content: package org.apache.lucene.index;
  
  /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  import java.io.File;
  import java.io.FilenameFilter;
  import java.util.HashSet;
  
  /**
   * Filename filter that accept filenames and extensions only created by Lucene.
   *
   * @lucene.internal
   */
  public class IndexFileNameFilter implements FilenameFilter {
  
    private static IndexFileNameFilter singleton = new IndexFileNameFilter();
    private HashSet<String> extensions;
    private HashSet<String> extensionsInCFS;
  
    // Prevent instantiation.
    private IndexFileNameFilter() {
      extensions = new HashSet<String>();
      for (String ext : IndexFileNames.INDEX_EXTENSIONS) {
        extensions.add(ext);
      }
      extensionsInCFS = new HashSet<String>();
      for (String ext : IndexFileNames.INDEX_EXTENSIONS_IN_COMPOUND_FILE) {
        extensionsInCFS.add(ext);
      }
    }
  
    /* (non-Javadoc)
     * @see java.io.FilenameFilter#accept(java.io.File, java.lang.String)
     */
    public boolean accept(File dir, String name) {
      int i = name.lastIndexOf('.');
      if (i != -1) {
        String extension = name.substring(1+i);
        if (extensions.contains(extension)) {
          return true;
        } else if (extension.startsWith("f") &&
                   extension.matches("f\\d+")) {
          return true;
        } else if (extension.startsWith("s") &&
                   extension.matches("s\\d+")) {
          return true;
        }
      } else {
        if (name.equals(IndexFileNames.DELETABLE)) return true;
        else if (name.startsWith(IndexFileNames.SEGMENTS)) return true;
      }
      return false;
    }
  
    /**
     * Returns true if this is a file that would be contained
     * in a CFS file.  This function should only be called on
     * files that pass the above "accept" (ie, are already
     * known to be a Lucene index file).
     */
    public boolean isCFSFile(String name) {
      int i = name.lastIndexOf('.');
      if (i != -1) {
        String extension = name.substring(1+i);
        if (extensionsInCFS.contains(extension)) {
          return true;
        }
        if (extension.startsWith("f") &&
            extension.matches("f\\d+")) {
          return true;
        }
      }
      return false;
    }
  
    public static IndexFileNameFilter getFilter() {
      return singleton;
    }
  }
  