MyBatis 源码篇-DataSource

public class C3P0DataSourceFactory extends UnpooledDataSourceFactory {

  public C3P0DataSourceFactory() {
    this.dataSource = new ComboPooledDataSource();
  }
}

<dataSource type="org.myproject.C3P0DataSourceFactory">
  <property name="driver" value="org.postgresql.Driver"/>
  <property name="url" value="jdbc:postgresql:mydb"/>
  <property name="username" value="postgres"/>
  <property name="password" value="root"/>
</dataSource>

private DataSourceFactory dataSourceElement(XNode context) throws Exception {
  if (context != null) {
    String type = context.getStringAttribute("type");
    Properties props = context.getChildrenAsProperties();
    // 根据type属性中配置的类路径生成对应的数据源工厂类
    DataSourceFactory factory = (DataSourceFactory) resolveClass(type).newInstance();
    // 为数据源设置配置的属性
    factory.setProperties(props);
    return factory;
  }
  throw new BuilderException("Environment declaration requires a DataSourceFactory.");
}

class PooledConnection implements InvocationHandler {

  private static final String CLOSE = "close";
  private static final Class<?>[] IFACES = new Class<?>[] { Connection.class };

  private final int hashCode;
  private final PooledDataSource dataSource;
  private final Connection realConnection;
  private final Connection proxyConnection;
  private long checkoutTimestamp;
  private long createdTimestamp;
  private long lastUsedTimestamp;
  private int connectionTypeCode;
  private boolean valid;

  /*
   * Constructor for SimplePooledConnection that uses the Connection and PooledDataSource passed in
   *
   * @param connection - the connection that is to be presented as a pooled connection
   * @param dataSource - the dataSource that the connection is from
   */
  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;
    // 创建代理对象
    this.proxyConnection = (Connection) Proxy.newProxyInstance(Connection.class.getClassLoader(), IFACES, this);
  }

  /*
   * Getter for the *real* connection that this wraps
   *
   * @return The connection
   */
  public Connection getRealConnection() {
    return realConnection;
  }

  /*
   * Getter for the proxy for the connection
   *
   * @return The proxy
   */
  public Connection getProxyConnection() {
    return proxyConnection;
  }

  /*
   * Required for InvocationHandler implementation.
   *
   * @param proxy  - not used
   * @param method - the method to be executed
   * @param args   - the parameters to be passed to the method
   * @see java.lang.reflect.InvocationHandler#invoke(Object, java.lang.reflect.Method, Object[])
   */
  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    String methodName = method.getName();
    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 Runtime
          checkConnection();
        }
        return method.invoke(realConnection, args);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
  }

  ......
}

@Override
public Connection getConnection() throws SQLException {
  return popConnection(dataSource.getUsername(), dataSource.getPassword()).getProxyConnection();
}

@Override
public Connection getConnection(String username, String password) throws SQLException {
  return popConnection(username, password).getProxyConnection();
}