Java Enterprise Best Practices

Choose an Appropriate Include Mechanism

JSP provides two ways to include content in a page: the include directive (<%@ include file=" . . . " %>) and the include action (<jsp:include page=" . . . " />). As shown earlier, JSTL adds an import action (<c:import url=" . . . " />) to the mix.

The include directive and the include action both include content from resources that belong to the same web application as the including file. The directive includes the source of the specified resource, either a static file or a file with JSP elements. When a JSP file is included this way, it shares the page scope (and all other scopes) as well as all scripting variables with the including file. The included file is rarely a syntactically complete JSP or HTML page, and I recommend that a different file extension be used to highlight this fact. Any extension will do, but good choices are .jspf and .htmlf, in which “f” stands for “fractional” (as described earlier). The JSP 1.2 specification leaves detecting changes in a file included by the include directive as an optional feature. In a container that doesn’t detect these changes, changes to an included file have no effect until you force a recompile of the including file (e.g., by removing the corresponding class file or “touching” the file).

The include action, on the other hand, includes the response produced by executing the specified resource, either a JSP page or a servlet. The included resource has access to the same scopes as the including ...