JSP Scripting Element

JSP Expressions

A JSP expression is used to insert Java values directly into the output.

It has the following form:

<%= Java Expression %>

The Java expression is evaluated, converted to a string, and inserted in the page. This evaluation is performed at run-time (when the page is requested), and thus has full access to information about the request.

For example, the following shows the date/time that the page was requested:

Current time: <%= new java.util.Date() %>

To simplify these expressions, there are a number of predefined variables that we can use.

These implicit objects are discussed in more detail later, but for the purpose of expressions, the most important ones are:

. request, the HttpServletRequest; . response, the HttpServletResponse; . session, the HttpSession associated with the request (if any); and . out, the PrintWriter (a buffered version of type JspWriter) used to send output to the client.

example:

hostname: <%= request.getRemoteHost() %>

Finally, note that XML authors can use an alternative syntax for JSP expressions:

<jsp:expression>      Java Expression </jsp:expression>

Remember that XML elements, unlike HTML ones, are case sensitive. So be sure to use lowercase.