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ServletExceptions doubt!

 
Joe Harry
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What is the difference between ServletException and UnavailableException, also in the service method, we only declare ServletException and does it mean that UnavailableException is a kind of RunTimeException that we don't have to explicitly declare in the service method?? Also what it means by saying Temporary Unavailability and Permanant Unavailability??
 
Joe Harry
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Any help guys?
 
Sergio Tridente
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Hi Jothi,

UnavailableException extends ServletException, so it is OK to throw UnavailableExceptiom from service() method.

Also, UnavailableException has a "permanent" boolean property (i.e. there is a isPermanent() method that returns a boolean). This is what the spec says about this in section SRV.14.2.25:


When a servlet or filter is permanently unavailable, something is wrong with it, and it cannot handle requests until some action is taken. For example, a servlet might be configured incorrectly, or a filter´┐Żs state may be corrupted. The component should log both the error and the corrective action that is needed.
A servlet or filter is temporarily unavailable if it cannot handle requests momentarily due to some system-wide problem. For example, a third-tier server might not be accessible, or there may be insufficient memory or disk storage to handle requests. A system administrator may need to take corrective action.
Servlet containers can safely treat both types of unavailable exceptions in the same way. However, treating temporary unavailability effectively makes the servlet container more robust. Specifically, the servlet container might block requests to the servlet or filter for a period of time suggested by the exception, rather than rejecting them until the servlet container restarts.
 
Joe Harry
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Ok..I got this now. Thanks Sergio!
 
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