Java tutorial
/* * 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. */ package org.apache.lucene.index; import java.util.regex.Pattern; import org.apache.lucene.codecs.Codec; /** * This class contains useful constants representing filenames and extensions * used by lucene, as well as convenience methods for querying whether a file * name matches an extension ({@link #matchesExtension(String, String) * matchesExtension}), as well as generating file names from a segment name, * generation and extension ( * {@link #fileNameFromGeneration(String, String, long) fileNameFromGeneration}, * {@link #segmentFileName(String, String, String) segmentFileName}). * * <p><b>NOTE</b>: extensions used by codecs are not * listed here. You must interact with the {@link Codec} * directly. * * @lucene.internal */ public final class IndexFileNames { /** No instance */ private IndexFileNames() { } /** Name of the index segment file */ public static final String SEGMENTS = "segments"; /** Name of pending index segment file */ public static final String PENDING_SEGMENTS = "pending_segments"; /** Name of the generation reference file name */ public static final String OLD_SEGMENTS_GEN = "segments.gen"; /** * Computes the full file name from base, extension and generation. If the * generation is -1, the file name is null. If it's 0, the file name is * <base>.<ext>. If it's > 0, the file name is * <base>_<gen>.<ext>.<br> * <b>NOTE:</b> .<ext> is added to the name only if <code>ext</code> is * not an empty string. * * @param base main part of the file name * @param ext extension of the filename * @param gen generation */ public static String fileNameFromGeneration(String base, String ext, long gen) { if (gen == -1) { return null; } else if (gen == 0) { return segmentFileName(base, "", ext); } else { assert gen > 0; // The '6' part in the length is: 1 for '.', 1 for '_' and 4 as estimate // to the gen length as string (hopefully an upper limit so SB won't // expand in the middle. StringBuilder res = new StringBuilder(base.length() + 6 + ext.length()).append(base).append('_') .append(Long.toString(gen, Character.MAX_RADIX)); if (ext.length() > 0) { res.append('.').append(ext); } return res.toString(); } } /** * Returns a file name that includes the given segment name, your own custom * name and extension. The format of the filename is: * <segmentName>(_<name>)(.<ext>). * <p> * <b>NOTE:</b> .<ext> is added to the result file name only if * <code>ext</code> is not empty. * <p> * <b>NOTE:</b> _<segmentSuffix> is added to the result file name only if * it's not the empty string * <p> * <b>NOTE:</b> all custom files should be named using this method, or * otherwise some structures may fail to handle them properly (such as if they * are added to compound files). */ public static String segmentFileName(String segmentName, String segmentSuffix, String ext) { if (ext.length() > 0 || segmentSuffix.length() > 0) { assert !ext.startsWith("."); StringBuilder sb = new StringBuilder(segmentName.length() + 2 + segmentSuffix.length() + ext.length()); sb.append(segmentName); if (segmentSuffix.length() > 0) { sb.append('_').append(segmentSuffix); } if (ext.length() > 0) { sb.append('.').append(ext); } return sb.toString(); } else { return segmentName; } } /** * Returns true if the given filename ends with the given extension. One * should provide a <i>pure</i> extension, without '.'. */ public static boolean matchesExtension(String filename, String ext) { // It doesn't make a difference whether we allocate a StringBuilder ourself // or not, since there's only 1 '+' operator. return filename.endsWith("." + ext); } /** locates the boundary of the segment name, or -1 */ private static int indexOfSegmentName(String filename) { // If it is a .del file, there's an '_' after the first character int idx = filename.indexOf('_', 1); if (idx == -1) { // If it's not, strip everything that's before the '.' idx = filename.indexOf('.'); } return idx; } /** * Strips the segment name out of the given file name. If you used * {@link #segmentFileName} or {@link #fileNameFromGeneration} to create your * files, then this method simply removes whatever comes before the first '.', * or the second '_' (excluding both). * * @return the filename with the segment name removed, or the given filename * if it does not contain a '.' and '_'. */ public static String stripSegmentName(String filename) { int idx = indexOfSegmentName(filename); if (idx != -1) { filename = filename.substring(idx); } return filename; } /** Returns the generation from this file name, or 0 if there is no * generation. */ public static long parseGeneration(String filename) { assert filename.startsWith("_"); String parts[] = stripExtension(filename).substring(1).split("_"); // 4 cases: // segment.ext // segment_gen.ext // segment_codec_suffix.ext // segment_gen_codec_suffix.ext if (parts.length == 2 || parts.length == 4) { return Long.parseLong(parts[1], Character.MAX_RADIX); } else { return 0; } } /** * Parses the segment name out of the given file name. * * @return the segment name only, or filename * if it does not contain a '.' and '_'. */ public static String parseSegmentName(String filename) { int idx = indexOfSegmentName(filename); if (idx != -1) { filename = filename.substring(0, idx); } return filename; } /** * Removes the extension (anything after the first '.'), * otherwise returns the original filename. */ public static String stripExtension(String filename) { int idx = filename.indexOf('.'); if (idx != -1) { filename = filename.substring(0, idx); } return filename; } /** * Return the extension (anything after the first '.'), * or null if there is no '.' in the file name. */ public static String getExtension(String filename) { final int idx = filename.indexOf('.'); if (idx == -1) { return null; } else { return filename.substring(idx + 1, filename.length()); } } /** * All files created by codecs much match this pattern (checked in * SegmentInfo). */ public static final Pattern CODEC_FILE_PATTERN = Pattern.compile("_[a-z0-9]+(_.*)?\\..*"); }