Java @Bean 和 @Autowired 的区别

Difference between @Bean and @Autowired

提问by zhuochen shen

Why can't I use @Autowiredin this case?

为什么我不能@Autowired在这种情况下使用？

@SpringBootApplication
public class Application {

    @Autowired
    BookingService bookingService;

    public static void main(String[] args) {
        bookingService.book("Alice", "Bob", "Carol");
    }
}

but can use @Bean

但可以使用 @Bean

@SpringBootApplication
public class Application {

    @Bean
    BookingService bookingService() {
        return new BookingService();
    }

    public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(Application.class, args);
        BookingService bookingService = ctx.getBean(BookingService.class);
        bookingService.book("Alice", "Bob", "Carol");
    }
}

Aren't the two ways to generate BookingServicethe same thing?

这两种方法不是产生BookingService相同的东西吗？

采纳答案by DaveyDaveDave

@Beanand @Autowireddo two very different things. The other answers here explain in a little more detail, but at a simpler level:

@Bean并@Autowired做两件非常不同的事情。这里的其他答案更详细地解释了，但在更简单的层面上：

• @Beantells Spring 'here is an instance of this class, please keep hold of it and give it back to me when I ask'.

• @Autowiredsays 'please give me an instance of this class, for example, one that I created with an @Beanannotation earlier'.

• @Bean告诉 Spring '这是这个类的一个实例，请保留它并在我要求时还给我'。

• @Autowired说'请给我一个这个类的实例，例如，一个我@Bean之前用注释创建的实例'。

Does that make sense? In your first example, you're asking Spring to give you an instance of BookingService, but you're never creating one, so Spring has nothing to give you. In your second example, you're creating a new instance of BookingService, telling Spring about it, and then, in the main()method, asking for it back.

那有意义吗？在您的第一个示例中，您要求 Spring 为您提供一个 实例BookingService，但您从未创建过一个实例，因此 Spring 没有任何东西可以提供给您。在您的第二个示例中，您正在创建 的一个新实例BookingService，将其告知 Spring，然后在该main()方法中要求返回它。

If you wanted, you could remove the two additional lines from the second main()method, and combine your two examples as below:

如果需要，您可以从第二种main()方法中删除另外两行，并将您的两个示例组合如下：

@SpringBootApplication
public class Application {

  @Autowired
  BookingService bookingService;

  @Bean
  BookingService bookingService() {
    return new BookingService();
  }

  public static void main(String[] args) {
    bookingService.book("Alice", "Bob", "Carol");
  }
}

In this case, the @Beanannotation gives Spring the BookingService, and the @Autowiredmakes use of it.

在这种情况下，@Bean注释为 Spring 提供了BookingService，并且@Autowired使用了它。

This would be a slightly pointless example, as you're using it all in the same class, but it becomes useful if you have the @Beandefined in one class, and the @Autowiredin a different one.

这将是一个有点无意义的例子，因为你在同一个类中使用它，但是如果你@Bean在一个类中定义了它，并且在另一个类中定义它会变得有用@Autowired。

回答by pmverma

@Bean
BookingService bookingService() {
    return new BookingService();
}

Annotating @Beanonly registers the service as a bean(kind of an Object) in spring application context. In simple words, it is just registration and nothing else.

注释@Bean仅将服务注册为 spring 应用程序上下文中的 bean（一种对象）。简单来说，就是注册而已。

@Autowired
BookingService bookingService;

Annotating a variable with @Autowiredinjects a BookingServicebean(i.e Object) from Spring Application Context.

使用Spring Application Context@Autowired注入BookingServicebean（即对象）来注释变量。

(i.e) The registered bean with @Beanannotation will be injected to the variable annotated with @Autowired.

(ie) 带有@Bean注解的注册 bean将被注入到带有注解的变量中@Autowired。

Hope this clears your doubt!

希望这能消除你的疑惑！

回答by Kris Swat

great answer by @DaveyDaveDave In the example instead of

@DaveyDaveDave 在示例中而不是

@Bean
  BookingService bookingService() {
    return new BookingService();
  }

You can use @Service annotation on BookingService class

您可以在 BookingService 类上使用 @Service 注释

回答by n0rtan

Here's good article about @Autowired annotation: http://www.baeldung.com/spring-autowire

这是关于@Autowired 注释的好文章：http: //www.baeldung.com/spring-autowire

The @Autowired annotation can instantiate your injectables by defining @ComponentScan("namespace.with.your.components.for.inject") on config class

@Autowired 注释可以通过在配置类上定义 @ComponentScan("namespace.with.your.components.for.inject") 来实例化您的可注入对象

@Configuration
@ComponentScan("com.baeldung.autowire.sample")
public class AppConfig {}

All components must be marked by @Component annotation. It replaces the @Bean annotation.

所有组件都必须用@Component 注解进行标记。它取代了@Bean 注释。

回答by SARIKA

@Bean is just for the metadata definition to create the bean(equivalent to tag). @Autowired is to inject the dependancy into a bean(equivalent to ref XML tag/attribute).

@Bean 只是为了元数据定义来创建bean（相当于标签）。@Autowired 是将依赖注入到一个 bean 中（相当于 ref XML 标签/属性）。