011 bean的作用域

狂神說Java：https://space.bilibili.com/95256449

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1、The Singleton Scope 單例模式（Spring默認機制）

對於同一個類，Spring容器只會創建一個實例。每次從容器中get的時候，都是同一個對象。

<?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:p="http://www.springframework.org/schema/p"
       xmlns:c="http://www.springframework.org/schema/c"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">
    
    <bean id="user" class="com.kuang.pojo.User" p:name="張三" p:age="33" scope="singleton"/>
</beans>

測試類

@Test
public void test2(){
    ApplicationContext context = new ClassPathXmlApplicationContext("userbeans.xml");
    User user = context.getBean("user", User.class);
    User user2 = context.getBean("user", User.class);
    System.out.println(user.hashCode());
    System.out.println(user2.hashCode());
}

結果

134310351
134310351

2、The Prototype Scope 原型模式

每次從容器中get的時候，都會產生一個新對象！

<?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:p="http://www.springframework.org/schema/p"
       xmlns:c="http://www.springframework.org/schema/c"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">
   
    <bean id="user" class="com.kuang.pojo.User" p:name="張三" p:age="33" scope="prototype"/>
</beans>

測試類

@Test
public void test2(){
    ApplicationContext context = new ClassPathXmlApplicationContext("userbeans.xml");
    User user = context.getBean("user", User.class);
    User user2 = context.getBean("user", User.class);
    System.out.println(user.hashCode());
    System.out.println(user2.hashCode());
}

結果

134310351
1411892748

3、其餘的request、session、application等只能在web開發中使用到！