MyBatis基础支持DataSource实现源码解析

package javax.sql;
public interface DataSource  extends CommonDataSource, Wrapper {
  // 最重要的方法
  Connection getConnection() throws SQLException;
  // 其他方法不再列出
}

public Connection getConnection() throws SQLException {
  return doGetConnection(username, password);
}
private Connection doGetConnection(Properties properties) throws SQLException {
  initializeDriver();
  Connection connection = DriverManager.getConnection(url, properties);
  configureConnection(connection);
  return connection;
}

public class PooledDataSource implements DataSource {
  // PooledDataSource真正管理连接状态的是PoolState，后面会详细说明
  private final PoolState state = new PoolState(this);
  // UnpooledDataSource上面说过和普通的Connection无异
  private final UnpooledDataSource dataSource;
  //正在使用连接的数量
  protected int poolMaximumActiveConnections = 10;
  //空闲连接数
  protected int poolMaximumIdleConnections = 5;
  //在被强制返回之前,池中连接被检查的时间
  protected int poolMaximumCheckoutTime = 20000;
  //这是给连接池一个打印日志状态机会的低层次设置,还有重新 尝试获得连接, 这些情况下往往需要很长时间 为了避免连接池没有配置时静默失 败)。
  protected int poolTimeToWait = 20000;
  //发送到数据的侦测查询,用来验证连接是否正常工作,并且准备 接受请求。默认是“NO PING QUERY SET” ,这会引起许多数据库驱动连接由一 个错误信息而导致失败
  protected String poolPingQuery = "NO PING QUERY SET";
  //开启或禁用侦测查询
  protected boolean poolPingEnabled = false;
  //用来配置 poolPingQuery 多次时间被用一次
  protected int poolPingConnectionsNotUsedFor = 0;
  private int expectedConnectionTypeCode;
}

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
  String methodName = method.getName();
  //如果调用close的话，忽略它，反而将这个connection加入到池中
  if (CLOSE.hashCode() == methodName.hashCode() && CLOSE.equals(methodName)) {
    dataSource.pushConnection(this);
    return null;
  } 
  return method.invoke(realConnection, args);
  // 其他逻辑省略....
}

public Connection getConnection() throws SQLException {
  return popConnection(dataSource.getUsername(), dataSource.getPassword()).getProxyConnection();
}
private PooledConnection popConnection(String username, String password) throws SQLException {
  //最外面是while死循环，如果一直拿不到connection，则不断尝试
  while (conn == null) {
    synchronized (state) {
      if (!state.idleConnections.isEmpty()) {
        //如果有空闲的连接的话，返回第一个空闲连接
        conn = state.idleConnections.remove(0);
      } else {
        //如果没有空闲的连接
        if (state.activeConnections.size() < poolMaximumActiveConnections) {
          //如果activeConnections太少,那就new一个PooledConnection
          conn = new PooledConnection(dataSource.getConnection(), this);
        } else {
          //如果activeConnections已经很多了，那不能再new了
          //取得activeConnections列表的第一个（最老的）
          PooledConnection oldestActiveConnection = state.activeConnections.get(0);
          long longestCheckoutTime = oldestActiveConnection.getCheckoutTime();
          if (longestCheckoutTime > poolMaximumCheckoutTime) {
            //如果checkout时间过长，则这个connection标记为overdue（过期）
            //删掉最老的连接，然后再new一个新连接
            conn = new PooledConnection(oldestActiveConnection.getRealConnection(), this);
            oldestActiveConnection.invalidate();
          } else {
            //如果checkout时间不够长，没办法，只能等待，在此分支会记录一些统计信息
          }
        }
      }
      if (conn != null) {
        if (conn.isValid()) {
          //如果已经拿到connection，则记录一些统计信息
        } else {
          //如果没拿到，统计信息：坏连接+1
          state.badConnectionCount++;
          localBadConnectionCount++;
          conn = null;
          //如果好几次都拿不到，就放弃了，抛出异常
        }
      }
    }
  }
  return conn;
}

protected void pushConnection(PooledConnection conn) throws SQLException {
  synchronized (state) {
    //先从activeConnections中删除此connection
    state.activeConnections.remove(conn);
    if (conn.isValid()) {
      if (state.idleConnections.size() < poolMaximumIdleConnections && conn.getConnectionTypeCode() == expectedConnectionTypeCode) {
        //如果空闲的连接太少，
        state.accumulatedCheckoutTime += conn.getCheckoutTime();
        if (!conn.getRealConnection().getAutoCommit()) {
          conn.getRealConnection().rollback();
        }
        //new一个新的Connection，加入到idle列表
        PooledConnection newConn = new PooledConnection(conn.getRealConnection(), this);
        state.idleConnections.add(newConn);
        //通知其他线程可以来抢connection了
        state.notifyAll();
      } else {
       //否则，即空闲的连接已经足够了
        state.accumulatedCheckoutTime += conn.getCheckoutTime();
        //那就将connection关闭就可以了，获取真正的connection对象并且关闭
        conn.getRealConnection().close();
        conn.invalidate();
      }
    } 
  }
}

public interface DataSourceFactory {
  //设置属性,被XMLConfigBuilder所调用
  void setProperties(Properties props);
  //生产数据源,直接得到javax.sql.DataSource
  DataSource getDataSource();
}

public class UnpooledDataSourceFactory implements DataSourceFactory {
  protected DataSource dataSource;
  public UnpooledDataSourceFactory() {
    this.dataSource = new UnpooledDataSource();
  }
  public DataSource getDataSource() {
    return dataSource;
  }
}

public class PooledDataSourceFactory extends UnpooledDataSourceFactory {
  //数据源换成了PooledDataSource
  public PooledDataSourceFactory() {
    this.dataSource = new PooledDataSource();
  }
}