Within your JSP you are using the EL and one of these expressions tries
to access the property id from an object that is of type
com.sitepoint.Data. This could look like ${data.id} though might be a
bit less obvious within iterations or if named unluckily.
The log files can be found within the GF install directory and here in
INSTALL_DIR/domains/domain1/logs. The interesting file is server.log.
You can see where GlassFish is installed from within NetBeans if you go
to Tools -> Server. In here select the GlassFish server. On the right
side you can see a form field containing the domains folder. This is
where to look.
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Wolfram Rittmeyer