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适读人群:Java-Netty 初级
Netty 自动重连机制
版本:netty 4.1.*
申明:本文旨在重新分享讨论 Netty 官方相关案例,添加部分个人理解与要点解析。
这个是 InChat 的案例地址,里面补充了详细的注释,比起官方会容易看一点。
官方案例地址:https://netty.io/4.1/xref/io/…
正文
- UptimeClient(客户端)
- UptimeClientHandler
- UptimeServer(服务端)
- UptimeServerHandler
要点介绍
- IdleStateHandler https://netty.io/4.1/api/io/n…
一个对 Channel 尚未执行读、写或两次操作的触发器
属性 | 含义 |
---|---|
readerIdleTime | 在 IdleStateEvent 其状态 IdleState.READER_IDLE 时的指定时间段没有执行读操作将被触发。指定 0 禁用。 |
writerIdleTime | 在 IdleStateEvent 其状态 IdleState.WRITER_IDLE 时的指定时间段没有执行写操作将被触发。指定 0 禁用。 |
allIdleTime | 一个 IdleStateEvent 其状态 IdleState.ALL_IDLE 时的时间在规定的时间进行读取和写入都将被触发。指定 0 禁用。 |
如下一个在没有信息时发送 ping 消息,且 30 秒没有入站信息则关闭连接
public class MyChannelInitializer extends ChannelInitializer<Channel> {
@Override
public void initChannel(Channel channel) {channel.pipeline().addLast("idleStateHandler", new IdleStateHandler(60, 30, 0));
channel.pipeline().addLast("myHandler", new MyHandler());
}
}
// Handler should handle the IdleStateEvent triggered by IdleStateHandler.
public class MyHandler extends ChannelDuplexHandler {
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {if (evt instanceof IdleStateEvent) {IdleStateEvent e = (IdleStateEvent) evt;
if (e.state() == IdleState.READER_IDLE) {ctx.close();
} else if (e.state() == IdleState.WRITER_IDLE) {ctx.writeAndFlush(new PingMessage());
}
}
}
}
项目源码
- UptimeClient
/**
* Created by MySelf on 2019/8/27.
*/
public final class UptimeClient {static final String HOST = System.getProperty("host", "127.0.0.1");
static final int PORT = Integer.parseInt(System.getProperty("port", "8080"));
// 重新连接前睡眠 5 秒
static final int RECONNECT_DELAY = Integer.parseInt(System.getProperty("reconnectDelay", "5"));
// 当服务器在 10 秒内不发送任何内容时重新连接。private static final int READ_TIMEOUT = Integer.parseInt(System.getProperty("readTimeout", "10"));
private static final UptimeClientHandler handler = new UptimeClientHandler();
private static final Bootstrap bs = new Bootstrap();
public static void main(String[] args) throws Exception {EventLoopGroup group = new NioEventLoopGroup();
bs.group(group)
.channel(NioSocketChannel.class)
.remoteAddress(HOST,PORT)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new IdleStateHandler(READ_TIMEOUT,0,0),handler);
}
});
bs.connect();}
static void connect(){bs.connect().addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {if (future.cause() != null){
handler.startTime = -1;
handler.println("Failed to connect:" + future.cause());
}
}
});
}
}
- UptimeClientHandler
/**
* Created by MySelf on 2019/8/27.
*/
@ChannelHandler.Sharable
public class UptimeClientHandler extends SimpleChannelInboundHandler<Object> {
long startTime = -1;
@Override
protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {//Discard received data}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {if (startTime < 0){startTime = System.currentTimeMillis();
}
println("Connected to:" + ctx.channel().remoteAddress());
}
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {println("Disconnected from:" + ctx.channel().remoteAddress());
}
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {if (!(evt instanceof IdleStateEvent)){return;}
IdleStateEvent e = (IdleStateEvent)evt;
if (e.state() == IdleState.READER_IDLE){
// 连接正常,但是没有读信息,关闭连接
println("Disconnecting due to no inbound traffic");
ctx.close();}
}
@Override
public void channelUnregistered(ChannelHandlerContext ctx) throws Exception {
// 睡眠 5 秒
println("Sleeping for:" + UptimeClient.RECONNECT_DELAY + 's');
// 启动线程重新连接
ctx.channel().eventLoop().schedule(new Runnable() {
@Override
public void run() {println("Reconnecting to:" + UptimeClient.HOST + ":" + UptimeClient.PORT);
UptimeClient.connect();}
},UptimeClient.RECONNECT_DELAY, TimeUnit.SECONDS);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();
ctx.close();}
void println(String msg){if (startTime < 0){System.err.format("[SERVER IS DOWN] %s%n",msg);
} else {System.err.format("[UPTIME: %5ds] %s%n",(System.currentTimeMillis() - startTime)/1000,msg);
}
}
}
- UptimeServer
/**
* Created by MySelf on 2019/8/27.
*/
public final class UptimeServer {private static final int PORT = Integer.parseInt(System.getProperty("port", "8080"));
private static final UptimeServerHandler handler = new UptimeServerHandler();
private UptimeServer(){}
public static void main(String[] args) throws Exception {EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup,workerGroup)
.channel(NioServerSocketChannel.class)
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(handler);
}
});
// Bind and start to accept incoming connections.
ChannelFuture f = b.bind(PORT).sync();
// Wait until the server socket is closed.
// In this example, this does not happen, but you can do that to gracefully
// shut down your server.
f.channel().closeFuture().sync();}finally {workerGroup.shutdownGracefully();
bossGroup.shutdownGracefully();}
}
}
- UptimeServerHandler
/**
* Created by MySelf on 2019/8/27.
*/
@ChannelHandler.Sharable
public class UptimeServerHandler extends SimpleChannelInboundHandler<Object> {
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
// Close the connection when an exception is raised.
cause.printStackTrace();
ctx.close();}
@Override
protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {// discard}
}