Bean的实例化(Spring)

1.构造器实例化

Spring容器通过Bean对应的类中默认的构造函数来实例化bean

<bean id="bean1" class="com.instance.contructor.Bean1"></bean>

2.静态工厂方式实例化

创建一个静态工厂来实例化Bean

Bean

package com.instance.static_factory;

public class Bean2 {

}

静态工厂创建示例

package com.instance.static_factory;

public class MyBean2Factory {

	public static Bean2 createBean() {
		return new Bean2();
	}
}

配置文件示例

需要在bean标签中设置factory-method属性的值，只需写上静态工厂类中创建Bean的静态方法名称即可。

<?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="bean2" class="com.instance.static_factory.MyBean2Factory" factory-method="createBean"></bean>
</beans>

 

3.实例工厂方式实例化

在配置文件中，通过factory-bean属性配置一个实例工厂，然后使用factory-method属性确定使用工厂中的哪个方法。

Bean：

package com.instance.factory;

public class Bean3 {

}

实例工厂类：

package com.instance.factory;

public class MyBean3Factory {

	public MyBean3Factory() {
		System.out.println("Bean3工厂实例化中...");
	}
	
	public Bean3 createBean() {
		return new Bean3();
	}
}

配置文件示例：

<?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="myBean3Factory" class="com.instance.factory.MyBean3Factory"></bean>
	<bean id="bean3" factory-bean="myBean3Factory" factory-method="createBean"></bean>
</beans>

测试代码：

package com.instance.static_factory;

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

public class InstanceTest2 {
	public static void main(String[] args) {
		//定义配置文件路径
		String xmlPath = "com/instance/static_factory/bean2.xml";
		//创建applicationContext对象
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);
		//获取Bean2的实例并输出
		System.out.println(applicationContext.getBean("bean2"));
	}

}