Error handling
When an error occurs on the Web tier, the Web Service returns an HTTP error to the browser. The UNICOM Intelligence Interviewer Server ISAPI extension uses different HTTP error codes for the various failure conditions, and you can customize or translate the error pages: see
Customizing web service tier error pages.
HTTP client errors
A client error is one where a program has made an invalid request to the Web tier. Examples of invalid client requests are:
▪A request that fails to specify either a Project or Session parameter
▪A request that has a Session parameter but no Engine parameter.
▪A request for a project that does not exist.
▪A request that cannot be interpreted by the specified HTML Player.
Client errors are mapped to HTTP 400 series errors. UNICOM Intelligence Interviewer uses the following 400 series error codes:
HTTP error: 400 Bad Request
Used whenever a required parameter is missing or the parameters cannot be interpreted.
HTTP error: 404 Not Found
Returned whenever a request is made for a Project or Session that does not exist.
A Warning level message is added to the ISE*.tmp log file whenever the Web tier returns a 400 series error. As client errors (such as a misspelled project name) can occur as part of normal operation, they are not treated as server-side errors.
HTTP server errors
A server error is one that arises when the Web tier cannot handle a request because a part of the system is unavailable. Examples of server failures include:
▪No session engines are registered to handle the request.
▪All of the session engines are at maximum load.
▪An unrecoverable error occurred rendering the page.
Server errors are mapped to HTTP 500 series errors. UNICOM Intelligence Interviewer uses the following 500 series error codes:
500 Internal Server Error
A general error has occurred either during initialization or normal operation that has made the Web tier unavailable.
503 Service Unavailable Sub code 1
No session engines are available to handle the request.
503 Service Unavailable Sub code 2
All of the session engines are at maximum percent loaded.
503 Service Unavailable Sub code 3
An error occurred processing the page.
An Error level message is added to the ISE*.tmp log file whenever the Web tier returns a 500 series error.
See also