JSP Compilation Problems With JSTL tags

Question

My JSP worked well when I used JSP expressions, scriptlets, .... I tried to use JSTL instead and encountered some compilation problems. I am unable to see my mistakes and need help:
Problme #1:
int offset = 0;
try
   <c:set var="offset" value="${requestScope.offset}" />
catch ( Exception e )
    // do nothing
}The above code has two compilation errors:
Generated servlet error:
[javac] Compiling 1 source file
illegal start of expression
<c:set var="offset" value="${requestScope.offset}" />
^
Generated servlet error:
';' expected
<c:set var="offset" value="${requestScope.offset}" />
^
Problem #2:
<c:set var="threadBean" value="${requestScope.ThreadBean}" />
int threadID_int = ParamUtil.getParameterInt( request, "thread" );
<c:if test="${threadBean.threadID} != threadID_int">
    throw new AssertionException( "The two threadID are not the same." );
</c:if>Generated servlet error:
illegal start of expression
<c:if test="${threadBean.threadID != threadID_int}">
^

Answer 1

I have deleted the Java code around the JSTL tags. Now, what is wrong with this <c:if test=" ... "> tag? It seems that I have problems to get JSTL tags right.
It seems that I have problems to get JSTL tags right....
<c:if test="${attachBean.attachMimeType.startsWith('image/')}">
     <html:img page="getattachment?attach=<c:out value='${attachBean.attachID}' />" alt="<c:out value='${attachBean.attachFilename}' />" title="<c:out value='${attachBean.attachFilename}' />" border="0" />
</c:if>error message:
74: tag = 'if' / attribute = 'test': An error occurred while parsing custom action attribute "test" with value "${attachBean.attachMimeType.startsWith('image/')}": Encountered "(", expected one of ["}", ".", ">", "gt", "<", "lt", "==", "eq", "<=", "le", ">=", "ge", "!=", "ne", "[", "+", "-", "*", "/", "div", "%", "mod", "and", "&&", "or", "||"]