JavaEE Spring框架学习笔记(理论学习之Bean的自动装配)

Bean的自动装配可实现无须配置xml即可完成Bean的装配，Bean的自动装配分为以下几种方式：

1.no 不使用自动装配（默认选项）
2.byName Bean通过实现set方法IOC就可以自动装载与该属性名（类名）跟xml中相同ID值的Bean的自动装载。 必须设置与该类型相同名称的id值
2.byType 这种方式IOC容器将自动装载xml文件中配置相同类型 即相同类名的Bean；无须设置ID值
3.constructor  构造器的方式! 通过构造器自动装载与该参数相同类型的Bean   id值为可选值

注意：byName 与byType 够必须实现set方法。  而constructor必须创建构造函数

官方说明：

Table 7.2. Autowiring modes

Mode	Explanation
no	(Default) No autowiring. Bean references must be defined via a ref element. Changing the default setting is not recommended for larger deployments, because specifying collaborators explicitly gives greater control and clarity. To some extent, it documents the structure of a system.
byName	Autowiring by property name. Spring looks for a bean with the same name as the property that needs to be autowired. For example, if a bean definition is set to autowire by name, and it contains a master property (that is, it has a setMaster(..) method), Spring looks for a bean definition named master, and uses it to set the property.
byType	Allows a property to be autowired if exactly one bean of the property type exists in the container. If more than one exists, a fatal exception is thrown, which indicates that you may not use byType autowiring for that bean. If there are no matching beans, nothing happens; the property is not set.
constructor	Analogous to byType, but applies to constructor arguments. If there is not exactly one bean of the constructor argument type in the container, a fatal error is raised.