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文章目录
1. BeanFactory
1.1 BeanFactory介绍
BeanFactory是Spring IOC各种容器的*接口，定义了创建Bean实例的一些行为，以及一些对Bean实例的判断行为和获取Bean类型属性的行为；
1.2 BeanFactory源码
public interface BeanFactory {
// FactoryBean的实例名称前缀
String FACTORY_BEAN_PREFIX = "&";
// 返回name名称的Bean实例(包含创建过程)
Object getBean(String name) throws BeansException;
<T> T getBean(String name, Class<T> requiredType) throws BeansException;
Object getBean(String name, Object... args) throws BeansException;
<T> T getBean(Class<T> requiredType) throws BeansException;
<T> T getBean(Class<T> requiredType, Object... args) throws BeansException;
// 返回name名称的Bean实例的提供程序
<T> ObjectProvider<T> getBeanProvider(Class<T> requiredType);
<T> ObjectProvider<T> getBeanProvider(ResolvableType requiredType);
// 判断name名称Bean实例的相关属性
boolean containsBean(String name);
boolean isSingleton(String name) throws NoSuchBeanDefinitionException;
boolean isPrototype(String name) throws NoSuchBeanDefinitionException;
boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException;
boolean isTypeMatch(String name, Class<?> typeToMatch) throws NoSuchBeanDefinitionException;
// 返回name名称Bean实例的Class类型
@Nullable
Class<?> getType(String name) throws NoSuchBeanDefinitionException;
@Nullable
Class<?> getType(String name, boolean allowFactoryBeanInit) throws NoSuchBeanDefinitionException;
// 返回name名称Bean实例的别名
String[] getAliases(String name);
}
1.3 BeanFactory继承体系
根据上面的UML图，可知日常经常使用的ApplicationContext、ClassPathXmlApplicationContext、以及AnnotationConfigApplicationContext的*接口都包含有BeanFactory；
2. FactoryBean
2.1 FactoryBean介绍
FactoryBean是一个工厂Bean，在日常代码中的Controller和ServiceImpl类基本都是被Spring通过反射去创建的Bean实例，而FactoryBean提供了另外一种创建Spring Bean实例的方式，就是实现它的getObject接口，然后返回的实例一样会被Spring IOC容器管理；
2.2 FactoryBean源码
public interface FactoryBean<T> {
String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType";
// 返回FactoryBean生成的Bean实例
@Nullable
T getObject() throws Exception;
// 返回FactoryBean生成的Bean实例的Class类型
@Nullable
Class<?> getObjectType();
// 返回FactoryBean生成的Bean实例是否为单例
default boolean isSingleton() {
return true;
}
}
2.3 FactoryBean实战
创建以下几个接口与类
动物接口：
public interface Animal {
void sayHello();
}
猫类实现动物接口：
public class Cat implements Animal {
@Override
public void sayHello() {
System.out.println("hello 喵喵喵");
}
}
狗类实现动物接口：
public class Dog implements Animal {
@Override
public void sayHello() {
System.out.println("hello 汪汪汪");
}
}
创建一个AnimalFactoryBean实现FactoryBean接口：
public class AnimalFactoryBean implements FactoryBean<Animal> {
private String type;
@Override
public Animal getObject() {
switch (type) {
case "cat":
return new Cat();
case "dog":
return new Dog();
default:
return null;
}
}
@Override
public Class<?> getObjectType() {
switch (type) {
case "cat":
return Cat.class;
case "dog":
return Dog.class;
default:
return null;
}
}
public void setType(String type) {
this.type = type;
}
}
在applicationContext.xml配置文件中配置AnimalFactoryBean：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<bean name="animalFactoryBean" class="cn.jackiegu.test.bean.AnimalFactoryBean" p:type="cat"/>
</beans>
创建一个测试类
public class AnimalBeanTest {
public static void main(String[] args) {
String path = "applicationContext.xml";
ApplicationContext applicationContext = new ClassPathXmlApplicationContext(path);
// FactoryBean工厂返回的实例
Animal animal = (Animal) applicationContext.getBean("animalFactoryBean");
animal.sayHello();
// FactoryBean工厂实例
AnimalFactoryBean animalFactoryBean = (AnimalFactoryBean) applicationContext.getBean("&animalFactoryBean");
System.out.println(animalFactoryBean);
}
}
// 运行结果
hello 喵喵喵
cn.jackiegu.test.bean.AnimalFactoryBean@77258e59