Saturday, 21 January 2012

Spring Integration - Payload Storage via Header Enrichment

There's often a need to temporarily store transient messages during design of Spring Integration flows - several different mechanisms are available in the toolkit.

It's pretty straight forward to take a message, use an SI header enricher construct and place the message in the header using a SpEL expression - in fact one for the header key name and one for the payload extraction.

The following SI flow demonstrates an example of how to do just that :

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:int="http://www.springframework.org/schema/integration"
       xsi:schemaLocation="http://www.springframework.org/schema/beans 
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/integration 
       http://www.springframework.org/schema/integration/spring-integration-2.1.xsd">

  <int:gateway id="headerManagementGateway" 
                 service-interface="com.l8mdv.sample.HeaderManagementGateway"/>
  <int:chain input-channel="request-message-storage-channel"
             output-channel="request-message-retrieval-channel">
    <int:header-enricher>
      <int:header name="#{T(com.l8mdv.sample.HeaderManagementGateway)
                   .REQUEST_PAYLOAD_HEADER_KEY}" expression="getPayload()"/>
    </int:header-enricher>
  </int:chain>

  <int:chain input-channel="request-message-retrieval-channel">
    <int:transformer expression="headers.get(T(com.l8mdv.sample.HeaderManagementGateway)
               .REQUEST_PAYLOAD_HEADER_KEY)"/>
  </int:chain>
</beans>

This example can be executed by implementing a gateway as follows:

package com.l8mdv.sample;

import org.springframework.integration.Message;
import org.springframework.integration.annotation.Gateway;

public interface HeaderManagementGateway {

    public static final String REQUEST_PAYLOAD_HEADER_KEY = "REQUEST_PAYLOAD_HEADER_KEY";

    @Gateway (requestChannel = "request-message-storage-channel")
    public Message<String> send(Message<String> message);
}

and then running a test such as this one:

package com.l8mdv.sample;

import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.integration.Message;
import org.springframework.integration.support.MessageBuilder;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import static com.l8mdv.sample.HeaderManagementGateway.REQUEST_PAYLOAD_HEADER_KEY;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath:META-INF/spring/header-management.xml"})
public class HeaderManagementIntegrationTest {

    @Autowired
    HeaderManagementGateway headerManagementGateway;

    @Test
    public void locatePayloadInHeader() {
        String payload = "Sample test message.";
        Message<String> message = MessageBuilder.withPayload(payload).build();
        Message<String> response = headerManagementGateway.send(message);

        Assert.assertTrue(response.getHeaders().get(REQUEST_PAYLOAD_HEADER_KEY).equals(payload));
    }

    @Test
    public void locateTransformedPayload() {
        String payload = "Sample test message.";
        Message<String> message = MessageBuilder.withPayload(payload).build();
        Message<String> response = headerManagementGateway.send(message);

        Assert.assertTrue(response.getPayload().contains(payload));
    }
}

For full source code and configuration, see the header-management maven module under git://github.com/L8MDV/l8mdv-si-samples.git

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