REST APIs are a natural match for microservices, and using JAX-RS, Swarm provides a simple way deploy RESTFul APIs as standalone applications.

Swarm also provides native integration with Swagger, which is a popular tool for providing documentation and an interactive UI on top of RESTful APIs.

Combining JAX-RS with Swagger gives you a very powerful way to build a self documenting REST API. Let’s take a look at how we can achieve this.

Our build script is very similar to the build scripts from previous Swarm demos. In this case we need the JAX-RS and swagger dependencies to give us the Java EE RESTful API library and the Swagger library that we will use to generate the JSON documentation of our API.

buildscript {
    repositories {
        mavenLocal()
        mavenCentral()
    }

    dependencies {
        classpath "org.wildfly.swarm:wildfly-swarm-plugin:1.0.0.Beta2"
    }
}

group 'com.matthewcasperson'
version '1.0-SNAPSHOT'

apply plugin: 'war'
apply plugin: 'wildfly-swarm'

swarm {
    mainClassName = "com.matthewcasperson.swarmdemo.MyMain"
}

sourceCompatibility = 1.8

def swarmVersionBeta1 = '1.0.0.Beta1'

repositories {
    mavenCentral()
    mavenLocal()
    maven {
        url 'http://repository.jboss.org/nexus/content/groups/public-jboss'
    }
    maven {
        url 'https://maven.repository.redhat.com/nexus/content/repositories/public'
    }
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.11'
    compile 'org.wildfly.swarm:bootstrap:' + swarmVersionBeta1
    compile 'org.wildfly.swarm:jaxrs:' + swarmVersionBeta1
    compile 'org.wildfly.swarm:swagger:' + swarmVersionBeta1
}

JAX-RS implementations need a class that extends the javax.ws.rs.core.Application class. You can use this class to configure the aspects of your RESTful API, but because this is just a simple demo, we rely on the defaults and do nothing more than extend the class.

package com.matthewcasperson.swarmdemo;

import javax.ws.rs.ApplicationPath;
import javax.ws.rs.core.Application;

/**
 * JAX-RS entry point
 */
@ApplicationPath("/")
public class MyApplication extends Application {

}

We also need a class to expose our REST API methods. This is all boilerplate JAX-RS, with the exception of the @Api annotation. This annotation provides details that are used to generate the Swagger documentation.

package com.matthewcasperson.swarmdemo;

import io.swagger.annotations.Api;

import javax.ws.rs.GET;
import javax.ws.rs.Path;

/**
 * Our REST interface
 */
@Path("/")
@Api(value = "/", description = "Sample REST API")
public class MyRest {
    @GET
    @Path("/helloWorld")
    public String helloWorld() {
        return "Hello World";
    }
}

Pulling this all together is the custom main method. Here we have defined our JAX-RS application, and add support the generation of Swagger documentation. The Swarm documentation details the deployment of JAX-RS applications, and configuring them to support Swagger.

You will also note that we have added a custom filter class called CORSFilter to the deployment. This allows us to make cross origin requests to the REST API and to the Swagger documentation.

package com.matthewcasperson.swarmdemo;

import org.jboss.shrinkwrap.api.ShrinkWrap;
import org.wildfly.swarm.container.Container;
import org.wildfly.swarm.jaxrs.JAXRSArchive;
import org.wildfly.swarm.swagger.SwaggerArchive;

/**
 * Swarm entry point
 */
public class MyMain {
    public static void main(final String... args) throws Exception {

        // Instantiate the container
        final Container container = new Container();

        final JAXRSArchive deployment = ShrinkWrap.create( JAXRSArchive.class );
        deployment.addResource( MyApplication.class );
        deployment.addResource( MyRest.class );
        deployment.addResource( CORSFilter.class );

        // Enable the swagger bits
        final SwaggerArchive archive = deployment.as(SwaggerArchive.class);
        // Tell swagger where our resources are
        archive.setResourcePackages("com.matthewcasperson.swarmdemo");
        archive.setTitle("Swagger Demo");

        container.start();
        container.deploy(deployment);
    }
}

The CORS filter is pretty simple, allowing access from everywhere. Production CORS filters would be a little more discerning, but for our test this is fine.

package com.matthewcasperson.swarmdemo;


import javax.ws.rs.container.ContainerRequestContext;
import javax.ws.rs.container.ContainerResponseContext;
import javax.ws.rs.container.ContainerResponseFilter;
import javax.ws.rs.ext.Provider;
import java.io.IOException;

/**
 * A CORS filter that will allow remote access to our API and Swagger documentation.
 */
@Provider
public class CORSFilter implements ContainerResponseFilter {
    public void filter(ContainerRequestContext paramContainerRequestContext,
                       ContainerResponseContext paramContainerResponseContext)
            throws IOException {
        paramContainerResponseContext.getHeaders().add("Access-Control-Allow-Origin", "*");
        paramContainerResponseContext.getHeaders().add("Access-Control-Allow-Headers", "origin, content-type, accept, authorization");
        paramContainerResponseContext.getHeaders().add("Access-Control-Allow-Credentials", "true");
        paramContainerResponseContext.getHeaders().add("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS, HEAD");
        paramContainerResponseContext.getHeaders().add("Access-Control-Max-Age", "1209600");
    }
}

Once compiled and run, you can open http://localhost:8080/helloWorld to execute the REST API method we exposed. The Swagger documentation is available at http://localhost:8080/swagger.

The Swagger documentation is not actually that easy to read in its raw state, but fortunately there is a UI that can consume this documentation and display it it a much more friendly manner. This UI has been deployed on the Swagger website, and while it shows the documentation of an example pet store by default, you can point the UI to any Swagger documentation file. In our case, entering http://localhost:8080/swagger into the text box at the top and clicking the Explore button will show our Swarm REST API documentation.

Grab the source code for this project from GitHub.