the server.
ChannelFuture f = b.bind(PORT).sync();
// Wait until the server socket is closed.
f.channel().closeFuture().sync();
} finally {
// Shut down all event loops to terminate all threads.
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
客户端测试
客户端用操作系统自带的 Telnet 程序即可:
telnet 127.0.0.1 8082
效果
源码
见 https://github.com/waylau/netty-4-user-guide-demos 中 heartbeat
包
参考
- Netty 4.x 用户指南 https://github.com/waylau/netty-4-user-guide
- Netty 实战(精髓) https://github.com/waylau/essential-netty-in-action