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Chapter 57. Netty

Available as of Apache Camel 2.3

The netty component in Apache Camel is a socket communication component, based on the JBoss Netty community offering (available under an Apache 2.0 license). Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. Netty greatly simplifies and streamlines network programming such as TCP and UDP socket server.

This Apache Camel component supports both producer and consumer endpoints.

The netty component has several options and allows fine-grained control of a number of TCP/UDP communication parameters (buffer sizes, keepAlives, tcpNoDelay etc) and facilitates both In-Only and In-Out communication on a Apache Camel route.

The URI scheme for a netty component is as follows

netty:tcp://localhost:99999[?options]
netty:udp://remotehost:99999/[?options]

This component supports producer and consumer endpoints for both TCP and UDP.

You can append query options to the URI in the following format, ?option=value&option=value&...

Name Default Value Description
keepAlive true Setting to ensure socket is not closed due to inactivity
tcpNoDelay true Setting to improve TCP protocol performance
broadcast false Setting to choose Multicast over UDP
connectTimeout 10000 Time to wait for a socket connection to be available. Value is in millis.
reuseAddress true Setting to facilitate socket multiplexing
sync true Setting to set endpoint as one-way or request-response
ssl false Setting to specify whether SSL encryption is applied to this endpoint
sendBufferSize 65536 bytes The TCP/UDP buffer sizes to be used during outbound communication. Size is bytes.
receiveBufferSize 65536 bytes The TCP/UDP buffer sizes to be used during inbound communication. Size is bytes.
corePoolSize 10 The number of allocated threads at component startup. Defaults to 10
maxPoolSize 100 The maximum number of threads that may be allocated to this endpoint. Defaults to 100
disconnect false Whether or not to disconnect(close) from Netty Channel right after use. Can be used for both consumer and producer.
lazyChannelCreation true Channels can be lazily created to avoid exceptions, if the remote server is not up and running when the Apache Camel producer is started.
transferExchange false Only used for TCP. You can transfer the exchange over the wire instead of just the body. The following fields are transferred: In body, Out body, fault body, In headers, Out headers, fault headers, exchange properties, exchange exception. This requires that the objects are serializable. Apache Camel will exclude any non-serializable objects and log it at WARN level.
disconnectOnNoReply true If sync is enabled then this option dictates NettyConsumer if it should disconnect where there is no reply to send back.
noReplyLogLevel WARN If sync is enabled this option dictates NettyConsumer which logging level to use when logging a there is no reply to send back. Values are: FATAL, ERROR, INFO, DEBUG, OFF.
allowDefaultCodec true Camel 2.4: The netty component installs a default codec if both, encoder/deocder is null and textline is false. Setting allowDefaultCodec to false prevents the netty component from installing a default codec as the first element in the filter chain.
textline false Camel 2.4: Only used for TCP. If no codec is specified, you can use this flag to indicate a text line based codec; if not specified or the value is false, then Object Serialization is assumed over TCP.
delimiter LINE Camel 2.4: The delimiter to use for the textline codec. Possible values are LINE and NULL.
decoderMaxLineLength 1024 Camel 2.4: The max line length to use for the textline codec.
autoAppendDelimiter true Camel 2.4: Whether or not to auto append missing end delimiter when sending using the textline codec.
encoding null Camel 2.4: The encoding (a charset name) to use for the textline codec. If not provided, Camel will use the JVM default Charset.

Codec Handlers and SSL Keystores can be enlisted in the Registry, such as in the Spring XML file. The values that could be passed in, are the following:

Name Description
passphrase password setting to use in order to encrypt/decrypt payloads sent using SSH
keyStoreFormat keystore format to be used for payload encryption. Defaults to "JKS" if not set
securityProvider Security provider to be used for payload encryption. Defaults to "SunX509" if not set.
keyStoreFile Client side certificate keystore to be used for encryption
trustStoreFile Server side certificate keystore to be used for encryption
sslHandler Reference to a class that could be used to return an SSL Handler
encoder A custom Handler class that can be used to perform special marshalling of outbound payloads. Must override org.jboss.netty.channel.ChannelDownStreamHandler.
encorders A list of encoder to be used. You can use a String which have values separated by comma, and have the values be looked up in the Registry. Just remember to prefix the value with # so Apache Camel knows it should lookup.
decoder A custom Handler class that can be used to perform special marshalling of inbound payloads. Must override org.jboss.netty.channel.ChannelUpStreamHandler.
decoders A list of decorder to be used. You can use a String which have values separated by comma, and have the values be looked up in the Registry. Just remember to prefix the value with # so Apache Camel knows it should lookup.

In Producer mode, the component provides the ability to send payloads to a socket endpoint using either TCP or UDP protocols (with optional SSL support).

The producer mode supports both one-way and request-response based operations.

In Consumer mode, the component provides the ability to:

The consumer mode supports both one-way and request-response based operations.

RouteBuilder builder = new RouteBuilder() {
  public void configure() {
    from("netty:udp://localhost:5155?sync=true")
      .process(new Processor() {
         public void process(Exchange exchange) throws Exception {
           Poetry poetry = (Poetry) exchange.getIn().getBody();
           poetry.setPoet("Dr. Sarojini Naidu");
           exchange.getOut().setBody(poetry);
         }
       }
    }
};
RouteBuilder builder = new RouteBuilder() {
  public void configure() {
       from("netty:tcp://localhost:5150")
           .to("mock:result"); 
  }
};
JndiRegistry registry = new JndiRegistry(createJndiContext());
registry.bind("password", "changeit");
registry.bind("ksf", new File("src/test/resources/keystore.jks"));
registry.bind("tsf", new File("src/test/resources/keystore.jks"));

context.createRegistry(registry);
context.addRoutes(new RouteBuilder() {
  public void configure() {
      String netty_ssl_endpoint = 
         "netty:tcp://localhost:5150?sync=true&ssl=true&passphrase=#password"
         + "&keyStoreFile=#ksf&trustStoreFile=#tsf";
      String return_string =
         "When You Go Home, Tell Them Of Us And Say,"
         + "For Your Tomorrow, We Gave Our Today.";
      
      from(netty_ssl_endpoint)
       .process(new Processor() {
          public void process(Exchange exchange) throws Exception {
            exchange.getOut().setBody(return_string);                           
          }
       }
  }
});

In certain cases it may be necessary to add chains of encoders and decoders to the netty pipeline. To add multpile codecs to a Apache Camel netty endpoint the 'encoders' and 'decoders' uri parameters should be used. Like the 'encoder' and 'decoder' parameters they are used to supply references (to lists of ChannelUpstreamHandlers and ChannelDownstreamHandlers) that should be added to the pipeline. Note that if encoders is specified then the encoder param will be ignored, similarly for decoders and the decoder param.

The lists of codecs need to be added to the Apache Camel's registry so they can be resolved when the endpoint is created.

LengthFieldBasedFrameDecoder lengthDecoder = new LengthFieldBasedFrameDecoder(1048576, 0, 4, 0, 4);
StringDecoder stringDecoder = new StringDecoder();
registry.bind("length-decoder", lengthDecoder);
registry.bind("string-decoder", stringDecoder);

LengthFieldPrepender lengthEncoder = new LengthFieldPrepender(4);
StringEncoder stringEncoder = new StringEncoder();
registry.bind("length-encoder", lengthEncoder);
registry.bind("string-encoder", stringEncoder);

List<ChannelUpstreamHandler> decoders = new ArrayList<ChannelUpstreamHandler>();
decoders.add(lengthDecoder);
decoders.add(stringDecoder);

List<ChannelDownstreamHandler> encoders = new ArrayList<ChannelDownstreamHandler>();
encoders.add(lengthEncoder);
encoders.add(stringEncoder);

registry.bind("encoders", encoders);
registry.bind("decoders", decoders);

Spring's native collections support can be used to specify the codec lists in an application context

    <util:list id="decoders" list-class="java.util.LinkedList">
        <bean class="org.jboss.netty.handler.codec.frame.LengthFieldBasedFrameDecoder">
            <constructor-arg value="1048576"/>
            <constructor-arg value="0"/>
            <constructor-arg value="4"/>
            <constructor-arg value="0"/>
            <constructor-arg value="4"/>
        </bean>
        <bean class="org.jboss.netty.handler.codec.string.StringDecoder"/>
    </util:list>

    <util:list id="encoders" list-class="java.util.LinkedList">
        <bean class="org.jboss.netty.handler.codec.frame.LengthFieldPrepender">
            <constructor-arg value="4"/>
        </bean>
        <bean class="org.jboss.netty.handler.codec.string.StringEncoder"/>
    </util:list>

    <bean id="length-encoder" class="org.jboss.netty.handler.codec.frame.LengthFieldPrepender">
        <constructor-arg value="4"/>
    </bean>
    <bean id="string-encoder" class="org.jboss.netty.handler.codec.string.StringEncoder"/>

    <bean id="length-decoder" class="org.jboss.netty.handler.codec.frame.LengthFieldBasedFrameDecoder">
        <constructor-arg value="1048576"/>
        <constructor-arg value="0"/>
        <constructor-arg value="4"/>
        <constructor-arg value="0"/>
        <constructor-arg value="4"/>
    </bean>
    <bean id="string-decoder" class="org.jboss.netty.handler.codec.string.StringDecoder"/>

</beans>

The bean names can then be used in netty endpoint definitions either as a comma separated list or contained in a List e.g.

                from("direct:multiple-codec").to("netty:tcp://localhost:5150?encoders=#encoders&sync=false");
                
                from("netty:tcp://localhost:5150?decoders=#length-decoder,#string-decoder&sync=false").to("mock:multiple-codec");
            }
        };
    }
}

or via spring.

<camelContext id="multiple-netty-codecs-context" xmlns="http://camel.apache.org/schema/spring">
    <route>
        <from uri="direct:multiple-codec"/>
        <to uri="netty:tcp://localhost:5150?encoders=#encoders&ync=false"/>
    </route>
    <route>
        <from uri="netty:tcp://localhost:5150?decoders=#length-decoder,#string-decoder&ync=false"/>
        <to uri="mock:multiple-codec"/>
    </route>
</camelContext>

When acting as a server you sometimes want to close the channel when, for example, a client conversion is finished. You can do this by simply setting the endpoint option disconnect=true.

However you can also instruct Apache Camel on a per message basis as follows. To instruct Apache Camel to close the channel, you should add a header with the key CamelNettyCloseChannelWhenComplete set to a boolean true value. For instance, the example below will close the channel after it has written the bye message back to the client:

        from("netty:tcp://localhost:8080").process(new Processor() {
            public void process(Exchange exchange) throws Exception {
                String body = exchange.getIn().getBody(String.class);
                exchange.getOut().setBody("Bye " + body);
                // some condition which determines if we should close
                if (close) {
                    exchange.getOut().setHeader(NettyConstants.NETTY_CLOSE_CHANNEL_WHEN_COMPLETE, true);
                }
            }
        });

Available as of Camel 2.5

Custom channel pipelines provide complete control to the user over the handler/interceptor chain by inserting custom handler(s), encoder(s) and decoders without having to specify them in the Netty Endpoint URL in a very simple way.

In order to add a custom pipeline, a custom channel pipeline factory must be created and registered with the context through the context registry (JNDIRegistry,or the Spring ApplicationContextRegistry etc).

A custom pipeline factory must be constructed as follows

The example below shows how ServerChannel Pipeline factory may be created

public class SampleServerChannelPipelineFactory extends ServerPipelineFactory {
    private int maxLineSize = 1024;
    private boolean invoked;

    public ChannelPipeline getPipeline() throws Exception {
        invoked = true;
      
        ChannelPipeline channelPipeline = Channels.pipeline();
      
        channelPipeline.addLast("encoder-SD", new StringEncoder(CharsetUtil.UTF_8));
        channelPipeline.addLast("decoder-DELIM", new DelimiterBasedFrameDecoder(maxLineSize, true, Delimiters.lineDelimiter()));
        channelPipeline.addLast("decoder-SD", new StringDecoder(CharsetUtil.UTF_8));
        channelPipeline.addLast("handler", new ServerChannelHandler(consumer));

        return channelPipeline;
    }
      
    public boolean isfactoryInvoked() {
        return invoked;
    }
}

The custom channel pipeline factory can then be added to the registry and instantiated/utilized on a camel route as follows:

Registry registry = camelContext.getRegistry();
serverPipelineFactory = new TestServerChannelPipelineFactory();
registry.bind("spf", serverPipelineFactory);
context.addRoutes(new RouteBuilder() {
    public void configure() {
        String netty_ssl_endpoint =
          "netty:tcp://localhost:5150?serverPipelineFactory=#spf";
        String return_string =
          "When You Go Home, Tell Them Of Us And Say,"
          + "For Your Tomorrow, We Gave Our Today.";
      
        from(netty_ssl_endpoint)
          .process(new Processor() {
            public void process(Exchange exchange) throws Exception {
              exchange.getOut().setBody(return_string);
            }
          }
    }
});