【Spring】学习笔记03-IOC创建对象

POJO

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;

}

beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">
    <!--使用Spring来创建对象,在Spring这些都成为Bean-->
    <bean id="user" class="com.wang.pojo.User">
        <!-- collaborators and configuration for this bean go here -->
        <property name="name" value="SPRING"/>
    </bean>
    <!-- more bean definitions go here -->
</beans>

单元测试

 @Test
    public void test01(){
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        User user = (User)context.getBean("user");
        System.out.println(user.getName());
    }

默认情况下，IOC通过实体类的无参构造创建对象，然后通过set方法注入属性

还可以使用构造器注入，此时我们去掉实体类的无参构造器

@Data
@AllArgsConstructor
public class User {
    private String name;

}

方法1：下标赋值

beans.xml

bean id="user1" class="com.wang.pojo.User">
        <constructor-arg index="0" value="Spring_construct_index"/>
    </bean>

单元测试

  @Test
    public void test02(){
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        User user = (User) context.getBean("user1");
        System.out.println(user.getName());
    }
//测试结果
//Spring_construct_index

//进程已结束，退出代码为 0

方法二：根据参数类型赋值

beans.xml

<bean id="user2" class="com.wang.pojo.User">
        <constructor-arg type="java.lang.String" value="Spring_contruct_type"/>
    </bean>

单元测试

   @Test
    public void test03(){
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        User user = (User) context.getBean("user2");
        System.out.println(user.getName());
    }
//Spring_contruct_type

//进程已结束，退出代码为 0

 

当前该方法是不建议使用的，在实体类含有多个相同类型的参数时。

方法三：直接通过参数创建对象

beans.xml

<bean id="user3" class="com.wang.pojo.User">
        <constructor-arg name="name" value="Spring_contruct_name"/>
    </bean>

单元测试：

   @Test
    public void test04(){
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        User user = (User) context.getBean("user3");
        System.out.println(user.getName());
    }