1 /* 2 * Copyright (C) 2007 Google Inc. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.io; 18 19 import com.google.common.base.Preconditions; 20 21 import java.io.IOException; 22 import java.io.Reader; 23 import java.nio.CharBuffer; 24 import java.util.LinkedList; 25 import java.util.Queue; 26 27 /** 28 * A class for reading lines of text. Provides the same functionality 29 * as {@link java.io.BufferedReader#readLine()} but for all {@link Readable} 30 * objects, not just instances of {@link Reader}. 31 * 32 * @author Chris Nokleberg 33 * @since 2009.09.15 <b>tentative</b> 34 */ 35 public final class LineReader { 36 private final Readable readable; 37 private final Reader reader; 38 private final char[] buf = new char[0x1000]; // 4K 39 private final CharBuffer cbuf = CharBuffer.wrap(buf); 40 41 private final Queue<String> lines = new LinkedList<String>(); 42 private final LineBuffer lineBuf = new LineBuffer() { 43 @Override protected void handleLine(String line, String end) { 44 lines.add(line); 45 } 46 }; 47 48 /** 49 * Creates a new instance that will read lines from the given 50 * {@code Readable} object. 51 */ LineReader(Readable readable)52 public LineReader(Readable readable) { 53 Preconditions.checkNotNull(readable); 54 this.readable = readable; 55 this.reader = (readable instanceof Reader) ? (Reader) readable : null; 56 } 57 58 /** 59 * Reads a line of text. A line is considered to be terminated by any 60 * one of a line feed ({@code '\n'}), a carriage return 61 * ({@code '\r'}), or a carriage return followed immediately by a linefeed 62 * ({@code "\r\n"}). 63 * 64 * @return a {@code String} containing the contents of the line, not 65 * including any line-termination characters, or {@code null} if the 66 * end of the stream has been reached. 67 * @throws IOException if an I/O error occurs 68 */ readLine()69 public String readLine() throws IOException { 70 while (lines.peek() == null) { 71 cbuf.clear(); 72 // The default implementation of Reader#read(CharBuffer) allocates a 73 // temporary char[], so we call Reader#read(char[], int, int) instead. 74 int read = (reader != null) 75 ? reader.read(buf, 0, buf.length) 76 : readable.read(cbuf); 77 if (read == -1) { 78 lineBuf.finish(); 79 break; 80 } 81 lineBuf.add(buf, 0, read); 82 } 83 return lines.poll(); 84 } 85 } 86