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.io.input.buffer; 018 019import java.io.IOException; 020import java.io.InputStream; 021import java.util.Objects; 022 023/** 024 * Implements a buffered input stream, which allows to peek into the buffers first bytes. This comes in handy when 025 * manually implementing scanners, lexers, parsers, and the like. 026 */ 027public class PeekableInputStream extends CircularBufferInputStream { 028 029 /** 030 * Creates a new instance, which filters the given input stream, and uses the given buffer size. 031 * 032 * @param inputStream The input stream, which is being buffered. 033 * @param bufferSize The size of the {@link CircularByteBuffer}, which is used internally. 034 */ 035 public PeekableInputStream(final InputStream inputStream, final int bufferSize) { 036 super(inputStream, bufferSize); 037 } 038 039 /** 040 * Creates a new instance, which filters the given input stream, and uses a reasonable default buffer size (8192). 041 * 042 * @param inputStream The input stream, which is being buffered. 043 */ 044 public PeekableInputStream(final InputStream inputStream) { 045 super(inputStream); 046 } 047 048 /** 049 * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}. This is equivalent to 050 * {@link #peek(byte[], int, int)} with {@code offset} == 0, and {@code length} == {@code sourceBuffer.length} 051 * 052 * @param sourceBuffer the buffer to compare against 053 * @return true if the next bytes are as given 054 * @throws IOException Refilling the buffer failed. 055 */ 056 public boolean peek(final byte[] sourceBuffer) throws IOException { 057 Objects.requireNonNull(sourceBuffer, "sourceBuffer"); 058 return peek(sourceBuffer, 0, sourceBuffer.length); 059 } 060 061 /** 062 * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}, {code offset}, and 063 * {@code length}. 064 * 065 * @param sourceBuffer the buffer to compare against 066 * @param offset the start offset 067 * @param length the length to compare 068 * @return true if the next bytes in the buffer are as given 069 * @throws IOException if there is a problem calling fillBuffer() 070 */ 071 public boolean peek(final byte[] sourceBuffer, final int offset, final int length) throws IOException { 072 Objects.requireNonNull(sourceBuffer, "sourceBuffer"); 073 if (sourceBuffer.length > bufferSize) { 074 throw new IllegalArgumentException("Peek request size of " + sourceBuffer.length 075 + " bytes exceeds buffer size of " + bufferSize + " bytes"); 076 } 077 if (buffer.getCurrentNumberOfBytes() < sourceBuffer.length) { 078 fillBuffer(); 079 } 080 return buffer.peek(sourceBuffer, offset, length); 081 } 082}