When building RESTful APIs with Java and Spring, it’s important to document the response formats and media types. Properly documenting your API response formats not only helps developers understand how to work with your API but also assists in client-side development and debugging.

One popular approach to documenting APIs is by using Java Spring REST Docs. REST Docs is an open-source framework that integrates with Spring MVC to generate documentation from your API’s integration tests.

In this blog post, we’ll explore how to use Java Spring REST Docs to document API response formats and media types in a Spring Boot application.

Step 1: Include REST Docs in your project

To start, you need to include the REST Docs dependency in your Spring Boot project. Open your build.gradle (or pom.xml for Maven) file and add the following dependency:

dependencies {
    // Other dependencies
    
    // REST Docs dependency
    testImplementation 'org.springframework.restdocs:spring-restdocs-mockmvc'
}

After adding the dependency, sync your project to download the required artifacts.

Step 2: Write integration tests

Next, you need to write integration tests for your API endpoints. Integration tests allow you to simulate API requests and capture the response formats.

Here’s an example of an integration test for getting a user:

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.restdocs.mockmvc.MockMvcRestDocumentation;
import org.springframework.restdocs.mockmvc.RestDocumentationRequestBuilders;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.ResultActions;
import org.springframework.test.web.servlet.result.MockMvcResultHandlers;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;

import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

class UserControllerIntegrationTest {

    @Autowired
    private MockMvc mockMvc;
    
    @Test
    void getUser() throws Exception {
        mockMvc = MockMvcBuilders.standaloneSetup(new UserController()).build();
        
        ResultActions resultActions = mockMvc.perform(
                RestDocumentationRequestBuilders.get("/users/{id}", 1)
                        .accept(MediaType.APPLICATION_JSON)
        )
                .andExpect(status().isOk())
                .andDo(MockMvcResultHandlers.document("getUser"));

        resultActions.andReturn().getResponse().getContentAsString();
    }

}

In the above example, we’re using Spring’s MockMvc to perform a GET request to /users/{id} endpoint and documenting the response format using MockMvcResultHandlers.document().

Step 3: Generate API documentation

After writing the integration tests, we can generate the API documentation using REST Docs. By running the integration tests, REST Docs will capture the response formats and generate documentation based on the captured data.

Here’s an example of generating the API documentation with REST Docs:

import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.documentationConfiguration;

class ApiDocumentation {

    @Rule
    public final JUnitRestDocumentation restDocumentation = new JUnitRestDocumentation();

    @Autowired
    private WebApplicationContext context;

    @Before
    public void setUp() {
        this.mockMvc = MockMvcBuilders.webAppContextSetup(this.context)
                .apply(documentationConfiguration(this.restDocumentation))
                .build();
    }

    @Test
    void generateApiDocumentation() throws Exception {
        this.mockMvc.perform(get("/users/{id}", 1))
                .andExpect(status().isOk())
                .andDo(document("getUser"))
                .andReturn().getResponse().getContentAsString();
    }
}

In the above example, we’re using documentationConfiguration() to configure REST Docs and generate the documentation files. The generated documentation will include information about the API endpoints, request/response formats, and media types.

Step 4: Review and share the generated documentation

Finally, after running the integration tests, REST Docs will generate the API documentation based on the captured data. Review the generated documentation to ensure it accurately describes the API response formats and media types.

The generated documentation typically includes HTML and/or Markdown files, providing detailed information about each API endpoint and its response formats. Share this documentation with your team and clients to assist in API consumption and client-side development.

Conclusion

Documenting API response formats and media types is crucial for effective API development. By using Java Spring REST Docs along with integration tests, you can automate the documentation process and ensure that accurate and up-to-date documentation is available to consumers of your API.

With properly documented response formats and media types, developers can easily understand and work with your API, resulting in faster development and fewer integration issues.