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总结FactoryBean以及BeanFactory相关的知识点
FactoryBean
一般情况下在spring配置文件或者通过注解的方式就可以定义一个bean加载到spring容器中，当需要加载一个复杂的bean，或者动态加载指定的bean的情况下，可以使用FactoryBean来完成，通过实现FactoryBean.getObject方法自定义实例化bean的过程。例如MyBatis中的SqlSessionFactoryBean就是利用FactoryBean来实现的。
xml配置使用案例
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
</dependency>
public class MyBean {
private String name;
private Integer age;
//getter,setter,toString...
}
public class MyFactoryBean implements FactoryBean<MyBean> {
private String name;
private Integer age;
@Override
public MyBean getObject() throws Exception {
MyBean myBean = new MyBean();
myBean.setName(this.name);
myBean.setAge(this.age);
return myBean;
}
@Override
public Class<?> getObjectType() {
return MyBean.class;
}
@Override
public boolean isSingleton() {
return true;
}
//getter,setter...
}
<!-- factory-bean.xml -->
<?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="mybean" class="com.qigang.sblc.factoryBean.MyFactoryBean">
<property name="name" value="zhangsan"/>
<property name="age" value="30"/>
</bean>
</beans>
public class SpringFactoryBeanApplication {
public static void main(String[] args) {
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("factory-bean.xml");
//xml中定义的是MyFactoryBean，但实际从容器拿到的是getObject方法返回的MyBean对象
MyBean myBean1 = (MyBean) applicationContext.getBean("mybean");
System.out.println(myBean1);
MyBean myBean2 = applicationContext.getBean(MyBean.class);
System.out.println(myBean2);
System.out.println(myBean1==myBean2);
//如果想获取到MyFactoryBean本身，在bean名称前加一个&符号即可
MyFactoryBean myFactoryBean = (MyFactoryBean) applicationContext.getBean("&mybean");
System.out.println(myFactoryBean);
}
}
注解使用案例
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
@SpringBootApplication
@RestController
public class SpringBootFactoryBeanApplication {
@Autowired
private MyBean myBean;
public static void main(String[] args) {
SpringApplication.run(SpringBootFactoryBeanApplication.class,args);
}
//单独注入bean，或者在MyFactoryBean上加@Component注解
@Bean
public MyFactoryBean getMyFactoryBean(){
MyFactoryBean myFactoryBean = new MyFactoryBean();
myFactoryBean.setName("zhangsan");
myFactoryBean.setAge(20);
return myFactoryBean;
}
@GetMapping("/getMyBean")
public String getMyBean(){
return myBean.toString();
}
}
BeanFactory
BeanFactory基础
接口类图
基础实现接口
- ListableBeanFactory 支持bean迭代
- HierarchicalBeanFactory 支持层级
- AutowireCapableBeanFactory 支持自动织入
默认实现类
- DefaultListableBeanFactory（纯粹的IOC容器实现）
//使用默认的DefaultListableBeanFactory来加载bean的简单示例代码
DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
reader.loadBeanDefinitions(new ClassPathResource("bean-factory.xml"));
MyBean bean = factory.getBean(MyBean.class);
System.out.println(bean.toString());
BeanDefinition
BeanDefinitionRegistry
DefaultListableBeanFactory是BeanDefinitionRegistry的一个实现，实现方法registerBeanDefinition中将载入的BeanDefinition加入到ConcurrentHashMap中
ApplicationContext
类图
AbstractApplicationContext.refresh（IOC初始化的核心方法）
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//加载BeanDefinition，注册BeanDefinition的逻辑都在这里，默认返回DefaultListableBeanFactory
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
// Bean的实例化在这个方法里面
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
Bean的创建过程（生命周期中的主要方法）
AbstractApplicationContext.refresh();
//这里的beanFactory就是默认创建的DefaultListableBeanFactory
finishBeanFactoryInitialization(beanFactory);
preInstantiateSingletons();
getBean();
doGetBean();
AbstractAutowireCapableBeanFactory.createBean();
AbstractAutowireCapableBeanFactory.resolveBeforeInstantiation();
//`applyBeanPostProcessorsBeforeInstantiation()`以及`applyBeanPostProcessorsAfterInitialization()`就是在这个方法里面调用的
AbstractAutowireCapableBeanFactory.doCreateBean();
在AbstractAutowireCapableBeanFactory.doCreateBean()方法中有几个重要方法：
//创建bean实例
createBeanInstance();
//执行BeanDefinitionPostProcessors
applyMergedBeanDefinitionPostProcessors();
//依赖注入
populateBean();
//初始化，调用各种aware接口方法，调用InitializingBean.afterPropertiesSet()，调用init-method
//调用applyBeanPostProcessorsBeforeInitialization、applyBeanPostProcessorsAfterInitialization
initializeBean();
AbstractAutowireCapableBeanFactory.initializeBean();
//*******************************************************************************
//如果设置了系统权限，则忽略权限检查，直接执行
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
return getInstantiationStrategy().instantiate(mbd, beanName, parent);
}
}, getAccessControlContext());
}
else {
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
}
//*******************************************************************************
SimpleInstantiationStrategy.instantiate();
//使用反射的方式创建bean实例
BeanUtils.instantiateClass();
ClassPathApplicationContext
