Bean的实例化

Bean的实例化

• 构造器实例化（最常用）

• 静态工厂方式实例化

• 实例工厂方式实例化

构造器实例化（最常用）

public class Bean1 {
}

<?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="bean1" class="com.itheima.instance.constructor.Bean1"></bean>
</beans>

public class InstanceTest1 {
    public static void main(String[] args) {
        String xmlPath = "com/itheima/instance/constructor/bean1.xml";
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);
        Bean1 bean = (Bean1) applicationContext.getBean("bean1");
        System.out.println(bean);
    }
}

静态工厂方式实例化

public class Bean2 {
}

public class MyBean2Factory {
    public static Bean2 createBean(){
        return new Bean2();
    }
}

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

public class InstanceTest2 {
    public static void main(String[] args) {
        String xmlPath = "com/itheima/instance/static_factory/bean2.xml";
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);
        Bean2 bean = (Bean2) applicationContext.getBean("bean2");
        System.out.println(bean);
    }
}

实例工厂方式实例化

public class Bean3 {
}

public class MyBean3Factory {
    public MyBean3Factory(){
        System.out.println("bean3工厂实例化中");
    }
    public Bean3 createBean(){
        return new Bean3();
    }
}

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

public class InstanceTest3 {
    public static void main(String[] args) {
        String xmlPath = "com/itheima/instance/factory/bean3.xml";
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);
        Bean3 bean = (Bean3) applicationContext.getBean("bean3");
        System.out.println(bean);
    }
}