企业搜索引擎开发之连接器connector（九）

接下来继续分析PusherFactory类 及Pusher类的相关源码实现

先浏览一下相关UML模型图：

我们从该图可以看到，连接器最终是通过FeedConnection类型对象向应用中心发送xmlfeed数据的

(勘误：企业搜索引擎开发之连接器connector（六）中的UML图 这部分有点出入)

PusherFactory类是Pusher类的工厂类，现在来看PusherFactory源码：

/**
 * Interface for a factory that creates {@link Pusher} instances for use by a
 * {@link com.google.enterprise.connector.traversal.Traverser Traverser}.
 */
public interface PusherFactory {
  /**
   * Create a new {@link Pusher} instance appropriate for the supplied
   * dataSource.
   *
   * @param dataSource a data source for a {@code Feed}, typically the name
   *        of a connector instance.
   * @return a {@link Pusher}
   * @throws PushException if no {@link Pusher} is assigned to the 
   *         {@code dataSource}.
   */
  public Pusher newPusher(String dataSource) throws PushException;
}

该接口就是生产Pusher类型对象，实现类DocPusherFactory如下：

/**
 * Factory that creates {@link DocPusher} instances that feed
 * {@link FeedConnection}.
 */
// TODO: Support multiple sinks where different connector instances
// might feed different sinks.
public class DocPusherFactory implements PusherFactory {
  /**
   * FeedConnection that is the sink for our generated XmlFeeds.
   */
  private final FeedConnection feedConnection;

  /**
   * Configured maximum document size and maximum feed file size supported.
   */
  private final FileSizeLimitInfo fileSizeLimit;

  /**
   * Creates a {@code DocPusherFactory} object from the specified
   * {@code feedConnection}.
   *
   * @param feedConnection a FeedConnection
   */
  public DocPusherFactory(FeedConnection feedConnection) {
    this(feedConnection, new FileSizeLimitInfo());
  }

  /**
   * Creates a {@code DocPusherFactory} object from the specified
   * {@code feedConnection}.  The supplied {@link FileSizeLimitInfo} specifies
   * constraints as to the size of a Document's content and the size of
   * generated Feed files.
   *
   * @param feedConnection a {@link FeedConnection} sink for documents.
   * @param fileSizeLimit {@link FileSizeLimitInfo} constraints on document
   *        content and feed size.
   */
  public DocPusherFactory(FeedConnection feedConnection,
                          FileSizeLimitInfo fileSizeLimit) {
    this.feedConnection = feedConnection;
    this.fileSizeLimit = fileSizeLimit;
  }

  //@Override
  public Pusher newPusher(String dataSource) {
    return new DocPusher(feedConnection, dataSource, fileSizeLimit);
  }
}

 Pusher接口方法如下：

/**
 * Interface for a Pusher - something that takes spi Documents
 * and sends them along on their way.
 */
public interface Pusher {

  /**
   * Takes an spi Document and pushes it along, presumably to the GSA Feed.
   *
   * @param document A Document
   * @return true if Pusher may accept more documents, false otherwise.
   * @throws RepositoryException if transient error accessing the Repository
   * @throws RepositoryDocumentException if fatal error accessing the Document
   * @throws FeedException if a transient Feed error occurs in the Pusher
   * @throws PushException if a transient error occurs in the Pusher
   */
  public boolean take(Document document)
      throws PushException, FeedException, RepositoryException;

  /**
   * Finishes processing a document feed.  If the caller anticipates no
   * further calls to {@link #take(Document)} will be made,
   * this method should be called, so that the Pusher may send a cached,
   * accumulated Feed to the feed processor.
   *
   * @throws RepositoryException if transient error accessing the Repository
   * @throws RepositoryDocumentException if fatal error accessing the Document
   * @throws FeedException if a transient Feed error occurs in the Pusher
   * @throws PushException if a transient error occurs in the Pusher
   */
  public void flush()
      throws PushException, FeedException, RepositoryException;

  /**
   * Cancels a feed.  Discard any accumulated feed data.
   */
  public void cancel();
}

实现类DocPusher源码如下：

/**
 * Class to generate xml feed for a document from the Document and send it
 * to GSA.
 */
public class DocPusher implements Pusher {
  private static final Logger LOGGER =
      Logger.getLogger(DocPusher.class.getName());

  private static final byte[] SPACE_CHAR = { 0x20 };  // UTF-8 space

  /**
   * Separate Logger for Feed Logging.
   */
  private static final Logger FEED_WRAPPER_LOGGER =
      Logger.getLogger(LOGGER.getName() + ".FEED_WRAPPER");
  private static final Logger FEED_LOGGER =
      Logger.getLogger(FEED_WRAPPER_LOGGER.getName() + ".FEED");
  private static final Level FEED_LOG_LEVEL = Level.FINER;

  /**
   * Configured maximum document size and maximum feed file size supported.
   */
  private final FileSizeLimitInfo fileSizeLimit;

  /**
   * FeedConnection that is the sink for our generated XmlFeeds.
   */
  private final FeedConnection feedConnection;

  /**
   * Encoding method to use for Document content.
   */
  private String contentEncoding;

  /**
   * The Connector name that is the dataSource for this Feed.
   */
  private final String connectorName;

  /**
   * ExcecutorService that submits a Feed to the GSA in a separate thread.
   * This allows us to overlap I/O reading content from the Repository
   * in the traversal thread, and submitting content to the GSA in
   * a submitFeed thread.
   */
  private final ExecutorService feedSender;

  /**
   * This is the list of outstanding asynchronous feed submissions.
   */
  private final LinkedList<FutureTask<String>> submissions;

  /**
   * This is used to build up a multi-record feed.  Documents are added to the
   * feed until the size of the feed exceeds the FileSizeLimitInfo.maxFeedSize
   * or we are finished with the batch of documents. The feed is then
   * submitted to the feed connection.
   */
  private XmlFeed xmlFeed = null;

  /**
   * This field is used to construct a feed record in parallel to the main feed
   * InputStream construction.  It is only used if the feed logging level is set
   * to the appropriate level.  It only exists during the time the main feed is
   * being constructed.  Once sufficient information has been appended to this
   * buffer its contents will be logged and it will be nulled.
   */
  private StringBuilder feedLog = null;

  // For use by unit tests.
  private String gsaResponse;

  /**
   * Creates a {@code DocPusher} object from the specified
   * {@code feedConnection} and {@code connectorName}.  The supplied
   * {@link FileSizeLimitInfo} specifies constraints as to the size of a
   * Document's content and the size of generated Feed files.
   *
   * @param feedConnection a FeedConnection
   * @param connectorName The connector name that is the source of the feed
   * @param fileSizeLimitInfo FileSizeLimitInfo constraints on document content
   *        and feed size.
   */
  public DocPusher(FeedConnection feedConnection, String connectorName,
                   FileSizeLimitInfo fileSizeLimitInfo) {
    this.feedConnection = feedConnection;
    this.connectorName = connectorName;
    this.fileSizeLimit = fileSizeLimitInfo;

    // Check to see if the GSA supports compressed content feeds.
    String supportedEncodings =
        feedConnection.getContentEncodings().toLowerCase();
    this.contentEncoding =
        (supportedEncodings.indexOf(XmlFeed.XML_BASE64COMPRESSED) >= 0) ?
        XmlFeed.XML_BASE64COMPRESSED : XmlFeed.XML_BASE64BINARY;

    // Initialize background feed submission.
    this.submissions = new LinkedList<FutureTask<String>>();
    this.feedSender = Executors.newSingleThreadExecutor();
  }

  /**
   * Return the Feed Logger.
   */
  public static Logger getFeedLogger() {
    return FEED_WRAPPER_LOGGER;
  }

  /**
   * Gets the response from GSA when the feed is sent. For testing only.
   *
   * @return gsaResponse response from GSA.
   */
  protected String getGsaResponse() {
    return gsaResponse;
  }

  /**
   * Takes a Document and sends a the feed to the GSA.
   *
   * @param document Document corresponding to the document.
   * @return true if Pusher should accept more documents, false otherwise.
   * @throws PushException if Pusher problem
   * @throws FeedException if transient Feed problem
   * @throws RepositoryDocumentException if fatal Document problem
   * @throws RepositoryException if transient Repository problem
   */
  public boolean take(Document document)
      throws PushException, FeedException, RepositoryException {
    if (feedSender.isShutdown()) {
      throw new IllegalStateException("Pusher is shut down");
    }
    checkSubmissions();

    String feedType;
    try {
      feedType = DocUtils.getFeedType(document);
    } catch (RuntimeException e) {
      LOGGER.log(Level.WARNING,
          "Rethrowing RuntimeException as RepositoryDocumentException", e);
      throw new RepositoryDocumentException(e);
    }

    // All feeds in a feed file must be of the same type.
    // If the feed would change type, send the feed off to the GSA
    // and start a new one.
    if ((xmlFeed != null) && (feedType != xmlFeed.getFeedType())) {
      if (LOGGER.isLoggable(Level.FINE)) {
        LOGGER.fine("A new feedType, " + feedType + ", requires a new feed for "
            + connectorName + ". Closing feed and sending to GSA.");
      }
      submitFeed();
    }

    if (xmlFeed == null) {
      if (LOGGER.isLoggable(Level.FINE)) {
        LOGGER.fine("Creating new " + feedType + " feed for " + connectorName);
      }
      try {
        startNewFeed(feedType);
      } catch (OutOfMemoryError me) {
        throw new PushException("Unable to allocate feed buffer.  Try reducing"
            + " the maxFeedSize setting, reducing the number of connector"
            + " intances, or adjusting the JVM heap size parameters.", me);
      }
    }

    boolean isThrowing = false;
    int resetPoint = xmlFeed.size();
    InputStream contentStream = null;
    try {
      // Add this document to the feed.
      contentStream = getContentStream(document, feedType);
      xmlFeed.addRecord(document, contentStream, contentEncoding);
      if (LOGGER.isLoggable(Level.FINER)) {
        LOGGER.finer("Document "
            + DocUtils.getRequiredString(document, SpiConstants.PROPNAME_DOCID)
            + " from connector " + connectorName + " added to feed.");
      }

      // If the feed is full, send it off to the GSA.
      if (xmlFeed.isFull() || lowMemory()) {
        if (LOGGER.isLoggable(Level.FINE)) {
          LOGGER.fine("Feed for " + connectorName + " has grown to "
              + xmlFeed.size() + " bytes. Closing feed and sending to GSA.");
        }
        submitFeed();

        // If we are running low on memory, don't start another feed -
        // tell the Traverser to finish this batch.
        if (lowMemory()) {
          return false;
        }

        // If the number of feeds waiting to be sent has backed up,
        // tell the Traverser to finish this batch.
        if ((checkSubmissions() > 10) || feedConnection.isBacklogged()) {
          return false;
        }
     }

      // Indicate that this Pusher may accept more documents.
      return true;

    } catch (OutOfMemoryError me) {
      xmlFeed.reset(resetPoint);
      throw new PushException("Out of memory building feed, retrying.", me);
    } catch (RuntimeException e) {
      xmlFeed.reset(resetPoint);
      LOGGER.log(Level.WARNING,
          "Rethrowing RuntimeException as RepositoryDocumentException", e);
      throw new RepositoryDocumentException(e);
    } catch (RepositoryDocumentException rde) {
      // Skipping this document, remove it from the feed.
      xmlFeed.reset(resetPoint);
      throw rde;
    } catch (IOException ioe) {
      LOGGER.log(Level.SEVERE, "IOException while reading: skipping", ioe);
      xmlFeed.reset(resetPoint);
      Throwable t = ioe.getCause();
      isThrowing = true;
      if (t != null && (t instanceof RepositoryException)) {
        throw (RepositoryException) t;
      } else {
        throw new RepositoryDocumentException("I/O error reading data", ioe);
      }
    } finally {
      if (contentStream != null) {
        try {
          contentStream.close();
        } catch (IOException e) {
          if (!isThrowing) {
            LOGGER.log(Level.WARNING,
                       "Rethrowing IOException as PushException", e);
            throw new PushException("IOException: " + e.getMessage(), e);
          }
        }
      }
    }
  }

  /**
   * Finish a feed.  No more documents are anticipated.
   * If there is an outstanding feed file, submit it to the GSA.
   *
   * @throws PushException if Pusher problem
   * @throws FeedException if transient Feed problem
   * @throws RepositoryException
   */
  public void flush() throws PushException, FeedException, RepositoryException {
    LOGGER.fine("Flushing accumulated feed to GSA");
    checkSubmissions();
    if (!feedSender.isShutdown()) {
      submitFeed();
      feedSender.shutdown();
    }
    while (!feedSender.isTerminated()) {
      try {
        feedSender.awaitTermination(10, TimeUnit.SECONDS);
      } catch (InterruptedException ie) {
        if (checkSubmissions() > 0) {
          throw new FeedException("Interrupted while waiting for feeds.");
        }
      }
    }
    checkSubmissions();
  }

  /**
   * Cancels any feed being constructed.  Any accumulated feed data is lost.
   */
  public void cancel() {
    // Discard any feed under construction.
    if (xmlFeed != null) {
      LOGGER.fine("Discarding accumulated feed for " + connectorName);
      xmlFeed = null;
    }
    if (feedLog != null) {
      feedLog = null;
    }
    // Cancel any feeds under asynchronous submission.
    feedSender.shutdownNow();
  }

  /**
   * Checks on asynchronously submitted feeds to see if they completed
   * or failed.  If any of the submissions failed, throw an Exception.
   *
   * @return number if items remaining in the submissions list
   */
  private int checkSubmissions()
      throws PushException, FeedException, RepositoryException {
    int count = 0;  // Count of outstanding items in the list.
    synchronized(submissions) {
      ListIterator<FutureTask<String>> iter = submissions.listIterator();
      while (iter.hasNext()) {
        FutureTask<String> future = iter.next();
        if (future.isDone()) {
          iter.remove();
          try {
            gsaResponse = future.get();
          } catch (InterruptedException ie) {
            // Shouldn't happen if isDone.
          } catch (ExecutionException ee) {
            Throwable cause = ee.getCause();
            if (cause == null) {
              cause = ee;
            }
            if (cause instanceof PushException) {
              throw (PushException) cause;
            } else if (cause instanceof FeedException) {
              throw (FeedException) cause;
            } else if (cause instanceof RepositoryException) {
              throw (RepositoryException) cause;
            } else {
              throw new FeedException("Error submitting feed", cause);
            }
          }
        } else {
          count++;
        }
      }
    }
    return count;
  }

  /**
   * Checks for low available memory condition.
   *
   * @return true if free memory is running low.
   */
  private boolean lowMemory() {
    long threshold = ((fileSizeLimit.maxFeedSize() + fileSizeLimit.maxDocumentSize()) * 4) / 3;
    Runtime rt = Runtime.getRuntime();
    if ((rt.maxMemory() - (rt.totalMemory() - rt.freeMemory())) < threshold) {
      rt.gc();
      if ((rt.maxMemory() - (rt.totalMemory() - rt.freeMemory())) < threshold) {
        return true;
      }
    }
    return false;
  }

  /**
   * Allocates initial memory for a new XmlFeed and feed logger.
   *
   * @param feedType
   */
  private void startNewFeed(String feedType) throws PushException {
    // Allocate a buffer to construct the feed log.
    try {
      if (FEED_LOGGER.isLoggable(FEED_LOG_LEVEL) && feedLog == null) {
        feedLog = new StringBuilder(256 * 1024);
        feedLog.append("Records generated for ").append(feedType);
        feedLog.append(" feed of ").append(connectorName).append(":\n");
      }
    } catch (OutOfMemoryError me) {
      throw new OutOfMemoryError(
           "Unable to allocate feed log buffer for connector " + connectorName);
    }

    // Allocate XmlFeed of the target size.
    int feedSize = (int) fileSizeLimit.maxFeedSize();
    try {
      try {
        xmlFeed = new XmlFeed(connectorName, feedType, feedSize, feedLog);
      } catch (OutOfMemoryError me) {
        // We shouldn't even have gotten this far under a low memory condition.
        // However, try to allocate a tiny feed buffer.  It should fill up on
        // the first document, forcing it to be submitted.  DocPusher.take()
        // should then return a signal to the caller to terminate the batch.
        LOGGER.warning("Insufficient memory available to allocate an optimally"
            + " sized feed - retrying with a much smaller feed allocation.");
        feedSize = 1024;
        try {
          xmlFeed = new XmlFeed(connectorName, feedType, feedSize, feedLog);
        } catch (OutOfMemoryError oome) {
          throw new OutOfMemoryError(
               "Unable to allocate feed buffer for connector " + connectorName);
        }
      }
    } catch (IOException ioe) {
      throw new PushException("Error creating feed", ioe);
    }

    LOGGER.fine("Allocated a new feed of size " + feedSize);
    return;
  }

  /**
   * Takes the accumulated XmlFeed and sends the feed to the GSA.
   *
   * @throws PushException if Pusher problem
   * @throws FeedException if transient Feed problem
   * @throws RepositoryException
   */
  private void submitFeed()
      throws PushException, FeedException, RepositoryException {
    if (xmlFeed == null) {
      return;
    }

    final XmlFeed feed = xmlFeed;
    xmlFeed = null;
    final String logMessage;
    if (feedLog != null) {
      logMessage = feedLog.toString();
      feedLog = null;
    } else {
      logMessage = null;
    }

    try {
      feed.close();
    } catch (IOException ioe) {
      throw new PushException("Error closing feed", ioe);
    }

    try {
      // Send the feed to the GSA in a separate thread.
      FutureTask<String> future = new FutureTask<String> (
          new Callable<String>() {
            public String call()
                throws PushException, FeedException, RepositoryException {
              try {
                NDC.push("Feed " + feed.getDataSource());
                return submitFeed(feed, logMessage);
              } finally {
                NDC.remove();
              }
            }
          }
        );
      feedSender.execute(future);
      // Add the future to list of outstanding submissions.
      synchronized(submissions) {
        submissions.add(future);
      }
    } catch (RejectedExecutionException ree) {
      throw new FeedException("Asynchronous feed was rejected. ", ree);
    }
  }

  /**
   * Takes the supplied XmlFeed and sends that feed to the GSA.
   *
   * @param feed an XmlFeed
   * @param logMessage a Feed Log message
   * @return response String from GSA
   * @throws PushException if Pusher problem
   * @throws FeedException if transient Feed problem
   * @throws RepositoryException
   */
  private String submitFeed(XmlFeed feed, String logMessage)
      throws PushException, FeedException, RepositoryException {

    if (LOGGER.isLoggable(Level.FINE)) {
      LOGGER.fine("Submitting " + feed.getFeedType() + " feed for "
          + feed.getDataSource() + " to the GSA. " + feed.getRecordCount()
          + " records totaling " + feed.size() + " bytes.");
    }

    // Write the generated feedLog message to the feed logger.
    if (logMessage != null && FEED_LOGGER.isLoggable(FEED_LOG_LEVEL)) {
      FEED_LOGGER.log(FEED_LOG_LEVEL, logMessage);
    }

    // Write the Feed to the TeedFeedFile, if one was specified.
    String teedFeedFilename = Context.getInstance().getTeedFeedFile();
    if (teedFeedFilename != null) {
      boolean isThrowing = false;
      OutputStream os = null;
      try {
        os = new FileOutputStream(teedFeedFilename, true);
        feed.writeTo(os);
      } catch (IOException e) {
        isThrowing = true;
        throw new FeedException("Cannot write to file: " + teedFeedFilename, e);
      } finally {
        if (os != null) {
          try {
            os.close();
          } catch (IOException e) {
            if (!isThrowing) {
              throw new FeedException(
                   "Cannot write to file: " + teedFeedFilename, e);
            }
          }
        }
      }
    }

    String gsaResponse = feedConnection.sendData(feed);
    if (!gsaResponse.equals(GsaFeedConnection.SUCCESS_RESPONSE)) {
      String eMessage = gsaResponse;
      if (GsaFeedConnection.UNAUTHORIZED_RESPONSE.equals(gsaResponse)) {
        eMessage += ": Client is not authorized to send feeds. Make "
            + "sure the GSA is configured to trust feeds from your host.";
      }
      if (GsaFeedConnection.INTERNAL_ERROR_RESPONSE.equals(gsaResponse)) {
        eMessage += ": Check GSA status or feed format.";
      }
      throw new PushException(eMessage);
    }
    return gsaResponse;
  }

  /**
   * Return an InputStream for the Document's content.
   */
  private InputStream getContentStream(Document document, String feedType)
      throws RepositoryException {
    InputStream contentStream = null;
    if (!feedType.equals(XmlFeed.XML_FEED_METADATA_AND_URL)) {
      InputStream encodedContentStream = getEncodedStream(
          new BigEmptyDocumentFilterInputStream(
              DocUtils.getOptionalStream(document,
              SpiConstants.PROPNAME_CONTENT), fileSizeLimit.maxDocumentSize()),
          (Context.getInstance().getTeedFeedFile() != null), 1024 * 1024);

      InputStream encodedAlternateStream = getEncodedStream(getAlternateContent(
          DocUtils.getOptionalString(document, SpiConstants.PROPNAME_TITLE)),
          false, 1024);

      contentStream = new AlternateContentFilterInputStream(
          encodedContentStream, encodedAlternateStream, xmlFeed);
    }
    return contentStream;
  }

  /**
   * Wrap the content stream with the suitable encoding (either
   * Base64 or Base64Compressed, based upon GSA encoding support.
   */
  // TODO: Don't compress tiny content or already compressed data
  // (based on mimetype).  This is harder than it sounds.
  private InputStream getEncodedStream(InputStream content, boolean wrapLines,
                                       int ioBufferSize) {
    if (XmlFeed.XML_BASE64COMPRESSED.equals(contentEncoding)) {
      return new Base64FilterInputStream(
          new CompressedFilterInputStream(content, ioBufferSize), wrapLines);
    } else {
      return new Base64FilterInputStream(content, wrapLines);
     }
  }

  /**
   * Construct the alternate content data for a feed item.  If the feed item
   * has null or empty content, or if the feed item has excessively large
   * content, substitute this data which will insure that the feed item gets
   * indexed by the GSA. The alternate content consists of the item's title,
   * or a single space, if it lacks a title.
   *
   * @param title from the feed item
   * @return an InputStream containing the alternate content
   */
  private static InputStream getAlternateContent(String title) {
    byte[] bytes = null;
    // Alternate content is a string that is substituted for null or empty
    // content streams, in order to make sure the GSA indexes the feed item.
    // If the feed item supplied a title property, we build an HTML fragment
    // containing that title.  This provides better looking search result
    // entries.
    if (title != null && title.trim().length() > 0) {
      try {
        String t = "<html><title>" + title.trim() + "</title></html>";
        bytes = t.getBytes("UTF-8");
      } catch (UnsupportedEncodingException uee) {
        // Don't be fancy.  Try the single space content.
      }
    }
    // If no title is available, we supply a single space as the content.
    if (bytes == null) {
      bytes = SPACE_CHAR;
    }
    return new ByteArrayInputStream(bytes);
  }

  /**
   * A FilterInput stream that protects against large documents and empty
   * documents.  If we have read more than FileSizeLimitInfo.maxDocumentSize
   * bytes from the input, we reset the feed to before we started reading
   * content, then provide the alternate content.  Similarly, if we get EOF
   * after reading zero bytes, we provide the alternate content.
   */
  private static class AlternateContentFilterInputStream
      extends FilterInputStream {
    private boolean useAlternate;
    private InputStream alternate;
    private final XmlFeed feed;
    private int resetPoint;

    /**
     * @param in InputStream containing raw document content
     * @param alternate InputStream containing alternate content to provide
     * @param feed XmlFeed under constructions (used for reseting size)
     */
    public AlternateContentFilterInputStream(InputStream in,
        InputStream alternate, XmlFeed feed) {
      super(in);
      this.useAlternate = false;
      this.alternate = alternate;
      this.feed = feed;
      this.resetPoint = -1;
    }

    // Reset the feed to its position when we started reading this stream,
    // and start reading from the alternate input.
    // TODO: WARNING: this will not work if using chunked HTTP transfer.
    private void switchToAlternate() {
      feed.reset(resetPoint);
      useAlternate = true;
    }

    @Override
    public int read() throws IOException {
      if (resetPoint == -1) {
        // If I have read nothing yet, remember the reset point in the feed.
        resetPoint = feed.size();
      }
      if (!useAlternate) {
        try {
          return super.read();
        } catch (EmptyDocumentException e) {
          switchToAlternate();
        } catch (BigDocumentException e) {
          LOGGER.finer("Document content exceeds the maximum configured "
                       + "document size, discarding content.");
          switchToAlternate();
        }
      }
      return alternate.read();
    }

    @Override
    public int read(byte b[], int off, int len) throws IOException {
      if (resetPoint == -1) {
        // If I have read nothing yet, remember the reset point in the feed.
        resetPoint = feed.size();
      }
      if (!useAlternate) {
        try {
          return super.read(b, off, len);
        } catch (EmptyDocumentException e) {
          switchToAlternate();
          return 0; // Return alternate content on subsequent call to read().
        } catch (BigDocumentException e) {
          LOGGER.finer("Document content exceeds the maximum configured "
                       + "document size, discarding content.");
          switchToAlternate();
          return 0; // Return alternate content on subsequent call to read().
        }
      }
      return alternate.read(b, off, len);
    }

    @Override
    public boolean markSupported() {
      return false;
    }

    @Override
    public void close() throws IOException {
      super.close();
      alternate.close();
    }
  }

  /**
   * A FilterInput stream that protects against large documents and empty
   * documents.  If we have read more than FileSizeLimitInfo.maxDocumentSize
   * bytes from the input, or if we get EOF after reading zero bytes,
   * we throw a subclass of IOException that is used as a signal for
   * AlternateContentFilterInputStream to switch to alternate content.
   */
  private static class BigEmptyDocumentFilterInputStream
      extends FilterInputStream {
    private final long maxDocumentSize;
    private long currentDocumentSize;

    /**
     * @param in InputStream containing raw document content
     * @param maxDocumentSize maximum allowed size in bytes of data read from in
     */
    public BigEmptyDocumentFilterInputStream(InputStream in,
                                             long maxDocumentSize) {
      super(in);
      this.maxDocumentSize = maxDocumentSize;
      this.currentDocumentSize = 0;
    }

    @Override
    public int read() throws IOException {
      if (in == null) {
        throw new EmptyDocumentException();
      }
      int val = super.read();
      if (val == -1) {
        if (currentDocumentSize == 0) {
          throw new EmptyDocumentException();
        }
      } else if (++currentDocumentSize > maxDocumentSize) {
        throw new BigDocumentException();
      }
      return val;
    }

    @Override
    public int read(byte b[], int off, int len) throws IOException {
      if (in == null) {
        throw new EmptyDocumentException();
      }
      int bytesRead = super.read(b, off,
          (int) Math.min(len, maxDocumentSize - currentDocumentSize + 1));
      if (bytesRead == -1) {
        if (currentDocumentSize == 0) {
          throw new EmptyDocumentException();
        }
      } else if ((currentDocumentSize += bytesRead) > maxDocumentSize) {
        throw new BigDocumentException();
      }
      return bytesRead;
    }

    @Override
    public boolean markSupported() {
      return false;
    }

    @Override
    public void close() throws IOException {
      if (in != null) {
        super.close();
      }
    }
  }

  /**
   * Subclass of IOException that is thrown when maximumDocumentSize
   * is exceeded.
   */
  private static class BigDocumentException extends IOException {
    public BigDocumentException() {
      super("Maximum Document size exceeded.");
    }
  }

  /**
   * Subclass of IOException that is thrown when the document has
   * no content.
   */
  private static class EmptyDocumentException extends IOException {
    public EmptyDocumentException() {
      super("Document has no content.");
    }
  }
}

这个类的代码是有点长的，take方法首先是将Document转化为InputStream流然后封装到XmlFeed数据载体里面

 然后以线程池方式提交XmlFeed数据（调用feedConnection.sendData(feed)方法）

我么可以发现提交xmlfeed数据前，如果我们在属性文件applicationContext.properties配置了teedFeedFile属性，连接器会同时将发送的xml数据写入该属性值的文件

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本文链接http://www.cnblogs.com/chenying99/archive/2013/03/19/2968423.html