IoC / DI 实操

1. 建三层类

包结构：

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

① 实体 Book

package com.lib.model;
public class Book {private Integer id;private String title;// 全参构造 + getter/setter/toString 省略
}

② Repository 接口

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

③ Repository 实现

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 构造器注入@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);}
}

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2. 三种注入方式对比

方式	写法		备注
构造器	@Autowired 全参构造		不可变、易测试
Setter	@Autowired setXxx		允许后期重配置
字段	直接 @Autowired		单元测试需反射

验证：
浏览器访问 http://localhost:8080/library/book/1 → 返回 JSON
{"id":1,"title":"Spring in Action"} 即注入成功。

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3. Bean 作用域实验

在 InMemoryBookRepository 类上加：

@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)

写测试控制器：

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

连续刷新页面：

• singleton（默认）→ hash 不变

• prototype → 每次 hash 变化

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4. 生命周期回调（30 min）

① 让 Repository 实现 2 个接口

@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 启动/关闭 Tomcat，观察控制台顺序：

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

截图保存，生命周期七连击完成。

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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 配置类

@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 验证

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

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8. 常见错误速查

异常	原因	解决
No qualifying bean of type 'BookRepository'	忘记 @Repository	加注解或 @ComponentScan
Bean instantiation failed: No default constructor	自己写了带参构造却未 @Autowired	补上构造器 @Autowired
@PreDestroy not called	外部 Tomcat 强杀	用 catalina stop 温和关闭