If care is not taken with the quoting of literals, the expression language (OGNL) will misinterpret a char as a String.
Wrong
<s:if test="aStringProperty == 'A'"> Why doesn't this work when myString is equal to A? </s:if>
The solution is simple: flip the double and single quotes.
Right
<s:if test='aStringProperty == "A"'> This works! </s:if>
Another solution is to escape the double quotes in the String.
Also Right
<s:if test="aStringProperty == \"A\""> This works too! </s:if>