/*** @author Clinton Begin* @author Eduardo Macarron*/
public class UnpooledDataSource implements DataSource {private ClassLoader driverClassLoader;private Properties driverProperties;private static Map<String, Driver> registeredDrivers = new ConcurrentHashMap<String, Driver>();//常规配置private String driver;private String url;private String username;private String password;//是否自动commit    事务的隔离级别private Boolean autoCommit;private Integer defaultTransactionIsolationLevel;//注册驱动static {Enumeration<Driver> drivers = DriverManager.getDrivers();while (drivers.hasMoreElements()) {Driver driver = drivers.nextElement();registeredDrivers.put(driver.getClass().getName(), driver);}}public UnpooledDataSource() {}public UnpooledDataSource(String driver, String url, String username, String password) {this.driver = driver;this.url = url;this.username = username;this.password = password;}//重点getconnnection  获取数据库连接，调用doGetConnection方法@Overridepublic Connection getConnection() throws SQLException {return doGetConnection(username, password);}@Overridepublic Connection getConnection(String username, String password) throws SQLException {return doGetConnection(username, password);}//用户名  密码   设置配置private Connection doGetConnection(String username, String password) throws SQLException {Properties props = new Properties();if (driverProperties != null) {props.putAll(driverProperties);}if (username != null) {props.setProperty("user", username);}if (password != null) {props.setProperty("password", password);}return doGetConnection(props);}//真正获取连接的方法，由此可见，每次调用getConnection方法是，都会新建一个Connection对象，可想当并发量高是，数据库的连接就会被占满private Connection doGetConnection(Properties properties) throws SQLException {initializeDriver();Connection connection = DriverManager.getConnection(url, properties);configureConnection(connection);return connection;}//初始化  在调用doGetConnection方法中，会先进行一下判断，判断mybatis的configuration中是否已经有数据库驱动，没有的话会通过反射加载驱动private synchronized void initializeDriver() throws SQLException {if (!registeredDrivers.containsKey(driver)) {Class<?> driverType;try {if (driverClassLoader != null) {driverType = Class.forName(driver, true, driverClassLoader);} else {driverType = Resources.classForName(driver);}// DriverManager requires the driver to be loaded via the system ClassLoader.// http://www.kfu.com/~nsayer/Java/dyn-jdbc.htmlDriver driverInstance = (Driver)driverType.newInstance();DriverManager.registerDriver(new DriverProxy(driverInstance));registeredDrivers.put(driver, driverInstance);} catch (Exception e) {throw new SQLException("Error setting driver on UnpooledDataSource. Cause: " + e);}}}//设置是否自动提交   事务的隔离级别private void configureConnection(Connection conn) throws SQLException {if (autoCommit != null && autoCommit != conn.getAutoCommit()) {conn.setAutoCommit(autoCommit);}if (defaultTransactionIsolationLevel != null) {conn.setTransactionIsolation(defaultTransactionIsolationLevel);}}}

public class PooledDataSource implements DataSource {private static final Log log = LogFactory.getLog(PooledDataSource.class);//PollState 充当锁对象，这个对象中也有例如  空闲连接集合，活跃链接集合，请求的数量，等一些变量private final PoolState state = new PoolState(this);//PolledDataSource中的数据源也是使用的UnpolledDataSource对象来实现的private final UnpooledDataSource dataSource;// OPTIONAL CONFIGURATION FIELDS 线程池的最大活跃数量，最大空闲数量，等待时间等等。。。protected int poolMaximumActiveConnections = 10;protected int poolMaximumIdleConnections = 5;protected int poolMaximumCheckoutTime = 20000;protected int poolTimeToWait = 20000;protected int poolMaximumLocalBadConnectionTolerance = 3;protected String poolPingQuery = "NO PING QUERY SET";protected boolean poolPingEnabled;protected int poolPingConnectionsNotUsedFor;//url+username+password连接起来的字符串的hashcode值private int expectedConnectionTypeCode;public PooledDataSource() {dataSource = new UnpooledDataSource();}public PooledDataSource(UnpooledDataSource dataSource) {this.dataSource = dataSource;}public PooledDataSource(String driver, String url, String username, String password) {dataSource = new UnpooledDataSource(driver, url, username, password);expectedConnectionTypeCode = assembleConnectionTypeCode(dataSource.getUrl(), dataSource.getUsername(), dataSource.getPassword());}//获取连接connection@Overridepublic Connection getConnection() throws SQLException {return popConnection(dataSource.getUsername(), dataSource.getPassword()).getProxyConnection();}@Overridepublic Connection getConnection(String username, String password) throws SQLException {return popConnection(username, password).getProxyConnection();}//线程安全的获取连接的方法（供PooledConnection中调用）  synchronizedprotected void pushConnection(PooledConnection conn) throws SQLException {//所对象为PoolStatesynchronized (state) {state.activeConnections.remove(conn);if (conn.isValid()) {if (state.idleConnections.size() < poolMaximumIdleConnections && conn.getConnectionTypeCode() == expectedConnectionTypeCode) {state.accumulatedCheckoutTime += conn.getCheckoutTime();if (!conn.getRealConnection().getAutoCommit()) {conn.getRealConnection().rollback();}PooledConnection newConn = new PooledConnection(conn.getRealConnection(), this);state.idleConnections.add(newConn);newConn.setCreatedTimestamp(conn.getCreatedTimestamp());newConn.setLastUsedTimestamp(conn.getLastUsedTimestamp());conn.invalidate();if (log.isDebugEnabled()) {log.debug("Returned connection " + newConn.getRealHashCode() + " to pool.");}state.notifyAll();} else {state.accumulatedCheckoutTime += conn.getCheckoutTime();if (!conn.getRealConnection().getAutoCommit()) {conn.getRealConnection().rollback();}conn.getRealConnection().close();if (log.isDebugEnabled()) {log.debug("Closed connection " + conn.getRealHashCode() + ".");}conn.invalidate();}} else {if (log.isDebugEnabled()) {log.debug("A bad connection (" + conn.getRealHashCode() + ") attempted to return to the pool, discarding connection.");}state.badConnectionCount++;}}}private PooledConnection popConnection(String username, String password) throws SQLException {boolean countedWait = false;PooledConnection conn = null;long t = System.currentTimeMillis();int localBadConnectionCount = 0;while (conn == null) {synchronized (state) {//如果state中空闲的连接不为空时，直接从state中的idelConnections集合中获取if (!state.idleConnections.isEmpty()) {// Pool has available connectionconn = state.idleConnections.remove(0);if (log.isDebugEnabled()) {log.debug("Checked out connection " + conn.getRealHashCode() + " from pool.");}} else {//state中的idelConnections集合中没有连接connection了，判断活跃的connection是否小于最大活跃线程数，小于的话就新建一个connection// Pool does not have available connection if (state.activeConnections.size() < poolMaximumActiveConnections) {// Can create new connectionconn = new PooledConnection(dataSource.getConnection(), this);if (log.isDebugEnabled()) {log.debug("Created connection " + conn.getRealHashCode() + ".");}} else {//当前活跃的connection数大于最大活跃connection数是，表明不能新建connection，这种情况下，会判断是否已经超过设定的时间20s，如果超过，会根据是否自动commit，/不是自动提交，会进行rollback操作
// Cannot create new connectionPooledConnection oldestActiveConnection = state.activeConnections.get(0);long longestCheckoutTime = oldestActiveConnection.getCheckoutTime();if (longestCheckoutTime > poolMaximumCheckoutTime) {//判断是否超时// Can claim overdue connectionstate.claimedOverdueConnectionCount++;state.accumulatedCheckoutTimeOfOverdueConnections += longestCheckoutTime;state.accumulatedCheckoutTime += longestCheckoutTime;state.activeConnections.remove(oldestActiveConnection);if (!oldestActiveConnection.getRealConnection().getAutoCommit()) {//判断是否设置了自动提交，不是自动提交的话，会进行rollbacktry {oldestActiveConnection.getRealConnection().rollback();} catch (SQLException e) {/*Just log a message for debug and continue to execute the followingstatement like nothing happend.Wrap the bad connection with a new PooledConnection, this will helpto not intterupt current executing thread and give current thread achance to join the next competion for another valid/good databaseconnection. At the end of this loop, bad {@link @conn} will be set as null.*/log.debug("Bad connection. Could not roll back");}  }//将之前rollback的connection进行处理，重新生成一个connection，并设置创建时间和最后使用时间conn = new PooledConnection(oldestActiveConnection.getRealConnection(), this);conn.setCreatedTimestamp(oldestActiveConnection.getCreatedTimestamp());conn.setLastUsedTimestamp(oldestActiveConnection.getLastUsedTimestamp());oldestActiveConnection.invalidate();if (log.isDebugEnabled()) {log.debug("Claimed overdue connection " + conn.getRealHashCode() + ".");}} else {//当活跃connection的集合中第一个connection不符合超时，则进行等待wait// Must waittry {if (!countedWait) {state.hadToWaitCount++;countedWait = true;}//pooltimeTowait默认也是20秒if (log.isDebugEnabled()) {log.debug("Waiting as long as " + poolTimeToWait + " milliseconds for connection.");}long wt = System.currentTimeMillis();state.wait(poolTimeToWait);state.accumulatedWaitTime += System.currentTimeMillis() - wt;} catch (InterruptedException e) {break;}}}}//经过以上处理，如果conn仍然没有值，则会循环走一行流程，第二次一定会获取到conn对象（默认的超时时间是20秒，第一次已经等待过20s了）if (conn != null) {//判断conn是否能用   通过ping能否ping通// ping to server and check the connection is valid or notif (conn.isValid()) {if (!conn.getRealConnection().getAutoCommit()) {conn.getRealConnection().rollback();}conn.setConnectionTypeCode(assembleConnectionTypeCode(dataSource.getUrl(), username, password));conn.setCheckoutTimestamp(System.currentTimeMillis());conn.setLastUsedTimestamp(System.currentTimeMillis());state.activeConnections.add(conn);state.requestCount++;state.accumulatedRequestTime += System.currentTimeMillis() - t;} else {if (log.isDebugEnabled()) {log.debug("A bad connection (" + conn.getRealHashCode() + ") was returned from the pool, getting another connection.");}state.badConnectionCount++;localBadConnectionCount++;conn = null;if (localBadConnectionCount > (poolMaximumIdleConnections + poolMaximumLocalBadConnectionTolerance)) {if (log.isDebugEnabled()) {log.debug("PooledDataSource: Could not get a good connection to the database.");}throw new SQLException("PooledDataSource: Could not get a good connection to the database.");}}}}}if (conn == null) {if (log.isDebugEnabled()) {log.debug("PooledDataSource: Unknown severe error condition.  The connection pool returned a null connection.");}throw new SQLException("PooledDataSource: Unknown severe error condition.  The connection pool returned a null connection.");}return conn;}
}

 // Pool does not have available connectionif (state.activeConnections.size() < poolMaximumActiveConnections) {// Can create new connectionconn = new PooledConnection(dataSource.getConnection(), this);if (log.isDebugEnabled()) {log.debug("Created connection " + conn.getRealHashCode() + ".");}}

  public PooledConnection(Connection connection, PooledDataSource dataSource) {this.hashCode = connection.hashCode();this.realConnection = connection;this.dataSource = dataSource;this.createdTimestamp = System.currentTimeMillis();this.lastUsedTimestamp = System.currentTimeMillis();this.valid = true;this.proxyConnection = (Connection) Proxy.newProxyInstance(Connection.class.getClassLoader(), IFACES, this);}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {String methodName = method.getName();//判断是否close，如果是close的话，会调用PooledDataSource中的pushConnection方法，将该conn从activeConnections删除，同时将此conn添加到idelConnections中if (CLOSE.hashCode() == methodName.hashCode() && CLOSE.equals(methodName)) {dataSource.pushConnection(this);return null;} else {try {if (!Object.class.equals(method.getDeclaringClass())) {// issue #579 toString() should never fail// throw an SQLException instead of a RuntimecheckConnection();}return method.invoke(realConnection, args);} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}}}