private void processGeneratedKeys(Executor executor, MappedStatement ms, Object parameter) {
    try {
      if (parameter != null && keyStatement != null && keyStatement.getKeyProperties() != null) {
        String[] keyProperties = keyStatement.getKeyProperties();
        final Configuration configuration = ms.getConfiguration();
        final MetaObject metaParam = configuration.newMetaObject(parameter);
        if (keyProperties != null) {
          // Do not close keyExecutor.
          // The transaction will be closed by parent executor.
          Executor keyExecutor = configuration.newExecutor(executor.getTransaction(), ExecutorType.SIMPLE);
          List<Object> values = keyExecutor.query(keyStatement, parameter, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER);
          if (values.size() == 0) {
            throw new ExecutorException("SelectKey returned no data.");            
          } else if (values.size() > 1) {
            throw new ExecutorException("SelectKey returned more than one value.");
          } else {
            MetaObject metaResult = configuration.newMetaObject(values.get(0));
            if (keyProperties.length == 1) {
              if (metaResult.hasGetter(keyProperties[0])) {
                setValue(metaParam, keyProperties[0], metaResult.getValue(keyProperties[0]));
              } else {
                // no getter for the property - maybe just a single value object
                // so try that
                setValue(metaParam, keyProperties[0], values.get(0));
              }
            } else {
              handleMultipleProperties(keyProperties, metaParam, metaResult);
            }
          }
        }
      }
    } catch (ExecutorException e) {
      throw e;
    } catch (Exception e) {
      throw new ExecutorException("Error selecting key or setting result to parameter object. Cause: " + e, e);
    }
  }
@author Clinton Begin
@author Jeff Butler
src/main/java/org/apache/ibatis/executor/keygen/SelectKeyGenerator.java