how to implement integration router in java - spring-integration

Question

i am trying to convert below XML snippet into Java version, appreciate any help here
<int:router input-channel="channel_in" default-output-channel="channel_default"
expression="payload.name" ignore-channel-name-resolution-failures="true">
<int:mapping value="foo" channel="channel_one" />
<int:mapping value="bar" channel="channel_two" />
</int:router>
Here is what i did for my concrete example
#Router(inputChannel = "routerChannel")
public String route(Account message) {
if (message.getType().equals("check")) {
return "checkChannel";
} else if (message.getType().equals("credit")) {
return "creditChannel";
}
return "errorChannel";
}
#Bean
public DirectChannel checkChannel() {
return new DirectChannel();
}
when i do above i am seeing below error
org.springframework.messaging.MessageDeliveryException: Dispatcher has no subscribers for channel 'application:8090.checkChannel'.;

Answer 1

All the Spring Integration custom tag has a description like this:
<xsd:element name="router" type="routerType">
<xsd:annotation>
<xsd:documentation>
Defines a Consumer Endpoint for the
'org.springframework.integration.router.AbstractMessageProcessingRouter' implementation
that serves as an adapter for invoking a method on any
Spring-managed object as specified by the "ref" and "method" attributes.
</xsd:documentation>
</xsd:annotation>
</xsd:element>
So, it becomes pretty clear that we need some AbstractMessageProcessingRouter implementation to be present in the Java Configuration.
Also we have a paragraph in the Reference Manual like this:
With XML configuration and Spring Integration Namespace support, the XML Parsers hide how target beans are declared and wired together. For Java & Annotation Configuration, it is important to understand the Framework API for target end-user applications.
According your expression="payload.name" we need to look for the ExpressionEvaluatingRouter and then also read a chapter about #Bean configuration:
#Bean
#Router(inputChannel = "channel_in")
public ExpressionEvaluatingRouter expressionRouter() {
ExpressionEvaluatingRouter router = new ExpressionEvaluatingRouter("payload.name");
router.setDefaultOutputChannelName("channel_default");
router.setChannelMapping("foo", "channel_one");
router.setChannelMapping("bar", "channel_two");
return router;
}