Many methods in the JNDI packages throw a
NamingException when they need to indicate that the operation requested cannot
be performed.
Commonly, you will see a
try/catch
wrapper around the methods that can throw a
NamingException:
try {
Context ctx = new InitialContext();
Object obj = ctx.lookup("somename");
} catch (NamingException e) {
// Handle the error
System.err.println(e);
}
Exception Class Hierarchy
The JNDI has a rich exception hierarchy stemming from
the NamingException class.
The class names of the exceptions are self-explanatory and are listed
here .
To handle a particular subclass of
NamingException specially, you catch the
subclass separately.
For example, the following code specially treats the AuthenticationException
and its subclasses.
try {
Context ctx = new InitialContext();
Object obj = ctx.lookup("somename");
} catch (AuthenticationException e) {
// attempt to reacquire the authentication information
...
} catch (NamingException e) {
// Handle the error
System.err.println(e);
}
Enumerations
Operations such as
Context.list()
and
DirContext.search() return a
NamingEnumeration . In
these cases, if an error occurs and no results are returned,
then
NamingException or one of its appropriate subclasses will be
thrown at the time that the method is invoked. If an error occurs but
there are some results to be returned, then a
NamingEnumeration is
returned so that you can get those results. When all of the results are
exhausted, invoking
NamingEnumeration.hasMore() will cause a
NamingException (or one of its subclasses) to be
thrown to indicate the
error. At that point, the enumeration becomes invalid and no more
methods should be invoked on it.
For example, if you perform a search() and specify a
count limit (n) of how many answers to return,
then the search()
will return an enumeration consisting of at most n
results. If the number of results exceeds n, then
when NamingEnumeration.hasMore() is invoked for the n+1
time, a SizeLimitExceededException will be thrown.
See the count limit discussion
of this lesson for a sample code.
Examples in This Tutorial
In the inline sample code that is embedded within the text of
this tutorial, the
try/catch clauses are usually omitted for
the sake of readability. Typically, because only code
fragments are shown here, only the lines that are directly useful in
illustrating a concept are included.
You will see appropriate placements of the
try/catch clauses for
NamingException
if you look in the source files that
accompany this tutorial.
The Exceptions in the javax.naming package can be found
here .
