Java_ConnectionPool

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class ConnectionPool {
    String url;
    List<Connection> available;
    List<Connection> busy;
    private static final int MAX_CONNECTION = 10;

    private ConnectionPool(String url, List<Connection> pool){
        this.url = url;
        this.available = pool;
        busy = new ArrayList<>();
    }

    public static ConnectionPool createPool(String url, int numberOfConnection) throws SQLException {
        if (numberOfConnection > MAX_CONNECTION)
            return null;
        List<Connection> pool = new ArrayList<>();
        for (int i = 0; i < numberOfConnection; i++) {
            pool.add(DriverManager.getConnection(url));
        }
        return new ConnectionPool(url, pool);
    }

    public Connection getConnection() {
        Connection connection = null;
        if (!available.isEmpty()) {
            connection = available.get(available.size() - 1);
            available.remove(connection);
            busy.add(connection);
        }
        return connection;
    }

    public boolean releaseConnection(Connection connection) {
        if (busy.contains(connection)) {
            available.add(connection);
            busy.remove(connection);
            return true;
        }
        return false;
    }

    public void releasePool() throws SQLException {
        for(Connection connection : available) {
            connection.close();
        }
        available.clear();
        for(Connection connection : busy) {
            connection.close();
        }
        busy.clear();
    }

    public int getSize() {
        return available.size() + busy.size();
    }

    public int getNumberAvailable() {
        return available.size();
    }
}