FirstApi approach with OpenAPI generator plugin and SpringDoc OpenAPI UI to your Spring Boot Project

Tested with Java 17 and SpringBoot 2.7.7

STEP 1

Add the following property version for openapitools in pom.xml:

<properties>
    <openapitools.generator.version>6.4.0</openapitools.generator.version>
</properties>

Add the following dependencies:

    <!--OPENAPI GENERATOR MAVEN PLUGIN-->
    <dependency>
        <groupId>org.openapitools</groupId>
        <artifactId>openapi-generator-maven-plugin</artifactId>
        <version>${openapitools.generator.version}</version>
        <scope>provided</scope>
    </dependency>
    
    <dependency>
        <groupId>org.openapitools</groupId>
        <artifactId>jackson-databind-nullable</artifactId>
        <version>0.2.4</version>
    </dependency>
    
    <!--SPRINGDOC OPENAPI-->
    <dependency>
        <groupId>org.springdoc</groupId>
        <artifactId>springdoc-openapi-ui</artifactId>
        <version>1.6.13</version>
    </dependency>

STEP 2

Generate your api.yaml file
You can use https://editor.swagger.io/
Generate a file called api.yaml and place it in src/main/resources

STEP 3

Add the following plugging in your pom.xml file

    <!--OpenApi Codegen-->
    <plugin>
        <groupId>org.openapitools</groupId>
        <artifactId>openapi-generator-maven-plugin</artifactId>
        <version>${openapitools.generator.version}</version>
        <executions>
            <execution>
                <goals>
                    <goal>generate</goal>
                </goals>
                <configuration>
                    <inputSpec>${project.basedir}/src/main/resources/api.yaml</inputSpec>
                    <generatorName>spring</generatorName>
                    <generateApiTests>false</generateApiTests>
                    <generateModelTests>false</generateModelTests>
                    <modelNameSuffix>Dto</modelNameSuffix>
                    <configOptions>
                        <sourceFolder>src/gen/java/main</sourceFolder>
                        <oas3>true</oas3>
                        <useSpringController>true</useSpringController>
                        <useSpringfox>false</useSpringfox>
                        <interfaceOnly>true</interfaceOnly>
                    </configOptions>
                </configuration>
            </execution>
        </executions>
    </plugin>

STEP 4

Add the following property in application.properties file
This is optional but could avoid few future problems

spring.mvc.pathmatch.matching-strategy=ant-path-matcher

STEP 5

Implement the generated methods
To complete your API, you can implement the generated methods by the codegen plugging on the default path:
target/generated_sources/openapi/src/gen/java

STEP 6

Check Swagger UI website
Run your application and access the following url to check your API documentation:

host:port/swagger-ui/index.html
http://localhost:8080/swagger-ui/index.html

http://localhost:8080/swagger-ui/index.html