JSP - General

HTML comment that is sent to the client but not displayed by the browser.
<!-- Blah -->

Developer comment that is not sent to the client
<%-- Blah --%>


Expression that is evaluated and sent to the client each time the page is requested:
<%= Java Value %>
Current time: <%= new java.util.Date() %>
Your hostname: <%= request.getRemoteHost() %>



Statement or statements that are executed each time the page is requested:
<% Java Statement %>

<%
String queryData = request.getQueryString();
out.println("Attached GET data: " + queryData);
%>




Field or method that becomes part of class definition when page is translated into a servlet:

<%! Field Definition %>
<%! Method Definition %>

<%!
private int accessCount = 0;
private String randomHeading() {
return("<H2>" + Math.random() + "</H2>");
}
%>




Directive: A JSP directive affects the overall structure of the servlet that results from the JSP page.  There are three main types of directives: page , include and taglib.

Example:
<%@ directive att="val" %>
<%@ page import="package.class1,...,package.classN" %>
is <jsp:directive.page  import="package.class1,...,package.classN" />

<%@ page contentType="application/vnd.ms-excel" %>
<%@ page contentType="someMimeType; charset=someCharacterSet" %>


e.g. (excel.jsp)
First Last Email Address
Marty Hall hall@coreservlets.com
Larry Brown brown@coreservlets.com
Steve Balmer balmer@ibm.com
Scott McNealy mcnealy@microsoft.com
<%@ page contentType="application/vnd.ms-excel" %>
<%-- There are tabs, not spaces, between columns. --%>

<%@ page session="true" %> <%-- Default --%>

<%@ page isErrorPage="true" %>
<%@ page isErrorPage="false" %> <%-- Default --%>




Include: JSP has three main capabilities for including external pieces into a JSP document:
. the jsp:include action: lets you include the output of a page at request time

<jsp:include page="/fragments/StandardHeading.jsp">
<jsp:param name="bgColor" value="YELLOW" />
</jsp:include>



.the include directive: lets you insert jsp code into the main page before that main page is translated into a servlet.
<%@ include file="Relative URL" %> is
<jsp:directive.include file="..." />

.the jsp:plugin action: used to insert applets that use tha java plug-in into JSP pages.


<jsp:plugin type="applet"
code="MyApplet.class"
width="475" height="350">
<jsp:params>
<jsp:param name="PARAM1" value="VALUE1" />
<jsp:param name="PARAM2" value="VALUE2" />
</jsp:params>
</jsp:plugin>



Shorthand JSP expression
${ EL Expression }

Invocation of custom tag

<prefix:name>
Body
</prefix:name>

predefined Variables:
.request, the HttpServletRequest
.response, the HttpServletResponse
.session, the HttpSession associated with the request
. out, the Write(a buffered version of type JspWriter) used to send output to the client
.application, the ServletContext. This is a data structure shared by all servlets and JSP pages in the Web application and is good for storing shared data.
.config: This variable is the servletconfig object for this page. In principle, you can use it to read initialization parameters.
.pagecontext: JSP introduced a class Called Pagecontext to give a single point to access to many of the page attributes. The PageContext class has methods getRequest,getResponse,getOut,getSession, and so forth.
.page, This variable is simply a synonym for this and is not very useful.