概述
工作中会经常会需要重写jar包中的一个类,开源的jar包或者是其他项目提供的share包,比较通用的做法是下载源码下来,修改后重新打包。但是很多时候我们只是重写一个类,下载源码打包太过繁琐,而且有可能别人的share没有提供源码下载。
可以通过下面几种方式重写:
1、直接同包路径,同报名,进行替换
这种方式简单粗暴,前提必须是同包路径,同类名。可以直接覆盖掉jar包中的类,spring项目会优先加载自定义的类。
比如重写:DefaultResourceFactory类
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIwczX0xiRGZkRGZ0Xy9GbvNGL2EzXlpXazxSP9EVY1YFWhFHbHJGcoJzY2R2MMBjVtJWd0ckW65UbM5WOHJWa5kHT20ESjBjUIF2X0hXZ0xCMx81dvRWYoNHLrdEZwZ1Rh5WNXp1bwNjW1ZUba9VZwlHdssmch1mclRXY39CXldWYtlWPzNXZj9mcw1ycz9WL49zZuBnL2AzN1QDO0cTM2ETOwkTMwIzLc52YucWbp5GZzNmLn9Gbi1yZtl2Lc9CX6MHc0RHaiojIsJye.png)
2)继承要替换的类,在配置类中进行配置,返回其子类
1)首先创建一个新的bean,继承需要被重写的bean
public class MyHealthMessageQueueLogService extends HealthMessageQueueLogService{
//需要被重写的方法
}
2)在启动类中排除父类
@ComponentScan(excludeFilters = {@Filter(type = FilterType.ASSIGNABLE_TYPE, value = HealthMessageQueueLogService.class)})
3)在配置类中创建子类
@Configuration
public class MessageQueueLogConfig {
@Bean
public HealthMessageQueueLogService healthMessageQueueLogService(){
return new MyHealthMessageQueueLogService();
}
}
3)使用BeanDefinitionRegistryPostProcessor
/**
* Created by zhangshukang on 2019/9/16.
*/
@Component
public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {
private static String SPECIAL_OVERRIDE_BEAN = "healthMessageQueueLogService";
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
boolean isContainsSpecialBean = ((DefaultListableBeanFactory) registry).containsBean(SPECIAL_OVERRIDE_BEAN);
if (isContainsSpecialBean) {
AnnotatedBeanDefinition healthMessageBeanDefinition = (AnnotatedBeanDefinition) registry.getBeanDefinition(SPECIAL_OVERRIDE_BEAN);
if (healthMessageBeanDefinition != null) {
AnnotatedGenericBeanDefinition myBeanDefinition = new AnnotatedGenericBeanDefinition(healthMessageBeanDefinition.getMetadata());
//忽略beanClass originatingBeanDefinition字段
BeanUtils.copyProperties(healthMessageBeanDefinition, myBeanDefinition,"beanClass","originatingBeanDefinition");
//设置自定义的bean class
myBeanDefinition.setBeanClass(MyHealthMessageQueueLogService.class);
//重新加载自定义的bean class
try {
myBeanDefinition.resolveBeanClass(Thread.currentThread().getContextClassLoader());
registry.registerBeanDefinition(SPECIAL_OVERRIDE_BEAN,myBeanDefinition);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
}
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
}
}