前言
在学习Spring Core中IOC容器时，你肯定会接触到BeanFactory这个Spring中最基础的IOC容器。这个应该是大家学习Spring源码时最先接触到的类了。Spring中还存在这一个FactoryBean类，两者拼写上十分相似，并且使用频率都十分得高。在一些Spring面试题，也会问你这两者有什么区别。
这里先说结论：
- BeanFactory：Spring中的IoC容器，所有Spring Bean 的Factory
- FactoryBean：一个Bean，一个不简单的Bean，一个能产生对象或者修饰对象生成的工厂Bean，它的实现与设计模式中的工厂模式和修饰器模式类似
在学习Spring源码和其他开源项目的源码的过程当中，发现FactoryBean是一些框架在做集成Spring时经常会使用到的类，本文具体讲述的也是FactoryBean的简单实用和具体应用拓展。
What is FactoryBean
Spring 中有两种类型的Bean，一种是普通Bean，另一种是工厂Bean 即 FactoryBean。
一般情况下，Spring 通过反射机制利用bean的class属性指定实现类来实例化bean 。在某些情况下，实例化bean 过程比较复杂，如果按照传统的方式，则需要在org.Springframework.bean.factory.FactoryBean的工厂类接口，用户可以通过实现该接口定制实例化bean的逻辑。（看后面的一些例子会理解更深刻）
所以说，当配置一个
接口定义
package org.springframework.beans.factory;
public interface FactoryBean {
T getObject() throws Exception;
Class getObjectType();
boolean isSingleton();
} 在一些开源框架上的使用
MyBatis-Spring # SqlSessionFactoryBean
public class SqlSessionFactoryBean
implements FactoryBean, InitializingBean, ApplicationListener {
...
} 阿里开源的分布式服务框架 Dubbo # ReferenceBean
com.alibaba.dubbo.config.spring.ReferenceBean 类
public class ReferenceBean extends ReferenceConfig implements FactoryBean, ApplicationContextAware, InitializingBean, DisposableBean {
...
} 拓展实践
涉及
- ProduceLocation 生产地区
- Material 材料
- ProductFactoryBean 产品工厂bean
- Product 产品
- Boostrap 启动类
- test-config.xml 测试配置文件
ProduceLocation
@Data
public class ProduceLocation {
private String locationName;
private double distanceKm;
private double pricePerPerKm;
}Material
@Data
public class Material {
private String name;
private double pricePerGram;
private double weight;
}Product
@Data
@Builder
public class Product {
private Material material;
private ProduceLocation location;
private double price;
}ProductFactoryBean
@Setter
@Getter
public class ProductFactoryBean implements FactoryBean {
private Material material;
private ProduceLocation produceLocation;
@Override
public Product getObject() throws Exception {
return Product.builder()
.location(produceLocation)
.material(material)
.price(cal(material, produceLocation))
.build();
}
private double cal(Material material, ProduceLocation produceLocation) {
return material.getPricePerGram() * material.getWeight()
+ produceLocation.getDistanceKm() * produceLocation.getPricePerPerKm();
}
@Override
public Class getObjectType() {
return Product.class;
}
@Override
public boolean isSingleton() {
return false;
}
} test-config.xml
Boostrap
/**
* @author Richard_yyf
* @version 1.0 2019/9/21
*/
public class Bootstrap {
public static void main(String[] args) throws Exception {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("test-config.xml");
Product product = (Product) context.getBean("product");
System.out.println(product.toString());
}
}输出
Product(material=Material(name=巧克力豆, pricePerGram=100.0, weight=50.0), location=ProduceLocation(locationName=杭州, distanceKm=3.1, pricePerPerKm=151.01), price=5468.131)上述的配置当然也可以改用java config 的方式来做。
上述是一个简单业务的示例，你还可以通过FactoryBean来对一些开源工具API使用进行一些封装，比如对httpClient创建过程做了一些封装，例如超时时间、连接池大小、http代理等。
特性
给定一个id=mybean的FactoryBean，getBean("mybean")得到的就是这个FactoryBean创建的对象实例，而getBean("&mybean")得到的确实FactoryBean自身对象。
根据上述的demo，运行如下代码
/**
* @author Richard_yyf
* @version 1.0 2019/9/21
*/
public class Bootstrap {
public static void main(String[] args) throws Exception {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("test-config.xml");
// Product product = (Product) context.getBean("product");
// System.out.println(product.toString());
FactoryBean factoryBean = (ProductFactoryBean) context.getBean("&product");
System.out.println(factoryBean.getObject().toString());
}
} Output
Product(material=Material(name=巧克力豆, pricePerGram=100.0, weight=50.0), location=ProduceLocation(locationName=杭州, distanceKm=3.1, pricePerPerKm=151.01), price=5468.131)对应源码
先直接锁定对应逻辑源码，
protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {
// Don't let calling code try to dereference the factory if the bean isn't a factory.
// BeanFactoryUtils.isFactoryDereference(name)方法判断name是否以&前缀
if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
}
// Now we have the bean instance, which may be a normal bean or a FactoryBean.
// If it's a FactoryBean, we use it to create a bean instance, unless the
// caller actually wants a reference to the factory.
if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
return beanInstance;
}
Object object = null;
if (mbd == null) {
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
// Return bean instance from factory.
FactoryBean factory = (FactoryBean) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}-
BeanFactoryUtils.isFactoryDereference(name)判断是否在获取FactoryBean的引用// 不为空且以”&“开头 public static boolean isFactoryDereference(String name) { return (name != null && name.startsWith(BeanFactory.FACTORY_BEAN_PREFIX)); } String FACTORY_BEAN_PREFIX = "&"; - 如果进来的
beanInstance不是FactoryBean，但调用者是用获取FactoryBean的引用时，抛出BeanIsNotAFactoryException异常 - 如果调用者是要获取
FactoryBean的引用，且beanInstance是FactoryBean(前面有判断)，则直接返回beanInstance - 如果进来的
beanInstance是普通bean，直接返回beanInstance - 通过进来的
FactoryBean来创建一个对应的bean