TCP Adapters

TCP inbound and outbound channel adapters that use connection factories mentioned earlier are provided. These adapters have two relevant attributes: connection-factory and channel. The connection-factory attribute indicates which connection factory is to be used to manage connections for the adapter. The channel attribute specifies the channel on which messages arrive at an outbound adapter and on which messages are placed by an inbound adapter. While both inbound and outbound adapters can share a connection factory, server connection factories are always “owned” by an inbound adapter. Client connection factories are always “owned” by an outbound adapter. Only one adapter of each type may get a reference to a connection factory. The following example shows how to define client and server TCP connection factories:

<bean id="javaSerializer"
      class="org.springframework.core.serializer.DefaultSerializer"/>
<bean id="javaDeserializer"
      class="org.springframework.core.serializer.DefaultDeserializer"/>

<int-ip:tcp-connection-factory id="server"
    type="server"
    port="1234"
    deserializer="javaDeserializer"
    serializer="javaSerializer"
    using-nio="true"
    single-use="true"/>

<int-ip:tcp-connection-factory id="client"
    type="client"
    host="localhost"
    port="#{server.port}"
    single-use="true"
    so-timeout="10000"
    deserializer="javaDeserializer"
    serializer="javaSerializer"/>

<int:channel id="input" />

<int:channel id="replies">
    <int:queue/>
</int:channel>

<int-ip:tcp-outbound-channel-adapter id="outboundClient"
    channel="input"
    connection-factory="client"/>

<int-ip:tcp-inbound-channel-adapter id="inboundClient"
    channel="replies"
    connection-factory="client"/>

<int-ip:tcp-inbound-channel-adapter id="inboundServer"
    channel="loop"
    connection-factory="server"/>

<int-ip:tcp-outbound-channel-adapter id="outboundServer"
    channel="loop"
    connection-factory="server"/>

<int:channel id="loop"/>

Also see Annotation-Based Configuration and Using the Java DSL for TCP Components.

In the preceding configuration, messages arriving in the input channel are serialized over connections created by client connection factory, received at the server, and placed on the loop channel. Since loop is the input channel for outboundServer, the message is looped back over the same connection, received by inboundClient, and deposited in the replies channel. Java serialization is used on the wire.

Normally, inbound adapters use a type="server" connection factory, which listens for incoming connection requests. In some cases, you may want to establish the connection in reverse, such that the inbound adapter connects to an external server and then waits for inbound messages on that connection.

This topology is supported by setting client-mode="true" on the inbound adapter. In this case, the connection factory must be of type client and must have single-use set to false.

Two additional attributes support this mechanism. The retry-interval specifies (in milliseconds) how often the framework attempts to reconnect after a connection failure. The scheduler supplies a TaskScheduler to schedule the connection attempts and to test that the connection is still active.

If you don’t provide a scheduler, the framework’s default taskScheduler bean is used.

For an outbound adapter, the connection is normally established when the first message is sent. The client-mode="true" on an outbound adapter causes the connection to be established when the adapter is started. By default, adapters are automatically started. Again, the connection factory must be of type client and have single-use="false". A retry-interval and scheduler are also supported. If a connection fails, it is re-established either by the scheduler or when the next message is sent.

For both inbound and outbound, if the adapter is started, you can force the adapter to establish a connection by sending a <control-bus /> command: @adapter_id.retryConnection(). Then you can examine the current state with @adapter_id.isClientModeConnected().