Basic API Documentation using Swagger and Spring RestDocs in a Spring Boot application

Documenting a Spring Boot application involves creating clear and comprehensive documentation for the API endpoints, request/response models, and other relevant information. Spring Boot provides tools like Swagger and Spring RestDocs to simplify the documentation process. Below is an example of using both Swagger and Spring RestDocs for documenting a simple Spring Boot REST API.

1. Swagger for API Documentation:

Step 1: Add Swagger dependencies to your pom.xml (if using Maven) or build.gradle (if using Gradle):

<!-- For Maven -->
<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-boot-starter</artifactId>
    <version>3.0.0</version>
</dependency>        

Step 2: Create a Swagger configuration class:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import springfox.documentation.builders.ApiInfoBuilder;
import springfox.documentation.builders.PathSelectors;
import springfox.documentation.builders.RequestHandlerSelectors;
import springfox.documentation.service.ApiInfo;
import springfox.documentation.spring.web.plugins.Docket;
import springfox.documentation.swagger2.annotations.EnableSwagger2;

@Configuration
@EnableSwagger2
public class SwaggerConfig {

    @Bean
    public Docket api() {
        return new Docket(springfox.documentation.spi.DocumentationType.SWAGGER_2)
                .select()
                .apis(RequestHandlerSelectors.basePackage("com.your.package.controller"))
                .paths(PathSelectors.any())
                .build()
                .apiInfo(apiInfo());
    }

    private ApiInfo apiInfo() {
        return new ApiInfoBuilder()
                .title("Your API Documentation")
                .description("Documentation for your awesome Spring Boot API")
                .version("1.0.0")
                .build();
    }
}        

Make sure to replace "com.your.package.controller" with the actual package where your controllers are located.

Step 3: Run your Spring Boot application, and Swagger UI should be accessible at https://localhost:8080/swagger-ui.html.

2. Spring RestDocs for Detailed API Documentation:

Step 1: Add Spring RestDocs dependencies to your pom.xml or build.gradle:

<!-- For Maven -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>        

Step 2: Create a test class for documenting your API using RestDocs:

import org.junit.jupiter.api.Test;
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.servlet.MockMvc;

import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.documentationConfiguration;
import static org.springframework.restdocs.operation.preprocess.Preprocessors.preprocessRequest;
import static org.springframework.restdocs.operation.preprocess.Preprocessors.preprocessResponse;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@SpringBootTest
@AutoConfigureMockMvc
@AutoConfigureRestDocs(outputDir = "target/snippets")
public class YourApiDocumentationTest {

    private final MockMvc mockMvc;

    public YourApiDocumentationTest(MockMvc mockMvc) {
        this.mockMvc = mockMvc;
    }

    @Test
    public void getExampleApi() throws Exception {
        this.mockMvc.perform(get("/api/example"))
                .andExpect(status().isOk())
                .andDo(document("example", preprocessRequest(prettyPrint()), preprocessResponse(prettyPrint())));
    }
}        

In the above example, replace "/api/example" with the actual endpoint you want to document.

Step 3: Run the tests, and Spring RestDocs will generate documentation snippets in the specified output directory.

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