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's 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.
| Modifier and Type | Field and Description |
|---|---|
| private final boolean | |
| private int | |
| private static final long |
| Access | Constructor and Description |
|---|---|
| public | UnavailableException(String
a msg)String specifying the descriptive messageConstructs a new exception with a descriptive message indicating that the servlet is permanently unavailable. |
| public | UnavailableException(String
a msg, int String specifying the descriptive message, which can be written to a log file or displayed
for the user.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 estimate seconds)Constructs a new exception with a descriptive message indicating that the servlet is temporarily unavailable and giving an estimate of how long it will be unavailable. |
| Modifier and Type | Method and Description |
|---|---|
| public int | Returns: an integer specifying the number of seconds the servlet will be temporarily unavailable, or a negative number if the servlet is permanently unavailable or cannot make an estimateReturns the number of seconds the servlet expects to be temporarily unavailable. |
| public boolean | Returns: true if the servlet is permanently unavailable; false if the servlet is available
or temporarily unavailableReturns a |
| permanent | back to summary |
|---|---|
| private final boolean permanent | |
| seconds | back to summary |
|---|---|
| private int seconds | |
| serialVersionUID | back to summary |
|---|---|
| private static final long serialVersionUID | |
| UnavailableException | back to summary |
|---|---|
| public UnavailableException(String msg) Constructs a new exception with a descriptive message indicating that the servlet is permanently unavailable.
| |
| UnavailableException | back to summary |
|---|---|
| public UnavailableException(String msg, int seconds) Constructs a new exception with a descriptive message indicating that the servlet is temporarily unavailable and giving an estimate of how long it will be unavailable.
In some cases, the servlet cannot make an estimate. For example, the servlet might know that a server it needs is not
running, but not be able to report how long it will take to be restored to functionality. This can be indicated with
a negative or zero value for the
| |
| getUnavailableSeconds | back to summary |
|---|---|
| public int getUnavailableSeconds() Returns the number of seconds the servlet expects to be temporarily unavailable. 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.
| |
| isPermanent | back to summary |
|---|---|
| public boolean isPermanent() Returns a
| |