【保姆级·创建对象】如何通过Supplier创建对象

迈不过友情╰ 2024-03-31 15:18 31阅读 0赞

**【Spring源码系列- IOC】**

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</table>

**本文目录**

创建测试所需文件

User.java

CreateSupplier.java

SupplierBeanFactoryPostProcessor.java

supplier.xml

TestSupplier.java

测试效果

Debug

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

Spring创建对象的主要方式有

*  通过**自定义BeanPostProcessor**，生成代理对象InstantiationAwareBeanPostProcessor
    
     *  createBean() -> resolveBeforeInstantiation()
 *  通过**supplier**创建对象
    
     *  createBean() -> doCreateBean() -> createBeanInstance() -> obtainFromSupplier()
 *  通过**FactoryMethod**创建对象
    
     *  createBean() -> doCreateBean() -> createBeanInstance() -> instantiateUsingFactoryMethod()
 *  通过**反射**创建对象
    
     *  createBean() -> doCreateBean() -> createBeanInstance() -> instantiateBean()
 *  通过**FactoryBean**创建对象

本文介绍下最后一种，如何通过supplier创建Bean（保姆级教程，建议收藏食用(｡･ω･｡)ﾉ）

### 创建测试所需文件 ###

#### User.java ####

![0fc9494059b8a4e41a9b5e062b041bba.png][]

public class User {
       private String name;
    
       public String getName() {
          return name;
       }
    
       public void setName(String name) {
          this.name = name;
       }
    
       public User(){
    
       }
       public User(String name) {
          this.name = name;
       }
    }

#### CreateSupplier.java ####

![3c784050115d63a1ef9977dc4d3135e5.png][]

public class CreateSupplier {
       public static User createUser() {
          return new User("aqin");
       }
    }

#### SupplierBeanFactoryPostProcessor.java ####

![156a08192a1545ef9ebfb9ecd4a858a6.png][]

public class SupplierBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
       @Override
       public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
          BeanDefinition beanDefinition = beanFactory.getBeanDefinition("user");
          GenericBeanDefinition genericBeanDefinition = (GenericBeanDefinition) beanDefinition;
          genericBeanDefinition.setInstanceSupplier(CreateSupplier::createUser);
          genericBeanDefinition.setBeanClass(User.class);
       }
    }

#### supplier.xml ####

![000e93e3c2ca8550dcb014940c21354c.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="user" class="com.aqin.custom.supplier.User"></bean>
 <bean id="supplierBeanFactoryPostProcessor" class="com.aqin.custom.supplier.SupplierBeanFactoryPostProcessor"></bean>
 </beans>

#### TestSupplier.java ####

![43b584ecec7a34c21433b261e5340a6a.png][]

public class TestSupplier {
       public static void main(String[] args) {
          ApplicationContext applicationContext = new ClassPathXmlApplicationContext("supplier.xml");
          User user = applicationContext.getBean(User.class);
          System.out.println(user.getName());
       }
    }

### 测试效果 ###

![63e99a5822c05b93c162199111242a16.png][]

### Debug ###

由于是测试创建Bean，我们需要在doCreateBean()上打个断点，启动debug，执行到断点位置，如下图：

![beaf3b624fb13123998088713419dbea.png][]

进入doCreateBean()，下一步到instanceWrapper = createBeanInstance(beanName, mbd, args);，进入createBeanInstance()方法中

![f48d3362f29908a04f58b8bd5c216139.png][]

进入createBeanInstance()方法后，下一步到Supplier<?> instanceSupplier = mbd.getInstanceSupplier();这里是判断当前beanDefinition中是否包含实例供应器的

![a8054e1ee278e727e592f0390c33bf62.png][]

继续下一步，我们会发现instanceSupplier=null，咦？……不应该呀？

![3cf8ecc092583b9c53fc1268d9dd6ae5.png][]

不用着急，我们仔细看上图中红框框圈住的内容，有一个是beanName，此时，beanName是"supplierBeanFactoryPostProcessor"，并非我们要创建的"user"

所以我们直接点击下图中的Resume Program再次进入之前的断点即可

![5ce3615a2249358aff7ad1f6b9e46dad.png][]

点击上图中的绿三角，就会再次停在一开始我们打断点的位置，如下图：

![ecda48a4c590332ff2c29a01f4a79914.png][]

此时可以看到，当前处理对象的beanName为"user"，继续下一步，直到再次执行到Supplier<?> instanceSupplier = mbd.getInstanceSupplier()

![65019554200b77d53cf33b578594e89e.png][]

进入getInstanceSupplier()，可以发现instanceWrapper已经不是null叻

![6063c7b4da05526ae9bb51779f793ba8.png][]

再向下执行一步，由于instanceSupplier已经有了值，所以会进入if的逻辑，通过obtainFromSupplier()方法返回已获取到的对象

![db5e45018ab4e2cc7e34543dad00a80e.png][]

obtainFromSupplier()从给定“供应商”处，获取Bean实例

![8fbfe048cac8768383f3396ddb8d95b9.png][]

然后包装一下，再进行初始化

![2846c541e22e9008659ba51201b31423.png][]

完成(｡･ω･｡)ﾉ

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