Hi all,
the docs at <http://jakarta.apache.org/commons/httpclient/threading.html> state
that this is the recommended way of using HttpClient to ensure connections are
released:
try {
client.executeMethod(get);
...
} finally {
get.releaseConnection();
}
Now, this is counterintuitive to me. I'd expect the usage to be:
client.executeMethod(get);
try {
...
} finally {
get.releaseConnection();
}
since it's the contract of all well-behaved libraries I came across to date that
methods that exit abruptly (i.e. throw an exception) must not leave any
resources allocated. Therefore, it must be safe to call executeMethod()
*outside* the try block, since if it exits with an exception, the connection
will not be allocated. I took the time to actually go through the source code of
HttpClient 2.0, and have found out that:
- HttpClient.java lines 650-678 make sure that the connection object gets
released if the connection can't be established.
- HttpMethodBase.java lines 2663-2696 make sure that the connection is closed if
an exception is encountered during sending request/receiving response.
These catch blocks have the "doneWithConnection = true" statement that'll in
turn cause releasing of the connection object in HttpMethodBase.java,
lines 1122-1124.
The only case an already allocated connection object won't get released in a
failed call to executeMethod() is in two cases of incorrect usage by the
library's client. These are:
- a HttpMethod object is reused without being recycle()d first, (exception
thrown in HttpMethodBase.java line 1007).
- preemptive authentication is used, but the supplied credentials aren't
username/password but some other kind of credentials (exception thrown in
HttpAuthenticator.java line 204).
(Now, you could claim that these conditions are incorrect usage of the library
and that you feel no obligation to release the connection under these
circumstances, but IMHO you should.)
Anyway, it'd be good if the documentation at the URL cited above would be
changed to indicate that the executeMethod() should be called *outside* the try
block - I think it's just the standard rule for all well-behaved libraries that
users of the library are expected to release a resource only after the method
that allocated the resource completes normally.
Regards,
Attila.
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