SpringMVC重定向导致的内存泄漏分析

我不是女神ヾ 2021-12-17 04:43 335阅读 0赞

SpringMVC重定向频繁会导致的内存泄漏，我们的产品也碰到的这样的问题。网上也有类似解决方案：  
[原文链接][Link 1]

@RequestMapping(method = RequestMethod.GET)
    public String test(String redirectUrl){
        return "redirect:"+redirectUrl;
    }

项目内一个热点接口，使用了如上代码做代码的重定向操作，而让人没想到的是：这样子的写法会有内存泄漏的风险

如果不处理，那么随着内存会耗尽。最终会导致频繁的fullgc，而OOM：gc overhead limit exceeded

先说原因：因为redirectUrl是带参数，动态的链接，redirect会构建ViewResolver\#create一个RedirectView，执行applyLifecycleMethods去initBean的时候，会使用了一个名为AdvisedBeans的ConcurrentHashMap去保存，这个map以redirect:redirectUrl为key，又没有做limit容量限制，而edirectUrl是一个动态的链接，所以每次redirect都会生成put一条数据到map中

图为pinpoint监控下，运行多天后，最近一天的内存变化图，最后内存降下来是因为修改后重启了。

温馨提示：如果您对分析过程没兴趣，那么看到这里就可以停止了，解决方案之一是采用HttpServletResponse的sendRedirect就可以解决。  
以下为我今天的处理、分析过程

发现fullgc如此频繁之后，首先是使用jmap dump出对应的堆hprof文件, jmap -dump:format=b,file=map.hprof pid  
使用jstack导出线程信息， jstack pid >> stack.log  
保存好gc的日志,gc.log，因为我们在一开始的jvm启动参数上就会对gc日志做保存  
重启项目，防止oom  
下载mat工具对map.hprof文件进行分析  
分析图如下

可以发现存在内存泄漏的情况，罪魁祸首是被ConcurrentHashMap(advisedBeans)引用的字符串，查看map的内容，发现如下，ref的key全部都是redirect开头的字符串，所以判断问题出在springmvc的redirect上

但是仅仅知道问题出在这里，还是不知道怎么解决，所以下面是简单的源码的一个分析过程，只写关键部分,可以按步骤自己对着源码看

首先将断点定位到org.springframework.web.servlet.DispatcherServlet\#doService()=>doDispatch()下，至于为什么？可能您需要了解一下springmvc的请求处理流程  
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception \{  
//…  
this.doDispatch(request, response);  
\}

在doDispatch()的最后，会调用org.springframework.web.servlet.DispatcherServlet#processDispatchResult()
    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        //....
        this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
    }
     
    
      org.springframework.web.servlet.DispatcherServlet#render()，从而调用#resolverViewName()进行viewName的解析
    private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
        //....
         if (mv != null && !mv.wasCleared()) {
                this.render(mv, request, response);
                if (errorView) {
                    WebUtils.clearErrorRequestAttributes(request);
                }
            } 
       //....
        
    }

org.springframework.web.servlet.view.AbstractCachingViewResolver\#resolverViewName()，在这里会进行一次缓存的判断，生成一个cacheKey，cacheKey是由viewName(redirect:redirectUrl)+"\_"+locale组成，存放到一个名为viewAccessCache的ConcurrentHashMap中，需要注意的是，这个map有做容量的上限限制为1024，具体做法是在存放到map的同时，也会存放一份到LinkedHashMap中，通过\#removeEldestEntry去实现，所以如果redirectUrl是固定的，那么在第二次访问的时候，会直接命中缓存，也不会有内存泄漏的问题  
protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale, HttpServletRequest request) throws Exception \{  
//…  
view = viewResolver.resolveViewName(viewName, locale);  
//…  
\}  
private final Map<Object, View> viewAccessCache = new ConcurrentHashMap(1024);  
private final Map<Object, View> viewCreationCache = new LinkedHashMap<Object, View>(1024, 0.75F, true) \{  
protected boolean removeEldestEntry(Entry<Object, View> eldest) \{  
if (this.size() > AbstractCachingViewResolver.this.getCacheLimit()) \{  
AbstractCachingViewResolver.this.viewAccessCache.remove(eldest.getKey());  
return true;  
\} else \{  
return false;  
\}  
\}  
\};  
public View resolveViewName(String viewName, Locale locale) throws Exception \{  
if (!this.isCache()) \{  
return this.createView(viewName, locale);  
\} else \{  
Object cacheKey = this.getCacheKey(viewName, locale);  
View view = (View)this.viewAccessCache.get(cacheKey);  
if (view == null) \{  
Map var5 = this.viewCreationCache;  
synchronized(this.viewCreationCache) \{  
view = (View)this.viewCreationCache.get(cacheKey);  
if (view == null) \{  
view = this.createView(viewName, locale);  
if (view == null && this.cacheUnresolved) \{  
view = UNRESOLVED\_VIEW;  
\}

if (view != null) {
                                this.viewAccessCache.put(cacheKey, view);
                                this.viewCreationCache.put(cacheKey, view);
                                if (this.logger.isTraceEnabled()) {
                                    this.logger.trace("Cached view [" + cacheKey + "]");
                                }
                            }
                        }
                    }
                }
     
                return view != UNRESOLVED_VIEW ? view : null;
            }
        }

调用org.springframework.web.servlet.view.UrlBasedViewResolver\#createView()，判断到viewName startWith redirect:的话，那么会构建一个RedirectView，并调用org.springframework.web.servlet.view.UrlBasedViewResolver的\#applyLifecycleMethods()  
protected View createView(String viewName, Locale locale) throws Exception \{  
//…  
if (viewName.startsWith(“redirect:”)) \{  
forwardUrl = viewName.substring(“redirect:”.length());  
RedirectView view = new RedirectView(forwardUrl, this.isRedirectContextRelative(), this.isRedirectHttp10Compatible());  
view.setHosts(this.getRedirectHosts());  
return this.applyLifecycleMethods(viewName, view);  
\}  
//…  
\}  
private View applyLifecycleMethods(String viewName, AbstractView view) \{  
return (View)this.getApplicationContext().getAutowireCapableBeanFactory().initializeBean(view, viewName);  
\}

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean()
    public Object initializeBean(Object existingBean, String beanName) {
            return this.initializeBean(beanName, existingBean, (RootBeanDefinition)null);
        }
     
    
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsAfterInitialization()
    protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
           //....
            if (mbd == null || !mbd.isSynthetic()) {
                wrappedBean = this.applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
            }
          //....
        }
     
    
    org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#postProcessAfterInitialization()
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException {
            Object result = existingBean;
            Iterator var4 = this.getBeanPostProcessors().iterator();
     
            do {
                if (!var4.hasNext()) {
                    return result;
                }
     
                BeanPostProcessor beanProcessor = (BeanPostProcessor)var4.next();
                result = beanProcessor.postProcessAfterInitialization(result, beanName);
            } while(result != null);
     
            return result;
        }
     
    
    org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#wrapIfNecessary()
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
            if (bean != null) {
                Object cacheKey = this.getCacheKey(bean.getClass(), beanName);
                if (!this.earlyProxyReferences.contains(cacheKey)) {
                    return this.wrapIfNecessary(bean, beanName, cacheKey);
                }
            }
     
            return bean;
        }

在这里会将viewName作为key，value=Boolean.False存入名advisedBeans的concurrentHashMap中，需要注意的是，这个map的无限的。

private final Map<Object, Boolean> advisedBeans = new ConcurrentHashMap(256);
    protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
            if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
                return bean;
            } else if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
                return bean;
            } else if (!this.isInfrastructureClass(bean.getClass()) && !this.shouldSkip(bean.getClass(), beanName)) {
                Object[] specificInterceptors = this.getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, (TargetSource)null);
                if (specificInterceptors != DO_NOT_PROXY) {
                    this.advisedBeans.put(cacheKey, Boolean.TRUE);
                    Object proxy = this.createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
                    this.proxyTypes.put(cacheKey, proxy.getClass());
                    return proxy;
                } else {
                    this.advisedBeans.put(cacheKey, Boolean.FALSE);
                    return bean;
                }
            } else {
                this.advisedBeans.put(cacheKey, Boolean.FALSE);
                return bean;
            }
        }

[Link 1]: https://blog.csdn.net/qq_26093341/article/details/85696884