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java.lang.Objectjava.lang.Throwable
java.lang.Exception
javax.servlet.ServletException
javax.servlet.UnavailableException
public class UnavailableException
Defines an exception that a servlet throws to indicate that it is permanently or temporarily unavailable.
When a servlet is permanently unavailable, something is wrong with the servlet, and it cannot handle requests until some action is taken. For example, the servlet might be configured incorrectly, or its state may be corrupted. A servlet should log both the error and the corrective action that is needed.
A servlet 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 for a period of time suggested by the exception, rather than rejecting them until the servlet container restarts.
Constructor Summary | |
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UnavailableException(int seconds,
Servlet servlet,
String msg)
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UnavailableException(Servlet servlet,
String msg)
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Method Summary | |
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Servlet |
getServlet()
Returns the servlet that is reporting its unavailability. |
int |
getUnavailableSeconds()
Returns the number of seconds the servlet expects to be temporarily unavailable. |
boolean |
isPermanent()
Returns a boolean indicating
whether the servlet is permanently unavailable. |
Methods inherited from class javax.servlet.ServletException |
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getRootCause |
Methods inherited from class java.lang.Throwable |
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fillInStackTrace, getCause, getLocalizedMessage, getMessage, getStackTrace, initCause, printStackTrace, printStackTrace, printStackTrace, setStackTrace, toString |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
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public UnavailableException(Servlet servlet, String msg)
servlet
- the Servlet
instance that is
unavailablemsg
- a String
specifying the
descriptive messagepublic UnavailableException(int seconds, Servlet servlet, String msg)
seconds
- an integer specifying the number of seconds
the servlet expects to be unavailable; if
zero or negative, indicates that the servlet
can't make an estimateservlet
- the Servlet
that is unavailablemsg
- a String
specifying the descriptive
message, which can be written to a log file or
displayed for the user.Method Detail |
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public boolean isPermanent()
boolean
indicating
whether the servlet is permanently unavailable.
If so, something is wrong with the servlet, and the
system administrator must take some corrective action.
true
if the servlet is
permanently unavailable; false
if the servlet is available or temporarily
unavailablepublic Servlet getServlet()
Servlet
object that is
throwing the UnavailableException
public int getUnavailableSeconds()
If this method returns a negative number, the servlet is permanently unavailable or cannot provide an estimate of how long it will be unavailable. No effort is made to correct for the time elapsed since the exception was first reported.
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