We ran into this earlier today. In Struts 2.1.6, the plain text result type was renamed to plainText, with a capital T. But the error message tells you “did you mean plaintext?” with a lower-case T, which is confusing.
So if you get the error below, just change the result type from plaintext to plainText.
Caused by: There is no result type defined for type 'plaintext' mapped with name '*'. Did you mean 'plaintext'? - result