Bean的實例化(Spring)

1.構造器實例化

Spring容器通過Bean對應的類中默認的構造函數來實例化bean

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

2.靜態工廠方式實例化

創建一個靜態工廠來實例化Bean

Bean

package com.instance.static_factory;

public class Bean2 {

}

靜態工廠創建示例

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標籤中設置factory-method屬性的值，只需寫上靜態工廠類中創建Bean的靜態方法名稱即可。

<?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.實例工廠方式實例化

在配置文件中，通過factory-bean屬性配置一個實例工廠，然後使用factory-method屬性確定使用工廠中的哪個方法。

Bean：

package com.instance.factory;

public class Bean3 {

}

實例工廠類：

package com.instance.factory;

public class MyBean3Factory {

	public MyBean3Factory() {
		System.out.println("Bean3工廠實例化中...");
	}
	
	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>

測試代碼：

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) {
		//定義配置文件路徑
		String xmlPath = "com/instance/static_factory/bean2.xml";
		//創建applicationContext對象
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);
		//獲取Bean2的實例並輸出
		System.out.println(applicationContext.getBean("bean2"));
	}

}