1. 建三層類

包結構：

com.lib  ├─ config  ├─ controller  ├─ service  ├─ repository  ├─ model  └─ annotation   // 自定義限定符

① 實體 Book

package com.lib.model;
public class Book {private Integer id;private String title;// 全參構造 + getter/setter/toString 省略
}

② Repository 接口

package com.lib.repository;
public interface BookRepository {Book findById(int id);
}

③ Repository 實現

package com.lib.repository;
@Repository
public class InMemoryBookRepository implements BookRepository {private Map<Integer, Book> store = new ConcurrentHashMap<>();public InMemoryBookRepository() {store.put(1, new Book(1, "Spring in Action"));}@Overridepublic Book findById(int id) {return store.get(id);}
}

④ Service

package com.lib.service;
@Service
public class BookService {private final BookRepository repo;   // ① 構造器注入@Autowiredpublic BookService(BookRepository repo) {this.repo = repo;}public Book query(int id) {return repo.findById(id);}
}

⑤ Controller

package com.lib.controller;
@Controller
@RequestMapping("/book")
public class BookController {private BookService bookService;   // ② 字段注入（演示用）@Autowiredpublic void setBookService(BookService bookService) {this.bookService = bookService; // ③ Setter 注入}@GetMapping("/{id}")@ResponseBodypublic Book get(@PathVariable int id) {return bookService.query(id);}
}

---

2. 三種注入方式對比

方式	寫法		備注
構造器	@Autowired?全參構造		不可變、易測試
Setter	@Autowired?setXxx		允許后期重配置
字段	直接?@Autowired		單元測試需反射

驗證：
瀏覽器訪問 http://localhost:8080/library/book/1 → 返回 JSON
{"id":1,"title":"Spring in Action"} 即注入成功。

---

3. Bean 作用域實驗

在 InMemoryBookRepository 類上加：

@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)

寫測試控制器：

@GetMapping("/repo")
@ResponseBody
public String repoScope() {return "repo hash=" + bookService.getRepoHash(); // 在 Service 里返回 repo.toString()
}

連續刷新頁面：

• singleton（默認）→ hash 不變

• prototype → 每次 hash 變化

---

4. 生命周期回調（30 min）

① 讓 Repository 實現 2 個接口

@Repository
public class InMemoryBookRepository implements BookRepository,InitializingBean, DisposableBean {@PostConstructpublic void init() {System.out.println("[@PostConstruct] repo init, store size=" + store.size());}@Overridepublic void afterPropertiesSet() throws Exception {System.out.println("[InitializingBean] afterPropertiesSet");}@PreDestroypublic void preDestroy() {System.out.println("[@PreDestroy] repo will destroy");}@Overridepublic void destroy() throws Exception {System.out.println("[DisposableBean] destroy");}
}

② 啟動/關閉 Tomcat，觀察控制臺順序：

[@PostConstruct] repo init...
[InitializingBean] afterPropertiesSet...
...
[@PreDestroy] repo will destroy...
[DisposableBean] destroy...

截圖保存，生命周期七連擊完成。

---

5. Environment & 外部化配置

① 新建?app.properties?放 classpath

library.default.book.id=99
library.default.book.title=Default Book

② 配置類

@Configuration
@PropertySource("classpath:app.properties")
public class AppConfig {@Beanpublic Book defaultBook(Environment env) {return new Book(env.getProperty("library.default.book.id", Integer.class),env.getProperty("library.default.book.title"));}
}

③ 驗證

@Autowired
private Book defaultBook;   // 字段注入，僅演示
@GetMapping("/default")
@ResponseBody
public Book def() {return defaultBook;  // {"id":99,"title":"Default Book"}
}

---

8. 常見錯誤速查

異常	原因	解決
No qualifying bean of type 'BookRepository'	忘記?@Repository	加注解或?@ComponentScan
Bean instantiation failed: No default constructor	自己寫了帶參構造卻未?@Autowired	補上構造器?@Autowired
@PreDestroy not called	外部 Tomcat 強殺	用?catalina stop?溫和關閉