@add(/api/books/getone)

- add new api get a book's info by id

src/main/kotlin/com/msksbr/bookmgr/controller/BookController.kt

@@ -14,7 +14,7 @@ import org.springframework.web.bind.annotation.RestController
 * 图书接口（面向普通用户）
 * 路径前缀（待定）：/api/books
 *
-* 计划接口：
+* 接口：
 *   - 图书列表查询（搜索）
 *   - 单本图书详情
 */
@@ -31,4 +31,14 @@ class BookController(private val bookService: BookService, private val ipExtract
         log.info("[Book] user agent: {}, ip={}", request.getHeader("User-Agent"), ipExtractor.getRealIp(request))
         return bookService.searchBook(query)
     }
+    @GetMapping("/getone")
+    fun getOneBook(
+        @RequestAttribute(required = false) username: String?,
+        request: HttpServletRequest,
+        id: Long
+    ): Result<Any?> {
+        log.info("[Book] getOne: user={}, id={}", username ?: "guest", id)
+        log.info("[Book] user agent: {}, ip={}", request.getHeader("User-Agent"), ipExtractor.getRealIp(request))
+        return bookService.getOneBook(id)
+    }
 }

src/main/kotlin/com/msksbr/bookmgr/service/BookService.kt

@@ -13,4 +13,10 @@ interface BookService {
     * @return 搜索结果列表，无匹配时返回 404
     */
     fun searchBook(query: String): Result<Any?>
+    /*
+    * 根据 ID 查询单本图书
+    * @param id 图书 ID，必须为正整数
+    * @return 图书实体，不存在时返回 404
+    */
+    fun getOneBook(id: Long): Result<Any?>
 }

src/main/kotlin/com/msksbr/bookmgr/service/impl/BookServiceImpl.kt

@@ -10,7 +10,7 @@ import com.msksbr.bookmgr.template.Result
 
 /*
 * 图书服务实现
-* 提供图书搜索功能，按书名或作者进行模糊匹配
+* 提供图书搜索和单本图书查询功能
 */
 @Service
 class BookServiceImpl(private val bookMapper: BookMapper) : BookService {
@@ -32,4 +32,21 @@ class BookServiceImpl(private val bookMapper: BookMapper) : BookService {
         log.info("[Book] search: found {} results for {}", result.size, query)
         return Result.success(result)
     }
+
+    override fun getOneBook(id: Long): Result<Any?> {
+        if (id < 1) {
+            log.warn("[Book] getOne: invalid id={}", id)
+            return Result.error("Invalid book ID")
+        }
+        val result = bookMapper.selectOne(
+            QueryWrapper<Book>()
+                .eq("id", id)
+        )
+        if (result==null) {
+            log.info("[Book] getOneBook: no results for {}", id)
+            return Result.notFound("Book not found")
+        }
+        log.info("[Book] getOne: found {}, author={}", result.name, result.author)
+        return Result.success(result)
+    }
 }