Creating web application with Spring Boot and Jersey

Spring Boot helps you accelerate the application development and makes it easy to create standalone applications that you can “just run”. Spring Boot embeds a web server, such as Tomcat or Jetty, in the application. So there’s no need to deploy a WAR file. It’s packed as a JAR and, to run it, you just need java -jar.

Jersey is the reference implementation of the JAX-RS 2.0 specification and provides a solid API for creating and consuming web services in Java.

In this post, let’s create a sample application with Spring Boot and Jersey.

Ensure your pom.xml file declares spring-boot-starter-parent as the parent project and declares all the dependencies and plugins shown below:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.cassiomolin</groupId>
    <artifactId>spring-jersey</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.0.RELEASE</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.glassfish.jersey.ext</groupId>
            <artifactId>jersey-spring3</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

The Spring Boot Maven plugin collects all the JARs on the classpath and builds a single, runnable uber JAR, which makes it more convenient to execute and transport the application. Besides it, the plugin searches for the public static void main() method to flag as a runnable class.

Create a Jersey resource class annotated with @Path and define a resource method to handle GET requests, producing text/plain:

@Path("/greetings")
public class GreetingResource {

    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public Response getGreeting() {
        return Response.ok("Hello, World!").build();
    }
}

Create a class that extends ResourceConfig or Application to register the Jersey resources:

@Component
@ApplicationPath("api")
public class JerseyConfig extends ResourceConfig {

    @PostConstruct
    private void init() {
        registerClasses(GreetingResource.class);
    }
}

And finally create a Spring Boot class to execute the application:

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

To test this web service, we can use the JAX-RS Client API:

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class GreetingResourceTest {

    @LocalServerPort
    private int port;

    private URI uri;

    @Before
    public void setUp() throws Exception {
        this.uri = new URI("http://localhost:" + port);
    }

    @Test
    public void testGreeting() {

        Client client = ClientBuilder.newClient();
        Response response = client.target(uri).path("api").path("greetings")
                                  .request(MediaType.TEXT_PLAIN).get();

        String entity = response.readEntity(String.class);
        assertEquals("Hello, World!", entity);
    }
}

To compile and run the application, follow these steps:

Open a command line window or terminal.
Navigate to the root directory of the project, where the pom.xml resides.
Compile the project: mvn clean compile.
Package the application: mvn package.
Look in the target directory. You should see a file with the following or a similar name: spring-jersey-1.0-SNAPSHOT.jar.
Change into the target directory.
Execute the JAR: java -jar spring-jersey-1.0-SNAPSHOT.jar.
The application should be available at http://localhost:8080/api/greetings.