HTTP API Simulation using Wiremock

In today's world of micro-services we typically integrate to many REST API (working on HTTP or HTTPS) for our application. We already saw one such simulation tool called Hoverfly.

Wiremock is another similar tool for simulation of the API's. Take a look at the documentation of the tool. It supports both standalone (or command-line) mode as well as Java API.

Lets look at a sample API simulation example using Wiremock with Java.

We will use maven to create a new application and add the following dependency

<dependency>
    <groupId>com.github.tomakehurst</groupId>
    <artifactId>wiremock-jre8</artifactId>
    <version>2.23.2</version>
</dependency>

Once the dependencies are installed we want to instantiate and start WireMock as below :

WireMockServer wireMockServer = new WireMockServer(WireMockConfiguration.wireMockConfig()
//        .dynamicPort()
//        .usingFilesUnderDirectory("~/simulation/")
          .port(8888));

wireMockServer.getOptions().filesRoot().child(WireMockApp.MAPPINGS_ROOT).createIfNecessary();
wireMockServer.getOptions().filesRoot().child(WireMockApp.FILES_ROOT).createIfNecessary();

wireMockServer.start();

Note that above before starting the server we actually create the necessary directories where the simulation files will get stored. They are stored under 'mappings' (as given by MAPPING_ROOT) and '__files' (as given by FILES_ROOT) under the root directory. The default root directory is 'src/test/resources'.

Once the server is started we want to start recording and capture the requests. This can be done as below :

// Start Recording the request and proxy all the requests to http://echo.jsontest.com
wireMockServer.startRecording("http://echo.jsontest.com/");

// Create a client to call the echo url. Note that we are calling 
// the wiremock server which will act as a proxy to the configured url
HttpClient client = HttpClientFactory.createClient();
HttpGet request = new HttpGet("https://localhost:8888/a/b/c/d");
HttpResponse response = client.execute(request);

System.out.println("Response Code : " + response.getStatusLine().getStatusCode());
BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
StringBuffer result = new StringBuffer();
String line = "";
while ((line = rd.readLine()) != null) {
    result.append(line);
}
System.out.println(result.toString());

// Stop the recording. The recorded mapping are stored inside the root directory
// and returned as result
SnapshotRecordResult recordedMappings = wireMockServer.stopRecording();

So now we have captured the recording it is time to test the simulated response. Here the recording is stopped but the wiremock server is still running. It will serve all the captured responses for similar requests.
Lets try it out

// We call the same URL and this time we will get simulated response
HttpGet same_request = new HttpGet("https://localhost:8888/a/b/c/d");
HttpResponse simulated_response = client.execute(same_request);
System.out.println("Response Code : " + simulated_response.getStatusLine().getStatusCode());
BufferedReader simBR = new BufferedReader(new InputStreamReader(simulated_response.getEntity().getContent()));
StringBuffer simBuffer = new StringBuffer();
line = "";
while ((line = simBR.readLine()) != null) {
    simBuffer.append(line);
}
System.out.println(simBuffer.toString());

// We call a different URL. As this is not captured it will return Not Found in the response
HttpGet different_request = new HttpGet("https://localhost:8888/e/f/g/h");
HttpResponse no_response = client.execute(different_request);
System.out.println("Response Code : " + no_response.getStatusLine().getStatusCode());
BufferedReader noBR = new BufferedReader(new InputStreamReader(no_response.getEntity().getContent()));
StringBuffer noBuffer = new StringBuffer();
line = "";
while ((line = noBR.readLine()) != null) {
    noBuffer.append(line);
}
System.out.println(noBuffer.toString());

At the end we need to stop the wiremock server as below

wireMockServer.stop();

Above we used record-replay to simulate the endpoints. Wiremock also provides methods for creating custom responses by using stub().

So happy simulating :)