Using Spring Boot With Mule
April 22, 2015 by Gregory Lawson
In recent years there has been a surge in the idea of microservices. Although this term is vague in nature there are some ideas on how to deploy and run applications with “microservices” in mind. Spring has come to the forefront of the microservice architecture with its “opinionated view of building production-ready Spring applications”. While Spring Boot provides several “starter” configurations for most application needs, Spring will at times have to integrate or take a back seat to other systems. By design, that is the beauty of Spring…it can utilized as a top level container or nicely integrated into your current solution. Check out its many use scenarios.
Many open source projects use Spring under the covers. Mule, Camel, ActiveMQ are a few examples that come to mind. In this blog, I plan to utilize Spring Boot along with Mule. Mule is a full featured Enterprise Service Bus (ESB) which is usually installed as a server to a file system. For major deployments this works extremely well. In the case of microservices this approach may be unwanted. To fully get the benefits of a microservices architecture, it would be ideal if Mule could be shipped as a stand alone artifact. This is the sweet spot of Spring Boot. Enough talking about microservices and ESBs. Let’s roll up our sleeves and get to work.
Mule Starter App
We will use a Mule Maven archetype to get us started. It can be found at Mule’s Maven Tools. In a bash shell issue type:
mvn archetype:generate -DarchetypeGroupId=org.mule.tools.Maven -DarchetypeArtifactId=Maven-achetype-mule-app -DarchetypeVersion=1.0 -DgroupId=org.taptech.app -DartifactId=mule-starter-app -Dversion=1.0-SNAPSHOT -DmuleVersion=3.6.1 -Dpackage=org.taptech.app -Dtransports=http,jms,vm,file,ftp -Dmodules=db,xml,jersey,json,ws
This should create/scaffold a Maven project. The standard Maven project contains one flow and a functional test. The directory structure is what you would expect for a Maven project with the addition of a src/main/app directory that has a Mule properties and config file.
The project has Mule jars which are dependent on a previous version of Spring. In order to get Spring Boot, which depends on Spring 4, to run with Mule we have to use a different version of Mule. We will also have to transform our pom.xml to use the Spring Boot as its parent.
We now have the dependencies , but we need to tell Spring Boot how to start the Mule in its context. This means using the Spring Boot application context as the parent context for running Mule embedded. I have created a class called MuleBootstrap for accomplishing that goal.
Look at the code snippet below or at Github:
import org.mule.api.MuleContext;
import org.mule.api.MuleException;
import org.mule.api.config.ConfigurationException;
import org.mule.api.lifecycle.InitialisationException;
import org.mule.config.spring.SpringXmlConfigurationBuilder;
import org.mule.context.DefaultMuleContextFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
import org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration;
import org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration;
import org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration;
import org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.StaticApplicationContext;
@ComponentScan
@Configuration
@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class,DispatcherServletAutoConfiguration.class,
WebMvcAutoConfiguration.class, EmbeddedServletContainerAutoConfiguration.class,HibernateJpaAutoConfiguration.class})
public class MuleBootstrap implements CommandLineRunner {
private static final Logger log = LoggerFactory.getLogger(MuleBootstrap.class);
@Autowired
private ApplicationContext context;
@Override
public void run(String... strings) throws Exception {
DefaultMuleContextFactory muleContextFactory = new DefaultMuleContextFactory();
SpringXmlConfigurationBuilder configBuilder = null;
try {
StaticApplicationContext staticApplicationContext = new StaticApplicationContext(context);
configBuilder = new SpringXmlConfigurationBuilder("mule-config.xml");
staticApplicationContext.refresh();
configBuilder.setParentContext(staticApplicationContext);
MuleContext muleContext = muleContextFactory.createMuleContext(configBuilder);
muleContext.start();
log.info("Started Mule!");
} catch (Exception e) {
log.error("Error starting Mule...",e);
}
}
public static void main(String... args) {
log.info("Starting SpringApplication...");
SpringApplication app = new SpringApplication(MuleBootstrap.class);
app.setWebEnvironment(false);
app.run(args);
log.info("SpringApplication has started...");
}
}
At this point the project should be ready to go.
You can try running it at command line:
mvn clean package && java -jar target/mule-starter-app-1.0-SNAPSHOT.jar
Congratulations, you just started Mule from a single, deployable, jar file with Spring Boot!
The complete source code and Github project can be found here.
####Further reading
