Interface ChannelHandler
- All Known Subinterfaces:
ChannelInboundHandler
,ChannelOutboundHandler
,WebSocketFrameDecoder
,WebSocketFrameEncoder
- All Known Implementing Classes:
AbstractBinaryMemcacheDecoder
,AbstractBinaryMemcacheEncoder
,AbstractMemcacheObjectAggregator
,AbstractMemcacheObjectDecoder
,AbstractMemcacheObjectEncoder
,AbstractRemoteAddressFilter
,AbstractSniHandler
,AbstractTrafficShapingHandler
,ApplicationProtocolNegotiationHandler
,Base64Decoder
,Base64Encoder
,BinaryMemcacheClientCodec
,BinaryMemcacheClientCodec.Decoder
,BinaryMemcacheClientCodec.Encoder
,BinaryMemcacheObjectAggregator
,BinaryMemcacheRequestDecoder
,BinaryMemcacheRequestEncoder
,BinaryMemcacheResponseDecoder
,BinaryMemcacheResponseEncoder
,BinaryMemcacheServerCodec
,ByteArrayDecoder
,ByteArrayEncoder
,ByteToMessageCodec
,ByteToMessageCodec.Encoder
,ByteToMessageDecoder
,Bzip2Decoder
,Bzip2Encoder
,ChannelDuplexHandler
,ChannelHandlerAdapter
,ChannelInboundHandlerAdapter
,ChannelInitializer
,ChannelOutboundHandlerAdapter
,ChannelTrafficShapingHandler
,ChunkedWriteHandler
,CleartextHttp2ServerUpgradeHandler
,CombinedChannelDuplexHandler
,CompatibleObjectEncoder
,CorsHandler
,DatagramDnsQueryDecoder
,DatagramDnsQueryEncoder
,DatagramDnsResponseDecoder
,DatagramDnsResponseEncoder
,DatagramPacketDecoder
,DatagramPacketEncoder
,DefaultChannelPipeline.HeadContext
,DefaultChannelPipeline.TailContext
,DeflateDecoder
,DeflateEncoder
,DelimiterBasedFrameDecoder
,DnsNameResolver.DnsResponseHandler
,DynamicAddressConnectHandler
,FastLzFrameDecoder
,FastLzFrameEncoder
,FixedLengthFrameDecoder
,FlowControlHandler
,FlushConsolidationHandler
,GlobalChannelTrafficShapingHandler
,GlobalTrafficShapingHandler
,HAProxyMessageDecoder
,HAProxyMessageEncoder
,Http2ChannelDuplexHandler
,Http2ConnectionHandler
,Http2FrameCodec
,Http2FrameLogger
,Http2MultiplexCodec
,Http2MultiplexHandler
,Http2StreamFrameToHttpObjectCodec
,HttpClientCodec
,HttpClientCodec.Decoder
,HttpClientCodec.Encoder
,HttpClientUpgradeHandler
,HttpContentCompressor
,HttpContentDecoder
,HttpContentDecompressor
,HttpContentEncoder
,HttpObjectAggregator
,HttpObjectDecoder
,HttpObjectEncoder
,HttpProxyHandler
,HttpProxyHandler.HttpClientCodecWrapper
,HttpRequestDecoder
,HttpRequestEncoder
,HttpResponseDecoder
,HttpResponseEncoder
,HttpServerCodec
,HttpServerCodec.HttpServerRequestDecoder
,HttpServerCodec.HttpServerResponseEncoder
,HttpServerExpectContinueHandler
,HttpServerKeepAliveHandler
,HttpServerUpgradeHandler
,HttpToHttp2ConnectionHandler
,IdleStateHandler
,InboundHttpToHttp2Adapter
,IpSubnetFilter
,JdkZlibDecoder
,JdkZlibEncoder
,JsonObjectDecoder
,JZlibDecoder
,JZlibEncoder
,LengthFieldBasedFrameDecoder
,LengthFieldPrepender
,LineBasedFrameDecoder
,LineEncoder
,LoggingHandler
,MessageAggregator
,MessageToByteEncoder
,MessageToMessageCodec
,MessageToMessageDecoder
,MessageToMessageEncoder
,MqttDecoder
,MqttEncoder
,ObjectDecoder
,ObjectEncoder
,OcspClient.Initializer
,OcspClientHandler
,OcspHttpHandler
,OcspServerCertificateValidator
,OptionalSslHandler
,PcapWriteHandler
,PerFrameDeflateDecoder
,PerFrameDeflateEncoder
,PerMessageDeflateDecoder
,PerMessageDeflateEncoder
,ProxyHandler
,ReadTimeoutHandler
,RedisArrayAggregator
,RedisBulkStringAggregator
,RedisDecoder
,RedisEncoder
,ReplayingDecoder
,ResolveAddressHandler
,RtspDecoder
,RtspEncoder
,RtspObjectDecoder
,RtspObjectEncoder
,RtspRequestDecoder
,RtspRequestEncoder
,RtspResponseDecoder
,RtspResponseEncoder
,RuleBasedIpFilter
,ServerBootstrap.ServerBootstrapAcceptor
,SimpleChannelInboundHandler
,SimpleUserEventChannelHandler
,SmtpRequestEncoder
,SmtpResponseDecoder
,SnappyFramedDecoder
,SnappyFrameDecoder
,SnappyFramedEncoder
,SnappyFrameEncoder
,SniHandler
,Socks4ClientDecoder
,Socks4ClientEncoder
,Socks4ProxyHandler
,Socks4ServerDecoder
,Socks4ServerEncoder
,Socks5ClientEncoder
,Socks5CommandRequestDecoder
,Socks5CommandResponseDecoder
,Socks5InitialRequestDecoder
,Socks5InitialResponseDecoder
,Socks5PasswordAuthRequestDecoder
,Socks5PasswordAuthResponseDecoder
,Socks5ProxyHandler
,Socks5ServerEncoder
,SocksAuthRequestDecoder
,SocksAuthResponseDecoder
,SocksCmdRequestDecoder
,SocksCmdResponseDecoder
,SocksInitRequestDecoder
,SocksInitResponseDecoder
,SocksMessageEncoder
,SocksPortUnificationServerHandler
,SpdyFrameCodec
,SpdyHttpCodec
,SpdyHttpDecoder
,SpdyHttpEncoder
,SpdyHttpResponseStreamIdHandler
,SpdySessionHandler
,SslClientHelloHandler
,SslHandler
,SslMasterKeyHandler
,SslMasterKeyHandler.WiresharkSslMasterKeyHandler
,StompSubframeAggregator
,StompSubframeDecoder
,StompSubframeEncoder
,StringDecoder
,StringEncoder
,TcpDnsQueryDecoder
,TcpDnsQueryEncoder
,TcpDnsResponseDecoder
,TcpDnsResponseEncoder
,UniqueIpFilter
,Utf8FrameValidator
,WebSocket00FrameDecoder
,WebSocket00FrameEncoder
,WebSocket07FrameDecoder
,WebSocket07FrameEncoder
,WebSocket08FrameDecoder
,WebSocket08FrameEncoder
,WebSocket13FrameDecoder
,WebSocket13FrameEncoder
,WebSocketClientCompressionHandler
,WebSocketClientExtensionHandler
,WebSocketClientProtocolHandler
,WebSocketClientProtocolHandshakeHandler
,WebSocketExtensionDecoder
,WebSocketExtensionEncoder
,WebSocketFrameAggregator
,WebSocketProtocolHandler
,WebSocketServerCompressionHandler
,WebSocketServerExtensionHandler
,WebSocketServerProtocolHandler
,WebSocketServerProtocolHandshakeHandler
,WriteTimeoutHandler
,XmlFrameDecoder
,ZlibDecoder
,ZlibEncoder
ChannelPipeline
.
Sub-types
ChannelHandler
itself does not provide many methods, but you usually have to implement one of its subtypes:
ChannelInboundHandler
to handle inbound I/O events, andChannelOutboundHandler
to handle outbound I/O operations.
Alternatively, the following adapter classes are provided for your convenience:
ChannelInboundHandlerAdapter
to handle inbound I/O events,ChannelOutboundHandlerAdapter
to handle outbound I/O operations, andChannelDuplexHandler
to handle both inbound and outbound events
For more information, please refer to the documentation of each subtype.
The context object
A ChannelHandler
is provided with a ChannelHandlerContext
object. A ChannelHandler
is supposed to interact with the
ChannelPipeline
it belongs to via a context object. Using the
context object, the ChannelHandler
can pass events upstream or
downstream, modify the pipeline dynamically, or store the information
(using AttributeKey
s) which is specific to the handler.
State management
AChannelHandler
often needs to store some stateful information.
The simplest and recommended approach is to use member variables:
public interface Message { // your methods here } public class DataServerHandler extendsBecause 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 an unauthenticated client can get the confidential information:SimpleChannelInboundHandler
<Message> { private boolean loggedIn;@Override
public void channelRead0(ChannelHandlerContext
ctx, Message message) { if (message instanceof LoginMessage) { authenticate((LoginMessage) message); loggedIn = true; } else (message instanceof GetDataMessage) { if (loggedIn) { ctx.writeAndFlush(fetchSecret((GetDataMessage) message)); } else { fail(); } } } ... }
// Create a new handler instance per channel. // SeeChannelInitializer.initChannel(Channel)
. public class DataServerInitializer extendsChannelInitializer
<Channel
> {@Override
public void initChannel(Channel
channel) { channel.pipeline().addLast("handler", new DataServerHandler()); } }
Using AttributeKey
s
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 AttributeKey
s which is provided by
ChannelHandlerContext
:
public interface Message { // your methods here }Now that the state of the handler is attached to the@Sharable
public class DataServerHandler extendsSimpleChannelInboundHandler
<Message> { private finalAttributeKey
<Boolean
> auth =AttributeKey.valueOf("auth")
;@Override
public void channelRead(ChannelHandlerContext
ctx, Message message) {Attribute
<Boolean
> attr = ctx.attr(auth); if (message instanceof LoginMessage) { authenticate((LoginMessage) o); attr.set(true); } else (message instanceof GetDataMessage) { if (Boolean.TRUE.equals(attr.get())) { ctx.writeAndFlush(fetchSecret((GetDataMessage) o)); } else { fail(); } } } ... }
ChannelHandlerContext
, you can add the
same handler instance to different pipelines:
public class DataServerInitializer extendsChannelInitializer
<Channel
> { private static final DataServerHandler SHARED = new DataServerHandler();@Override
public void initChannel(Channel
channel) { channel.pipeline().addLast("handler", SHARED); } }
The @Sharable
annotation
In the example above which used an AttributeKey
,
you might have noticed the @Sharable
annotation.
If a ChannelHandler
is annotated with the @Sharable
annotation, it means you can create an instance of the handler just once and
add it to one or more 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 ChannelHandler
, and
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.
-
Nested Class Summary
Nested ClassesModifier and TypeInterfaceDescriptionstatic @interface
Indicates that the same instance of the annotatedChannelHandler
can be added to one or moreChannelPipeline
s multiple times without a race condition. -
Method Summary
Modifier and TypeMethodDescriptionvoid
exceptionCaught
(ChannelHandlerContext ctx, Throwable cause) Deprecated.void
Gets called after theChannelHandler
was added to the actual context and it's ready to handle events.void
Gets called after theChannelHandler
was removed from the actual context and it doesn't handle events anymore.
-
Method Details
-
handlerAdded
Gets called after theChannelHandler
was added to the actual context and it's ready to handle events.- Throws:
Exception
-
handlerRemoved
Gets called after theChannelHandler
was removed from the actual context and it doesn't handle events anymore.- Throws:
Exception
-
exceptionCaught
Deprecated.if you want to handle this event you should implementChannelInboundHandler
and implement the method there.Gets called if aThrowable
was thrown.- Throws:
Exception
-
ChannelInboundHandler
and implement the method there.