Netty 超時機制的介紹

Netty 的超時類型 IdleState 主要分為：

ALL_IDLE : 一段時間內沒有數據接收或者發送
READER_IDLE ：一段時間內沒有數據接收
WRITER_IDLE ：一段時間內沒有數據發送

在 Netty 的 timeout 包下，主要類有：

IdleStateEvent ：超時的事件
IdleStateHandler ：超時狀態處理
ReadTimeoutHandler ：讀超時狀態處理
WriteTimeoutHandler ：寫超時狀態處理

其中 IdleStateHandler 包含了讀\寫超時狀態處理，比如

private static final int READ_IDEL_TIME_OUT = 4; // 讀超時
private static final int WRITE_IDEL_TIME_OUT = 5;// 寫超時
private static final int ALL_IDEL_TIME_OUT = 7; // 所有超時
new IdleStateHandler(READ_IDEL_TIME_OUT,
WRITE_IDEL_TIME_OUT, ALL_IDEL_TIME_OUT, TimeUnit.SECONDS));

上述例子，在 IdleStateHandler 中定義了讀超時的時間是 4 秒，寫超時的時間是 5 秒，其他所有的超時時間是 7 秒。

應用 IdleStateHandler

既然 IdleStateHandler 包括了讀\寫超時狀態處理，那麼很多時候 ReadTimeoutHandler 、 WriteTimeoutHandler 都可以不用使用。定義另一個名為 HeartbeatHandlerInitializer 的 ChannelInitializer ：

public class HeartbeatHandlerInitializer extends ChannelInitializer {
private static final int READ_IDEL_TIME_OUT = 4; // 讀超時
private static final int WRITE_IDEL_TIME_OUT = 5;// 寫超時
private static final int ALL_IDEL_TIME_OUT = 7; // 所有超時
@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 ，分別設置了讀、寫超時的時間

定義了一個 HeartbeatServerHandler 處理器，用來處理超時時，發送心跳

定義了一個心跳處理器

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()+"超時類型：" + type);
} else {
super.userEventTriggered(ctx, evt);
}
}
}

定義了心跳時，要發送的內容

判斷是否是 IdleStateEvent 事件，是則處理

將心跳內容發送給客戶端

服務器

服務器代碼比較簡單，啟動後偵聽 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();
}
}
}