How to turn my Jersey REST API into an executable JAR?

Question

I am using Jersey, Maven; and could use Jetty, Tomcat or J2EE Preview (is that embeddable?).

1. What is the easiest way to port my REST API as a standalone/executable JAR?
2. Can I do it without Spring Boot?

Answer 1

Follow these steps to create a standalone application with Jersey and Jetty:

Adding Maven dependencies

Add the following dependencies and properties to your pom.xml:

<properties>
    <jetty.version>9.4.7.v20170914</jetty.version>
    <jersey.version>2.26</jersey.version>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

<dependencies>
    <dependency>
        <groupId>org.eclipse.jetty</groupId>
        <artifactId>jetty-server</artifactId>
        <version>${jetty.version}</version>
    </dependency>
    <dependency>
        <groupId>org.eclipse.jetty</groupId>
        <artifactId>jetty-servlet</artifactId>
        <version>${jetty.version}</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <artifactId>jersey-container-jetty-servlet</artifactId>
        <version>${jersey.version}</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.inject</groupId>
        <artifactId>jersey-hk2</artifactId>
        <version>${jersey.version}</version>
    </dependency>
</dependencies>

Creating JAX-RS resource classes

Define your JAX-RS resource class(es). The following is just an example:

@Path("hello")
public class HelloWorldResource {

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

Creating a Jersey configuration class

Create a class to configure your Jersey application:

public class JerseyConfiguration extends ResourceConfig {

    public JerseyConfiguration() {
        packages("com.example");
    }
}

Creating a launcher class for Jetty

Create a class to launch Jetty and deployment your application:

public class Launcher {

    private static final String JERSEY_SERVLET_NAME = "jersey-container-servlet";

    public static void main(String[] args) throws Exception {
        new Launcher().start();
    }

    void start() throws Exception {

        String port = System.getenv("PORT");
        if (port == null || port.isEmpty()) {
            port = "8080";
        }

        Server server = new Server(Integer.valueOf(port));
        ServletContextHandler context = new ServletContextHandler(server, "/");

        ServletHolder servlet = new ServletHolder(JERSEY_SERVLET_NAME,
                new ServletContainer(new JerseyConfiguration()));
        context.addServlet(servlet, "/api/*");

        try {
            server.start();
            server.join();
        } finally {
            server.destroy();
        }
    }
}

Adding Maven plugin for creating an executable JAR

Finally add the Maven Shade plugin to create an executable JAR, where the mainClass attribute references the launch class:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>2.4.3</version>
            <configuration>
                <finalName>jetty-embedded-example-${project.version}</finalName>
            </configuration>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                    <configuration>
                        <transformers>
                            <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                <mainClass>com.example.Launcher</mainClass>
                            </transformer>
                        </transformers>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Compiling and running the application

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: jetty-embedded-example-1.0-SNAPSHOT.jar.
• Change into the target directory.
• Execute the JAR: java -jar jetty-embedded-example-1.0-SNAPSHOT.jar.
• The application should be available at http://localhost:8080/api/hello.

See more

• How to deploy a JAX-RS application on a Java SE environment?

Answer 2

Follow these steps to create a standalone application with Jersey and Tomcat:

Adding Maven dependencies

Add the following dependencies and properties to your pom.xml:

<properties>
    <tomcat.version>8.5.23</tomcat.version>
    <jersey.version>2.26</jersey.version>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

<dependencies>
    <dependency>
        <groupId>org.apache.tomcat.embed</groupId>
        <artifactId>tomcat-embed-core</artifactId>
        <version>${tomcat.version}</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <artifactId>jersey-container-servlet</artifactId>
        <version>${jersey.version}</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.inject</groupId>
        <artifactId>jersey-hk2</artifactId>
        <version>${jersey.version}</version>
    </dependency>
</dependencies>

Creating JAX-RS resource classes

Define your JAX-RS resource class(es). The following is just an example:

@Path("hello")
public class HelloWorldResource {

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

Creating a Jersey configuration class

Create a class to configure your Jersey application:

public class JerseyConfiguration extends ResourceConfig {

    public JerseyConfiguration() {
        packages("com.example");
    }
}

Creating a launcher class for Tomcat

Create a class to launch Tomcat and deployment your application:

public class Launcher {

    private static final String JERSEY_SERVLET_NAME = "jersey-container-servlet";

    public static void main(String[] args) throws Exception {
        new Launcher().start();
    }

    void start() throws Exception {

        String port = System.getenv("PORT");
        if (port == null || port.isEmpty()) {
            port = "8080";
        }

        String contextPath = "";
        String appBase = ".";

        Tomcat tomcat = new Tomcat();
        tomcat.setPort(Integer.valueOf(port));
        tomcat.getHost().setAppBase(appBase);

        Context context = tomcat.addContext(contextPath, appBase);
        Tomcat.addServlet(context, JERSEY_SERVLET_NAME,
                new ServletContainer(new JerseyConfiguration()));
        context.addServletMappingDecoded("/api/*", JERSEY_SERVLET_NAME);

        tomcat.start();
        tomcat.getServer().await();
    }
}

Adding Maven plugin for creating an executable JAR

Finally add the Maven Shade plugin to create an executable JAR, where the mainClass attribute references the launch class:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>2.4.3</version>
            <configuration>
                <finalName>tomcat-embedded-example-${project.version}</finalName>
            </configuration>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                    <configuration>
                        <transformers>
                            <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                <mainClass>com.example.Launcher</mainClass>
                            </transformer>
                        </transformers>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Compiling and running the application

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: tomcat-embedded-example-1.0-SNAPSHOT.jar.
• Change into the target directory.
• Execute the JAR: java -jar tomcat-embedded-example-1.0-SNAPSHOT.jar.
• The application should be available at http://localhost:8080/api/hello.

See more

• How to deploy a JAX-RS application on a Java SE environment?