“java.lang.IllegalStateException: strict servlet API: cannot call getWriter() after getOutputStream(

 There is a lot of getWriter() errors in the weblogic app server log. The root cause is weblogic or springframework? How to fix it?
####<Jun 23, 2010 12:08:08 PM EDT> <Notice> <Stdout> <mag-prd02-app.ibs.aol.com> <sub-sf-prd02> <[ACTIVE] ExecuteThread: '1' for queue: 'weblogic.kernel.Default (self-tuning)'> <<WLS Kernel>> <> <> <1277309288987> <000000> <FATAL 2010-06-23 12:08:08,986 com.elasticpath.commons.filter.impl.EncodingFilter.handleFilter(EncodingFilter.java:160) - Exception caught in EncodingFilter:
org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.IllegalStateException: strict servlet API: cannot call getWriter() after getOutputStream()
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:583)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:501)