Spring beans are classes. Instead of instantiating a class (using new), you get an instance as a bean cast to your class type from the application context, where the bean is what you configured in the application context configuration. This way, the whole application maintains singleton-scope instance throughout the application. All beans are initialized following their configuration order right after the application context is instantiated. Even if you don't get any beans in your application, all beans instances are already created the moment after you created the application context.

就Spring引导应用程序而言，bean只是一个Java对象，它是在应用程序启动时由Spring框架创建的。

对象的用途可以是任何东西——配置、服务、数据库连接工厂等等——Spring并不关心这些。

大多数bean依赖于其他bean才能工作，例如实体管理器可能需要一个数据库连接。Spring框架能够找出如何将bean自动连接在一起。从应用程序开发人员的角度来看，您只需声明所需的bean，它们就会“神奇地”出现在您的应用程序中，随时可以使用。

bean是Spring Container管理的类的实例。

For Spring, all objects are beans! The fundamental step in the Spring Framework is to define your objects as beans. Beans are nothing but object instances that would be created by the spring framework by looking at their class definitions. These definitions basically form the configuration metadata. The framework then creates a plan for which objects need to be instantiated, which dependencies need to be set and injected, the scope of the newly created instance, etc., based on this configuration metadata. The metadata can be supplied in a simple XML file, just like in the first chapter. Alternatively, one could provide the metadata as Annotation or Java Configuration.

书:Just Spring

Spring beans are classes. Instead of instantiating a class (using new), you get an instance as a bean cast to your class type from the application context, where the bean is what you configured in the application context configuration. This way, the whole application maintains singleton-scope instance throughout the application. All beans are initialized following their configuration order right after the application context is instantiated. Even if you don't get any beans in your application, all beans instances are already created the moment after you created the application context.

Spring的XML配置由bean组成，而bean基本上是类。它们只是我们在ApplicationContext中使用的pojo。定义bean可以看作是替换关键字new。所以无论你在应用程序中使用关键字new，比如:

MyRepository myRepository =new MyRepository ();

当你使用关键字new时你可以删除配置并将其放入XML文件中。 所以我们将像这样编码:

<bean name="myRepository " 
      class="com.demo.repository.MyRepository " />

现在我们可以简单地使用Setter注入/构造函数注入。我正在使用Setter注入。

public class MyServiceImpl implements MyService {
    private MyRepository myRepository;
    public void setMyRepository(MyRepository myRepository)
        {
    this.myRepository = myRepository ;
        }
public List<Customer> findAll() {
        return myRepository.findAll();
    }
}