I'd like to suggest better/more detailed error reports when WFS
transactions fails.
My use case is that I've put a constraint in PostGIS st_isvalid(geom)
= true which means that certain updates or inserts will be rejected.
I'd like to be able to communicate to users what the cause of the
error is, but from Geoserver (1.7.3) the below exceptionreport is as
detailed information I can get - unless I'm missing something?
My analysis of the current code is that the WFSException is thrown in
UpdateElementHandler.java line 239 and then put togheter into a
response in Transaction.java but the cause of the WFSException is only
used for logging not the response. Wouldn't it be nice if the
exception that caused the WFSException would be output into the
response in some way (the first cause, at least)
I'd be happy to contribute improvement, if I can and if this is
something that you folks can agree is needed 
<?xml version="1.0" encoding="UTF-8"?>
<ows:ExceptionReport version="1.0.0"
xsi:schemaLocation="http://www.opengis.net/ows
http://10.250.250.2:80/geoserver/schemas/ows/1.0.0/owsExceptionReport
.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ows="http://www.opengis.net/ows">
<ows:Exception exceptionCode="InvalidParameterValue">
<ows:ExceptionText>update error</ows:ExceptionText>
<ows:ExceptionText>Details:</ows:ExceptionText>
<ows:ExceptionText>org.geoserver.wfs.WFSException:
update error at
org.geoserver.wfs.response.v1_1_0.TransactionResponse.write(TransactionResponse.java:49)
at
org.geoserver.ows.Dispatcher.response(Dispatcher.java:711)
at
org.geoserver.ows.Dispatcher.handleRequestInternal(Dispatcher.java:215)
at
org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:153
)
at
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter
.java:48)
at
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:875)
at
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:809)
at
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:571)
at
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:511)
at
javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290
)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at
org.vfny.geoserver.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java
:108)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235
)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at
org.acegisecurity.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:264)
at
org.acegisecurity.intercept.web.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java
:107)
at
org.acegisecurity.intercept.web.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java
:72)
at
org.acegisecurity.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:274)
at
org.acegisecurity.ui.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:110)
at
org.acegisecurity.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:274)
at
org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter
.java:125)
at
org.acegisecurity.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:274)
at
org.acegisecurity.ui.basicauth.BasicProcessingFilter.doFilter(BasicProcessingFilter.java:178)
at
org.acegisecurity.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:274)
at
org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter
.java:229)
at
org.acegisecurity.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:274)
at
org.acegisecurity.util.FilterChainProxy.doFilter(FilterChainProxy.java:148)
at
org.acegisecurity.util.FilterToBeanProxy.doFilter(FilterToBeanProxy.java:98)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235
)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at
org.geoserver.filters.LoggingFilter.doFilter(LoggingFilter.java:73)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235
)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at
org.geoserver.filters.ReverseProxyFilter.doFilter(ReverseProxyFilter.java:163)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235
)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at
org.geoserver.filters.GZIPFilter.doFilter(GZIPFilter.java:41)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235
)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at
org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:190)
at
org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:283)
at
org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:767)
at
org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:697)
at
org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:889)
at
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:690)
at java.lang.Thread.run(Thread.java:619) </ows:ExceptionText>
</ows:Exception>
</ows:ExceptionReport>