Simple server mock for REST services

When working on a mobile Android application, I was confronted with the fact that the backend server wasn’t available yet to deliver the REST service. But I needed a server or good dummy for testing the Android client against the REST services. So I began my search for a REST mock server.

I started out using the SoapUI REST functionality, but that still lacks a good implementation for my purpose of reacting on REST calls. I ended up with a 10-minute build-your-own REST mock using the Play framework. This blogs describes how this was accomplished.

The Play framework crossed my path earlier. It is a very simple yet powerful application framework for web applications. It is almost trivial to set it up for mocking REST services. First make sure you download and unpack the framework. Then execute the following commands to create a new project:

play new RestMockServer play eclipsify RestMockServer play run RestMockServer

The project is running and now ready to be worked on in eclipse (see ‘play help’ for other IDEs). Changes in code and configuration will be picked up by the framework automatically. Just point your browser to https://xebia.com/blog:9000/ to see the application running.

The next step is to add the REST URLs to the routing table. Let us say I ‘m creating a system for storing photos containing meta data and the image URL. Open the file ‘conf/routes’ and add the following lines before the ‘Catch all’ entry:

PUT /photo PhotoController.create POST /photo PhotoController.update GET /photo/{id} PhotoController.read DELETE /photo/{id} PhotoController.delete

This defines the CRUD actions on a photo object. First in line is the http method on which the framework should react. The second part is the URL with optional parameters which will be mapped onto the method indicated in the first part.

The following action is to define a controller handling the calls. The implementation uses a very simple response technique based on text. The mapping of the id to the actual response is left to the reader to implement. You could for example read a file based on the URL parameter and return the content of it. For now, we just return the identifier specified in the URL.

Save the file below as ‘PhotoController.java’ and call

https://xebia.com/blog:9000/photo/123

and see your favorite number showing on screen. Note that the name between curly braces should match the name of the parameter. The mapping on type will be done auto-magically by the framework.

[java title="controllers/PhotoController.java"]
package controllers;
import java.util.Random;
import com.google.gson.JsonObject;
import play.mvc.Controller;
public class PhotoController extends Controller {
public static void read(int id) {
try {
response.contentType = "application/json";
renderText(id);
} catch (Exception e) {
notFound(e.getMessage());
}
}
}
[/java]

The next step is to implement the other methods. Since I’m using JSON as data format, I have to add a specific binder for the JsonObject type, used both by the create and update method. The ‘ok’ just returns a 200 status code. Upon creation of an object I need the identifier of the newly stored data object, so for test purposes I return a random integer.

Add the following method implementations to PhotoController.java:

[java title="snippet"]
public static void delete(int id) {
ok();
}
public static void update(JsonObject body) {
ok();
}
public static void create(JsonObject body) {
response.contentType = "application/json";
renderText("\"id\":"+Math.abs(new Random().nextInt()));
}
[/java]

The binder is also automatically found by the framework. I’ve created a new package ‘util’ in which I placed the following class:

[java title="util/GsonBinder.java"]
package util;
import java.lang.annotation.*;
import java.lang.reflect.Type;
import com.google.gson.*;
import play.data.binding.*;
@Global
public class GsonBinder implements TypeBinder<jsonobject> {
@Override
public Object bind(String name, Annotation[] a, String value, Class c, Type t) throws Exception
{
return new JsonParser().parse(value);
}
}
[/java]

And that is basically all to set up your mock server for REST services using the Play framework! From your favorite REST client, call the URL:

https://xebia.com/blog:9000/photo

with a PUT request and set the entity of the request to some JSON content.

Happy development!