企业搜索引擎开发之连接器connector（二十）

连接器里面衔接数据源与数据推送对象的是QueryTraverser类对象，该类实现了Traverser接口

/**
 * Interface presented by a Traverser.  Used by the Scheduler.
 */
public interface Traverser {

  /**
   * Interval to wait after a transient error before retrying a traversal.
   */
  public static final int ERROR_WAIT_MILLIS = 15 * 60 * 1000;

  /**
   * Runs a batch of documents. The Traversal method may be hard (impossible?)
   * to interrupt while it is executing runBatch(). It is expected that a
   * thread loop running a traversal method would call runBatch(), then check
   * for InterruptedException, then decide whether it wants to stop of itself,
   * for scheduling reasons, or for a clean shutdown. It could then re-adjust
   * the batch hint if desired, then repeat.
   *
   * @param  batchSize A {@link BatchSize} instructs the traversal method to
   *         process approximately {@code batchSize.getHint()}, but no more
   *         than {@code batchSize.getMaximum()} number of documents in this
   *         batch.
   * @return A {@link BatchResult} containing the actual number of documents
   *         from this batch given to the feed and a possible policy to delay
   *         before requesting another batch.
   */
  public BatchResult runBatch(BatchSize batchSize);

  /**
   * Cancel the Batch in progress.  Discard the batch.  This might be called
   * when the workItem times out, connector deletion or reconfiguration, or
   * during shutdown.
   */
  public void cancelBatch();
}

即上面的BatchResult runBatch(BatchSize batchSize)方法，参数BatchSize batchSize表示批次大小

QueryTraverser类对象通过引用TraversalManager queryTraversalManager对象实例获取数据源数据，同时引用PusherFactory pusherFactory对象实例实例化docPuser对象实例发送document对象数据，成员变量TraversalStateStore stateStore用于获取状态和保存状态(用于断点发送)

 @Override
  public BatchResult runBatch(BatchSize batchSize) {
      //开始时间
    final long startTime = clock.getTimeMillis();
    //超时时间
    final long timeoutTime = startTime
      + traversalContext.traversalTimeLimitSeconds() * 1000;
    //已取消
    if (isCancelled()) {
        LOGGER.warning("Attempting to run a cancelled QueryTraverser");
      return new BatchResult(TraversalDelayPolicy.ERROR);
    }
    try {
      //批次大小
      queryTraversalManager.setBatchHint(batchSize.getHint());
    } catch (RepositoryException e) {
      LOGGER.log(Level.WARNING, "Unable to set batch hint", e);
    }

    String connectorState;
    try {
      if (stateStore != null) {
        //获取断点状态
        connectorState = stateStore.getTraversalState();
      } else {
        throw new IllegalStateException("null TraversalStateStore");
      }
    } catch (IllegalStateException ise) {
      // We get here if the store for the connector is disabled.
      // That happens if the connector was deleted while we were asleep.
      // Our connector seems to have been deleted.  Don't process a batch.
      LOGGER.fine("Halting traversal for connector " + connectorName
                  + ": " + ise.getMessage());
      return new BatchResult(TraversalDelayPolicy.ERROR);
    }

    DocumentList resultSet = null;
    if (connectorState == null) {
      try {
        LOGGER.fine("START TRAVERSAL: Starting traversal for connector "
                    + connectorName);
        resultSet = queryTraversalManager.startTraversal();
      } catch (Exception e) {
        LOGGER.log(Level.WARNING, "startTraversal threw exception: ", e);
        return new BatchResult(TraversalDelayPolicy.ERROR);
      }
    } else {
      try {
        LOGGER.fine("RESUME TRAVERSAL: Resuming traversal for connector "
            + connectorName + " from checkpoint " + connectorState);
        resultSet = queryTraversalManager.resumeTraversal(connectorState);
      } catch (Exception e) {
        LOGGER.log(Level.WARNING, "resumeTraversal threw exception: ", e);
        return new BatchResult(TraversalDelayPolicy.ERROR);
      }
    }

    // If the traversal returns null, that means that the repository has
    // no new content to traverse.
    if (resultSet == null) {
      LOGGER.fine("Result set from connector " + connectorName
                  + " is NULL, no documents returned for traversal.");
      return new BatchResult(TraversalDelayPolicy.POLL, 0);
    }

    Pusher pusher = null;
    //反馈信息
    BatchResult result = null;
    int counter = 0;
    try {
        //同一批次同一个pusher实例
      // Get a Pusher for feeding the returned Documents.
      pusher = pusherFactory.newPusher(connectorName);

      while (true) {
        if (Thread.currentThread().isInterrupted() || isCancelled()) {
          LOGGER.fine("Traversal for connector " + connectorName
                      + " has been interrupted; breaking out of batch run.");
          break;
        }
        if (clock.getTimeMillis() >= timeoutTime) {
          LOGGER.fine("Traversal batch for connector " + connectorName
              + " is completing due to time limit.");
          break;
        }

        String docid = null;
        try {
          LOGGER.finer("Pulling next document from connector " + connectorName);         
          
          Document nextDocument = resultSet.nextDocument();          
          //该resultSet数据集合批次已发送完毕
          if (nextDocument == null) {
            LOGGER.finer("Traversal batch for connector " + connectorName
                + " at end after processing " + counter + " documents.");

            break;
          } else {
            //System.out.println("resultSet.getClass().getName():"+resultSet.getClass().getName());
            //System.out.println("nextDocument.getClass().getName():"+nextDocument.getClass().getName());
            // Since there are a couple of places below that could throw
            // exceptions but not exit the while loop, the counter should be
            // incremented here to insure it represents documents returned from
            // the list.  Note the call to nextDocument() could also throw a
            // RepositoryDocumentException signaling a skipped document in which
            // case the call will not be counted against the batch maximum.
            counter++;
            // Fetch DocId to use in messages.
            try {
              docid = Value.getSingleValueString(nextDocument,
                                                 SpiConstants.PROPNAME_DOCID);
            } catch (IllegalArgumentException e1) {
                LOGGER.finer("Unable to get document id for document ("
                             + nextDocument + "): " + e1.getMessage());
            } catch (RepositoryException e1) {
                LOGGER.finer("Unable to get document id for document ("
                             + nextDocument + "): " + e1.getMessage());
            }
          }
          LOGGER.finer("Sending document (" + docid + ") from connector "
              + connectorName + " to Pusher");
          //发布document
          if (pusher.take(nextDocument) != PusherStatus.OK) {
            LOGGER.fine("Traversal batch for connector " + connectorName
                + " is completing at the request of the Pusher,"
                + " after processing " + counter + " documents.");
            break;
          }
        } catch (SkippedDocumentException e) {
          /* TODO (bmj): This is a temporary solution and should be replaced.
           * It uses Exceptions for non-exceptional cases.
           */
          // Skip this document.  Proceed on to the next one.
          logSkippedDocument(docid, e);
        } catch (RepositoryDocumentException e) {
          // Skip individual documents that fail.  Proceed on to the next one.
          logSkippedDocument(docid, e);
        } catch (RuntimeException e) {
          // Skip individual documents that fail.  Proceed on to the next one.
          logSkippedDocument(docid, e);
        }
      }
      // No more documents. Wrap up any accumulated feed data and send it off.
      if (!isCancelled()) {
        pusher.flush();
      }
    } catch (OutOfMemoryError e) {
      pusher.cancel();
      System.runFinalization();
      System.gc();
      result = new BatchResult(TraversalDelayPolicy.ERROR);
      try {
        LOGGER.severe("Out of JVM Heap Space.  Will retry later.");
        LOGGER.log(Level.FINEST, e.getMessage(), e);
      } catch (Throwable t) {
        // OutOfMemory state may prevent us from logging the error.
        // Don't make matters worse by rethrowing something meaningless.
      }
    } catch (RepositoryException e) {
      // Drop the entire batch on the floor.  Do not call checkpoint
      // (as there is a discrepancy between what the Connector thinks
      // it has fed, and what actually has been pushed).
      LOGGER.log(Level.SEVERE, "Repository Exception during traversal.", e);
      result = new BatchResult(TraversalDelayPolicy.ERROR);
    } catch (PushException e) {
      LOGGER.log(Level.SEVERE, "Push Exception during traversal.", e);
      // Drop the entire batch on the floor.  Do not call checkpoint
      // (as there is a discrepancy between what the Connector thinks
      // it has fed, and what actually has been pushed).
      result = new BatchResult(TraversalDelayPolicy.ERROR);
    } catch (FeedException e) {
      LOGGER.log(Level.SEVERE, "Feed Exception during traversal.", e);
      // Drop the entire batch on the floor.  Do not call checkpoint
      // (as there is a discrepancy between what the Connector thinks
      // it has fed, and what actually has been pushed).
      result = new BatchResult(TraversalDelayPolicy.ERROR);
    } catch (Throwable t) {
      LOGGER.log(Level.SEVERE, "Uncaught Exception during traversal.", t);
      // Drop the entire batch on the floor.  Do not call checkpoint
      // (as there is a discrepancy between what the Connector thinks
      // it has fed, and what actually has been pushed).
      result = new BatchResult(TraversalDelayPolicy.ERROR);
   } finally {
      // If we have cancelled the work, abandon the batch.
      if (isCancelled()) {
        result = new BatchResult(TraversalDelayPolicy.ERROR);
      }
      
      //更新断点状态
      // Checkpoint completed work as well as skip past troublesome documents
      // (e.g. documents that are too large and will always fail).
      if ((result == null) && (checkpointAndSave(resultSet) == null)) {
        // Unable to get a checkpoint, so wait a while, then retry batch.
        result = new BatchResult(TraversalDelayPolicy.ERROR);
      }
    }
    if (result == null) {
      result = new BatchResult(TraversalDelayPolicy.IMMEDIATE, counter,
                               startTime, clock.getTimeMillis());
    } else if (pusher != null) {
      // We are returning an error from this batch. Cancel any feed that
      // might be in progress.
      pusher.cancel();
    }
    return result;
  }

关键代码本人已作了注释，通过遍历该数据集合批次，向docPusher对象提交document对象，遍历document对象执行完毕后更新断点状态用于下次从数据源获取数据

/**
   * 保存断点状态
   * @param pm
   * @return
   */
  private String checkpointAndSave(DocumentList pm) {
    String connectorState = null;
    LOGGER.fine("CHECKPOINT: Generating checkpoint for connector "
                + connectorName);
    try {
      connectorState = pm.checkpoint();
    } catch (RepositoryException re) {
      // If checkpoint() throws RepositoryException, it means there is no
      // new checkpoint.
      LOGGER.log(Level.FINE, "Failed to obtain checkpoint for connector "
                 + connectorName, re);
      return null;
    } catch (Exception e) {
      LOGGER.log(Level.INFO, "Failed to obtain checkpoint for connector "
                 + connectorName, e);
      return null;
    }
    try {
      if (connectorState != null) {
        if (stateStore != null) {
          stateStore.storeTraversalState(connectorState);
        } else {
          throw new IllegalStateException("null TraversalStateStore");
        }
        LOGGER.fine("CHECKPOINT: " + connectorState);
      }
      return connectorState;
    } catch (IllegalStateException ise) {
      // We get here if the store for the connector is disabled.
      // That happens if the connector was deleted while we were working.
      // Our connector seems to have been deleted.  Don't save a checkpoint.
      LOGGER.fine("Checkpoint discarded: " + connectorState);
    }
    return null;
  }

取消执行方法通过设置布尔变量值，注意需要考虑同步

/**
   * 取消执行
   */
  @Override
  public void cancelBatch() {
    synchronized(cancelLock) {
      cancelWork = true;
    }
    LOGGER.fine("Cancelling traversal for connector " + connectorName);
  }

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