REST with Jersey and Jetty part 3

REST with Jersey and Jetty part 3

Adding JSON support.

The first two parts  in this small series of posts were about setting up the server and be able to run it with Jersey. [REST with Jersey and Jetty part 1, REST with Jersey and Jetty part 2].

This time there will be a bit more work. And I will take it step by step.

The service we will implement will handle tasks. To start with, there will only be one task list where all tasks will go.

The api will be the following.
Task class:
package model; import java.util.Date; import java.util.UUID; import javax.xml.bind.annotation.XmlAccessType; import javax.xml.bind.annotation.XmlAccessorType; import javax.xml.bind.annotation.XmlRootElement; @XmlRootElement @XmlAccessorType(XmlAccessType.FIELD) public class Task { private String id; private String title; private String description; private Date dueDate; public Task() { } public static Task of(String title, String description, Date dueDate) { UUID randomUUID = UUID.randomUUID(); return new Task(randomUUID.toString(), title, description, dueDate); } private Task(String id, String title, String description, Date dueDate) { this.id = id; this.title = title; this.description = description; this.dueDate = dueDate; } // getters/setters @Override public String toString() { return "Task{" + "id=" + id + ", title=" + title + ", description=" + description + ", dueDate=" + dueDate + '}'; } }

To start with we add support for getting the list, there will be some hardcoding until we have the working JSON support, since the first thing we want is a working Jersey with JSON support, not to complicate things further. When we have that, we can start adding functionality. But in the end, we will try to support:

• list all
• show a single task
• create a task
• update a task
• remove a task
• show range of tasks
• get task count

But starting with some hardcoded stuff, to get the server running with JSON, this will be the stating point for the TaskResource
package rest; import java.util.Date; import java.util.ArrayList; import java.util.List; import javax.ws.rs.GET; import javax.ws.rs.Path; import javax.ws.rs.Produces; import javax.ws.rs.core.MediaType; import model.Task; @Path("tasks") public class TaskResource { @GET @Produces(MediaType.APPLICATION_JSON) public List<task> getAll() { List<task> all = new ArrayList<>(); all.add(Task.of("Testtask", "Task to test", new Date())); return all; } }

If you start the server and try to surf to this [http://localhost:2001/api/tasks] will yield the following in the log.

maj 02, 2015 11:02:34 FM org.glassfish.jersey.message.internal.WriterInterceptorExecutor$TerminalWriterInterceptor aroundWriteTo SEVERE: MessageBodyWriter not found for media type=application/json, type=class java.util.ArrayList, genericType=java.util.List<model.Task>.
so we need to add some stuff to have JSON support.

Well, just a shor Googling, and it was pretty easy to add. [http://stackoverflow.com/questions/25474223/jersey-rest-messagebodywriter-not-found-for-media-type-application-jso] gives a hint. Just added moxy and it works to get JSON with the @GET.
<dependency> <groupid>org.glassfish.jersey.media</groupId> <artifactid>jersey-media-moxy</artifactId> <version>2.17</version> </dependency>
So lets go for some real coding. We will add a simple cache, To avoid having a database for this simple example it will only contain a map with the tasks.

Lets start with some simple support of the cache:

package rest; import java.util.HashMap; import java.util.Map; import java.util.Optional; import model.Task; public enum TaskCache { INST; private Map<String, Task> tasks; private TaskCache() { tasks = new HashMap<>(); } public Optional<task> getTask(String id) { return Optional.ofNullable(tasks.get(id)); } public void putTask(Task task) { tasks.put(task.getId(), task); } public void removeTask(Task task) { tasks.remove(task.getId()); } public List<task> getTasks() { return new ArrayList(tasks.values()); } }
Lets first add a method to create a task and one for getting a specific task.
@POST @Consumes(MediaType.APPLICATION_JSON) public Response create(Task task) { TaskCache.INST.addTask(task); URI id = URI.create("tasks/" + task.getId()); Response resp = Response.created(id).build(); return resp; } @GET @Produces(MediaType.APPLICATION_JSON) @Path("{id}") public Response getTask(@PathParam("id") String id) { Optional<task> task = TaskCache.INST.getTask(id); Response resp = null; if (task.isPresent()) { resp = Response.ok(task.get()).build(); } else { resp = Response.noContent().build(); } return resp; }
To test this, we will need to also add a method to get a single task and a client to test it.

First, the client.
package app; import java.net.URI; import java.util.Date; import javax.ws.rs.client.Client; import javax.ws.rs.client.ClientBuilder; import javax.ws.rs.client.Entity; import javax.ws.rs.client.WebTarget; import javax.ws.rs.core.MediaType; import javax.ws.rs.core.Response; import model.Task; public class JerseyClient { public static void main(String[] args) { Client client = ClientBuilder.newClient(); WebTarget postTarget = client.target("http://localhost:2001").path("api").path("tasks"); Response postResponse = postTarget.request(MediaType.APPLICATION_JSON) .post(Entity.json(Task.of("Testclient", "Using test client to create", new Date()))); System.out.println(postResponse.getStatus()); URI location = postResponse.getLocation(); System.out.println(location); WebTarget getTarget = client.target(location); Response getResponse = getTarget.request(MediaType.APPLICATION_JSON).get(); System.out.println(getResponse.getStatus()); System.out.println(getResponse.readEntity(Task.class)); } }

So far the client just adds a Task, gets the URI to the created Task and then gets it using the @GET for the methods added above.

Next step, fix the getAll().
The client cannot handle a List without wrapping it in a GenericType, but that is really all there is too it, we can still return List from the method.

// TaskResource.java @GET @Produces(MediaType.APPLICATION_JSON) public List<task> getAll() { return TaskCache.INST.getTasks(); } // JerseyClient.java WebTarget allTarget = client.target("http://localhost:2001").path("api").path("tasks"); GenericType<List<task>> genericType = new GenericType<List<task>>() {}; List<task> all = allTarget.request(MediaType.APPLICATION_JSON).get(genericType); for (Task task : all) { System.out.println(task); }
The only thing we need to add now is update and delete. We will also add some code to test it in the client.
@PUT @Consumes(MediaType.APPLICATION_JSON) @Path("{id}") public Response update(Task task) { // Just replace the one there System.out.println("Updating task: " + task); TaskCache.INST.putTask(task); return Response.ok().build(); } @DELETE @Path("{id}") public Response delete(@PathParam("id") String id) { System.out.println("Deleting task: " + id); TaskCache.INST.removeTask(id); return Response.ok().build(); }
I also made some changes in the client: public static void main(String[] args) { Client client = ClientBuilder.newClient(); List<uri> locations = new ArrayList<>(); WebTarget target = client.target("http://localhost:2001").path("api").path("tasks"); Response postResponse = target.request(MediaType.APPLICATION_JSON) .post(Entity.json(Task.of("Testclient1", "Using test client to create", new Date()))); locations.add(postResponse.getLocation()); postResponse = target.request(MediaType.APPLICATION_JSON) .post(Entity.json(Task.of("Testclient2", "Using test client to create", new Date()))); locations.add(postResponse.getLocation()); postResponse = target.request(MediaType.APPLICATION_JSON) .post(Entity.json(Task.of("Testclient3", "Using test client to create", new Date()))); locations.add(postResponse.getLocation()); // Get first one WebTarget getTarget = client.target(locations.get(0)); Response getResponse = getTarget.request(MediaType.APPLICATION_JSON).get(); System.out.println(getResponse.getStatus()); System.out.println(getResponse.readEntity(Task.class)); // Change second one getTarget = client.target(locations.get(1)); getResponse = getTarget.request(MediaType.APPLICATION_JSON).get(); Task aTask = getResponse.readEntity(Task.class); aTask.setTitle("This title is changed"); client.target(locations.get(1)).request(MediaType.APPLICATION_JSON).put(Entity.json(aTask)); // Delete thirs one client.target(locations.get(2)).request().delete(); WebTarget allTarget = client.target("http://localhost:2001").path("api").path("tasks"); GenericType<List<task>> genericType = new GenericType<List<task>>() {}; List<task> all = allTarget.request(MediaType.APPLICATION_JSON).get(genericType); for (Task task : all) { System.out.println(task); } }
Enjoy your Task microservice in REST using embedded Jetty with Jersey.

Read more about Jersey [https://jersey.java.net/documentation/latest/index.html]