While developing web applications you will often have to go through long stacktraces when an error is caught. If you get an error in a jsp or controller you will at least go through a bunch of lines added by the application server (tomcat, catalina, and jasper components if you are using tomcat) and by any of the j2ee filter added in web.xml. Most of the time you are not interested at all in these entries and they make harder to find the interesting lines in the stack.
A simple stack trace will probably be not shorter than the following:
NullPointerException Stacktrace: org.myapp.web.MyClass.doNpe(MyClass.java:99) org.myapp.web.MyClass.doSomething(MyClass.java:199) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) java.lang.reflect.Method.invoke(Method.java:324) org.myapp.web.MyClass.doOther(MyClass.java:349) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) java.lang.reflect.Method.invoke(Method.java:324) org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186) org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157) org.myapp.web.ControllerGeek.doSomething(ControllerGeek.java:38) org.myapp.web.ControllerGeek.doNot(ControllerGeek.java:99) org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186) org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157) javax.servlet.http.HttpServlet.service(HttpServlet.java:689) javax.servlet.http.HttpServlet.service(HttpServlet.java:802) org.myapp.web.filters.MessageFilter.doFilter(MessageFilter.java:36) org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237) org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157) com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:118) com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:52) org.myapp.web.filters.LoginFilter.doFilter(LoginFilter.java:36) org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186) org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157) org.myapp.web.filters.EncodingFilter.doFilter(EncodingFilter.java:36) org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186) org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157) org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214) org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104) org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520) org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198) org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152) org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104) org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520) org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137) org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:118) org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102) org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520) org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104) org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520) org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929) org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160) org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799) org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705) org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577) org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683) java.lang.Thread.run(Thread.java:534)
As you can see most of the lines are useless for you in this stack trace... you already know than the execution flow has gone throgh tomcat and through you filters, so you could just save some time by trimming down the stack to a few interesting lines.
The org.apache.log4j.ConsoleAppender will do that for you. Just replace the class appender attribute and add any number of Filter parameters. This is a sample configuration:
<appender name="console" class="org.apache.log4j.ConsoleAppender">
<layout class="it.openutils.log4j.FilteredPatternLayout">
<param name="ConversionPattern" value="%-5p %c %F(%M:%L) %d{dd.MM.yyyy HH:mm:ss} %m%n" />
<param name="Filter" value="org.apache.catalina" />
<param name="Filter" value="org.apache.tomcat" />
<param name="Filter" value="org.apache.coyote" />
<param name="Filter" value="org.myapp.web.filters" />
<param name="Filter" value="com.opensymphony.module.sitemesh.filter" />
<param name="Filter" value="sun.reflect" />
<param name="Filter" value="javax.servlet.http" />
</layout>
</appender>
... and this will be the same stacktrace as above, purged from useless lines:
NullPointerException Stacktrace: org.myapp.web.MyClass.doNpe(MyClass.java:99) org.myapp.web.MyClass.doSomething(MyClass.java:199) org.myapp.web.MyClass.doOther(MyClass.java:349) org.myapp.web.ControllerGeek.doSomething(ControllerGeek.java:38) org.myapp.web.ControllerGeek.doNot(ControllerGeek.java:99) java.lang.Thread.run(Thread.java:534)
This kind of configuration is particularly useful in development, while you will probably look at error messages in your IDE console. It can also be useful in production in order to avoid huge log files or email messages (it can be used together with the DynamicSubjectSMTPAppender appender provided by openutils).
Warning: be careful while configuring the stacktrace filters: having a trimmed down stacktrace often makes easier to find errors, but if the error come from the classes you removed from the stacktrace you will never be able to find the cause. For example if you are developing a servlet filter don't remove it from the stacktrace, also if it will show up in all the stacktraces from the application. It's up to you too choose what is not useful between what you commonly see in stacktraces.