The offending 

java.lang.Throwable

 describing the error that occurred is stored in the 

javax.ServletRequest

 instance for the client request using the 

putAttribute()

method, using the name  

javax.servlet.jsp.jspException

 . Names starting with 

the prefixes  

java

  and  

javax

  are reserved by the different specifications of the Java 

platform; the  

javax.servlet

  prefix is used by the Servlet and JSP specifications.

If the 

errorPage

 attribute of a 

page

 directive names a URL that refers to another JSP, and 

that JSP indicates that it is an error page (by setting the 

page 

directive's

 isErrorPage

attribute to 

true

) then the  

exception

  implicit scripting language variable of that page 

is initialized to the offending 

Throwable

 reference.

2.3

Comments

There are two types of comments in a JSP page: comments to the JSP page itself, 

documenting what the page is doing; and comments that are intended to appear in the 

generated document sent to the client.

Generating Comments in Output to Client

In order to generate comments that appear in the response output stream to the requesting 

client, the HTML and XML comment syntax is used, as follows:

These comments are treated as uninterpreted template text by the JSP container. If the 

generated comment is to have dynamic data, this can be obtained through an expression 

syntax, as in:

 more comments ...   >

JSP Comments

A JSP comment is of the form

<%   anything but a closing   %> ...   %>

The body of the content is ignored completely. Comments are useful for documentation but 

also to  comment out  some portions of a JSP page. Note that JSP comments do not nest.

Note that an alternative way to place a  comment  in JSP is to do so by using the comment 

mechanism of the scripting language. For example:

<% /** this is a comment ... **/ %>

Chapter 2

Standard Syntax and Semantics

38