閱讀對象##
搭框架人員,或者其他感興趣的開發人員
背景##
一般來說在業務代碼中,加上 @Component
, @Service
,@Repository
, @Controller
等注解就可以實現將bean注冊到Spring中了。
但是在寫框架,可能有些類會動態生成,怎么動態注冊到Spring中呢?
BeanDefinitionRegistryPostProcessor
接口##
BeanDefinitionRegistryPostProcessor接口是一個可以修改spring工廠中已定義的bean的接口,該接口有個postProcessBeanDefinitionRegistry方法。
/**
* Modify the application context's internal bean definition registry after its
* standard initialization. All regular bean definitions will have been loaded,
* but no beans will have been instantiated yet. This allows for adding further
* bean definitions before the next post-processing phase kicks in.
* [@param](https://my.oschina.net/u/2303379) registry the bean definition registry used by the application context
* [@throws](https://my.oschina.net/throws) org.springframework.beans.BeansException in case of errors
*/
void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
實現##
代碼###
public class App implements BeanDefinitionRegistryPostProcessor{
@Override
public void postProcessBeanDefinitionRegistry(
BeanDefinitionRegistry registry) throws BeansException {
registry.registerBeanDefinition("demoEntityDao", getDefinition(AcAlert.class));
}
private BeanDefinition getDefinition(Class<?> cls) {
DaoInterfaceGenerator g = new DaoInterfaceGenerator(cls);
Class<?> daoClass = g.generateClass();
GenericBeanDefinition bd = new GenericBeanDefinition();
bd.setBeanClass(MapperFactoryBean.class);
bd.getConstructorArgumentValues().addGenericArgumentValue(daoClass);
bd.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference("sqlSessionFactory"));
return bd;
}
}
步驟說明###
- 實現
BeanDefinitionRegistryPostProcessor
接口 - 處理
postProcessBeanDefinitionRegistry
方法 - 生成
BeanDefinition
,上面展示了動態添加一個mybatis Dao的bean注冊過程
我遇到的坑##
當動態生成生成mybatis的dao接口時,報這個錯誤:
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'demoEntityDao': Post-processing of FactoryBean's singleton object failed; nested exception is java.lang.IllegalArgumentException: interface com.dhcc.ac.domain.AcAlertDao is not visible from class loader
at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:116)
at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1590)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:254)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1054)
at com.dhcc.framework.App.main(App.java:48)
Caused by: java.lang.IllegalArgumentException: interface com.dhcc.ac.domain.AcAlertDao is not visible from class loader
at java.lang.reflect.Proxy$ProxyClassFactory.apply(Proxy.java:581)
at java.lang.reflect.Proxy$ProxyClassFactory.apply(Proxy.java:557)
at java.lang.reflect.WeakCache$Factory.get(WeakCache.java:230)
at java.lang.reflect.WeakCache.get(WeakCache.java:127)
at java.lang.reflect.Proxy.getProxyClass0(Proxy.java:419)
at java.lang.reflect.Proxy.newProxyInstance(Proxy.java:719)
at org.springframework.aop.framework.JdkDynamicAopProxy.getProxy(JdkDynamicAopProxy.java:121)
at org.springframework.aop.framework.ProxyFactory.getProxy(ProxyFactory.java:109)
at org.springframework.aop.framework.AbstractAdvisingBeanPostProcessor.postProcessAfterInitialization(AbstractAdvisingBeanPostProcessor.java:90)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:422)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.postProcessObjectFromFactoryBean(AbstractAutowireCapableBeanFactory.java:1723)
at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:113)
... 5 more
錯誤原因在於動態生成的class加載的classloader,與Proxy.newProxyInstance
使用的ClassLoader,不是同一個classloader,所以在Proxy.newProxyInstance
找不到這個新生成的類。
解決辦法###
動態加載類,一般都是用defineClass動態加載到ClassLoader里去。
但defineClass不是public,所以在這里卡了一段時間。
后來,突然之間找到了解決辦法,使用反射調用defineClass就好了呀。
小結##
技術沒什么高深的,我后面將要寫的一個功能,用到了本篇的技術,這里先介紹一下。
我的微信zouhaibin294148,不知不覺寫了10多年代碼了