The isThreadSafe Attribute

Format

<%@ page isThreadSafe="true" %> <%   Default   %>

<%@ page isThreadSafe="false" %>

Purpose

To tell the system when your code is not threadsafe, so 

that the system can prevent concurrent access

Instructs servlet to implement SingleThreadModel

Notes

Default is true    system assumes you have synchronized 

updates to fields & other shared data

Supplying a value of false can degrade performance

43

JSP

www.corewebprogramming.com

Example of Non Threadsafe

Code (IDs Must Be Unique)

What s wrong with this code?

<%! private int idNum = 0; %>

<% 

String userID = "userID" + idNum;

out.println("Your ID is " + userID + ".");

idNum = idNum + 1; 

%>

44

JSP

www.corewebprogramming.com

22