【Netty源码学习】BootStrap
BootStrap是客户端的启动类,其主要功能就是设置必要的参数然后启动客户端。
实现如下:
Bootstrap b = new Bootstrap(); b.group(group) .channel(NioSocketChannel.class) .option(ChannelOption.TCP_NODELAY, true) .handler(new ChannelInitializer<SocketChannel>() { @Override public void initChannel(SocketChannel ch) throws Exception { ChannelPipeline p = ch.pipeline(); p.addLast("decoder", new StringDecoder()); p.addLast("encoder", new StringEncoder()); p.addLast(new ClientHandler()); } }); ChannelFuture future = b.connect(HOST, PORT).sync();
首先是创建实例,然后设置group、channel、option和handler。
接下来就是连接服务器,主要的操作都在这部分进行操作。
public ChannelFuture connect(String inetHost, int inetPort) { return connect(InetSocketAddress.createUnresolved(inetHost, inetPort)); } public ChannelFuture connect(InetAddress inetHost, int inetPort) { return connect(new InetSocketAddress(inetHost, inetPort)); } public ChannelFuture connect(SocketAddress remoteAddress) { if (remoteAddress == null) { throw new NullPointerException("remoteAddress"); } validate(); return doResolveAndConnect(remoteAddress, config.localAddress()); }
private ChannelFuture doResolveAndConnect(final SocketAddress remoteAddress, final SocketAddress localAddress) { final ChannelFuture regFuture = initAndRegister(); final Channel channel = regFuture.channel(); if (regFuture.isDone()) { if (!regFuture.isSuccess()) { return regFuture; } return doResolveAndConnect0(channel, remoteAddress, localAddress, channel.newPromise()); } else { // Registration future is almost always fulfilled already, but just in case it's not. final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel); regFuture.addListener(new ChannelFutureListener() { @Override public void operationComplete(ChannelFuture future) throws Exception { // Direclty obtain the cause and do a null check so we only need one volatile read in case of a // failure. Throwable cause = future.cause(); if (cause != null) { // Registration on the EventLoop failed so fail the ChannelPromise directly to not cause an // IllegalStateException once we try to access the EventLoop of the Channel. promise.setFailure(cause); } else { // Registration was successful, so set the correct executor to use. // See https://github.com/netty/netty/issues/2586 promise.registered(); doResolveAndConnect0(channel, remoteAddress, localAddress, promise); } } }); return promise; } }
首先是执行final ChannelFuture regFuture = initAndRegister();调用父类的initAndRegister()函数,实现将Channel注册到Selector中,实现如下,调用config().group().register(channel),实现将Channel注册到Selector中。
final ChannelFuture initAndRegister() { Channel channel = null; try { channel = channelFactory.newChannel(); init(channel); } catch (Throwable t) { if (channel != null) { channel.unsafe().closeForcibly(); } return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t); } ChannelFuture regFuture = config().group().register(channel); if (regFuture.cause() != null) { if (channel.isRegistered()) { channel.close(); } else { channel.unsafe().closeForcibly(); } } return regFuture; }
接下的操作是将NioSocketChannel连接到Server端,实现的函数是doResolveAndConnect0,看如下代码,连接的具体实现在doContect中。
private ChannelFuture doResolveAndConnect0(final Channel channel, SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise promise) { try { final EventLoop eventLoop = channel.eventLoop(); final AddressResolver<SocketAddress> resolver = this.resolver.getResolver(eventLoop); if (!resolver.isSupported(remoteAddress) || resolver.isResolved(remoteAddress)) { // Resolver has no idea about what to do with the specified remote address or it's resolved already. doConnect(remoteAddress, localAddress, promise); return promise; } final Future<SocketAddress> resolveFuture = resolver.resolve(remoteAddress); if (resolveFuture.isDone()) { final Throwable resolveFailureCause = resolveFuture.cause(); if (resolveFailureCause != null) { // Failed to resolve immediately channel.close(); promise.setFailure(resolveFailureCause); } else { // Succeeded to resolve immediately; cached? (or did a blocking lookup) doConnect(resolveFuture.getNow(), localAddress, promise); } return promise; } // Wait until the name resolution is finished. resolveFuture.addListener(new FutureListener<SocketAddress>() { @Override public void operationComplete(Future<SocketAddress> future) throws Exception { if (future.cause() != null) { channel.close(); promise.setFailure(future.cause()); } else { doConnect(future.getNow(), localAddress, promise); } } }); } catch (Throwable cause) { promise.tryFailure(cause); } return promise; }
private static void doConnect( final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise connectPromise) { // This method is invoked before channelRegistered() is triggered. Give user handlers a chance to set up // the pipeline in its channelRegistered() implementation. final Channel channel = connectPromise.channel(); channel.eventLoop().execute(new Runnable() { @Override public void run() { if (localAddress == null) { channel.connect(remoteAddress, connectPromise); } else { channel.connect(remoteAddress, localAddress, connectPromise); } connectPromise.addListener(ChannelFutureListener.CLOSE_ON_FAILURE); } }); }
BootStrap总结起来有两个主要的功能,
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