java - spring-boot: Autowiring 2 个变量但指向一个 bean

Question

例如，有2个 bean 。parentClass 是泛型类

// parentClass
@Service
public class ParentService<T> {
    public ParentService(){
        System.out.println("ParentService:   class"+this.getClass()+"  "+this);
    }
}

//子类subClass扩展了parentClass并表明泛型是一个“字符串”类型

@Service
public class ChildService extends ParentService<String> {
    public ChildService(){
        System.out.println("ChildService:   class"+this.getClass()+"  "+this);
    }
}

//测试用例 Autowiring 泛型为 String 的 subClass 和 parentClass

@RunWith(SpringRunner.class)
@SpringBootTest
public class OneBeanApplicationTests {
    @Autowired
    private ChildService childService;
    @Autowired
    private ParentService<String> stringParentService;

    @Test
    public void contextLoads() {
        System.out.println(childService == stringParentService);// true
    }

}

答案是:正确
我对此感到困惑

=====================================如果我编辑测试类

    @Autowired
    private ParentService parentService;

......

    parentService==stringParentService; // false

这是示例项目:https://github.com/AshameL/WhyIsSameBean你可以拉它并运行测试类

Answer 1

我创建了一个 Controller 类并尝试了这个

@Autowired
ParentService<String> stringParentService;

@Autowired
ChildService childService;

@Autowired
ParentService parentService;  // Object class 



@GetMapping("/test123")
public void contextLoads() {
    System.out.println(childService.hashCode()+" : "+stringParentService.hashCode());
    System.out.println(childService == stringParentService);
    System.out.println(childService.equals(stringParentService));
    System.out.println(Integer.toHexString(System.identityHashCode(childService)));
    System.out.println(Integer.toHexString(System.identityHashCode(stringParentService)));
    System.out.println("=====================");
    System.out.println(parentService == stringParentService);
    System.out.println(parentService.hashCode()+" : "+stringParentService.hashCode());
}

OUTPUT:

563182512 : 563182512
true
true
21917bb0
21917bb0
=====================
false
196061929 : 563182512

当我们有 ParentService<String>, 时这是预期的因为哈希码没有被覆盖，父类和子类共享相同的对象

如果是ParentService默认类型 pass 是 Object，因此不同的哈希码和不同的 Object。

编辑 1:

在服务器启动期间我可以看到以下日志

ParentService:   classclass com.example.demo.service.ChildService  com.example.demo.service.ChildService@2dc6b83f
ChildService:   classclass com.example.demo.service.ChildService  com.example.demo.service.ChildService@2dc6b83f
ParentService:   classclass com.example.demo.service.ParentService  com.example.demo.service.ParentService@349131e3

当我用下面的代码做同样的事情时

public static void main(String[] args) {
    ParentService parentService = new ChildService();
    ParentService parentService1 = new ParentService();
}

OUTPUT:

ParentService:   classclass com.example.demo.service.ChildService  com.example.demo.service.ChildService@1d44bcfa
ChildService:   classclass com.example.demo.service.ChildService  com.example.demo.service.ChildService@1d44bcfa
ParentService:   classclass com.example.demo.service.ParentService  com.example.demo.service.ParentService@266474c2

结论是

@Autowired
ChildService childService;

@Autowired
ParentService<String> stringParentService;

是ChildService的实例由于扩展类。