How to parse Spring Integration HTTP gateway response into a Bean? - spring

Question

I've been trying to get a simple integration workflow for practice purposes. The thing is I just started working with Spring and I'm having a hard time understanding Integration and how it works.
Right now I've got a really simple backend app with Spring MVC that returns
[
{"id":1,"name":"Series test","synopsis":"Testing reading items from JSON.","imageUrl":"http://some.where/images/some_image.png"},
{"id":2,"name":"Arrow","synopsis":"Some guy in a hood shooting arrows to some guys with superpowers.","imageUrl":"http://some.where/images/some_image.png"},
{"id":3,"name":"Primeval","synopsis":"Some guys with guns killing dinosaurs and lots of infidelity.","imageUrl":"http://some.where/images/some_image.png"},
{"id":4,"name":"Dr. Who","synopsis":"It's bigger on the inside.","imageUrl":"http://some.where/images/some_image.png"},
{"id":5,"name":"Fringe","synopsis":"Weird things happen.","imageUrl":"http://some.where/images/some_image.png"},
{"id":6,"name":"Monster Hunter Freedom Unite","synopsis":"Wait. This is a game.","imageUrl":"http://some.where/images/some_image.png"}
]
to http://localhost:9000/api/series/findAll and a runnable Spring project that, with Integration, attempts to recover that data and convert it to a Series (bean with the same properties as the JSON) array.
If I don't add a reply-channel to the outbound-gateway everything works just fine. But when I send it to another channel to parse it into a Series object I start getting "Dispatcher has no subscribers" on the new channel. It makes sense but it leaves me not knowing how to proceed now.
My project files, apart from Series, look like this right now:
Startup.java
package com.txus.integration;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import java.util.List;
import java.util.concurrent.Future;
public class Startup {
#Autowired
RequestGateway requestGateway;
public static void main(String[] args) throws Exception {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("/META-INF/spring/integration-components.xml");
RequestGateway requestGateway = context.getBean(RequestGateway.class);
Future<String> promise = requestGateway.getSeries("");
while (!promise.isDone()) {
Thread.sleep(1000);
}
String response = promise.get();
printReadable(response);
context.close();
System.exit(0);
}
public static void printReadable(String string) {
String separator = "= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =";
System.out.println("\n" + separator + "\n" + string + "\n" + separator + "\n");
}
public static void printReadable(List<String> strings) {
for (String string : strings) printReadable(string);
}
}
RequestGateway
package com.txus.integration;
import com.txus.entities.Series;
import org.springframework.integration.annotation.Gateway;
import java.util.concurrent.Future;
public interface RequestGateway {
#Gateway(requestChannel="responseChannel")
Future<String> getSeries(String jsonString);
#Gateway(requestChannel="responseChannel")
Future<String> getSeries(Series series);
}
integration-components.xml
<beans:beans
xmlns="http://www.springframework.org/schema/integration"
xmlns:beans="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:http="http://www.springframework.org/schema/integration/http"
xmlns:task="http://www.springframework.org/schema/task"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
http://www.springframework.org/schema/integration http://www.springframework.org/schema/integration/spring-integration.xsd
http://www.springframework.org/schema/integration/http http://www.springframework.org/schema/integration/http/spring-integration-http.xsd
http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task.xsd">
<context:annotation-config/>
<context:component-scan base-package="com.txus"/>
<!-- START: Spring Integration -->
<!-- Integration: Channels -->
<channel id="requestChannel"/>
<channel id="responseChannel"/>
<channel id="failedChannel"/>
<!-- Integration: Loggers -->
<logging-channel-adapter
id="payloadLogger" level="DEBUG" expression="'### Message [' + headers.id + '] payload: ' + payload"/>
<logging-channel-adapter
id="headersLogger" level="DEBUG" expression="'### Message [' + headers.id + '] headers: ' + headers"/>
<!-- Integration: Flow -->
<gateway
service-interface="com.txus.integration.RequestGateway"
default-request-timeout="5000" async-executor="executor">
<method name="getSeries" request-channel="inputChannel"/>
</gateway>
<task:executor id="executor" pool-size="100"/>
<payload-type-router input-channel="inputChannel" default-output-channel="failedChannel">
<mapping type="java.lang.String" channel="requestChannel"/>
<mapping type="com.txus.entities.Series" channel="objectToJSONChannel"/>
</payload-type-router>
<object-to-json-transformer
id="objectToJsonTransformer" input-channel="objectToJSONChannel" output-channel="requestChannel"/>
<http:outbound-gateway
http-method="GET"
expected-response-type="java.lang.String"
url="http://localhost:9000/api/series/findAll"
request-channel="requestChannel"
reply-channel="jsonToSeries"
reply-timeout="30000"/>
<map-to-object-transformer
input-channel="jsonToSeries" output-channel="responseChannel" type="com.txus.entities.Series"/>
<!-- END: Spring Integration -->
</beans:beans>

Answer 1

You have an issue with the last component where you configure output-channel="responseChannel". There is just nothing which is subscribed to that channel.
I see your #Gateway config on the matter, but it is a bit wrong. XML configuration has a precedence over annotations there. Hence the requestChannel in the end is exactly inputChannel.
If you'd like to send the result of <map-to-object-transformer> to the responseChannel and accept it as a return from the RequestGateway invocation, you should specify that responseChannel as a reply-channel on the gateway configuration.
From other side you just don't need it there and the TemporaryReplyChannel comes to the rescue.
Please, refer for more information to the Spring Integration Manual.