关键词

spring Java eclipse bean 多例模式 prototype 懒加载 lazy-init

写在后面

• 性能简述：对于多例模式的懒加载配置是否失效的测试。
• 刚接触，摸索中，低级谬误，只是做个记录，轻喷。

（有谬误）Xml 配置文件（片段）

<?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 ">            
        <!-- 对于多例模式，即使加了懒加载配置也没用 -->
        <bean id="myFactoryPrototypeExample" class="instance.BeanInstanceFactory"
            scope="prototype" lazy-init="false"/>
            
        <bean id="instanceFactoryInstancePrototypeExample" factory-bean="myFactoryPrototypeExample" 
            scope="prototype" lazy-init="false"/>
</beans>

运行的测试代码

package test;

import java.util.Calendar;

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

import instance.BeanClass;
import instance.Person;
import instance.User;

public class TestInstance {    
    // 对于多例模式，默认懒加载，即使设置 lazy-init="false" 也有效
    @Test
    public void test06(){ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        System.out.println("获取对象前");
        // 参数是 xml 中待创立的对象的 id
        BeanClass bc3 = (BeanClass)context.getBean("instanceFactoryInstancePrototypeExample");
        System.out.println(bc3+bc3.message);    
    }
}

解决

• 思路：查看 xml 配置文件
• 起因：xml 配置文件有误。
• 解决：最初一个 bean 标签少写了 factory-method 属性。

（正确的）Xml 配置文件（片段）

<?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 ">            
        <!-- 对于多例模式，即使加了懒加载配置也没用 -->
        <bean id="myFactoryPrototypeExample" class="instance.BeanInstanceFactory"
            scope="prototype" lazy-init="false"/>


        <!-- 上面这里少写了 factory-method-->
        <bean id="instanceFactoryInstancePrototypeExample" factory-bean="myFactoryPrototypeExample"
            factory-method="createBeanClassInstance" scope="prototype" lazy-init="false"/>
</beans>

包构造

（补充）BeanInstanceFactory 类

package instance;

public class BeanInstanceFactory {public BeanInstanceFactory(){System.out.println("我是一个实例工厂");            
        }
        public BeanClass createBeanClassInstance(){return new BeanClass("调用实例工厂办法实例化 Bean");
        }
}

（补充）BeanClass 类

package instance;

public class BeanClass {
    public String message;    
    public BeanClass() {this.message = "构造方法实例化 Bean";}
    public BeanClass(String message) {this.message = message;}
}

运行后果

参考

org.springframework.beans.factory.BeanCreationException:No bean class specified on bean definition