[Opensource] ConcurrentModificationException

[S. W.]

Hi All,

I am new to Expresso. I have used Expresso to build a
small applications. When I run my codes which I used a
vector to store the data retrieved from MySQL and
iterated through this vector to get the data and
display the data in front-end, I got the following
error:

Apache Tomcat/4.0.6 - HTTP Status 500 - Internal
Server Error

--------------------------------------------------------------------------------

type Exception report

message Internal Server Error

description The server encountered an internal error
(Internal Server Error) that prevented it from
fulfilling this request.

exception 

java.util.ConcurrentModificationException
	at
java.util.HashMap$HashIterator.nextEntry(HashMap.java:762)
	at
java.util.HashMap$KeyIterator.next(HashMap.java:798)
	at
org.apache.catalina.util.Enumerator.nextElement(Enumerator.java:166)
	at
org.netbeans.modules.web.monitor.server.MonitorFilter.getSessionAttributes(MonitorFilter.java:809)
	at
org.netbeans.modules.web.monitor.server.MonitorFilter.getSessionIn(MonitorFilter.java:746)
	at
org.netbeans.modules.web.monitor.server.MonitorFilter.getDataBefore(MonitorFilter.java:488)
	at
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:182)
	at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
	at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
	at
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:243)
	at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at
org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:190)
	at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at
org.apache.catalina.valves.CertificatesValve.invoke(CertificatesValve.java:246)
	at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at
org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at
org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2347)
	at
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
	at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at
org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170)
	at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:170)
	at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:468)
	at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at
org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
	at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at
org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at
org.apache.catalina.connector.http.HttpProcessor.process(HttpProcessor.java:1027)
	at
org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.java:1125)
	at java.lang.Thread.run(Thread.java:536)

What caused the problem? I can't figure out. Anybody
knows.

Thanks in advance!

Regards,

Sally

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