DatabaseManager

public class DatabaseManager {
    private Properties mysqlProperties;
    private List<DatabaseClient> databaseClientList;
    private Thread poolThread;
    private Boolean isAlive = true;

    public DatabaseManager(Properties mysqlProperties) {
        this.mysqlProperties = mysqlProperties;
        this.databaseClientList = new ArrayList<DatabaseClient>();
    }

    public void start() {
        this.startPool();
        this.test();
    }

    public void stop() {
        try {
            // Thread kill.
            this.isAlive = false;
            this.poolThread.join();
            this.poolThread.interrupt();

            // Dispose.
            this.poolThread = null;
            this.mysqlProperties = null;
            this.databaseClientList = null;
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    private void startPool() {
        this.poolThread = new Thread(() -> {
            while(this.isAlive) {
                try {
                    int count = 0;

                    if(this.databaseClientList.size() > 0) {
                        Iterator<DatabaseClient> databaseIterator = this.databaseClientList.iterator();

                        // Killer
                        if(this.databaseClientList.size() > 0) {
                            while(databaseIterator.hasNext()) {
                                DatabaseClient client = (DatabaseClient)databaseIterator.next();
                                if((System.currentTimeMillis() - client.getLastUsed()) > Integer.parseInt(this.mysqlProperties.getProperty("maxDelayTime")) && !client.isUsed()) {
                                    client.dispose();
                                    databaseIterator.remove();
                                    count++;
                                }
                            }
                        }
                        if(count > 0)
                            System.out.println("-> Removed ".concat(String.valueOf(count)).concat(" connection/s"));
                    }

                    // Sleep
                    Thread.sleep(Integer.parseInt(this.mysqlProperties.getProperty("sleepTime")));
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    // e.printStackTrace();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
        this.poolThread.setName("DatabasePool - Nexus");
        this.poolThread.setPriority(Thread.NORM_PRIORITY);
        this.poolThread.start();
    }

    public void test() {
        DatabaseClient testClient = this.generateConnection();
        testClient.finish();
    }

    public DatabaseClient generateConnection() {
        DatabaseClient databaseClient = null;
        try {
            // Is maxPool size.
            while(this.databaseClientList.size() > Integer.parseInt(this.mysqlProperties.getProperty("maxPoolSize"))) {
                System.err.println("MAX POOL SIZE... WAITING FOR A KILL. AUGMENT MYSQL POOL SIZE!");
                Thread.sleep(1000); // STOP ALL... LAG...
            }

            // Are a connection not used?
            if(this.databaseClientList.size() > 0) {
                Iterator<DatabaseClient> databaseIterator = this.databaseClientList.iterator();
                while(databaseIterator.hasNext()) {
                    DatabaseClient client = databaseIterator.next();
                    if((System.currentTimeMillis() - client.getLastUsed()) > (Integer.parseInt(this.mysqlProperties.getProperty("maxDelayTime")) - 1000) && !client.isUsed()) {
                        client.restart();
                        return client;
                    }
                }
            }

            // Create connection.
            Connection temporalConnection = DriverManager.getConnection(this.mysqlProperties.getProperty("url"), this.mysqlProperties.getProperty("user"), this.mysqlProperties.getProperty("pass"));
            databaseClient = new DatabaseClient(temporalConnection);

            // Save connection.
            this.databaseClientList.add(databaseClient);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            databaseClient = null;
        }
        return databaseClient;
    }
}