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 023import org.apache.commons.io.IOUtils; 024 025/** 026 * Implements a buffered input stream, which allows to peek into the buffers first bytes. This comes in handy when 027 * manually implementing scanners, lexers, parsers, and the like. 028 */ 029public class PeekableInputStream extends CircularBufferInputStream { 030 031 /** 032 * Constructs a new instance, which filters the given input stream, and uses a reasonable default buffer size ({@link IOUtils#DEFAULT_BUFFER_SIZE}). 033 * 034 * @param inputStream The input stream, which is being buffered. 035 */ 036 public PeekableInputStream(final InputStream inputStream) { 037 super(inputStream); 038 } 039 040 /** 041 * Constructs a new instance, which filters the given input stream, and uses the given buffer size. 042 * 043 * @param inputStream The input stream, which is being buffered. 044 * @param bufferSize The size of the {@link CircularByteBuffer}, which is used internally. 045 */ 046 public PeekableInputStream(final InputStream inputStream, final int bufferSize) { 047 super(inputStream, bufferSize); 048 } 049 050 /** 051 * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}. This is equivalent to 052 * {@link #peek(byte[], int, int)} with {@code offset} == 0, and {@code length} == {@code sourceBuffer.length} 053 * 054 * @param sourceBuffer the buffer to compare against 055 * @return true if the next bytes are as given 056 * @throws IOException Refilling the buffer failed. 057 */ 058 public boolean peek(final byte[] sourceBuffer) throws IOException { 059 Objects.requireNonNull(sourceBuffer, "sourceBuffer"); 060 return peek(sourceBuffer, 0, sourceBuffer.length); 061 } 062 063 /** 064 * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}, {code offset}, and 065 * {@code length}. 066 * 067 * @param sourceBuffer the buffer to compare against 068 * @param offset the start offset 069 * @param length the length to compare 070 * @return true if the next bytes in the buffer are as given 071 * @throws IOException if there is a problem calling fillBuffer() 072 */ 073 public boolean peek(final byte[] sourceBuffer, final int offset, final int length) throws IOException { 074 Objects.requireNonNull(sourceBuffer, "sourceBuffer"); 075 if (sourceBuffer.length > bufferSize) { 076 throw new IllegalArgumentException("Peek request size of " + sourceBuffer.length 077 + " bytes exceeds buffer size of " + bufferSize + " bytes"); 078 } 079 if (buffer.getCurrentNumberOfBytes() < sourceBuffer.length) { 080 fillBuffer(); 081 } 082 return buffer.peek(sourceBuffer, offset, length); 083 } 084}