Skip to main content

The RequestDispatcher

Defines an object that receives requests from the clicent and sends them to any //resource(such as a servlet, HTML file , or JSP file) on the server. The servlet container creates the //RequestDispatcher object, which is used as a wrapper around a server resource located at a particular //path or given by a particular name.
RequestDispatcher dispatcher = request.getRequestDispatcher(address);
dispatcher.forward(request, response);
// in JSp, you can use <jsp:forward page="<%= destination %>" />

An alternative to forward is include. With include, the servlet can combine its output with that of one or more JSP pages. More commonly, the servlet still relies on JSP pages to produce the output, but the servlet invokes different JSP pages to create different sections of the pages.

This approach is most common when your servlets create portal sites that let users specify where on the page they want various pieces of content to be displayed. e.g. as follows,

String firstTable, secondTable, thirdTable;
if (someCondition) {
firstTable = "/WEB-INF/Sports-Scores.jsp";
secondTable = "/WEB-INF/Stock-Prices.jsp";
thirdTable = "/WEB-INF/Weather.jsp";
} else if (...) { ... }
RequestDispatcher dispatcher =
dispatcher.include(request, response);
dispatcher =
dispatcher.include(request, response);
dispatcher =
dispatcher.include(request, response);
dispatcher =
dispatcher.include(request, response);
dispatcher =
dispatcher.include(request, response);


Popular posts from this blog

Stretch a row if data overflows in jasper reports

It is very common that some columns of the report need to stretch to show all the content in that column. But  if you just specify the property " stretch with overflow' to that column(we called text field in jasper report world) , it will just stretch that column and won't change other columns, so the row could be ridiculous. Haven't find the solution from internet yet. So I just review the properties in iReport one by one and find two useful properties(the bold highlighted in example below) which resolve the problems.   example:
<band height="20" splitType="Stretch"> <textField isStretchWithOverflow="true" pattern="" isBlankWhenNull="true"> <reportElement stretchType="RelativeToTallestObject" mode="Opaque" x="192" y="0" width="183" height="20"/> <box leftPadding="2"> <pen lineWidth="0.25"/> …

JasperReports - Configuration Reference

Live - solving the jasper report out of memory and high cpu usage problems

I still can not find the solution. So I summary all the things and tell my boss about it. If any one knows the solution, please let me know.

Symptom: 1.The JVM became Out of memory when creating big consumption report 2.Those JRTemplateElement-instances is still there occupied even if I logged out the system
Reason:         1. There is a large number of JRTemplateElement-instances cached in the memory 2.The clearobjects() method in ReportThread class has not been triggered when logging out
Action I tried:      About the Virtualizer: 1.Replacing the JRSwapFileVirtualizer with JRFileVirtualizer 2.Not use any FileVirtualizer for cache the report in the hard disk Result: The japserreport still creating the a large number of JRTemplateElement-instances in the memory     About the work around below,      I tried: item 3(in below work around list) – result: it helps to reduce  the size of the JRTemplateElement Object                Item 4,5 – result : it helps a lot to reduce the number of  JRTemplateE…