2. Supplier<?> 创建对象

通过用户指定的 Supplier 来创建对象。我们可以在扩展点中给 bean 定义增加自定义的 Supplier。

// 通过给定的函数获取对象
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
    return obtainFromSupplier(instanceSupplier, beanName);
}

代码测试

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

自定义Supplier

public class OrgSupplier {
    public static SuA create() {
        return new SuA("Hello");
    }
}

扩展点注入Supplier

public class SupplierBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        BeanDefinition beanDefinition = beanFactory.getBeanDefinition("sua");
        GenericBeanDefinition genericBeanDefinition = (GenericBeanDefinition) beanDefinition;
        genericBeanDefinition.setInstanceSupplier(OrgSupplier::create);
        genericBeanDefinition.setBeanClass(SuA.class);
    }
}

加入IOC容器

<?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-3.0.xsd">
    <bean id="sua" class="cn.lichenghao.supplier.SuA"/>
    <bean id="supplierBeanFactoryPostProcessor" class="cn.lichenghao.supplier.SupplierBeanFactoryPostProcessor"/>
</beans>

测试

@DisplayName("自定义supplier")
@Test
public void supplierTest() {
    // 根据配置文件加载bean
    ClassPathXmlApplicationContext classPathXmlApplicationContext
            = new ClassPathXmlApplicationContext("supplier-test.xml");
    SuA bean = classPathXmlApplicationContext.getBean(SuA.class);
    System.out.println(bean);
}

然后打一个条件断点。

进入断点，发现我们的自定义 Supplier 已经成功加入。

接下来进入obtainFromSupplier方法创建对象即可。
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#obtainFromSupplier

protected BeanWrapper obtainFromSupplier(Supplier<?> instanceSupplier, String beanName) {
    Object instance;
    String outerBean = this.currentlyCreatedBean.get();
    this.currentlyCreatedBean.set(beanName);
    try {
        instance = instanceSupplier.get();
    } finally {
        if (outerBean != null) {
            this.currentlyCreatedBean.set(outerBean);
        } else {
            this.currentlyCreatedBean.remove();
        }
    }
    if (instance == null) {
        instance = new NullBean();
    }
    BeanWrapper bw = new BeanWrapperImpl(instance);
    initBeanWrapper(bw);
    return bw;
}