I recently got an uncomfortable exception in struts2 I could not resolve easily. The exception "java.lang.IllegalStateException: STREAM" 'suddenly' started appearing, and broke my ajax-requests. After some fiddling, I found that I had included one to many property in my action-super-class: servletRequest. A getter on this property made the JSONWriter try to parse the whole servletRequest to json, leading to a crash with java.lang.IllegalStateException: STREAM.
The solution for me was to add servletRequest to the excludeProperties-property in my struts-config:
<action class="personSearchAction" method="getPerson" name="personSearchApi">
<result type="json">
<param name="ignoreHierarchy" />false
<param name="excludeProperties" />
servletRequest, actionErrors,actionMessages
</result>
</action>
