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Using JSP I can use implicit object exception when my JSP page is declared with <%@ page isErrorPage="true" %> directive. But how to get this reference programmatically, for example with a servlet ?

Luigi Viggiano

It is possible to get a reference to the exception even if our page is not declared with isErrorPage="true" attribute, or inside a servlet.

The Java Servlet Specification Version 2.3 / JSP 1.2 (paragraph SRV.9.9.1 "Request Attributes"), introduced a new request attribute to get the exception object. So you can write following code with any Servlet container implementing Servlet specifications 2.3 / JSP 1.2 (i.e. Tomcat 4):

Throwable exception = (Throwable)request.getAttribute("javax.servlet.error.exception");
If you are using Servlet specifications 2.2 / JSP 1.1 (i.e. Tomcat 3.x) you can explore JSP generated code to discover that it does a similar thing to get the exception object within a JSP error page:
Throwable exception = (Throwable) request.getAttribute("javax.servlet.jsp.jspException");
as specified in the JavaServer Pages™ Specification (paragraph 2.2.2 "Client Request Time Processing Errors" page 38, see also pag. 47).

This should work in all JSP 1.1. engines, and Servlet 2.2 containers.