懒得笔记4 spring annotation

1, 要加入 aop 包， 不然会报

org.springframework.beans.factory.BeanDefinitionStoreException: Unexpected exception parsing XML document from class path resource [beans.xml]; nested exception is java.lang.NoClassDefFoundError: org/springframework/aop/TargetSource

2，xml 文档

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd         http://www.springframework.org/schema/context         http://www.springframework.org/schema/context/spring-context.xsd"> 
    <context:annotation-config/>

</beans>

3，注解

1，@Autowired

按类型再按名字@qualifier

在setter之前标志（As expected, you can apply the

@Autowired

annotation
to "traditional" setter methods:）

2，@Required

This annotation simply indicates that the affected bean property must be populated at configuration time, through an explicit property value in a bean definition or through autowiring. The container throws an exception if the affected bean property
has not been populated; this allows for eager and explicit failure, avoiding NullPointerExceptions or the like later on. It is still recommended that you put assertions into the bean class itself, for example, into an init method. Doing so enforces those required
references and values even when you use the class outside of a container.

仅仅在配置时就用于检测是否有合适的值与bean配置。防止出现NullPointerExceptions

3，@Resource(name="UserDAO")

按名字再按类型

4,@component

在xml中加入以下这句话，便可以不用在xml里定义 bean 系统自动到指定的地方去扫描找到对应的bean，写在对应的类里

<context:component-scan base-package="com.bjsxt"/>

在bean中加入 @Component("u") 来指定bean 的id 也可不写，默认为类名小写