Difference between JSP include directive and JSP include action

• <%@ include file=”filename” %> is the JSP include directive.
  At JSP page translation time, the content of the file given in the include directive is ‘pasted’ as it is, in the place where the JSP include directive is used. Then the source JSP page is converted into a java servlet class. The included file can be a static resource or a JSP page. Generally JSP include directive is used to include header banners and footers.

  The JSP compilation procedure is that, the source JSP page gets compiled only if that page has changed. If there is a change in the included JSP file, the source JSP file will not be compiled and therefore the modification will not get reflected in the output.

• <jsp:include page=”relativeURL” /> is the JSP include action element.
  The jsp:include action element is like a function call. At runtime, the included file will be ‘executed’ and the result content will be included with the soure JSP page. When the included JSP page is called, both the request and response objects are passed as parameters.

  If there is a need to pass additional parameters, then jsp:param element can be used. If the resource is static, its content is inserted into the calling JSP file, since there is no processing needed.

• 所以用<jsp:include page="${actionjs}" />可以动态指定要包含的file，因为这个动作元素可以是在执行jsp文件生成的class可编译文件的时候才去找page属性相关的那个文件。

• 而用<jsp:directive.include file="/js/erp/hr/genericReport/GenericReportAction.js" />只能写死包含的文件。