This Chapter explains how to use RMI specific channel adapters to distribute a system over multiple JVMs. The first section will deal with sending messages over RMI. The second section shows how to receive messages over RMI. The last section shows how to define rmi channel adapters through the namespace support.

To send messages from a channel over RMI, simply define an RmiOutboundGateway. This gateway will use Spring’s RmiProxyFactoryBean internally to create a proxy for a remote gateway. Note that to invoke a remote interface that doesn’t use Spring Integration you should use a service activator in combination with Spring’s RmiProxyFactoryBean.

To configure the outbound gateway write a bean definition like this:

<bean id="rmiOutGateway" class=org.spf.integration.rmi.RmiOutboundGateway>
    <constructor-arg value="rmi://host"/>
    <property name="replyChannel" value="replies"/>
</bean>

To receive messages over RMI you need to use a RmiInboundGateway. This gateway can be configured like this

<bean id="rmiInGateway" class=org.spf.integration.rmi.RmiInboundGateway>
    <property name="requestChannel" value="requests"/>
</bean>

Important

If you use an errorChannel on an inbound gateway, it would be normal for the error flow to return a result (or throw an exception). This is because it is likely that there is a corresponding outbound gateway waiting for a response of some kind. Consuming a message on the error flow, and not replying, will result in no reply at the inbound gateway. Exceptions (on the main flow when there is no errorChannel, or on the error flow) will be propagated to the corresponding inbound gateway.

To configure the inbound gateway you can choose to use the namespace support for it. The following code snippet shows the different configuration options that are supported.

<int-rmi:inbound-gateway id="gatewayWithDefaults" request-channel="testChannel"/>

<int-rmi:inbound-gateway id="gatewayWithCustomProperties" request-channel="testChannel"
    expect-reply="false" request-timeout="123" reply-timeout="456"/>

<int-rmi:inbound-gateway id="gatewayWithHost" request-channel="testChannel"
    registry-host="localhost"/>

<int-rmi:inbound-gateway id="gatewayWithPort" request-channel="testChannel"
    registry-port="1234" error-channel="rmiErrorChannel"/>

<int-rmi:inbound-gateway id="gatewayWithExecutorRef" request-channel="testChannel"
    remote-invocation-executor="invocationExecutor"/>

To configure the outbound gateway you can use the namespace support as well. The following code snippet shows the different configuration for an outbound rmi gateway.

<int-rmi:outbound-gateway id="gateway"
    request-channel="localChannel"
    remote-channel="testChannel"
    host="localhost"/>

@Bean
public RmiInboundGateway inbound() {
    RmiInboundGateway gateway = new RmiInboundGateway();
    gateway.setRequestChannel(requestChannel());
    gateway.setRegistryHost("host");
    gateway.setRegistryPort(port);
    return gateway;
}

@Bean
@ServiceActivator(inputChannel="inChannel")
public RmiOutboundGateway outbound() {
    RmiOutboundGateway gateway = new RmiOutboundGateway("rmi://host:port/"
        + RmiInboundGateway.SERVICE_NAME_PREFIX + "remoteChannelName");
    return gateway;
}

Starting with version 4.3, the outbound gateway has a second constructor that takes a RmiProxyFactoryBeanConfigurer instance along with the service url argument. This allows further configuration before the proxy is created; for example, to inject a Spring Security ContextPropagatingRemoteInvocationFactory:

@Bean
@ServiceActivator(inputChannel="inChannel")
public RmiOutboundGateway outbound() {
    RmiOutboundGateway gateway = new RmiOutboundGateway("rmi://host:port/"
                + RmiInboundGateway.SERVICE_NAME_PREFIX + "remoteChannelName",
        pfb -> {
            pfb.setRemoteInvocationFactory(new ContextPropagatingRemoteInvocationFactory());
        });
    return gateway;
}

Starting with version 5.0, this can be set using the XML namespace, using the configurer attribute.