负一、目录
零、bean 实例化方式
1. 构造器实例化 （常用）
1. 静态工厂实例化
2. 实例工厂实例化
一、构造器实例化
Spring 容器通过Bean 对应类中默认无参构造方法来实例化Bean。
//Bean1.java package com.itheima.instance.constructor; public class Bean1 { }
<!--beans1.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" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- id: Bean唯一标识符； class：Bean实例具体实现类，必须是一个完整类名，使用类的全限定名 --> <bean id="bean1" class="com.itheima.instance.constructor.Bean1"/> </beans>
//InstanceTest1 package com.itheima.instance.constructor; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class InstanceTest1 { public static void main(String[] args) { //配置文件路径 String xmlPath = "com/itheima/instance/constructor/beans1.xml"; //加载配置文件 ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath); //实例化Bean Bean1 bean = (Bean1) applicationContext.getBean("bean1"); System.out.println(bean); } }
二、静态工厂实例化
创建一个静态工厂类来创建Bean的实例，Bean配置中的class属性所指定的不再是Bean实例实现的类，而是静态工厂类，同时还需要使用 factory-method 属性指定所创建的静态工厂方法。
//bean2.java package com.itheima.instance.static_factory; public class Bean2 { }
//MyBean2Factory.java package com.itheima.instance.static_factory; public class MyBean2Factory { public static Bean2 createBean() { return new Bean2(); } }
<!--bean2.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" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- class：静态工厂类完全限定名 factory-method：定义所需的工厂方法 --> <bean id="bean2" class="com.itheima.instance.static_factory.MyBean2Factory" factory-method="createBean"/> </beans>
//InstanceTest2 package com.itheima.instance.static_factory; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class InstanceTest2 { public static void main(String[] args) { String xmlPath = "com/itheima/instance/static_factory/beans2.xml"; ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath); System.out.println(applicationContext.getBean("bean2")); } }
三、实例化工厂实例化
配置文件中需要实例化的Bean通过 factory-bean 属性指向配置的实例工厂，然后使用 factory-method 确定使用的是工厂中的哪个方法。
//Bean3.java package com.itheima.instance.factory; public class Bean3 { }
//MyBean3Factory.java package com.itheima.instance.factory; public class MyBean3Factory { public MyBean3Factory() { System.out.println("bean3 工厂实例化中"); } public Bean3 createBean() { return new Bean3(); } }
<!--bean3.xml--> <?xml version="1.0" encoding="UTF-8" ?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xis="http://www.w3.org/2001/XMLSchema-instance" xis:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <!--配置工厂--> <bean id="myBean3Factory" class="com.itheima.instance.factory.MyBean3Factory"/> <!--配置实例工厂和使用的方法--> <bean id="bean3" factory-bean="myBean3Factory" factory-method="createBean"/> </beans>
//InstanceTest3.java package com.itheima.instance.factory; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class InstanceTest3 { public static void main(String[] args) { String xmlPath = "com/itheima/instance/factory/beans3.xml"; ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath); System.out.println(applicationContext.getBean("bean3")); } }
本节源码下载地址：
https://pan.baidu.com/s/1gbHdTRGozS4MHMFivaO9jw
提取码：gr6m