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.compress.utils; 019 020import java.io.FilterInputStream; 021import java.io.IOException; 022import java.io.InputStream; 023 024/** 025 * A wrapper that overwrites {@link #skip} and delegates to {@link #read} instead. 026 * 027 * <p>Some implementations of {@link InputStream} implement {@link 028 * InputStream#skip} in a way that throws an exception if the stream 029 * is not seekable - {@link System#in System.in} is known to behave 030 * that way. For such a stream it is impossible to invoke skip at all 031 * and you have to read from the stream (and discard the data read) 032 * instead. Skipping is potentially much faster than reading so we do 033 * want to invoke {@code skip} when possible. We provide this class so 034 * you can wrap your own {@link InputStream} in it if you encounter 035 * problems with {@code skip} throwing an exception.</p> 036 * 037 * @since 1.17 038 */ 039public class SkipShieldingInputStream extends FilterInputStream { 040 private static final int SKIP_BUFFER_SIZE = 8192; 041 // we can use a shared buffer as the content is discarded anyway 042 private static final byte[] SKIP_BUFFER = new byte[SKIP_BUFFER_SIZE]; 043 public SkipShieldingInputStream(final InputStream in) { 044 super(in); 045 } 046 047 @Override 048 public long skip(final long n) throws IOException { 049 return n < 0 ? 0 : read(SKIP_BUFFER, 0, (int) Math.min(n, SKIP_BUFFER_SIZE)); 050 } 051}