Make sure you are closing all opened connection  after using it. To find out the connection leak use the following parameters for connection pooling

<parameter> <name>removeAbandoned</name> <value>true</value> </parameter>
<parameter>
<name>removeAbandonedTimeout</name>
<value>60</value>
</parameter>
<parameter>
<name>logAbandoned</name>
<value>true</value>
</parameter>

I am closing the connection  immeidately with following code in each file

servlet
--------
public void destroy() {
try {if (conn != null) conn.close();} catch (SQLException e) {}
}

jsp
----
public void jspDestroy()
{
try {if (conn != null) conn.close();} catch (SQLException e) {}
}

Please suggest me if any mistake in above code

Can you message log trace to this, so that we can get some idea where the error  is?

quick opinion here

1) I assume it would be a good practice to close the conn in finally part,
2) I assume you're opening and closing the conn in the right place, but I guess I've come across this problem when oracle  runs out of memory either on dynamic memory or physical(out of space) and it closes the connection  (hard to expect from oracle but it happens) it usually happens on expensive queries or those that return millions of rows which leads to revisiting the queries. check processes and run diagnostics on oracle itself to see what's the status of processes when this happens

does oracle log has anything more to say i.e. error  number? cause it would not close a conn without a legitimate error , check the log, it might give some guidance

Check out a tutorial on tomcat jdbc connection pool