private final MimeTypeDetector mimeTypeDetector = new MimeTypeDetector();  private DBClient client;  private String connectionUrl;  private String connectorName;  private String login;  private String password;  private String sqlQuery;  private String authZQuery;  private String googleConnectorWorkDir;  private String primaryKeys;  private String xslt;  private String driverClassName;  private String documentURLField;  private String documentIdField;  private String baseURL;  private String lobField;  private String fetchURLField;  private String lastModifiedDate;  private String extMetadataType;  private int numberOfRows = 500;  private Integer minValue = http://www.mamicode.com/-1;  private boolean publicFeed = true;  private boolean parameterizedQueryFlag = false;  private Boolean nullsSortLow = null;  private Collator collator;  public DBContext() {  }  public void init() throws DBException {    client.setDBContext(this);    // If the NULL value sort behaviour has not been explicitly overriden    // in the configuration, fetch it from the DatabaseMetadata.    if (nullsSortLow == null) {      nullsSortLow = client.nullsAreSortedLow();      if (nullsSortLow == null) {        throw new DBException("nullsSortLowFlag must be set in configuration.");      }    }  }

private boolean hasCustomCollationQuery = false;  protected DBContext dbContext;  protected SqlSessionFactory sqlSessionFactory;  protected DatabaseType databaseType;  static {    org.apache.ibatis.logging.LogFactory.useJdkLogging();  }  public DBClient() {  }  public void setDBContext(DBContext dbContext) throws DBException {    this.dbContext = dbContext;    generateSqlMap();    this.sqlSessionFactory = getSqlSessionFactory(generateMyBatisConfig());    LOG.info("DBClient for database " + getDatabaseInfo() + " is instantiated");    this.databaseType = getDatabaseType();  }  /**   * Constructor used for testing purpose. DBCLient initialized with sqlMap   * having crawl query without CDATA section.   */  @VisibleForTesting  DBClient(DBContext dbContext) throws DBException {    this.dbContext = dbContext;    this.sqlSessionFactory = getSqlSessionFactory(generateMyBatisConfig());    this.databaseType = getDatabaseType();  }  private SqlSessionFactory getSqlSessionFactory(String config) {    try {      SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();      return builder.build(new StringReader(config));    } catch (RuntimeException e) {      throw new RuntimeException("XML is not well formed", e);    }  }  /**   * @return a SqlSession   */  @VisibleForTesting  SqlSession getSqlSession()      throws SnapshotRepositoryRuntimeException {    try {      return sqlSessionFactory.openSession();    } catch (RuntimeException e) {      Throwable cause = (e.getCause() != null &&          e.getCause() instanceof SQLException) ? e.getCause() : e;      LOG.log(Level.WARNING, "Unable to connect to the database.", cause);      throw new SnapshotRepositoryRuntimeException(          "Unable to connect to the database.", cause);    }  }

/**   * @param skipRows number of rows to skip in the database.   * @param maxRows max number of rows to return.   * @return rows - subset of the result of executing the SQL query. E.g.,   *         result table with columns id and lastName and two rows will be   *         returned as   *   *         <pre>   *         [{id=1, lastName=last_01}, {id=2, lastName=last_02}]   * </pre>   * @throws DBException   */  public List<Map<String, Object>> executePartialQuery(int skipRows, int maxRows)      throws SnapshotRepositoryRuntimeException {    // TODO(meghna): Think about a better way to scroll through the result set.    List<Map<String, Object>> rows;    LOG.info("Executing partial query with skipRows = " + skipRows + " and "        + "maxRows = " + maxRows);    SqlSession session = getSqlSession();    try {      rows = session.selectList("IbatisDBClient.getAll", null,                                new RowBounds(skipRows, maxRows));      LOG.info("Sucessfully executed partial query with skipRows = "          + skipRows + " and maxRows = " + maxRows);    } catch (RuntimeException e) {      checkDBConnection(session, e);      rows = new ArrayList<Map<String, Object>>();    } finally {      session.close();    }    LOG.info("Number of rows returned " + rows.size());    return rows;  }

/**   * 实际调用的默认是这个实现类   * @author Administrator   *   */  private class PartialQueryStrategy implements QueryStrategy {    private int skipRows = 0;    @Override    public List<Map<String, Object>> executeQuery() {      return dbClient.executePartialQuery(skipRows,            dbContext.getNumberOfRows());    }    @Override    public void resetCursor() {      skipRows = 0;    }    @Override    public void updateCursor(List<Map<String, Object>> rows) {      skipRows += rows.size();    }    @Override    public void logComplete() {      LOG.info("Total " + skipRows          + " records are crawled during this crawl cycle");    }  }

/**   * 重启后都是重新开始获取数据，不记录批次信息   * Function for fetching database rows and providing a collection of   * snapshots.   */  public List<DocumentSnapshot> executeQueryAndAddDocs()      throws SnapshotRepositoryRuntimeException {    List<Map<String, Object>> rows = null;    try {      rows = queryStrategy.executeQuery();    } catch (SnapshotRepositoryRuntimeException e) {      LOG.info("Repository Unreachable. Resetting DB cursor to "          + "start traversal from begining after recovery.");      queryStrategy.resetCursor();      LOG.warning("Unable to connect to the database\n" + e.toString());      throw new SnapshotRepositoryRuntimeException(          "Unable to connect to the database.", e);    }    if (rows.size() == 0) {      queryStrategy.logComplete();      LOG.info("Crawl cycle of database is complete. Resetting DB cursor to "          + "start traversal from begining");      queryStrategy.resetCursor();    } else {      queryStrategy.updateCursor(rows);    }    if (traversalContext == null) {      LOG.info("Setting Traversal Context");      traversalContext = traversalContextManager.getTraversalContext();      JsonDocument.setTraversalContext(traversalContext);    }    return getDocList(rows);  }

/**   * 将数据包装为List<DocumentSnapshot>   * @param rows   * @return   */  private List<DocumentSnapshot> getDocList(List<Map<String, Object>> rows) {    LOG.log(Level.FINE, "Building document snapshots for {0} rows.",        rows.size());    List<DocumentSnapshot> docList = Lists.newArrayList();    for (Map<String, Object> row : rows) {      try {        DocumentSnapshot snapshot = docBuilder.getDocumentSnapshot(row);        if (snapshot != null) {          if (LOG.isLoggable(Level.FINER)) {            LOG.finer("DBSnapshotRepository returns document with docID "                + snapshot.getDocumentId());          }          docList.add(snapshot);        }      } catch (DBException e) {        // See the similar log message in DBSnapshot.getDocumentHandle.        LOG.log(Level.WARNING, "Cannot convert database record to snapshot "            + "for record " + row, e);      }    }    LOG.info(docList.size() + " document(s) to be fed to GSA");    return docList;  }

/** * Iterates over the collections of {@link DocumentSnapshot} objects * produced by a {@code RepositoryHandler}. */public class RepositoryHandlerIterator    extends AbstractIterator<DocumentSnapshot> {  private final RepositoryHandler repositoryHandler;  private Iterator<DocumentSnapshot> current;  /**   * @param repositoryHandler RepositoryHandler object for fetching DB rows in   *        DocumentSnapshot form.   */  public RepositoryHandlerIterator(RepositoryHandler repositoryHandler) {    this.repositoryHandler = repositoryHandler;    this.current = Iterators.emptyIterator();  }  @Override  protected DocumentSnapshot computeNext() {    if (current.hasNext()) {      return current.next();    } else {      current = repositoryHandler.executeQueryAndAddDocs().iterator();      if (current.hasNext()) {        return current.next();      } else {        return endOfData();      }    }  }}

/** * An iterable over the database rows. The main building block for * interacting with the diffing package. */public class DBSnapshotRepository    implements SnapshotRepository<DocumentSnapshot> {  private final RepositoryHandler repositoryHandler;  public DBSnapshotRepository(RepositoryHandler repositoryHandler) {    this.repositoryHandler = repositoryHandler;  }  @Override  public Iterator<DocumentSnapshot> iterator()      throws SnapshotRepositoryRuntimeException {    return new RepositoryHandlerIterator(repositoryHandler);  }  @Override  public String getName() {    return DBSnapshotRepository.class.getName();  }}