Lightweight REST API using Jersey on embedded Jetty server

Application.java

package root;

import root.resources.HelloResource;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;
import org.glassfish.jersey.server.ResourceConfig;
import org.glassfish.jersey.servlet.ServletContainer;

public class Application {

    public static void main(String[] args) throws Exception {
        ServletContextHandler handler = buildUsingResourceConfig(); // or buildUsingInitParameter()
        Server server = new Server(8080);
        server.setHandler(handler);
        try {
            server.start();
            server.join();
        } finally {
            server.destroy();
        }
    }

    static ServletContextHandler buildUsingResourceConfig() {
        ServletContextHandler handler = new ServletContextHandler(ServletContextHandler.NO_SESSIONS);
        handler.setContextPath("/");

        ResourceConfig resourceConfig = new ResourceConfig();
        resourceConfig.register(HelloResource.class);
        resourceConfig.register(HelloResource.GreetingMessageBodyWriter.class);
        handler.addServlet(new ServletHolder(new ServletContainer(resourceConfig)), "/api/*");
        return handler;
    }

    static ServletContextHandler buildUsingInitParameter() {
        ServletContextHandler handler = new ServletContextHandler(ServletContextHandler.NO_SESSIONS);
        handler.setContextPath("/");

        ServletHolder servletHolder = handler.addServlet(ServletContainer.class, "/api/*");
        servletHolder.setInitOrder(0);
        servletHolder.setInitParameter("jersey.config.server.provider.packages", "root.resources");
        return handler;
    }
}

build.gradle

ext {
    slf4jVersion = '1.7.30'
    jettyVersion = '9.4.28.v20200408'
    jerseyVersion = '2.31'
}

dependencies {
    compile "org.slf4j:slf4j-api:${slf4jVersion}"
    compile "org.slf4j:slf4j-simple:${slf4jVersion}"

    compile "org.eclipse.jetty:jetty-server:${jettyVersion}"
    compile "org.eclipse.jetty:jetty-servlet:${jettyVersion}"

    compile "org.glassfish.jersey.core:jersey-server:${jerseyVersion}"
    compile "org.glassfish.jersey.containers:jersey-container-servlet-core:${jerseyVersion}"
    compile "org.glassfish.jersey.containers:jersey-container-jetty-http:${jerseyVersion}"
    compile "org.glassfish.jersey.media:jersey-media-json-jackson:${jerseyVersion}"
    compile "org.glassfish.jersey.inject:jersey-hk2:${jerseyVersion}"
}

HelloResource.java

package root.resources;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.nio.charset.StandardCharsets;

@Path("/hello")
public class HelloResource {

    public static class Greeting {
        private String message;

        public Greeting() {
        }

        public Greeting(String message) {
            this.message = message;
        }

        public String getMessage() {
            return message;
        }

        public void setMessage(String message) {
            this.message = message;
        }
    }

    @GET
    @Path("/{param}")
    @Produces(MediaType.APPLICATION_JSON)
    public Greeting hello(@PathParam("param") String name) {
        return new Greeting("Hello " + name);
    }

    @Provider
    @Produces(MediaType.TEXT_PLAIN)
    public static class GreetingMessageBodyWriter implements MessageBodyWriter<Greeting> {

        @Override
        public boolean isWriteable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
            return type == Greeting.class;
        }

        @Override
        public void writeTo(Greeting greeting, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType, MultivaluedMap<String, Object> httpHeaders, OutputStream out) throws IOException, WebApplicationException {
            out.write(greeting.getMessage().getBytes(StandardCharsets.UTF_8));
            out.flush();
        }
    }

    @GET
    @Path("/{param}.txt")
    @Produces(MediaType.TEXT_PLAIN)
    public Greeting helloText(@PathParam("param") String name) {
        return new Greeting("Hello " + name);
    }

}