Question

我不明白弹簧靴注释@Autowired是如何正确工作的。这是一个简单的例子：

@SpringBootApplication
public class App {
    @Autowired
    public Starter starter;

    public static void main(String[] args) {
        SpringApplication.run(App.class, args);
    }
    public App() {
        System.out.println("init App");
        //starter.init();
    }
}

-

@Repository
public class Starter {
    public Starter() {System.out.println("init Starter");}
    public void init() { System.out.println("call init"); }
}

当我执行此代码时，我会得到日志init App和init Starter，因此Spring会创建此对象。但是当我从Starter中的App调用init方法时，我得到NullPointerException。是否还需要使用注释@Autowired来初始化我的对象？

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'app': Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [{package}.App$$EnhancerBySpringCGLIB$$87a7ccf]: Constructor threw exception; nested exception is java.lang.NullPointerException

Answer 1

当您从类init的构造函数调用App方法时，Spring尚未将依赖项自动装入App对象。如果要在Spring完成创建并自动装配App对象后调用此方法，请添加一个带有@PostConstruct注释的方法来执行此操作，例如：

@SpringBootApplication
public class App {
    @Autowired
    public Starter starter;

    public static void main(String[] args) {
        SpringApplication.run(App.class, args);
    }

    public App() {
        System.out.println("constructor of App");
    }

    @PostConstruct
    public void init() {
        System.out.println("Calling starter.init");
        starter.init();
    }
}

了解Spring Boot @Autowired

1 个答案: