    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.io;
    019
    020import java.io.IOException;
    021import java.io.RandomAccessFile;
    022import java.nio.channels.SeekableByteChannel;
    023import java.util.Objects;
    024
    025import org.apache.commons.io.channels.FileChannels;
    026
    027/**
    028 * Works with {@link RandomAccessFile}.
    029 *
    030 * @since 2.13.0
    031 */
    032public class RandomAccessFiles {
    033
    034    /**
    035     * Tests if two RandomAccessFile contents are equal.
    036     *
    037     * @param raf1 A RandomAccessFile.
    038     * @param raf2 Another RandomAccessFile.
    039     * @return true if the contents of both RandomAccessFiles are equal, false otherwise.
    040     * @throws IOException if an I/O error occurs.
    041     * @since 2.15.0
    042     */
    043    @SuppressWarnings("resource") // See comments
    044    public static boolean contentEquals(final RandomAccessFile raf1, final RandomAccessFile raf2) throws IOException {
    045        // Short-circuit test
    046        if (Objects.equals(raf1, raf2)) {
    047            return true;
    048        }
    049        // Short-circuit test
    050        final long length1 = length(raf1);
    051        final long length2 = length(raf2);
    052        if (length1 != length2) {
    053            return false;
    054        }
    055        if (length1 == 0 && length2 == 0) {
    056            return true;
    057        }
    058        // Dig in and to the work
    059        // We do not close FileChannels because that would close the owning RandomAccessFile.
    060        // Instead, the caller is assumed to manage the given RandomAccessFile objects.
    061        return FileChannels.contentEquals((SeekableByteChannel) raf1.getChannel(), raf2.getChannel(), IOUtils.DEFAULT_BUFFER_SIZE);
    062    }
    063
    064    private static long length(final RandomAccessFile raf) throws IOException {
    065        return raf != null ? raf.length() : 0;
    066    }
    067
    068    /**
    069     * Reads a byte array starting at "position" for "length" bytes.
    070     *
    071     * @param input    The source RandomAccessFile.
    072     * @param position The offset position, measured in bytes from the beginning of the file, at which to set the file pointer.
    073     * @param length   How many bytes to read.
    074     * @return a new byte array.
    075     * @throws IOException If the first byte cannot be read for any reason other than end of file, or if the random access file has been closed, or if some
    076     *                     other I/O error occurs.
    077     */
    078    public static byte[] read(final RandomAccessFile input, final long position, final int length) throws IOException {
    079        input.seek(position);
    080        return IOUtils.toByteArray(input::read, length);
    081    }
    082
    083    /**
    084     * Resets the given file to position 0.
    085     *
    086     * @param raf The RandomAccessFile to reset.
    087     * @return The given RandomAccessFile.
    088     * @throws IOException If {@code pos} is less than {@code 0} or if an I/O error occurs.
    089     * @since 2.15.0
    090     */
    091    public static RandomAccessFile reset(final RandomAccessFile raf) throws IOException {
    092        raf.seek(0);
    093        return raf;
    094    }
    095
    096    /**
    097     * Make private in 3.0.
    098     *
    099     * @deprecated TODO Make private in 3.0.
    100     */
    101    @Deprecated
    102    public RandomAccessFiles() {
    103        // empty
    104    }
    105}