createBean中 factory-method创建bean实例

作用

静态工厂/非静态工厂创建bean实例

factory-method 实例

前期准备bean

public class Student {
    private String studentName;
}

提前声明的静态工厂

public class StaticFactoryMethod {

    public static Student getStudent(){
        Student student = new Student();
        student.setStudentName("li si");
        return student;
    }
}

提前声明的非静态工厂

public class NonStaticFactoryMethod {

    public Student getStudent(){
        Student student = new Student();
        student.setStudentName("zhang san");
        return student;
    }
}

xml文件中声明 factory-method属性

<?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="studentA" class="com.spring.learn.bean.factorymethod.StaticFactoryMethod" factory-method="getStudent"/>

    <bean id="nonStaticFactoryMethod" class="com.spring.learn.bean.factorymethod.NonStaticFactoryMethod"/>

    <bean id="studentB" class="com.spring.learn.common.staff.Student" factory-bean="nonStaticFactoryMethod" factory-method="getStudent"/>
</beans>

测试方法

public class SpringFactoryMethodStart {

    public static void main(String[] args) {
        ClassPathXmlApplicationContext ac = new ClassPathXmlApplicationContext("bean/factorymethod/factorymethod.xml");

        Student studentA = ac.getBean("studentA", Student.class);
        Student studentB = ac.getBean("studentB", Student.class);

        System.out.println(studentA.getStudentName());
        System.out.println(studentB.getStudentName());
    }
    /**
     * 结果：
     * li si
     * zhang san
     */
}

factory-method 源码流程

// AbstractAutowireCapableBeanFactory类中的
// doCreateBean方法中
// 1、582行：起始位置，实例化bean
instanceWrapper = createBeanInstance(beanName, mbd, args);
// 2、1194行：BeanDefinition中 factoryMethodName属性存在的情况下，使用factory-method创建bean
if (mbd.getFactoryMethodName() != null) {
    return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// ConstructorResolver类中的
// instantiateUsingFactoryMethod 方法
// 3、factory-method实例化bean 流程细节

// 4、397~453行：检查方法是否是静态方法、筛选重载方法、参数排序
//    404~427行：如果factory-bean属性存在，此处是非静态工厂；属性不存在，此处是静态工厂

// 5、638行：本质上调用 instantiate 方法，实例化bean
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, factoryMethodToUse, argsToUse));

// 6、返回创建的bean实例
return bw;