【保姆级·创建对象】如何通过factory-method创建对象

青旅半醒 2024-03-31 15:43 48阅读 0赞

**【Spring源码系列- IOC】**

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 <td colspan="1" style="vertical-align:middle;"> 18 </td> 
 <td colspan="1" style="vertical-align:middle;"> <a href="https://blog.csdn.net/aqin1012/article/details/127472470" title="【Spring源码】17.创建Bean这篇认真的@(・●・)@" rel="nofollow">【Spring源码】17.创建Bean这篇认真的@(・●・)@</a> </td> 
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 <td colspan="2" style="vertical-align:middle;"> <a href="https://blog.csdn.net/aqin1012/article/details/128632696" title="【Spring源码】19. 没合适的构造器？找determineCandidateConstructors()！" rel="nofollow">【Spring源码】19. 没合适的构造器？找determineCandidateConstructors()！</a> </td> 
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 <td colspan="1" style="vertical-align:middle;"> <a href="https://blog.csdn.net/aqin1012/article/details/128633664" title="【Spring源码】20. MergedBeanDefinitionPostProcessor修改/合并bean定义" rel="nofollow">【Spring源码】20. MergedBeanDefinitionPostProcessor修改/合并bean定义</a> </td> 
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 <td colspan="1" style="vertical-align:middle;"> <a href="https://blog.csdn.net/aqin1012/article/details/128656295" title="【Spring源码】21. 初探循环依赖" rel="nofollow">【Spring源码】21. 初探循环依赖</a> </td> 
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 <td colspan="1" style="vertical-align:middle;"> <a href="https://blog.csdn.net/aqin1012/article/details/128800736" title="【Spring源码】22. 属性填充populateBean()详解" rel="nofollow">【Spring源码】22. 属性填充populateBean()详解</a> </td> 
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 <td colspan="1" style="vertical-align:middle;"> 24 </td> 
 <td colspan="2" style="vertical-align:middle;"> <a href="https://blog.csdn.net/aqin1012/article/details/128949267" title="【Spring源码】23. 执行初始化逻辑：initializeBean()" rel="nofollow">【Spring源码】23. 执行初始化逻辑：initializeBean()</a> </td> 
 </tr> 
 </tbody> 
</table>

**本文目录**

创建文件

Student.java

StudentStaticFactory.java

StudentInstanceFactory.java

xml配置文件

测试类

测试结果

Debug分析

--------------------

这个步骤在createBeanInstance()方法中有使用，我们先来看下这个方法中都干了些啥(｡･ω･｡)ﾉ 首先，方法开头确认了beanClass是否被加载（因为只有被加载叻的对象才是可以实例化的）

![4c8d88215aced2ddb5c61cd5832bb191.png][]

然后，判断当前beanDefinition中是否包含实例供应器，此步骤如果instanceSupplier!=null的话，则会直接通过obtainFromSupplier(instanceSupplier, beanName);方法直接返回一个Bean的包装类BeanWrapper而不会再进行下面的逻辑叻（保姆级测试教程戳戳

[【保姆级·创建对象】如何通过Supplier创建对象\_AQin1012的博客-CSDN博客][Supplier_AQin1012_-CSDN]

![85df79fbd287421b934786cdd7ba4726.jpeg][]

）

所以只有在不满足这一条判断的前提下，才会进入我们今天要分析的使用`factory-method`创建对象

![3bd12aca918beb61e362452db06762e4.png][]

来～开始٩(˃̶͈̀௰˂̶͈́)و

首先，需要啰嗦下通过工厂模式创建实例对象主要有两种方式：

*  静态工厂（无需工厂的实例对象）

*  实例工厂（需要创建工厂的实例对象）

所以本案例中我们创建了两个工厂类（静态工厂类：StudentStaticFactory.java和实例工厂类：StudentInstanceFactory.java）

### 创建文件 ###

#### Student.java ####

![7cae26b9d6ba24443ccfc27aa841dc56.png][]

public class Student {
       private String name;
       private Integer age;
    
       public String getName() {
          return name;
       }
    
       public void setName(String name) {
          this.name = name;
       }
    
       public Integer getAge() {
          return age;
       }
    
       public void setAge(Integer age) {
          this.age = age;
       }
    }

#### StudentStaticFactory.java ####

![8d640a72ae92a48a41d0f9a1d6ac2c14.png][]

public class StudentStaticFactory {
       public static Student getStudent(String name) {
          Student student = new Student();
          student.setName(name);
          student.setAge(88);
          return student;
       }
    }

#### StudentInstanceFactory.java ####

![d3f3d3551e03287f7d0f34e2e660d373.png][]

public class StudentInstanceFactory {
       public Student getStudent(String name) {
          Student student = new Student();
          student.setName(name);
          student.setAge(88);
          return student;
       }
    }

#### xml配置文件 ####

![923de8a1c42ba6e8c45554d49e47ea1f.png][]

<?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="student" class="com.aqin.custom.factoryMethod.StudentStaticFactory" factory-method="getStudent">
 <constructor-arg value="aqin"></constructor-arg>
 </bean>
 
 <bean id="studentInstanceFactory" class="com.aqin.custom.factoryMethod.StudentInstanceFactory"></bean>
 <bean id="student2" class="com.aqin.custom.factoryMethod.Student" factory-bean="studentInstanceFactory"
 factory-method="getStudent">
 <constructor-arg value="aqin2"></constructor-arg>
 </bean>
 
 </beans>

**参数说明**

*  factory-bean="personStaticFactory"：指定使用的工厂实例是"personStaticFactory"
 *  factory-method="getStudent"：指定使用的工厂实例的方法为"getStudent"
 *  constructor-arg value="aqin"：为方法指定参数

### 测试类 ###

![7b624d33686e8b36dcf7219db2b0498d.png][]

public class TestFactoryMethod {
       public static void main(String[] args) {
          ApplicationContext applicationContext = new ClassPathXmlApplicationContext("factoryMethod.xml");
          Student bean = applicationContext.getBean("student", Student.class);
          System.out.println(bean.getName());
          System.out.println("-------------------------------");
          Student bean2 = applicationContext.getBean("student2", Student.class);
          System.out.println(bean2.getName());
       }
    }

### 测试结果 ###

![a5f9e79256159befd503e1603a59d3dd.png][]

### Debug分析 ###

在使用工厂方法初始化策略的位置打个断点，如下图

![7228c7f9d4de64831311916d6122d4da.png][]

默认情况（在未创建案例中的文件时），会发现mbd.getFactoryMethodName()=null，不会进入if的逻辑中

![8a11a5887c983fa602b810019a8727d4.png][]

当执行案例中的测试方法

![41b4f8480b5ce04d76556c6884e01b61.png][]

会发现，此时mbd.getFactoryMethodName()="getStudent"，所以我们进入了if的逻辑中(\*≧ω≦) 点击进入，进入instantiateUsingFactoryMethod()方法中（这里先捋下执行逻辑，后续会对这个方法做详细介绍，毕竟行数300+的方法，值得单独拎出来瞅瞅(˶‾᷄ ⁻̫ ‾᷅˵)），instantiateUsingFactoryMethod()方法是通过一个命名的工厂方法来实例化Bean的，会返回一个Bean的包装类BeanWrapper

![49f9a097d065274578b774e94553f6d1.png][]

然后就不会再向下继续，而会直接回到createBeanInstance()方法中，继续后面的包装以及初始化的逻辑

![9d0b98b1c87bad71e712f9de9e5cc73b.png][]

[4c8d88215aced2ddb5c61cd5832bb191.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/6992855be026412e8e293337afc09f23.png
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