05 Bean的作用域

通过在<bean>标签中设置scope属性来指定作用域

• singleton:默认的.容器初始时创建Bean实例.在整个容器的生命周期内只创建这一个Bean
• prototype:容器初始化时不创建Bean实例.每次请求时创建一个新的实例

1. singleton

Address.java

package relation;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/10 23:30
 * @Version 1.0
 */

/**
 * @author Sheng Wenzeng
 * @ClassName Address
 * @Description TODO
 * @Date 2019/8/10 23:30
 * @Version 1.0
 */
public class Address {
    private String city;
    private String street;

    public Address() {
        System.out.println("Address' construction...");
    }

    @Override
    public String toString() {
        return "Address{" +
                "city='" + city + '\'' +
                ", street='" + street + '\'' +
                '}';
    }

    public void setCity(String city) {
        this.city = city;
    }

    public void setStreet(String street) {
        this.street = street;
    }
}

Main.java

package relation;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/10 23:31
 * @Version 1.0
 */

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

/**
 * @author Sheng Wenzeng
 * @ClassName Main
 * @Description TODO
 * @Date 2019/8/10 23:31
 * @Version 1.0
 */
public class Main {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        Address address = (Address) applicationContext.getBean("address");
        Address address_1 = (Address) applicationContext.getBean("address");
        System.out.println(address == address_1);
    }
}

applicationContext.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" xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean scope="singleton" id="address" class="relation.Address" p:city="Beijing" p:street="NanJingLu"/>
</beans>

输出结果为:

Address' construction...
true

可见只是在容器初始化时创建了一次Bean,而后获取的Bean都是同一个对象

2. prototype

将上面的xml文件修改如下:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean scope="prototype" id="address" class="relation.Address" p:city="Beijing" p:street="NanJingLu"/>
</beans>

而后运行,结果为:

Address' construction...
Address' construction...
false

可见容器初始化时没有新建Bean对象,而是每次请求时创建一个新的Bean对象