Dubbox加入C3P0
框架集成很簡單，正常集成，正常添加；
報錯操作
添加了Dubbo的Filter，代碼如下，provider.xml中添加
<dubbo:provider filter="AppInvokeLogFilter"/>META-INF下添加dubbo/com.aliababa.dubbo.rpc.Filter文件，內容如下：
AppInvokerLogFilter=com.saillen.demo.filter.AppInvokeLogFilter報錯日誌：
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報錯分析：
刪除provider.xml中關於provider的filter配置後可以正常啓動，所以初步懷疑以下三點原因：
- dubbo的filter中有和c3p0衝突的包；
- dubbo的filter書寫方式不正確，或者和tomcat容器集成有問題；
- NoClassDefFoundError前還有一個Illegal access提示，可能是Tomcat的內存設置不夠，或者C3P0佔用內存過大（OOM？），加入了filter後，需要load更多class，方法區內存不夠？（可能性不大）
嘗試修復方案
- Filter配置有問題； META-INF中配置的filter得name和xml中的有拼寫差別；
- 將C3P0的初始值調低； – 日誌報錯有變化
- 加大Tomcat內存；– 日誌報錯有變化
- 去除dubbo中對commons pool包的引用，框架中只使用commons pool2包；
總結
報錯原因和拋出的日誌不一致，這個問題有待追查。Dubbo的Filter發現機制是基於JVM的SPI機制的，這個機制一定要注意META-INF下配置的name保持一致；