jvm看java.lang.OutOfMemoryError: PermGen space

異常現象

異常信息如下

java.lang.OutOfMemoryError: PermGen space
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2374)
    at org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:846)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1313)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1172)
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2625)
    at java.lang.Class.getDeclaredMethods(Class.java:1868)
    at org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor.findPersistenceMetadata(PersistenceAnnotationBeanPostProcessor.java:383)
    at org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(PersistenceAnnotationBeanPostProcessor.java:321)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyMergedBeanDefinitionPostProcessors(AbstractAutowireCapableBeanFactory.java:830)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:493)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:585)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:913)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:464)
    at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:385)
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:284)
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:111)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4812)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5278)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.StandardContext.reload(StandardContext.java:3859)
    at org.apache.catalina.startup.HostConfig.reload(HostConfig.java:1410)
    at org.apache.catalina.startup.HostConfig.checkResources(HostConfig.java:1383)
    at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1619)

剖析原因

嗯。。。很眼熟吧，這個是jdk1.8以下特有的異常了（jdk1.8換成了meta space了（類似於ArrayList會自動擴容），缺點是會占用其他內存）。我們用jvisualvm查看下

點擊監視勾上內存，從堆上切換到PermGen（永久代）上。（稍微解釋一下，jvm數據區分為堆和方法區。堆是存儲對象的，方法區是存儲類信息、常量池、靜態變量之類的。從JMM上來看，年輕代和老年代是堆，永久帶是方法區）

發現PermGen的使用大小和PermGen大小一樣。這種情況就是方法區（永久代）不夠用了。

解決辦法 

開發中

如果是在開發中，沒有stop直接redeploy，你會發現PermGen會直線上升。這種情況直接stop就好了，因為在線程啟動時類信息就被加載到方法區中，線程不死之前的類信息就一直存在。

線上

如果是在線上跑着出現這種問題，直接設置方法區初始大小-XX:PermSize和方法區最大大小-XX:MaxPermSize