Master Spring Boot 2.x: Build RESTful APIs with @RestController and Unit Tests

First, review the key Spring MVC annotations used in the quick‑start tutorial: @Controller, @RestController, and @RequestMapping. If you are unfamiliar with Spring MVC, read the quick‑start guide before proceeding. @Controller: marks a class as an HTTP request handler. @RestController: combines @Controller and @ResponseBody, returning JSON by default. @RequestMapping: configures URL mapping; newer method‑specific annotations such as GetMapping, PostMapping, DeleteMapping, and PutMapping are now preferred.

We then implement a RESTful API for managing User objects using Spring MVC, demonstrating request mapping, parameter binding, and unit testing.

Define User Entity

@Data
public class User {

    private Long id;
    private String name;
    private Integer age;
}

The @Data annotation from Lombok automatically generates getters, setters, and other boilerplate methods. Add the Lombok dependency to your pom.xml:

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
</dependency>

Implement User Operations Controller

@RestController
@RequestMapping(value = "/users") // all mappings under /users
public class UserController {

    // thread‑safe map simulating storage
    static Map<Long, User> users = Collections.synchronizedMap(new HashMap<>());

    @GetMapping("/")
    public List<User> getUserList() {
        return new ArrayList<>(users.values());
    }

    @PostMapping("/")
    public String postUser(@RequestBody User user) {
        users.put(user.getId(), user);
        return "success";
    }

    @GetMapping("/{id}")
    public User getUser(@PathVariable Long id) {
        return users.get(id);
    }

    @PutMapping("/{id}")
    public String putUser(@PathVariable Long id, @RequestBody User user) {
        User u = users.get(id);
        u.setName(user.getName());
        u.setAge(user.getAge());
        users.put(id, u);
        return "success";
    }

    @DeleteMapping("/{id}")
    public String deleteUser(@PathVariable Long id) {
        users.remove(id);
        return "success";
    }
}

Compared with the 1.x tutorial, the newer version replaces the generic @RequestMapping with method‑specific annotations ( @GetMapping , @PostMapping , etc.) and uses @RequestBody for JSON payloads instead of @ModelAttribute .

Write Unit Tests

The following test class uses MockMvc to verify each CRUD operation:

@RunWith(SpringRunner.class)
@SpringBootTest
public class Chapter21ApplicationTests {

    private MockMvc mvc;

    @Before
    public void setUp() {
        mvc = MockMvcBuilders.standaloneSetup(new UserController()).build();
    }

    @Test
    public void testUserController() throws Exception {
        // 1. GET empty list
        mvc.perform(get("/users/"))
           .andExpect(status().isOk())
           .andExpect(content().string(equalTo("[]")));

        // 2. POST a user
        mvc.perform(post("/users/")
           .contentType(MediaType.APPLICATION_JSON)
           .content("{\"id\":1,\"name\":\"Test Master\",\"age\":20}"))
           .andExpect(content().string(equalTo("success")));

        // 3. GET list with the new user
        mvc.perform(get("/users/"))
           .andExpect(status().isOk())
           .andExpect(content().string(equalTo("[{\"id\":1,\"name\":\"Test Master\",\"age\":20}]")));

        // 4. PUT to update the user
        mvc.perform(put("/users/1")
           .contentType(MediaType.APPLICATION_JSON)
           .content("{\"name\":\"Ultimate Master\",\"age\":30}"))
           .andExpect(content().string(equalTo("success")));

        // 5. GET the updated user
        mvc.perform(get("/users/1"))
           .andExpect(content().string(equalTo("{\"id\":1,\"name\":\"Ultimate Master\",\"age\":30}")));

        // 6. DELETE the user
        mvc.perform(delete("/users/1"))
           .andExpect(content().string(equalTo("success")));

        // 7. GET empty list again
        mvc.perform(get("/users/"))
           .andExpect(status().isOk())
           .andExpect(content().string(equalTo("[]")));
    }
}

For MockMvc users, remember to import the static helper methods:

import static org.hamcrest.Matchers.equalTo;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

By adding the spring-boot-starter-web dependency (no extra configuration needed), you can quickly create a fully functional RESTful API for the User entity and verify it with comprehensive unit tests. The tutorial also highlights the most common Spring MVC annotations: @RestController, @RequestMapping, @PathVariable, and @RequestBody.