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.

        if (ws.isRejected()) {
          if (firstHandler == null) {
            firstHandler = wsHandler;
          }
        } else {
          ChannelHandler handler = ctx.pipeline().get(HttpChunkContentCompressor.class);
          if (handler != null) {
            // remove compressor as its not needed anymore once connection was upgraded to websockets
            ctx.pipeline().remove(handler);
          }
          ws.connectNow();

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    // Flush out all pending data
    endReadAndFlush();


    // remove old http handlers and replace the old handler with one that handle plain sockets
    ChannelPipeline pipeline = channel.pipeline();
    ChannelHandler compressor = pipeline.get(HttpChunkContentCompressor.class);
    if (compressor != null) {
      pipeline.remove(compressor);
    }


    pipeline.remove("httpDecoder");

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        final AtomicBoolean isOn = new AtomicBoolean(true);


        final InetSocketAddress addr1 = UnitHelp.localSocketAddress();
        final InetSocketAddress addr2 = UnitHelp.localSocketAddress();


        final ChannelHandler handler1 = new EchoMessageHandler(rate, size);
        final ChannelHandler handler2 = new EchoMessageHandler(null, size);


        final NioEventLoopGroup group1 =
                new NioEventLoopGroup(1, new DefaultExecutorServiceFactory("group1"), NioUdtProvider.MESSAGE_PROVIDER);
        final NioEventLoopGroup group2 =
                new NioEventLoopGroup(1, new DefaultExecutorServiceFactory("group2"), NioUdtProvider.MESSAGE_PROVIDER);

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                        }
                        if (!ch.isRegistered()) {
                            continue;
                        }
                        //EventForwardHandler forwardHandler = forwarders[random.nextInt(forwarders.length)];
                        ChannelHandler handler = ch.pipeline().removeFirst();
                        ch.pipeline().addBefore(groups[random.nextInt(groups.length)], "recorder",
                                UUID.randomUUID().toString(), handler);
                    }
                }
            });

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    @Test
    public void testConstructWithChannelInitializer() {
        final Integer first = 1;
        final Integer second = 2;


        final ChannelHandler handler = new ChannelInboundHandlerAdapter() {
            @Override
            public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
                ctx.fireChannelRead(first);
                ctx.fireChannelRead(second);
            }

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    @Test
    public void testTooBigObject() throws IOException {
        MarshallerFactory marshallerFactory = createMarshallerFactory();
        MarshallingConfiguration configuration = createMarshallingConfig();


        ChannelHandler mDecoder = createDecoder(4);
        EmbeddedChannel ch = new EmbeddedChannel(mDecoder);


        ByteArrayOutputStream bout = new ByteArrayOutputStream();
        Marshaller marshaller = marshallerFactory.createMarshaller(configuration);
        marshaller.start(Marshalling.createByteOutput(bout));

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        if (handler() != null) {
            p.addLast(handler());
        }


        final EventLoopGroup currentChildGroup = childGroup;
        final ChannelHandler currentChildHandler = childHandler;
        final Entry<ChannelOption<?>, Object>[] currentChildOptions;
        final Entry<AttributeKey<?>, Object>[] currentChildAttrs;
        synchronized (childOptions) {
            currentChildOptions = childOptions.entrySet().toArray(newOptionArray(childOptions.size()));
        }

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            out.write(random.nextInt());
        }


        out.close();


        ChannelHandler ch = new SimpleChannelInboundHandler<Object>() {
            @Override
            public void messageReceived(ChannelHandlerContext ctx, Object msg) throws Exception {
            }


            @Override

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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