Are there any good tutorials or examples on how to use Java ObjectPool/pools?

Question

I am trying to create a pool of channels/connections to a queue server and was trying to use ObjectPool but am having trouble using it from the example on their site.

So far I have threads that do work but I want each of them to grab a channel from the pool and then return it. I understand how to use it(borrowObject/returnObjects) but not sure how to create the intial pool.

Here's how channels are made in rabbitmq:

ConnectionFactory factory = new ConnectionFactory();
    factory.setHost("localhost");
    Connection connection = factory.newConnection();
    Channel channel = connection.createChannel();

and my code just uses channel to do stuff. I'm confused because the only example I could find (on their site) starts it like this:

private ObjectPool<StringBuffer> pool;

    public ReaderUtil(ObjectPool<StringBuffer> pool) { 
        this.pool = pool;
    }

Which does not make sense to me. I realized this is common to establishing database connections so I tried to find tutorials using databases and ObjectPool but they seem to use DBCP which is specific to databases(and I can't seem to use the logic for my queue server).

Any suggestions on how to use it? Or is there a another approach used for pools in java?

Answer 1

They create a class that creates objects & knows what to do when they are returned. That might be something like this for you:

public class PoolConnectionFactory extends BasePoolableObjectFactory<Connection> { 

    private final ConnectionFactory factory;
    public PoolConnectionFactory() {
        factory = new ConnectionFactory();
        factory.setHost("localhost");
    }

    // for makeObject we'll simply return a new Connection
    public Connection makeObject() { 
        return factory.newConnection();
    } 

    // when an object is returned to the pool,  
    // we'll clear it out 
    public void passivateObject(Connection con) { 
        con.I_don't_know_what_to_do(); 
    } 

    // for all other methods, the no-op  
    // implementation in BasePoolableObjectFactory 
    // will suffice 
}

now you create a ObjectPool<Connection> somewhere:

ObjectPool<Connection> pool = new StackObjectPool<Connection>(new PoolConnectionFactory());

then you can use pool inside your threads like

Connection c = pool.borrowObject();
c.doSomethingWithMe();
pool.returnObject(c);

The lines that don't make sense to you are a way to pass the pool object to a different class. See last line, they create the pool while creating the reader.

new ReaderUtil(new StackObjectPool<StringBuffer>(new StringBufferFactory()))