Examples of io.netty.channel.ChannelHandler

io.netty.channel.ChannelHandler
methods here } public class DataServerHandler extends {@link ChannelInboundMessageHandlerAdapter}<Message> { private boolean loggedIn; {@code @Override}public void messageReceived( {@link ChannelHandlerContext} ctx, Message message) {{@link Channel} ch = e.getChannel();if (message instanceof LoginMessage) { authenticate((LoginMessage) message); loggedIn = true; } else (message instanceof GetDataMessage) { if (loggedIn) { ch.write(fetchSecret((GetDataMessage) message)); } else { fail(); } } } ... } Because the handler instance has a state variable which is dedicated to one connection, you have to create a new handler instance for each new channel to avoid a race condition where a unauthenticated client can get the confidential information:
```
 // Create a new handler instance per channel. // See  {@link ChannelInitializer#initChannel(Channel)}. public class DataServerInitializer extends  {@link ChannelInitializer}< {@link Channel}> { {@code @Override}public void initChannel( {@link Channel} channel) {channel.pipeline().addLast("handler", new DataServerHandler()); } } 
```
Using an attachment
Although it's recommended to use member variables to store the state of a handler, for some reason you might not want to create many handler instances. In such a case, you can use an attachment which is provided by {@link ChannelHandlerContext}:
```
 public interface Message { // your methods here } {@code @Sharable}public class DataServerHandler extends  {@link ChannelInboundMessageHandlerAdapter}<Message> { private final  {@link AttributeKey}< {@link Boolean}> auth = new  {@link AttributeKey}< {@link Boolean}>("auth"); // This handler will receive a sequence of increasing integers starting // from 1. {@code @Override}public void messageReceived( {@link ChannelHandlerContext} ctx, {@link Integer} integer) {{@link Attribute}< {@link Boolean}> attr = ctx.getAttr(auth); {@code @Override}public void messageReceived( {@link ChannelHandlerContext} ctx, Message message) {{@link Channel} ch = ctx.channel();if (message instanceof LoginMessage) { authenticate((LoginMessage) o); attr.set(true); } else (message instanceof GetDataMessage) { if (Boolean.TRUE.equals(attr.get())) { ch.write(fetchSecret((GetDataMessage) o)); } else { fail(); } } } ... } 
```
Now that the state of the handler is stored as an attachment, you can add the same handler instance to different pipelines:
```
 public class DataServerInitializer extends  {@link ChannelInitializer}< {@link Channel}> { private static final DataServerHandler SHARED = new DataServerHandler(); {@code @Override}public void initChannel( {@link Channel} channel) {channel.pipeline().addLast("handler", SHARED); } } 
```
The {@code @Sharable} annotation
In the examples above which used an attachment, you might have noticed the {@code @Sharable} annotation.
If a {@link ChannelHandler} is annotated with the {@code @Sharable}annotation, it means you can create an instance of the handler just once and add it to one or more {@link ChannelPipeline}s multiple times without a race condition.
If this annotation is not specified, you have to create a new handler instance every time you add it to a pipeline because it has unshared state such as member variables.
This annotation is provided for documentation purpose, just like the JCIP annotations.
Additional resources worth reading

Please refer to the {@link ChannelHandler}, and {@link ChannelPipeline} to find out more about inbound and outbound operations,what fundamental differences they have, how they flow in a pipeline, and how to handle the operation in your application.

        }
       
        pipeline.addLast("decoder", new HttpRequestDecoder());
        List<ChannelHandler> decoders = consumer.getConfiguration().getDecoders();
        for (int x = 0; x < decoders.size(); x++) {
            ChannelHandler decoder = decoders.get(x);
            if (decoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                decoder = ((ChannelHandlerFactory) decoder).newChannelHandler();
            }
            pipeline.addLast("decoder-" + x, decoder);
        }
        pipeline.addLast("aggregator", new HttpObjectAggregator(configuration.getChunkedMaxContentLength()));


        pipeline.addLast("encoder", new HttpResponseEncoder());
        List<ChannelHandler> encoders = consumer.getConfiguration().getEncoders();
        for (int x = 0; x < encoders.size(); x++) {
            ChannelHandler encoder = encoders.get(x);
            if (encoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                encoder = ((ChannelHandlerFactory) encoder).newChannelHandler();
            }
            pipeline.addLast("encoder-" + x, encoder);
        }
        if (supportCompressed()) {
            pipeline.addLast("deflater", new HttpContentCompressor());
        }
        
        int port = consumer.getConfiguration().getPort();
        ChannelHandler handler = consumer.getEndpoint().getComponent().getMultiplexChannelHandler(port).getChannelHandler();
        
        if (consumer.getConfiguration().isUsingExecutorService()) {
            EventExecutorGroup applicationExecutor = consumer.getEndpoint().getComponent().getExecutorService();
            pipeline.addLast(applicationExecutor, "handler", handler);
        } else {

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        pipeline.addLast("http", new HttpClientCodec());
        
        List<ChannelHandler> encoders = producer.getConfiguration().getEncoders();
        for (int x = 0; x < encoders.size(); x++) {
            ChannelHandler encoder = encoders.get(x);
            if (encoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                encoder = ((ChannelHandlerFactory) encoder).newChannelHandler();
            }
            pipeline.addLast("encoder-" + x, encoder);
        }


        List<ChannelHandler> decoders = producer.getConfiguration().getDecoders();
        for (int x = 0; x < decoders.size(); x++) {
            ChannelHandler decoder = decoders.get(x);
            if (decoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                decoder = ((ChannelHandlerFactory) decoder).newChannelHandler();
            }
            pipeline.addLast("decoder-" + x, decoder);
        }
        pipeline.addLast("aggregator", new HttpObjectAggregator(configuration.getChunkedMaxContentLength()));


        if (producer.getConfiguration().getRequestTimeout() > 0) {
            if (LOG.isTraceEnabled()) {
                LOG.trace("Using request timeout {} millis", producer.getConfiguration().getRequestTimeout());
            }
            ChannelHandler timeout = new ReadTimeoutHandler(producer.getConfiguration().getRequestTimeout(), TimeUnit.MILLISECONDS);
            pipeline.addLast("timeout", timeout);
        }
       
        // handler to route Camel messages
        pipeline.addLast("handler", new HttpClientChannelHandler(producer));

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            addToPipeline("ssl", channelPipeline, sslHandler);
        }


        List<ChannelHandler> decoders = producer.getConfiguration().getDecoders();
        for (int x = 0; x < decoders.size(); x++) {
            ChannelHandler decoder = decoders.get(x);
            if (decoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                decoder = ((ChannelHandlerFactory) decoder).newChannelHandler();
            }
            addToPipeline("decoder-" + x, channelPipeline, decoder);
        }


        List<ChannelHandler> encoders = producer.getConfiguration().getEncoders();
        for (int x = 0; x < encoders.size(); x++) {
            ChannelHandler encoder = encoders.get(x);
            if (encoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                encoder = ((ChannelHandlerFactory) encoder).newChannelHandler();
            }
            addToPipeline("encoder-" + x, channelPipeline, encoder);
        }


        // do we use request timeout?
        if (producer.getConfiguration().getRequestTimeout() > 0) {
            if (LOG.isTraceEnabled()) {
                LOG.trace("Using request timeout {} millis", producer.getConfiguration().getRequestTimeout());
            }
            ChannelHandler timeout = new ReadTimeoutHandler(producer.getConfiguration().getRequestTimeout(), TimeUnit.MILLISECONDS);
            addToPipeline("timeout", channelPipeline, timeout);
        }


        // our handler must be added last
        addToPipeline("handler", channelPipeline, new ClientChannelHandler(producer));

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            addToPipeline("ssl", channelPipeline, sslHandler);
        }


        List<ChannelHandler> encoders = consumer.getConfiguration().getEncoders();
        for (int x = 0; x < encoders.size(); x++) {
            ChannelHandler encoder = encoders.get(x);
            if (encoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                encoder = ((ChannelHandlerFactory) encoder).newChannelHandler();
            }
            addToPipeline("encoder-" + x, channelPipeline, encoder);
        }


        List<ChannelHandler> decoders = consumer.getConfiguration().getDecoders();
        for (int x = 0; x < decoders.size(); x++) {
            ChannelHandler decoder = decoders.get(x);
            if (decoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                decoder = ((ChannelHandlerFactory) decoder).newChannelHandler();
            }
            addToPipeline("decoder-" + x, channelPipeline, decoder);

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        if (producer.getConfiguration().getRequestTimeout() > 0) {
            if (LOG.isTraceEnabled()) {
                LOG.trace("Using request timeout {} millis", producer.getConfiguration().getRequestTimeout());
            }
            ChannelHandler timeout = new ReadTimeoutHandler(producer.getConfiguration().getRequestTimeout(), TimeUnit.MILLISECONDS);
            pipeline.addLast("timeout", timeout);
        }


        // handler to route Camel messages
        pipeline.addLast("handler", new HttpClientChannelHandler(producer));

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        if (supportCompressed()) {
            pipeline.addLast("deflater", new HttpContentCompressor());
        }


        int port = consumer.getConfiguration().getPort();
        ChannelHandler handler = consumer.getEndpoint().getComponent().getMultiplexChannelHandler(port).getChannelHandler();
        
        if (consumer.getConfiguration().isUsingExecutorService()) {
            EventExecutorGroup applicationExecutor = consumer.getEndpoint().getComponent().getExecutorService();
            pipeline.addLast(applicationExecutor, "handler", handler);
        } else {

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        if (LOG.isTraceEnabled()) {
            LOG.trace("Message received: {}", msg);
        }


        if (producer.getConfiguration().getRequestTimeout() > 0) {
            ChannelHandler handler = ctx.pipeline().get("timeout");
            if (handler != null) {
                LOG.trace("Removing timeout channel as we received message");
                ctx.pipeline().remove(handler);
            }
        }

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            addToPipeline("ssl", channelPipeline, sslHandler);
        }


        List<ChannelHandler> encoders = consumer.getConfiguration().getEncoders();
        for (int x = 0; x < encoders.size(); x++) {
            ChannelHandler encoder = encoders.get(x);
            if (encoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                encoder = ((ChannelHandlerFactory) encoder).newChannelHandler();
            }
            addToPipeline("encoder-" + x, channelPipeline, encoder);
        }


        List<ChannelHandler> decoders = consumer.getConfiguration().getDecoders();
        for (int x = 0; x < decoders.size(); x++) {
            ChannelHandler decoder = decoders.get(x);
            if (decoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                decoder = ((ChannelHandlerFactory) decoder).newChannelHandler();
            }
            addToPipeline("decoder-" + x, channelPipeline, decoder);

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            addToPipeline("ssl", channelPipeline, sslHandler);
        }


        List<ChannelHandler> decoders = producer.getConfiguration().getDecoders();
        for (int x = 0; x < decoders.size(); x++) {
            ChannelHandler decoder = decoders.get(x);
            if (decoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                decoder = ((ChannelHandlerFactory) decoder).newChannelHandler();
            }
            addToPipeline("decoder-" + x, channelPipeline, decoder);
        }


        List<ChannelHandler> encoders = producer.getConfiguration().getEncoders();
        for (int x = 0; x < encoders.size(); x++) {
            ChannelHandler encoder = encoders.get(x);
            if (encoder instanceof ChannelHandlerFactory) {
                // use the factory to create a new instance of the channel as it may not be shareable
                encoder = ((ChannelHandlerFactory) encoder).newChannelHandler();
            }
            addToPipeline("encoder-" + x, channelPipeline, encoder);
        }


        // do we use request timeout?
        if (producer.getConfiguration().getRequestTimeout() > 0) {
            if (LOG.isTraceEnabled()) {
                LOG.trace("Using request timeout {} millis", producer.getConfiguration().getRequestTimeout());
            }
            ChannelHandler timeout = new ReadTimeoutHandler(producer.getConfiguration().getRequestTimeout(), TimeUnit.MILLISECONDS);
            addToPipeline("timeout", channelPipeline, timeout);
        }


        // our handler must be added last
        addToPipeline("handler", channelPipeline, new ClientChannelHandler(producer));

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        pipeline.addFirst(READ_TIMEOUT_LIFECYCLE_MANAGER_HANDLER_NAME, new ReadTimeoutHandlerLifecycleManager());
    }


    public static void disableReadTimeout(ChannelPipeline pipeline) {


        /**
         * Since, ChannelPipeline.remove() is blocking when not called from the associated eventloop, we do not remove
         * the handler. Instead we decativate the handler (invoked by the associated eventloop) here so that it does not
         * generate any more timeouts.
         * The handler is activated on next write to this pipeline.
         *

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Examples of io.netty.channel.ChannelHandler

Using an attachment

The {@code @Sharable} annotation

Additional resources worth reading

Related Classes of io.netty.channel.ChannelHandler