Mocking the servlet container with MockMvc

The design behind the Spring MVC test is to test the controller by performing actual requests and generating responses, as they would be at runtime. MockMvc is used to mock the servlet container, and it can perform a request and verify the resulting response status and response elements. We'll build a Spring controller to generate a JSON response as in the case of a rest controller and then use MockMvc to unit test the request and the response:

  1. Create a serializable Employee POJO class that holds employee information, such as ID, name, and salary.
  2. Create a controller to return a specific employee and all employees with /employees/{id} and /employees/ urls. We'll create a HashMap and store dummy employees. The following is the class:
    @Controller
public class HRController {
  private Map<Integer, Employee> database = new HashMap<Integer, 
        Employee>();
  public HRController() {
    loadDummyData();
  }
  private void loadDummyData() {
    Employee john = new Employee();
    john.setId(1);
    john.setName("John Doe");
    john.setSalary(100.00);
    database.put(1, john);
    Employee karen = new Employee();
    karen.setId(2);
    karen.setName("Karen Cushing");
    karen.setSalary(500.00);
    database.put(2, karen);
  }

  @RequestMapping(value = "/employees/{id}", method =
         RequestMethod.GET)
  public @ResponseBody
  Employee retrieve(@PathVariable int id) {
    return database.get(id);
  }

  @RequestMapping(value = "/employees", method = 
        RequestMethod.GET)
  public @ResponseBody
  List<Employee> retrieveAll() {
    return new ArrayList<Employee>(database.values());
  }

}

    Note that the retrieve and retrieveAll methods are annotated with @RequestMapping(value = "/employees/{id}", method = RequestMethod.GET) and @RequestMapping(value = "/employees", method = RequestMethod.GET), respectively to map the URLs. Also, both the methods are annotated with an @ResponseBody annotation to return response as JSON object.

  3. When we run the web application and open the explorer to load the http://localhost:8080/SpringWebTest/employees/ URL, the following JSON output is displayed:
    Mocking the servlet container with MockMvc
  4. When we type http://localhost:8080/SpringWebTest/employees/1, this is how the output looks:
    Mocking the servlet container with MockMvc
  5. We can examine the integration of the web tier with other tiers in isolation from a web container using the org.springframework.test.web.servlet.MockMvc, org.springframework.test.web.servlet.request.MockMvcRequestBuilders, and org.springframework.test.web.servlet.result.MockMvcResultMatchers classes. The following JUnit test demonstrates the usages of MockMvc:
    @RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations ="classpath:beans.xml")
@WebAppConfiguration
public class HRControllerTest {
  @Autowired
    private WebApplicationContext wac;
    private MockMvc mockMvc;

    @Before  public void setup() {
        this.mockMvc = 
        MockMvcBuilders.webAppContextSetup
             (this.wac).build();
    }

    @Test public void getEmployee() throws Exception {
    this.mockMvc.perform(get("/employees/1").
    accept(MediaType.parseMediaType(
        "application/json;charset=UTF-8")))
            .andExpect(status().isOk())
            .andExpect(content().contentType(
                "application/json;charset=UTF-8"))
            .andExpect(jsonPath("$.name").value("John
                 Doe"))
            .andExpect(jsonPath("$.salary").value(100.00))
            .andExpect(jsonPath("$.id").value(1));
    }
}

    The MockMvcBuilders class needs a WebApplicationContext to build a MockMvc object; the WebApplicationContext is autowired using the @WebAppConfiguration annotation. The MockMvc object is used to perform a GET request to /employees/1 and then it verifies that the response status is 200 (isOk()) as well as the JSON response. The jsonPath("$.name").value("John Doe") statement checks whether the output JSON contains a name field and its value is John Doe. So, we just bypassed the servlet container to test the real request/response handling.

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