I have been inserting log4j entries into a mongodb database and each entry has been given an ISODate timestamp:

"timestamp" : ISODate("2012-01-17T22:30:19.839Z")

To create a mapping for this, I had to manually add the timestamp as Spring Roo did not allow timestamp to be used as it was a reserved word.
So I manually added:

@DateTimeFormat(style="MM/dd/yyyy")
private java.util.Date timestamp;

But I started getting the following error:

Invalid style specification: MM/dd/yyyy

The stack trace for that error was:

org.joda.time.format.DateTimeFormat.createFormatterForStyle(DateTimeFormat.java:702)
org.joda.time.format.DateTimeFormat.patternForStyle(DateTimeFormat.java:212)
com.comcast.uivr.web.LoggingController_Roo_Controller.ajc$interMethod$com_comcast_uivr_web_LoggingController_Roo_Controller$com_comcast_uivr_web_LoggingController$addDateTimeFormatPatterns(LoggingController_Roo_Controller.aj:98)
com.comcast.uivr.web.LoggingController.ajc$interMethodDispatch2$com_comcast_uivr_web$addDateTimeFormatPatterns(LoggingController.java:1)
com.comcast.uivr.web.LoggingController_Roo_Controller.ajc$interMethodDispatch1$com_comcast_uivr_web_LoggingController_Roo_Controller$com_comcast_uivr_web_LoggingController$addDateTimeFormatPatterns(LoggingController_Roo_Controller.aj)
com.comcast.uivr.web.LoggingController_Roo_Controller.ajc$interMethod$com_comcast_uivr_web_LoggingController_Roo_Controller$com_comcast_uivr_web_LoggingController$list(LoggingController_Roo_Controller.aj:66)
com.comcast.uivr.web.LoggingController.list(LoggingController.java:1)
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:597)
org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:212)
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:96)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:900)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:827)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
java.lang.Thread.run(Thread.java:662)

To fix this I attempted to add the ISO date format for the @DateTimeFormat

@DateTimeFormat(style="yyyyMMdd'T'HHmmss.SSSZ")
private java.util.Date timestamp;

Which still did not work and had the error.

To resolve this I shitched to use ISO.DATE_TIME as the style:

@DateTimeFormat(iso=ISO.DATE_TIME)
private java.util.Date timestamp;

From http://www.baselogic.com/blog/development/springframework/mapping-mongodb-isodate-spring-roo-entity/