Dubbox加入C3P0
框架集成很简单，正常集成，正常添加；
报错操作
添加了Dubbo的Filter，代码如下，provider.xml中添加
<dubbo:provider filter="AppInvokeLogFilter"/>META-INF下添加dubbo/com.aliababa.dubbo.rpc.Filter文件，内容如下：
AppInvokerLogFilter=com.saillen.demo.filter.AppInvokeLogFilter报错日志：
07-Mar-2017 18:02:20.578 ?? [Timer-0] org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading Illegal access: this web application instance has been stopped already. Could not load [com.mchange.v2.resourcepool.BasicResourcePool$AsyncTestIdleResourceTask]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already. Could not load [com.mchange.v2.resourcepool.BasicResourcePool$AsyncTestIdleResourceTask]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading(WebappClassLoaderBase.java:1305)
at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForClassLoading(WebappClassLoaderBase.java:1293)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1158)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1119)
at com.mchange.v2.resourcepool.BasicResourcePool.checkIdleResources(BasicResourcePool.java:1481)
at com.mchange.v2.resourcepool.BasicResourcePool.access$2000(BasicResourcePool.java:32)
at com.mchange.v2.resourcepool.BasicResourcePool$CheckIdleResourcesTask.run(BasicResourcePool.java:1964)
at java.util.TimerThread.mainLoop(Timer.java:555)
at java.util.TimerThread.run(Timer.java:505)
Exception in thread "Timer-0" java.lang.NoClassDefFoundError: com/mchange/v2/resourcepool/BasicResourcePool$AsyncTestIdleResourceTask
at com.mchange.v2.resourcepool.BasicResourcePool.checkIdleResources(BasicResourcePool.java:1481)
at com.mchange.v2.resourcepool.BasicResourcePool.access$2000(BasicResourcePool.java:32)
at com.mchange.v2.resourcepool.BasicResourcePool$CheckIdleResourcesTask.run(BasicResourcePool.java:1964)
at java.util.TimerThread.mainLoop(Timer.java:555)
at java.util.TimerThread.run(Timer.java:505)
Caused by: java.lang.ClassNotFoundException: Illegal access: this web application instance has been stopped already. Could not load [com.mchange.v2.resourcepool.BasicResourcePool$AsyncTestIdleResourceTask]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForClassLoading(WebappClassLoaderBase.java:1295)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1158)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1119)
... 5 more
Caused by: java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already. Could not load [com.mchange.v2.resourcepool.BasicResourcePool$AsyncTestIdleResourceTask]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading(WebappClassLoaderBase.java:1305)
at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForClassLoading(WebappClassLoaderBase.java:1293)
... 7 more报错分析：
删除provider.xml中关于provider的filter配置后可以正常启动，所以初步怀疑以下三点原因：
- dubbo的filter中有和c3p0冲突的包；
- dubbo的filter书写方式不正确，或者和tomcat容器集成有问题；
- NoClassDefFoundError前还有一个Illegal access提示，可能是Tomcat的内存设置不够，或者C3P0占用内存过大（OOM？），加入了filter后，需要load更多class，方法区内存不够？（可能性不大）
尝试修复方案
- Filter配置有问题； META-INF中配置的filter得name和xml中的有拼写差别；
- 将C3P0的初始值调低； – 日志报错有变化
- 加大Tomcat内存；– 日志报错有变化
- 去除dubbo中对commons pool包的引用，框架中只使用commons pool2包；
总结
报错原因和抛出的日志不一致，这个问题有待追查。Dubbo的Filter发现机制是基于JVM的SPI机制的，这个机制一定要注意META-INF下配置的name保持一致；