JDBC 使用连接池查询

Question

I have a connection pool interface:

public interface ConnectionPool {
    Connection getConnection() throws SQLException;
    boolean releaseConnection(Connection connection);
}

I need to implement this methods. I found an example of realization of connection pool. Here is the code:

public class ConnectionPoolImpl implements ConnectionPool{

    private List<Connection>availableConnections = new ArrayList<Connection>();
    private List<Connection>usedConnections = new ArrayList<Connection>();
    private final int MAX_CONNECTIONS = 5;

    private String URL;
    private String USERID;
    private String PASSWORD;


    /** Initialize all 5 Connections and put them in the Pool **/
    public ConnectionPoolImpl(String Url, String UserId, String password) throws SQLException {
        this.URL = Url;
        this.USERID = UserId;
        this.PASSWORD = password;

        for (int count = 0; count <MAX_CONNECTIONS; count++) {
            availableConnections.add(this.createConnection());
        }
    }

    /** Private function,
     used by the Pool to create new connection internally **/

    private Connection createConnection() throws SQLException {
        return DriverManager
                .getConnection(this.URL, this.USERID, this.PASSWORD);
    }


    /** Public function, used by us to get connection from Pool **/
    public Connection getConnection() {
        if (availableConnections.size() == 0) {
            System.out.println("All connections are Used !!");
            return null;
        } else {
            Connection con =
                    availableConnections.remove(
                            availableConnections.size() - 1);
            usedConnections.add(con);
            return con;
        }
    }

    /** Public function, to return connection back to the Pool **/
    public boolean releaseConnection(Connection con) {
        if (null != con) {
            usedConnections.remove(con);
            availableConnections.add(con);
            return true;
        }
        return false;
    }

    /** Utility function to check the number of Available Connections **/
    public int getFreeConnectionCount() {
        return availableConnections.size();
    }

}

Now I have a problem of using this pool in my DAO.

My DAO realization:

public class EmployeeImpl implements Employee {

private ConnectionPool connectionPool;

public Employee getById(Long id) {
        try (Connection connection = connectionPool.getConnection();
            PreparedStatement statement = connection.prepareStatement(SELECT_QUERY))
        {
       // 
            }
    

     return employee;
}

I dont know how its better to connect to my pool. Better create object ConnectionPoolImpl like this in my EmployeeImpl class:

ConnectionPoolImpl conn = new ConnectionPoolImpl("MyUrl", "user", "password");

and then conn.getConnection to each my query. But this realization doesn't include my interface (field). How it is better to connect to my pool? The only constraint is I need to implement my interface. Explanation will be appreciated.

Answer 1

I would use like HikariCP connection pooling library to handle database connection pool effectively and configure the number of connections than handling it as described in your questions because there are a lot of things to take care which in my view better to use these kind of pooling library and wrap it to the implementation of ConnectionPool .

For the implementation I would prefer to have constructor in EmployeeImpl with parameter ConnectionPool . I would create ConnectionPool instance with ConnectionPool conn = new ConnectionPoolImpl("MyUrl", "user", "password");and while creating EmployeeImpl instance I would pass the conn in this way my EmployeeImpl is tied to the interface not the implementation which gives me the flexibility of changing the ConnectionPool implementation and does not require any kind of update in EmployeeImpl if I want to create another implementation of ConnectionPool .