spring5入门（九）：基于注解管理bean，创建对象

• 注解简介

注解是代码特殊标记，格式：@注解名称(属性名称=属性值, 属性名称=属性值..)
使用注解，注解作用在类上面，方法上面，属性上面
使用注解目的：简化 xml 配置

• 有关bean的注解

@Component
@Service
@Controller
@Repository

• 使用注解创建对象

• 添加依赖
  

• 开启组件扫描

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

</beans>

• 创建bean，如果不指定value，默认时类名的首字母小写

@Component(value = "userService")
public class UserService {

    public void add() {
        System.out.println("service add.......");
    }

}

• 测试方法

public class Test3 {

    @Test
    public void testAdd() {
        ApplicationContext context = new ClassPathXmlApplicationContext("bean7.xml");
        UserService userService = context.getBean("userService", UserService.class);
        System.out.println(userService);
        userService.add();
    }

}

• 控制台

com.ychen.spring.ser.UserService@452e19ca
service add.......

Process finished with exit code 0

• 组件扫描详情

<!-- 表示不扫描所有组件，只扫描带Controller注解的类 -->
<context:component-scan base-package="com.atguigu" use-defaultfilters="false">
    <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
</context:component-scan>

<!-- 表示除了带Controller注解的类都扫描 -->
<context:component-scan base-package="com.atguigu">
    <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
</context:component-scan>