Debugging JSP includes

Question

We are having a debate on what type of jsp includes to use.
One option is the static include:
<%@ include file="testinclude.jsp" %>
The other the dynamic include
<jsp:include page="testinclude.jsp" flush="true" />
A major stumbling block to using the former is that we can not seem to debug using it - a breakpoint set at that line appears to be ignored, and any breakpoints within the include itself also appear to be ignored. Why is that?
Also, are there opinions on the pros and cons between these two methods?
Thanks,
Amy Schmieder
Rentals.com

Answer 1

Hi Amy,
The difference between the two tags is that <%@ include> (the "include directive") is processed at compile time, and <jsp:include> (the "JSP include tag") is processed at runtime.
A JSP is compiled into a Java servlet. When the compiler sees the include directive, it finds the relevant code, compiles it, and drops it straight in. A breakpoint on the directive is never reached because the directive doesn't exist in the compiled version at all (it's been replaced with the included code), and breakpoints in the included code are forgotten when the code is inserted (since they're not stored in the code itself).
The jsp include tag, on the other hand, functions sort of like a method call to the included code. It's invoked at runtime.
Advantages and disadvantages:
On repeat hits, the include directive is faster, since it only needs to be processed once, at compile time.
However, for just this reason, it's more limited. The jsp include tag can be dynamic--you can programmatically figure out, within your JSP, what you want to include (or, say, what parameters you want to pass the included page). An include directive won't let you do that--information about what exactly will be included must be present at compile time.
So, for example,
<jsp:include page="<%= includePage %>" flush ="ture"/>
is perfectly legal, but
<%@ include file="<%= includePage %>" %>
isn't.
Hope this helps,
Avrom
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