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 */ 017package org.apache.commons.compress.utils; 018 019import java.io.FilterInputStream; 020import java.io.IOException; 021import java.io.InputStream; 022 023/** 024 * A wrapper that overwrites {@link #skip} and delegates to {@link #read} instead. 025 * 026 * <p>Some implementations of {@link InputStream} implement {@link 027 * InputStream#skip} in a way that throws an exception if the stream 028 * is not seekable - {@link System#in System.in} is known to behave 029 * that way. For such a stream it is impossible to invoke skip at all 030 * and you have to read from the stream (and discard the data read) 031 * instead. Skipping is potentially much faster than reading so we do 032 * want to invoke {@code skip} when possible. We provide this class so 033 * you can wrap your own {@link InputStream} in it if you encounter 034 * problems with {@code skip} throwing an exception.</p> 035 * 036 * @since 1.17 037 */ 038public class SkipShieldingInputStream extends FilterInputStream { 039 private static final int SKIP_BUFFER_SIZE = 8192; 040 // we can use a shared buffer as the content is discarded anyway 041 private static final byte[] SKIP_BUFFER = new byte[SKIP_BUFFER_SIZE]; 042 public SkipShieldingInputStream(final InputStream in) { 043 super(in); 044 } 045 046 @Override 047 public long skip(final long n) throws IOException { 048 return n < 0 ? 0 : read(SKIP_BUFFER, 0, (int) Math.min(n, SKIP_BUFFER_SIZE)); 049 } 050}