Java-Beispiel zum Veranschaulichen von Verbindungspooling

GILT FÜR: Azure-Datenbank für MySQL - Single Server

Wichtig

Azure Database for MySQL Single Server wird eingestellt. Es wird dringend empfohlen, ein Upgrade auf Azure Database for MySQL Flexible Server auszuführen. Weitere Informationen zum Migrieren zu Azure Database for MySQL Flexible Server finden Sie unter Was geschieht mit Azure Database for MySQL Single Server?

Der folgende Beispielcode veranschaulicht das Verbindungspooling in Java.

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.HashSet;
import java.util.Set;
import java.util.Stack;

public class MySQLConnectionPool {
	private String databaseUrl;
	private String userName;
	private String password;
	private int maxPoolSize = 10;
	private int connNum = 0;

	private static final String SQL_VERIFYCONN = "select 1";

	Stack<Connection> freePool = new Stack<>();
	Set<Connection> occupiedPool = new HashSet<>();

	/**
	 * Constructor
	 * 
	 * @param databaseUrl
	 *            The connection url
	 * @param userName
	 *            user name
	 * @param password
	 *            password
	 * @param maxSize
	 *            max size of the connection pool
	 */
	public MySQLConnectionPool(String databaseUrl, String userName,
			String password, int maxSize) {
		this.databaseUrl = databaseUrl;
		this.userName = userName;
		this.password = password;
		this.maxPoolSize = maxSize;
	}

	/**
	 * Get an available connection
	 * 
	 * @return An available connection
	 * @throws SQLException
	 *             Fail to get an available connection
	 */
	public synchronized Connection getConnection() throws SQLException {
		Connection conn = null;

		if (isFull()) {
			throw new SQLException("The connection pool is full.");
		}

		conn = getConnectionFromPool();

		// If there is no free connection, create a new one.
		if (conn == null) {
			conn = createNewConnectionForPool();
		}

		// For Azure Database for MySQL, if there is no action on one connection for some
		// time, the connection is lost. By this, make sure the connection is
		// active. Otherwise reconnect it.
		conn = makeAvailable(conn);
		return conn;
	}

	/**
	 * Return a connection to the pool
	 * 
	 * @param conn
	 *            The connection
	 * @throws SQLException
	 *             When the connection is returned already or it isn't gotten
	 *             from the pool.
	 */
	public synchronized void returnConnection(Connection conn)
			throws SQLException {
		if (conn == null) {
			throw new NullPointerException();
		}
		if (!occupiedPool.remove(conn)) {
			throw new SQLException(
					"The connection is returned already or it isn't for this pool");
		}
		freePool.push(conn);
	}

	/**
	 * Verify if the connection is full.
	 * 
	 * @return if the connection is full
	 */
	private synchronized boolean isFull() {
		return ((freePool.size() == 0) && (connNum >= maxPoolSize));
	}

	/**
	 * Create a connection for the pool
	 * 
	 * @return the new created connection
	 * @throws SQLException
	 *             When fail to create a new connection.
	 */
	private Connection createNewConnectionForPool() throws SQLException {
		Connection conn = createNewConnection();
		connNum++;
		occupiedPool.add(conn);
		return conn;
	}

	/**
	 * Crate a new connection
	 * 
	 * @return the new created connection
	 * @throws SQLException
	 *             When fail to create a new connection.
	 */
	private Connection createNewConnection() throws SQLException {
		Connection conn = null;
		conn = DriverManager.getConnection(databaseUrl, userName, password);
		return conn;
	}

	/**
	 * Get a connection from the pool. If there is no free connection, return
	 * null
	 * 
	 * @return the connection.
	 */
	private Connection getConnectionFromPool() {
		Connection conn = null;
		if (freePool.size() > 0) {
			conn = freePool.pop();
			occupiedPool.add(conn);
		}
		return conn;
	}

	/**
	 * Make sure the connection is available now. Otherwise, reconnect it.
	 * 
	 * @param conn
	 *            The connection for verification.
	 * @return the available connection.
	 * @throws SQLException
	 *             Fail to get an available connection
	 */
	private Connection makeAvailable(Connection conn) throws SQLException {
		if (isConnectionAvailable(conn)) {
			return conn;
		}

		// If the connection is't available, reconnect it.
		occupiedPool.remove(conn);
		connNum--;
		conn.close();

		conn = createNewConnection();
		occupiedPool.add(conn);
		connNum++;
		return conn;
	}

	/**
	 * By running a sql to verify if the connection is available
	 * 
	 * @param conn
	 *            The connection for verification
	 * @return if the connection is available for now.
	 */
	private boolean isConnectionAvailable(Connection conn) {
		try (Statement st = conn.createStatement()) {
			st.executeQuery(SQL_VERIFYCONN);
			return true;
		} catch (SQLException e) {
			return false;
		}
	}
	
	// Just an Example
	public static void main(String[] args) throws SQLException {
		Connection conn = null;
		MySQLConnectionPool pool = new MySQLConnectionPool(
				"jdbc:mysql://mysqlaasdevintic-sha.cloudapp.net:3306/<Your DB name>",
				"<Your user>", "<Your Password>", 2);
		try {
			conn = pool.getConnection();
			try (Statement statement = conn.createStatement())
			{
				ResultSet res = statement.executeQuery("show tables");
				System.out.println("There are below tables:");
				while (res.next()) {
					String tblName = res.getString(1);
					System.out.println(tblName);
				}
			}
		}
		 finally {
			if (conn != null) {
				pool.returnConnection(conn);
			}
		}
	}

}