CODEWITHSUNDEEP
javapool
Ibolit
Ibolit

Reputation: 9720

java, object pool: make object unusable after it is returned to the pool?

I am writing an SshConnectionPool, which stores and returns SshConnections. The idea is that a user should do something like this: 

SshConnection sc = SshPool.getInstance().getConnection(server, user, password, port);
// use connection in some way
SshPool.getInstance().release(sc);

And after that I want the sc reference to be unusable. I know I can't set it to null in the implementation of the release() method. But how can I do that?

Upvotes: 0

Views: 298

Answers (3)

Ibolit
Ibolit

Reputation: 9720

For the brave who will someday follow my footsteps:

What I did eventually was: I declared the SshSession as an interface and created 3 implementations of it: a real/live/working session (RealSession) which has all functionality, the variables are set to real values and methods do real work (e.g. exec(String command) will execute a command on a remote machine), a dummy session (DummySession) which has all the ivars, but throws exceptions when "doing" methods are called (e.g., it returns real host name on ssh.hostname(), but throws an exception on ssh.exec(command), and a session wrapper that has an SshSession implementation within it and all the methods in the session wrapper call the corresponding methods on the wrapped session.

The SshPool stores within it a map of RealSessions, but returns a SessionWrapper with a RealSession wrapped into it. So outside of the pool you can only deal with SessionWrappers. Thus, when you call pool.release(sessionwrapper), the pool returns the session from the wrapper into the pool, and puts a DummySession into the wrapper. That way you can still access the info about the session (e.g. host, user, etc), but cannot call any methods on it.

I know some code would not go amiss, but I hope the description is clear enough.

Upvotes: 0

fge
fge

Reputation: 121780

No idea how you will "reuse" SshConnection objects but anyway, my suggestion is that you:

  • add a parameter to its constructor which is the SshPool itself;
  • make the SshConnection object implement Closeable, and in .close(), give the object back to the pool.

As in:

private final SshPool pool;

SshConnection(final SshPool pool, other parameters)
{
    this.pool = pool;
    // etc
}

@Override
public void close()
    throws IOException
{
    pool.release(this);
    // other instructions here
}

This means among other things that you'll be able to use such objects in a try-with-resources statement; and the only requirement on the user of the API is that they .close() once used, which they should do anyway for any Closeable object.

Upvotes: 2

Th3Nic3Guy
Th3Nic3Guy

Reputation: 1979

If i understood the question correct..then u need to make the class as immutable

with that the object instance will be usable by the variable but for any change the object will be discarded and a new instance will be created

how to make immutable

Upvotes: 0

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