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Expanded Audience – Frontegg – Security (partner)
announcement - icon User management is very complex, when implemented properly. No surprise here.

Not having to roll all of that out manually, but instead integrating a mature, fully-fledged solution - yeah, that makes a lot of sense.
That's basically what Frontegg is - User Management for your application. It's focused on making your app scalable, secure and enjoyable for your users.
From signup to authentication, it supports simple scenarios all the way to complex and custom application logic.

Have a look:

>> Elegant User Management, Tailor-made for B2B SaaS

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NPI – Lightrun – Spring (partner)

We rely on other people’s code in our own work. Every day. It might be the language you’re writing in, the framework you’re building on, or some esoteric piece of software that does one thing so well you never found the need to implement it yourself.

The problem is, of course, when things fall apart in production - debugging the implementation of a 3rd party library you have no intimate knowledge of is, to say the least, tricky. It’s difficult to understand what talks to what and, specifically, which part of the underlying library is at fault.

Lightrun is a new kind of debugger.

It's one geared specifically towards real-life production environments. Using Lightrun, you can drill down into running applications, including 3rd party dependencies, with real-time logs, snapshots, and metrics. No hotfixes, redeployments, or restarts required.

Learn more in this quick, 5-minute Lightrun tutorial:

>> The Essential List of Spring Boot Annotations and Their Use Cases

1. Overview

These days, we expect to call REST APIs in most of our services. Spring provides a few options for building a REST client, and WebClient is recommended.

In this quick tutorial, we'll learn how to unit test services that use WebClient to call APIs.

2. Mocking

We have two main options for mocking in our tests:

3. Using Mockito

Mockito is the most common mocking library for Java. It's good at providing pre-defined responses to method calls, but things get challenging when mocking fluent APIs. This is because in a fluent API, a lot of objects pass between the calling code and the mock.

For example, let's have an EmployeeService class with a getEmployeeById method fetch data via HTTP using WebClient:

public class EmployeeService {

    public EmployeeService(String baseUrl) {
        this.webClient = WebClient.create(baseUrl);
    public Mono<Employee> getEmployeeById(Integer employeeId) {
        return webClient
                .uri("http://localhost:8080/employee/{id}", employeeId)

We can use Mockito to mock this:

public class EmployeeServiceTest {
    void givenEmployeeId_whenGetEmployeeById_thenReturnEmployee() {

        Integer employeeId = 100;
        Employee mockEmployee = new Employee(100, "Adam", "Sandler", 
          32, Role.LEAD_ENGINEER);
        when(requestHeadersUriMock.uri("/employee/{id}", employeeId))

        Mono<Employee> employeeMono = employeeService.getEmployeeById(employeeId);

          .expectNextMatches(employee -> employee.getRole()


As we can see, we need to provide a different mock object for each call in the chain, with four different when/thenReturn calls required. This is verbose and cumbersome. It also requires us to know the implementation details of how exactly our service uses WebClient, making this a brittle way of testing.

So how can we write better tests for WebClient?

4. Using MockWebServer

MockWebServer, built by the Square team, is a small web server that can receive and respond to HTTP requests.

Interacting with MockWebServer from our test cases allows our code to use real HTTP calls to a local endpoint. We get the benefit of testing the intended HTTP interactions, and none of the challenges of mocking a complex fluent client.

Using MockWebServer is recommended by the Spring Team for writing integration tests.

4.1. MockWebServer Dependencies

To use MockWebServer, we need to add the Maven dependencies for both okhttp and mockwebserver to our pom.xml:


4.2. Adding MockWebServer to Our Test

Let's test our EmployeeService with MockWebServer:

public class EmployeeServiceMockWebServerTest {

    public static MockWebServer mockBackEnd;

    static void setUp() throws IOException {
        mockBackEnd = new MockWebServer();

    static void tearDown() throws IOException {

In the above JUnit Test class, the setUp and tearDown method takes care of creating and shutting down the MockWebServer.

The next step is to map the port of the actual REST service call to the MockWebServer's port:

void initialize() {
    String baseUrl = String.format("http://localhost:%s", 
    employeeService = new EmployeeService(baseUrl);

Now it's time to create a stub so that the MockWebServer can respond to an HttpRequest.

4.3. Stubbing a Response

Let's use MockWebServer's handy enqueue method to queue a test response on the webserver:

void getEmployeeById() throws Exception {
    Employee mockEmployee = new Employee(100, "Adam", "Sandler", 
      32, Role.LEAD_ENGINEER);
    mockBackEnd.enqueue(new MockResponse()
      .addHeader("Content-Type", "application/json"));

    Mono<Employee> employeeMono = employeeService.getEmployeeById(100);

      .expectNextMatches(employee -> employee.getRole()

When the actual API call is made from the getEmployeeById(Integer employeeId) method in our EmployeeService class, MockWebServer will respond with the queued stub.

4.4. Checking a Request

We may also want to make sure that the MockWebServer was sent the correct HttpRequest.

MockWebServer has a handy method named takeRequest that returns an instance of RecordedRequest:

RecordedRequest recordedRequest = mockBackEnd.takeRequest();
assertEquals("GET", recordedRequest.getMethod());
assertEquals("/employee/100", recordedRequest.getPath());

With RecordedRequest, we can verify the HttpRequest that was received to make sure our WebClient sent it correctly.

5. Conclusion

In this article, we demonstrated the two main options available to mock WebClient based REST client code.

While Mockito worked, and may be a good option for simple examples, the recommended approach is to use MockWebServer.

As always, the source code for this article is available over on GitHub.

November Discount Launch 2022 – Bottom
We’re finally running a Black Friday launch. All Courses are 30% off until the end of this week:


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