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Programmers Guide > Error Handling
Error Handling
Default Error Handling:
A JOT Servlet handles an uncaught exception with the
failureResponse() method. The exception is logged with the precise
JOT Template line number and context information
(see Logging and Debugging).
Default error handling sends a response to the client with the
ResponseException
respond() method. The response includes a specified HTTP status
code and a "friendly" client message if the exception implements
ServletResponseException.
A catch() clause can also use the
wrapResponseException() utility method. The following example logs
an IllegalArgumentsException and sends the client
message "Unable to process your request. Please try again"
with an HTTP 400 status code (Bad Request):
catch (IllegalArgumentsException iaex) {
throw ResponseException.wrapResponseException(iaex, 400,
"Unable to process your request. Please try again", false);
}
Customized Error Handling:
A JotHttpServlet subclass can override
exceptionResponse() and render a JOT Component error page
with context sensitive content, as in this example:
public void exceptionResponse(
JotServletServiceContext serviceContext,
JotServletException jsex)
throws JotServletException
{
serviceContext.log(jsex.getJotException());
JotViews.serviceRequest(context, MyErrorHandlerJotResponseBean.class);
}
An example of this approach is the PickaNumServlet
exceptionResponse() method.
JotException Request Attribute:
The JOT Views rendering engine throws
JotServletException. JOT JSP tags throw
JotJspException. These events save the JotException object
in the JOT_SERVLET_EXCEPTION Request attribute. The JotException
can be accessed by an error handler, as in this example:
JotException jex = (JotException)
getRequest().getAttribute(JotServletException.JOT_SERVLET_EXCEPTION);
Since Request attributes are automatic properties, the exception can also be
used on a JOT Template as shown in the following example that tests for the
ClientMessage property:
JOT.JOT_SERVLET_EXCEPTION.IfProperty(ClientMessage,"System is totally hosed")
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