Connection pool implementation

package testconnpoolproject;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;

public abstract class TestPool<T> {
    long             deadTime;
    HashMap<T, Long> available;
    HashMap<T, Long> used;

    TestPool() {
        deadTime = 50 * 1000;
        available = new HashMap<T, Long>();
        used = new HashMap<T, Long>();
    }

    abstract T create();

    abstract long dead(T o);

    abstract boolean validate(T o);

    synchronized void putBack(T obj) {
        used.remove(obj);
        available.put(obj, System.currentTimeMillis());
    }

    synchronized T getObject() {
        long cuTime = System.currentTimeMillis();
        T t = null;
        if (available.size() > 0) {
            Set<T> keys = available.keySet();
            if (keys != null && keys.size() > 0) {
                Iterator<T> iter = keys.iterator();
                if (iter.hasNext()) {
                    t = iter.next();
                    Long sleepTime = available.get(t);
                    if ((cuTime - sleepTime) > deadTime) {
                        available.remove(t);
                        dead(t);
                        t = null;
                    } else {
                        if (validate(t)) {
                            available.remove(t);
                            used.put(t, cuTime);
                            return (t);
                        } else {
                            available.remove(t);
                            dead(t);
                            t = null;
                        }
                    }
                }
            }
        }

        t = create();
        available.put(t, cuTime);
        return t;
    }

}


package testconnpoolproject;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class MyConnectionPool extends TestPool<Connection> {
    String dsn, usr, pwd;

    MyConnectionPool(String driver, String dsn, String usr, String pwd) {
        super();
        try {
            Class.forName(driver).newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }
        this.dsn = dsn;
        this.usr = usr;
        this.pwd = pwd;
    }

    @Override
    Connection create() {
        try {
            return DriverManager.getConnection(dsn, usr, pwd);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    long dead(Connection o) {
        try {
            o.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return 0;
    }

    @Override
    boolean validate(Connection o) {
        try {
            return (!((Connection) o).isClosed());
        } catch (SQLException e) {
            e.printStackTrace();
            return (false);
        }
    }

}


public class ConnectionPool {
    public static void main() {
        MyConnectionPool conn = new MyConnectionPool("org.hsqldb.jdbcDriver", "jdbc:hsqldb: //localhost/mydb", "sa",
                "password");
        conn.getObject();
    }
}