Exam Notes
for the Sun Certified Web Component Developer (SCWCD) Exam
4. Designing and
Developing Servlets to Handle Server-Side Exceptions
4.1. For each of
the following cases, identify correctly constructed code
for handling business logic exceptions, and match that
code with correct statements about the code's behavior:
4.1.1. return an
http error using setStatus
4.1.1.1. public void HttpServletResponse.setStatus(int
statusCode)
4.1.1.2. if this is not called, the server by default sets
the status code to SC_OK(200).
4.1.1.3. example status codes:
HttpServletResponse.SC_OK(200), SC_NOT_FOUND(404),
SC_NO_CONTENT, SC_MOVED_TEMPORARILY/PERMANENTLY,
SC_UNAUTHORIZED, SC_INTERNAL_SERVER_ERROR,
SC_NOT_IMPLEMENTED, SC_SERVICE_UNAVAILABLE
4.1.1.4. calling setStatus() on an error leaves a servlet
with the responsibility of generating the error page
4.1.1.5. must be called before the response is committed,
otherwise call is ignored
4.1.2. return an http error using sendError
4.1.2.1. public void HttpServletResponse.sendError(int
statusCode[, String statusMessage]) throws
IllegalStateException, IOException
4.1.2.2. the sendError() method causes the server to
generate and send an appropriate server-specific page
describing the error (unless <error-page> defined in
web.xml)
4.1.2.3. with the two argument version of this method, the
server may include the status message in the error page,
depending on the server implementation
4.1.2.4. must be called before response body is committed,
else throws IllegalStateException
4.2. Given a set
of business logic exceptions, identify the following:
4.2.1. configuring
deployment descriptor for error handling
4.2.1.1. <web-app> …
<error-page>
<error-code>404</ error-code>
<location> /404.html </location>
</error-page> …
</web-app>
4.2.1.2. this specifies that any call to sendError(), from
within this web app, with 404 error code should display
/404.html; this includes requests for static pages that
result in 404 error code
4.2.1.3. the value of location must begin with '/', is
treated as based in the context root, and must refer to a
resource within the context
4.2.1.4. <location> may be dynamic (e.g. jsp,
servlet); for these, the server makes available the
following request attributes:
javax.servlet.error.status_code and
javax.servlet.error.message
4.2.2. configuring deployment descriptor for exception
handling
4.2.2.1. <web-app> …
<error-page>
<exception-type> javax.servlet.ServletException</
exception-type >
<location> /servlet/ErrorDisplay </location>
</error-page> …
</web-app>
4.2.2.2. how the server handles exceptions thrown by a
servlet is server-dependent, unless an <error-page>
entry exists for a specific exception type or a superclass
4.2.2.3. <location> may be dynamic (e.g. jsp,
servlet); for these, the server makes available the
following request attributes:
javax.servlet.error.exception_type &
javax.servlet.error.message; the exception object itself
is not made available; hence no way to get a stack trace
4.2.2.4. servlets must catch all exceptions except those
that subclass ServletException, IOException and
RuntimeException (IOException may be caused by client
closing the socket by exiting the browser)
4.2.2.5. a ServletException may be created with a message
and a "root cause", both optional, e.g. { throw
new ServletException("execution interrupted",
InterruptedException); }
4.2.2.6. public Throwable ServletException.getRootCause()
returns the root cause exception
4.2.2.7. javax.servlet package also defines a subclass of
ServletException called UnavailableException(String msg[,
int seconds]), which causes server to take servlet out of
service
4.2.3. using RequestDispatcher to forward to an error
page: see section 1.6 above
4.3. Identify the
method used for the following:
4.3.1. writing a
message to the Web App log:
4.3.1.1. void log(String msg) - Writes the specified
message to a servlet log file, usually an event log.
4.3.1.2. void log(String message, java.lang.Throwable
throwable) - Writes an explanatory message and a stack
trace for a given Throwable exception to the servlet log
file.
4.3.1.3. these are methods are available in GenericServlet
and ServletContext
4.3.2. writing a message and an exception to the Web App
log:
4.3.2.1. public void GenericServlet.log(String msg,
Throwable t)
4.3.2.2. writes the given message and the Throwable's
stack trace to a servlet log; exact output format and
location of log are server specific
Java
SCJP 6 Exam Download
Java
SCJP 6 Exam Details
Previous
Contents
Next
|
