Simulating HTTP Requests in Java and Kotlin

There are times when we need to simulate an HTTP request in our Java tests. In this article, I will show you how to do it.

MockWebServer

MockWebServer is a project created by Square that is available for both Kotlin and Java. In this example, we will use Java.

Adding Dependencies

We will use Maven. Add the following dependency to your pom.xml file:

    <dependency>
        <groupId>com.squareup.okhttp3</groupId>
        <artifactId>mockwebserver</artifactId>
        <version>5.0.0-alpha.14</version>
        <scope>test</scope>
    </dependency>

Additionally, we will use JUnit5 for testing.

Creating a Basic Service

Let’s create a basic service that will make a request to a server.

    private final WebClient webClient;

    public MyService() {
        this.webClient =  WebClient.create();
    }

    public String get(String url) {
        return webClient.get()
                .uri(url)
                .retrieve()
                .bodyToMono(String.class)
                .block();
    }

Creating a Test

Now let’s create a test that will simulate the server’s response.

    public static final String RESPONSE = "This is a simulated response";
    private MockWebServer mockServer;

    private MyService service;

    @BeforeEach
    void setUp() throws IOException {
        this.service = new MyService();
        mockServer = new MockWebServer();
        mockServer.start();
    }

    @AfterEach
    void tearDown() throws IOException {
        mockServer.shutdown();
    }

    @Test
    void get(){
        //GIVEN
        mockServer.enqueue(new MockResponse().setBody(RESPONSE));
        HttpUrl baseUrl = mockServer.url("api/chat");
        //WHEN
        String result = service.get(baseUrl.toString());
        //THEN
        assertEquals(RESPONSE, result);
    }

Conclusion

MockWebServer is an excellent tool for simulating HTTP requests in Java and Kotlin. It is easy to use and very powerful.