Spring-Spring懒加载

懒加载

Spring默认的情况下，在容器创建的时候会创建JavaBean的对象，
当开启懒加载之后将在使用的时候创建JavaBean的对象

比如对于一个User类通过Spring创建对象

• User类

public class User {
	public User() {
		System.out.println("创建user对象");
	}
}

• 配置文件

<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="user" class="com.wl.spring.User">bean>
beans>

• 运行测试代码

七月 08, 2019 9:16:28 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@300ffa5d: startup date [Mon Jul 08 21:16:28 CST 2019]; root of context hierarchy
七月 08, 2019 9:16:28 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [applicationContext.xml]
创建user对象

结果

七月 08, 2019 9:16:28 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@300ffa5d: startup date [Mon Jul 08 21:16:28 CST 2019]; root of context hierarchy
七月 08, 2019 9:16:28 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [applicationContext.xml]
创建user对象

如何开启懒加载

• 开启全局懒加载在配置文件中

<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"
	default-lazy-init="true"
>
	<bean id="user" class="com.wl.spring.User" >bean>
beans>

• 对一个Bean设置懒加载

<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="user" class="com.wl.spring.User" lazy-init="true">bean>
beans>

注意：当全局懒加载和每个Bean设置懒加载都存在遵从就近原则

测试

public class StartSpring {
	public static void main(String[] args) {
		ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
	}
}

运行之后没有除了日志信息，没有结果输出
使用user对象

public class StartSpring {
	public static void main(String[] args) {
		ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
		User bean = (User) context.getBean("user");
	}
}

结果输出

七月 08, 2019 9:36:31 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@300ffa5d: startup date [Mon Jul 08 21:36:31 CST 2019]; root of context hierarchy
七月 08, 2019 9:36:31 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [applicationContext.xml]
创建user对象