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.flume.channel.file; import com.google.common.base.Preconditions; import com.google.common.base.Throwables; import org.apache.commons.io.FileUtils; import org.apache.flume.annotations.InterfaceAudience; import org.apache.flume.annotations.InterfaceStability; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import javax.annotation.Nullable; import java.io.BufferedInputStream; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.io.RandomAccessFile; import java.util.Collections; import java.util.Set; @InterfaceAudience.Private @InterfaceStability.Unstable public class Serialization { private Serialization() { } static final long SIZE_OF_INT = 4; static final int SIZE_OF_LONG = 8; static final int VERSION_2 = 2; static final int VERSION_3 = 3; public static final String METADATA_FILENAME = ".meta"; public static final String METADATA_TMP_FILENAME = ".tmp"; public static final String OLD_METADATA_FILENAME = METADATA_FILENAME + ".old"; // 64 K buffer to copy files. private static final int FILE_COPY_BUFFER_SIZE = 64 * 1024; public static final Logger LOG = LoggerFactory.getLogger(Serialization.class); static File getMetaDataTempFile(File metaDataFile) { String metaDataFileName = metaDataFile.getName() + METADATA_TMP_FILENAME; return new File(metaDataFile.getParentFile(), metaDataFileName); } static File getMetaDataFile(File file) { String metaDataFileName = file.getName() + METADATA_FILENAME; return new File(file.getParentFile(), metaDataFileName); } // Support platforms that cannot do atomic renames - FLUME-1699 static File getOldMetaDataFile(File file) { String oldMetaDataFileName = file.getName() + OLD_METADATA_FILENAME; return new File(file.getParentFile(), oldMetaDataFileName); } /** * Deletes all files in given directory. * @param checkpointDir - The directory whose files are to be deleted * @param excludes - Names of files which should not be deleted from this * directory. * @return - true if all files were successfully deleted, false otherwise. */ static boolean deleteAllFiles(File checkpointDir, @Nullable Set<String> excludes) { if (!checkpointDir.isDirectory()) { return false; } File[] files = checkpointDir.listFiles(); if (files == null) { return false; } StringBuilder builder; if (files.length == 0) { return true; } else { builder = new StringBuilder("Deleted the following files: "); } if (excludes == null) { excludes = Collections.EMPTY_SET; } for (File file : files) { if (excludes.contains(file.getName())) { LOG.info("Skipping " + file.getName() + " because it is in excludes " + "set"); continue; } if (!FileUtils.deleteQuietly(file)) { LOG.info(builder.toString()); LOG.error("Error while attempting to delete: " + file.getAbsolutePath()); return false; } builder.append(", ").append(file.getName()); } builder.append("."); LOG.info(builder.toString()); return true; } /** * Copy a file using a 64K size buffer. This method will copy the file and * then fsync to disk * @param from File to copy - this file should exist * @param to Destination file - this file should not exist * @return true if the copy was successful */ public static boolean copyFile(File from, File to) throws IOException { Preconditions.checkNotNull(from, "Source file is null, file copy failed."); Preconditions.checkNotNull(to, "Destination file is null, " + "file copy failed."); Preconditions.checkState(from.exists(), "Source file: " + from.toString() + " does not exist."); Preconditions.checkState(!to.exists(), "Destination file: " + to.toString() + " unexpectedly exists."); BufferedInputStream in = null; RandomAccessFile out = null; //use a RandomAccessFile for easy fsync try { in = new BufferedInputStream(new FileInputStream(from)); out = new RandomAccessFile(to, "rw"); byte[] buf = new byte[FILE_COPY_BUFFER_SIZE]; int total = 0; while (true) { int read = in.read(buf); if (read == -1) { break; } out.write(buf, 0, read); total += read; } out.getFD().sync(); Preconditions.checkState(total == from.length(), "The size of the origin file and destination file are not equal."); return true; } catch (Exception ex) { LOG.error("Error while attempting to copy " + from.toString() + " to " + to.toString() + ".", ex); Throwables.propagate(ex); } finally { Throwable th = null; try { if (in != null) { in.close(); } } catch (Throwable ex) { LOG.error("Error while closing input file.", ex); th = ex; } try { if (out != null) { out.close(); } } catch (IOException ex) { LOG.error("Error while closing output file.", ex); Throwables.propagate(ex); } if (th != null) { Throwables.propagate(th); } } // Should never reach here. throw new IOException("Copying file: " + from.toString() + " to: " + to.toString() + " may have failed."); } }