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Error pointing to a Hashtable but I don't have a Hashtable

 
Darren Alexandria
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Good day!

Oct 10, 2007 9:41:41 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet ControllerServlet threw exception

I have a program with these parts, Bean.java, ControllerServlet.java, read.jsp, ReadWrite.java., it reads data from a machine and it works fine the first time I load it but when I click the button which supposed to read data again, this error occurs.

java.lang.NullPointerException
at java.util.Hashtable.get(Hashtable.java:336)
at org.apache.tomcat.util.http.Parameters.getParameterValues(Parameters.java:193)
at org.apache.tomcat.util.http.Parameters.getParameter(Parameters.java:238)
at org.apache.catalina.connector.Request.getParameter(Request.java:1007)
at org.apache.catalina.connector.RequestFacade.getParameter(RequestFacade.java:353)
at com.amkor.stripmap.ControllerServlet.doPost(ControllerServlet.java:34)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:210)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:151)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:870)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685)
at java.lang.Thread.run(Thread.java:595)


I don't understand this error. First of all, I did not use Hashtable.

Thanks.

[ October 09, 2007: Message edited by: Darren Alexandria ]
[ October 09, 2007: Message edited by: Darren Alexandria ]
 
Mark Vedder
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Posts: 624
IntelliJ IDE Java
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The root cause is a NullPointerException, shown at the top of the stack trace. If you continue down the stack, you will see, as you noted, that the get method of the HashTable class threw the NullPointerException. If we continue down the stack trace, we see that the HashTable is used by the Parameters class (org.apache.tomcat.util.http.Parameters) that is part of Tomcat (at org.apache.tomcat.util.http.Parameters.getParameterValues(Parameters.java:193)). This in turn was used by other Tomcat classes. So we can deduce that Tomcat is using a HashTable to store the name/value (or key/value) pairs for parameters.

If we look at the JavaDoc for the HashTable's get(Object) method, it states:


Throws:
NullPointerException - if the specified key is null


So, ultimately, the issue is that somewhere your code is asking Tomcat to fetch a parameter value, but the parameter key you are passing in is a null value.
 
Darren Alexandria
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wow, thanks, I will try to search where in my code is that value that is always null. I will first try to remove it and see what will happen.

Thanks so much.

Darren
 
Mark Vedder
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Originally posted by Darren Alexandria:
I will try to search where in my code that value that is always null


my "guess" would be line 34 of your ControllerServlet

...
at com.amkor.stripmap.ControllerServlet.doPost(ControllerServlet.java:34)
 
Darren Alexandria
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okay, I have removed it already.
That error doesn't appear anymore.
Thanks. Next time, I will try to analyze the stack trace.

Now I have a new problem. I can't get the button to Read the data again.
Anyway, thanks for your replies.

God bless.

Darren
 
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