spring 运行时替换 单例bean 实现
前言
kafka、redis 这些中间件可能会出现超时，这时候我们可能会需要修改他们的链接地址，此时就需要动态替换这些bean
思路
首先要知道这bean 是怎么放到spring 容器中的，是放在哪里的？这个不做详细赘述
可以简易的理解为两步
- 根据需要创建bean
- 放在
DefaultSingletonBeanRegistry三级缓存中，尤其是org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#singletonObjects
代码准备
一个简单的controller
@RequestMapping()
@RestController
@Slf4j
public class DemoController {
@Autowired
InService inService;
@GetMapping("print")
public void print() {
System.out.println(inService.getCourseService().toString());
//System.out.println(courseInService.toString());
}
}
@Component
@Getter
@Setter
public class CourseInService {
@Autowired
OkService okService;
}
@Service
public class InService implements SpringCacheHelper{
@Autowired
CourseInService courseService;
public CourseInService getCourseService() {
return courseService;
}
}
@Service
public class OkService{
}
我们要做的就是替换掉InService 中的courseService
创建bean的大致源码
源码调试很简单，既然知道bean最终会放到singletonObjects,根据代码查看，只有DefaultSingletonBeanRegistry#addSingleton 这个方法会对singletonObjects add 操作，这里打个断点即可
然后启动项目就能看到如下的堆栈
最关键的方法就是AbstractBeanFactory#doGetBean
大致流程就是
- 先创建bean
- 在放入
singletonObjects
那我们替换的时候也是如此操作
代码
// 原有的bean
CourseInService bean = BaseSpringContext.getApplicationContext().getBean(CourseInService.class);
log.info("更新之前 {}", bean.toString());
// 获取beanFactory
DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory) BaseSpringContext.getApplicationContext().getAutowireCapableBeanFactory();
// 获取beanName
String beanName = beanFactory.getBeanNamesForType(CourseInService.class)[0];
// mdb
Method getMergedLocalBeanDefinitionM = MethodUtils.getMatchingMethod(AbstractBeanFactory.class, "getMergedLocalBeanDefinition", String.class);
getMergedLocalBeanDefinitionM.setAccessible(true);
RootBeanDefinition definition = (RootBeanDefinition)getMergedLocalBeanDefinitionM.invoke(beanFactory, beanName);
//反射调用 createBean(beanName, mbd, args);
Method createBeanM = MethodUtils.getMatchingMethod(AbstractAutowireCapableBeanFactory.class, "createBean", String.class, RootBeanDefinition.class, Object[].class);
createBeanM.setAccessible(true);
CourseInService courseInService = (CourseInService) createBeanM.invoke(beanFactory, beanName, definition, null);
// 反射更新 singletonObjects 中缓存
Method addSingletonM = MethodUtils.getMatchingMethod(DefaultSingletonBeanRegistry.class, "addSingleton", String.class, Object.class);
addSingletonM.setAccessible(true);
addSingletonM.invoke(beanFactory, beanName, courseInService);
//如果有依赖的需要立马更新，比如Inservice
Field singletonObjectsF = FieldUtils.getDeclaredField(DefaultSingletonBeanRegistry.class, "singletonObjects", true);
ConcurrentHashMap<String, Object> singletonObjects = (ConcurrentHashMap) singletonObjectsF.get(beanFactory);
for (Object value : singletonObjects.values()) {
// 过滤非项目bean
if (!value.getClass().getName().startsWith("com.hgf")) {
continue;
}
Field[] declaredFields = value.getClass().getDeclaredFields();
for (Field declaredField : declaredFields) {
if (!declaredField.getType().equals(CourseInService.class)) {
continue;
}
log.info("{} 更新依赖", value.getClass().getName());
FieldUtils.writeField(declaredField, value, courseInService, true);
}
}
log.info("更新之后 {}", bean.toString());
然后在controller加入接口，调用之后打印日志如下
2022-06-10 15:32:05.476 INFO 26322 --- [io-13399-exec-1] c.h.z.controller.DemoController : 更新之前 com.hgf.zulu_spring_demo.service.CourseInService@5c1388f3
2022-06-10 15:32:07.516 INFO 26322 --- [io-13399-exec-1] c.h.z.controller.DemoController : com.hgf.zulu_spring_demo.service.InService 更新依赖
2022-06-10 15:32:07.516 INFO 26322 --- [io-13399-exec-1] c.h.z.controller.DemoController : 更新之后 com.hgf.zulu_spring_demo.service.CourseInService@709060f7
到这里已经差不多了，但是有个小bug，如果依赖的类是切面的话，就会有问题。比如说在controller 中依赖CourseInService
@Component
@Aspect
@Order(0)
@Slf4j
public class ValidationAspect {
private Logger logger = LoggerFactory.getLogger(this.getClass());
@Pointcut("execution(public * com.hgf.zulu_spring_demo.controller..*.*(..))")
public void validationPointCut(){};
@Around("validationPointCut()")
public Object valid(ProceedingJoinPoint joinPoint) throws Throwable {
return joinPoint.proceed();
}
}
这时候调用发现，controller 没有更新依赖，因为此时的controller是proxy类
优化
这时候大致两种方案
- 想办法找到切面类中的真实controller bean，然后修改
- 直接修改controller bean
第一种方式需要深入研究源码，不可取，第二种方式就是缓存，在类加载完的时候全部加入到自己的缓存中
@Component
public class SpringCacheHelper implements BeanPostProcessor {
private static final Map<String, Object> beanCacheMap = new ConcurrentHashMap<>(256);
public static void addCache(String beanName, Object singletonObject) {
synchronized (beanName) {
beanCacheMap.put(beanName, singletonObject);
}
}
public static Map<String,Object> getBeanCacheMap(){
return beanCacheMap;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (!bean.getClass().getName().startsWith("com.hgf")) {
beanCacheMap.put(beanName, bean);
}
return bean;
}
}
然后修改依赖替换部分
Collection<Object> values = SpringCacheHelper.getBeanCacheMap().values();
for (Object value : values) {
Field[] declaredFields = value.getClass().getDeclaredFields();
for (Field declaredField : declaredFields) {
if (!declaredField.getType().equals(CourseInService.class)) {
continue;
}
log.info("{} 更新依赖", value.getClass().getName());
FieldUtils.writeField(declaredField, value, courseInService, true);
}
}
大功告成
核心代码
public void registry() throws Exception {
CourseInService bean = BaseSpringContext.getApplicationContext().getBean(CourseInService.class);
log.info("更新之前 {}", bean.toString());
// 获取beanFactory
DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory) BaseSpringContext.getApplicationContext().getAutowireCapableBeanFactory();
// 获取beanName
String beanName = beanFactory.getBeanNamesForType(CourseInService.class)[0];
// mdb
Method getMergedLocalBeanDefinitionM = MethodUtils.getMatchingMethod(AbstractBeanFactory.class, "getMergedLocalBeanDefinition", String.class);
getMergedLocalBeanDefinitionM.setAccessible(true);
RootBeanDefinition definition = (RootBeanDefinition)getMergedLocalBeanDefinitionM.invoke(beanFactory, beanName);
//createBean(beanName, mbd, args);
Method createBeanM = MethodUtils.getMatchingMethod(AbstractAutowireCapableBeanFactory.class, "createBean", String.class, RootBeanDefinition.class, Object[].class);
createBeanM.setAccessible(true);
CourseInService courseInService = (CourseInService) createBeanM.invoke(beanFactory, beanName, definition, null);
// 更新 singletonObjects 中缓存
Method addSingletonM = MethodUtils.getMatchingMethod(DefaultSingletonBeanRegistry.class, "addSingleton", String.class, Object.class);
addSingletonM.setAccessible(true);
addSingletonM.invoke(beanFactory, beanName, courseInService);
//如果有依赖的需要立马更新
Field singletonObjectsF = FieldUtils.getDeclaredField(DefaultSingletonBeanRegistry.class, "singletonObjects", true);
ConcurrentHashMap<String, Object> singletonObjects = (ConcurrentHashMap) singletonObjectsF.get(beanFactory);
for (Object value : singletonObjects.values()) {
// 过滤非项目bean
if (!value.getClass().getName().startsWith("com.hgf")) {
continue;
}
Field[] declaredFields = value.getClass().getDeclaredFields();
for (Field declaredField : declaredFields) {
if (!declaredField.getType().equals(CourseInService.class)) {
continue;
}
log.info("{} 更新依赖", value.getClass().getName());
FieldUtils.writeField(declaredField, value, courseInService, true);
}
}
bean = BaseSpringContext.getApplicationContext().getBean(CourseInService.class);
Collection<Object> values = SpringCacheHelper.getBeanCacheMap().values();
for (Object value : values) {
Field[] declaredFields = value.getClass().getDeclaredFields();
for (Field declaredField : declaredFields) {
if (!declaredField.getType().equals(CourseInService.class)) {
continue;
}
log.info("{} 更新依赖", value.getClass().getName());
FieldUtils.writeField(declaredField, value, courseInService, true);
}
}
log.info("更新之后 {}", bean.toString());
}