BAEL-4956: add source code for describng REST API in openapi

spring-boot-modules/spring-boot-springdoc/src/main/java/com/baeldung/tagopenapi/Application.java

@@ -0,0 +1,12 @@
+package com.baeldung.tagopenapi;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication()
+public class Application {
+
+    public static void main(String[] args) {
+        SpringApplication.run(Application.class, args);
+    }
+}

spring-boot-modules/spring-boot-springdoc/src/main/java/com/baeldung/tagopenapi/config/OpenApi.java

@@ -0,0 +1,20 @@
+package com.baeldung.tagopenapi.config;
+
+import io.swagger.v3.oas.models.OpenAPI;
+import io.swagger.v3.oas.models.info.Info;
+import io.swagger.v3.oas.models.info.License;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+
+public class OpenApi {
+
+    @Bean
+    public OpenAPI customOpenAPI(@Value("${springdoc.version}") String appVersion) {
+        return new OpenAPI().info(new Info().title("Controller API")
+                .version(appVersion)
+                .description("This is a sample server created using springdocs - a library for OpenAPI 3 with spring boot.")
+                .termsOfService("http://swagger.io/terms/")
+                .license(new License().name("Apache 2.0")
+                        .url("http://springdoc.org")));
+    }
+}

spring-boot-modules/spring-boot-springdoc/src/main/java/com/baeldung/tagopenapi/controller/BookController.java

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+package com.baeldung.tagopenapi.controller;
+
+import io.swagger.v3.oas.annotations.tags.Tag;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.Arrays;
+import java.util.List;
+
+@RestController
+@RequestMapping("/api/book")
+@Tag(name = "book service", description = "the book API with description tag annotation")
+public class BookController {
+
+    @GetMapping("/")
+    public List<String> getBooks() {
+        return Arrays.asList("book1", "book2");
+    }
+}