netty中pipeline如何添加handler
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pipeline无疑是 netty中非常重要的一环,在io处理中netty通过已存放在pipeline中的handler有序处理socket中的信息,而pipeline中包含的都是一个个的handler，它是怎么添加进去的呢
创建代码如下:其中有handler和childhandler
public void start() throws Exception {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup group = new NioEventLoopGroup();
try {
ServerBootstrap sb = new ServerBootstrap();
sb.option(ChannelOption.SO_BACKLOG, 1024);
// 绑定线程池
sb.group(group, bossGroup)
// 指定使用的channel
.channel(NioServerSocketChannel.class)
// 绑定监听端口
.localAddress(this.port)
.handler(new LoggingHandler(LogLevel.INFO))
// 绑定客户端连接时候触发操作
.childHandler(new ChannelInitializer() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));
pipeline.addLast(new LengthFieldPrepender(4));
//字符串解码
pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
//字符串编码
pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
pipeline.addLast(new IdleStateHandler(0, 0, 120, TimeUnit.SECONDS));
}
});
// 服务器异步创建绑定
ChannelFuture cf = sb.bind().sync();
log.info(NettyServer.class + " 启动正在监听： " + cf.channel().localAddress());
// 关闭服务器通道
cf.channel().closeFuture().sync();
} finally {
// 释放线程池资源
group.shutdownGracefully().sync();
bossGroup.shutdownGracefully().sync();
}
} 顺着服务端bind方法点进去会看到如下:创建完channel实例后 会调用一个init方法
final ChannelFuture initAndRegister() {
Channel channel = null;
try {
channel = channelFactory.newChannel();
init(channel);
} catch (Throwable t) {
if (channel != null) {
// channel can be null if newChannel crashed (eg SocketException("too many open files"))
channel.unsafe().closeForcibly();
// as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor
return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t);
}
// as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor
return new DefaultChannelPromise(new FailedChannel(), 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;
}init方法为抽象方法 服务端实现如下
void init(Channel channel) throws Exception {
//省略若干
ChannelPipeline p = channel.pipeline();
final EventLoopGroup currentChildGroup = childGroup;
final ChannelHandler currentChildHandler = childHandler;
final Entry, Object>[] currentChildOptions;
final Entry, Object>[] currentChildAttrs;
synchronized (childOptions) {
currentChildOptions = childOptions.entrySet().toArray(newOptionArray(0));
}
synchronized (childAttrs) {
currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(0));
}
//看这里 添加了一个ChannelInitializer实例 实例中实现了initChannel 获取配置的handler添加到pipeline
p.addLast(new ChannelInitializer() {
@Override
public void initChannel(final Channel ch) throws Exception {
final ChannelPipeline pipeline = ch.pipeline();
ChannelHandler handler = config.handler();
if (handler != null) {
pipeline.addLast(handler);
}
ch.eventLoop().execute(new Runnable() {
@Override
public void run() {
pipeline.addLast(new ServerBootstrapAcceptor(
ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));
}
});
}
});
} 而pipeline的addlast方法如下
public final ChannelPipeline addLast(EventExecutorGroup group, String name, ChannelHandler handler) {
final AbstractChannelHandlerContext newCtx;
synchronized (this) {
checkMultiplicity(handler);
newCtx = newContext(group, filterName(name, handler), handler);
//这方法很简单 添加到链表中 但是此时添加的是上文的ChannelInitializer 而不是我们定义的handler
addLast0(newCtx);
// If the registered is false it means that the channel was not registered on an eventLoop yet.
// In this case we add the context to the pipeline and add a task that will call
// ChannelHandler.handlerAdded(...) once the channel is registered.
if (!registered) {
newCtx.setAddPending();
callHandlerCallbackLater(newCtx, true);
return this;
}
EventExecutor executor = newCtx.executor();
if (!executor.inEventLoop()) {
callHandlerAddedInEventLoop(newCtx, executor);
return this;
}
}
//这个方法就是关键 将ChannelInitializer中的handler添加到pipeline中 以及删除ChannelInitializer
//但请注意 首次注册不会走到这里 在前面的判断就会返回 会在注册的逻辑中触发 最终调用的一致
callHandlerAdded0(newCtx);
return this;
}查看ChannelInitializer中的关键代码如下 OK 通过如下代码我们就看到 调用了ChannelInitializer的initChannel方法 就是在最开始我们定义的那个，然后里面就用继续调用pipeline add我们真正的handler
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
if (ctx.channel().isRegistered()) {
// This should always be true with our current DefaultChannelPipeline implementation.
// The good thing about calling initChannel(...) in handlerAdded(...) is that there will be no ordering
// surprises if a ChannelInitializer will add another ChannelInitializer. This is as all handlers
// will be added in the expected order.
if (initChannel(ctx)) {
// We are done with init the Channel, removing the initializer now.
removeState(ctx);
}
}
}
private boolean initChannel(ChannelHandlerContext ctx) throws Exception {
if (initMap.add(ctx)) { // Guard against re-entrance.
try {
initChannel((C) ctx.channel());
} catch (Throwable cause) {
// Explicitly call exceptionCaught(...) as we removed the handler before calling initChannel(...).
// We do so to prevent multiple calls to initChannel(...).
exceptionCaught(ctx, cause);
} finally {
//看这里删除pipeline中的 ChannelInitializer ChannelInitializer 其实就是一个handler 只是它重写了handlerAdded方法
ChannelPipeline pipeline = ctx.pipeline();
if (pipeline.context(this) != null) {
pipeline.remove(this);
}
}
return true;
}
return false;
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