Spring入门第八课

Posted 2020-09-19 alittlecomputer

看如下代码

 

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd">
    
    <bean id="car" class="logan.spring.study.autowire.Car">
        <property name="brand" value="Audi"></property>
        <property name="price" value="3000000"></property>
    </bean>
</beans>

package logan.spring.study.scope;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import logan.spring.study.autowire.Car;

public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-scope.xml");
        
        Car car1 = (Car) ctx.getBean("car");
        Car car2 = (Car) ctx.getBean("car");
        
        System.out.println(car1 == car2);
        
        

    }

}

输出结果为：

五月 20, 2017 4:39:17 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org[email protected]3eb07fd3: startup date [Sat May 20 16:39:17 CST 2017]; root of context hierarchy
五月 20, 2017 4:39:17 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-scope.xml]
true

可以看到从IOT获得的Car实例是单例的。

事实上，我们可以设置bean的作用域，如下：

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd">
    
    <bean id="car" class="logan.spring.study.autowire.Car" scope="prototype">
        <property name="brand" value="Audi"></property>
        <property name="price" value="3000000"></property>
    </bean>
</beans>

package logan.spring.study.scope;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import logan.spring.study.autowire.Car;

public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-scope.xml");
        
        Car car1 = (Car) ctx.getBean("car");
        Car car2 = (Car) ctx.getBean("car");
        
        System.out.println(car1 == car2);
    }
}

下面是输出结果

五月 20, 2017 4:42:00 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org[email protected]3eb07fd3: startup date [Sat May 20 16:42:00 CST 2017]; root of context hierarchy
五月 20, 2017 4:42:00 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-scope.xml]
false

使用prototype作用域，bean的实例就不是单例的了。每次获取Bean的时候返回的都是新的Bean。默认值是单例的。