33-bean概述.md

3.3 Bean概述

A Spring IoC container manages one or more beans. These beans are created with the configuration metadata that you supply to the container, for example, in the form of XML `` definitions.

Within the container itself, these bean definitions are represented as BeanDefinition objects, which contain (among other information) the following metadata:

• A package-qualified class name: typically the actual implementation class of the bean being defined.
• Bean behavioral configuration elements, which state how the bean should behave in the container (scope, lifecycle callbacks, and so forth).
• References to other beans that are needed for the bean to do its work; these references are also called collaborators or dependencies.
• Other configuration settings to set in the newly created object, for example, the number of connections to use in a bean that manages a connection pool, or the size limit of the pool.

This metadata translates to a set of properties that make up each bean definition.

Spring IoC容器管理一个或多个* beans *。这些bean是使用您提供给容器的配置元数据创建的，例如，以XML“定义”的形式。

在容器本身内，这些bean定义表示为BeanDefinition对象，它包含（除其他信息之外）以下元数据：

• *包限定类名：*通常是定义的bean的实际实现类。
• Bean行为配置元素，它说明了bean在容器中的行为（范围，生命周期回调等等）。
• 引用其他bean的bean需要做的工作;这些引用也称为协作者或依赖性。
• 在新创建的对象中设置的其他配置设置，例如，在管理连接池的bean中使用的连接数，或者池的大小限制。

此元数据转换为构成每个bean定义的一组属性。

Table 3.1. The bean definition

Property	Explained in…​ 解释所在地方... ​
class	Section 3.3.2, “Instantiating beans”
name	Section 3.3.1, “Naming beans”
scope	Section 3.5, “Bean scopes”
constructor arguments	Section 3.4.1, “Dependency Injection”
properties	Section 3.4.1, “Dependency Injection”
autowiring mode	Section 3.4.5, “Autowiring collaborators”
lazy-initialization mode	Section 3.4.4, “Lazy-initialized beans”
initialization method	the section called “Initialization callbacks”
destruction method	the section called “Destruction callbacks”

In addition to bean definitions that contain information on how to create a specific bean, the ApplicationContext implementations also permit the registration of existing objects that are created outside the container, by users. This is done by accessing the ApplicationContext’s BeanFactory via the method getBeanFactory()which returns the BeanFactory implementation DefaultListableBeanFactory. DefaultListableBeanFactory supports this registration through the methods registerSingleton(..) and registerBeanDefinition(..). However, typical applications work solely with beans defined through metadata bean definitions.

除了包含如何创建特定bean的bean定义之外，ApplicationContext实现还允许注册由用户在容器外部创建的现有对象。 这是通过访问ApplicationContext的BeanFactory通过方法getBeanFactory()来实现的，它返回BeanFactory实现DefaultListableBeanFactory。 DefaultListableBeanFactory通过方法registerSingleton(..)和registerBeanDefinition(..)支持这种注册。 然而,典型的应用程序只能通过元数据定义的 bean 来定义。

Bean元数据和手动提供的单例实例需要尽早注册，以便容器在自动装配和其他自检步骤期间正确地进行推理。 虽然在某种程度上支持覆盖现有元数据和现有单例实例，但是在运行时（与动态访问工厂同时）对新bean的注册未被官方支持，并且可能导致并发访问异常和/或bean容器中的不一致状态 。