ChannelInitializer Class — netty Architecture

Source Code

transport/src/main/java/io/netty/channel/ChannelInitializer.java lines 53–158

@Sharable
public abstract class ChannelInitializer<C extends Channel> extends ChannelInboundHandlerAdapter {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(ChannelInitializer.class);
    // We use a Set as a ChannelInitializer is usually shared between all Channels in a Bootstrap /
    // ServerBootstrap. This way we can reduce the memory usage compared to use Attributes.
    private final Set<ChannelHandlerContext> initMap = ConcurrentHashMap.newKeySet();

    /**
     * This method will be called once the {@link Channel} was registered. After the method returns this instance
     * will be removed from the {@link ChannelPipeline} of the {@link Channel}.
     *
     * @param ch            the {@link Channel} which was registered.
     * @throws Exception    is thrown if an error occurs. In that case it will be handled by
     *                      {@link #exceptionCaught(ChannelHandlerContext, Throwable)} which will by default close
     *                      the {@link Channel}.
     */
    protected abstract void initChannel(C ch) throws Exception;

    @Override
    @SuppressWarnings("unchecked")
    public final void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        // Normally this method will never be called as handlerAdded(...) should call initChannel(...) and remove
        // the handler.
        if (initChannel(ctx)) {
            // we called initChannel(...) so we need to call now pipeline.fireChannelRegistered() to ensure we not
            // miss an event.
            ctx.pipeline().fireChannelRegistered();

            // We are done with init the Channel, removing all the state for the Channel now.
            removeState(ctx);
        } else {
            // Called initChannel(...) before which is the expected behavior, so just forward the event.
            ctx.fireChannelRegistered();
        }
    }

    /**
     * Handle the {@link Throwable} by logging and closing the {@link Channel}. Sub-classes may override this.
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        if (logger.isWarnEnabled()) {
            logger.warn("Failed to initialize a channel. Closing: " + ctx.channel(), cause);
        }
        ctx.close();
    }

    /**
     * {@inheritDoc} If override this method ensure you call super!
     */
    @Override
    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);
            }
        }
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        initMap.remove(ctx);
    }

    @SuppressWarnings("unchecked")
    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 {