1 /* 2 * Copyright (C) 2007 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 5 * in compliance with the License. You may obtain a copy of the License at 6 * 7 * http://www.apache.org/licenses/LICENSE-2.0 8 * 9 * Unless required by applicable law or agreed to in writing, software distributed under the License 10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 11 * or implied. See the License for the specific language governing permissions and limitations under 12 * the License. 13 */ 14 15 package com.google.common.io; 16 17 import static com.google.common.base.Preconditions.checkNotNull; 18 import static com.google.common.io.CharStreams.createBuffer; 19 20 import com.google.common.annotations.Beta; 21 import com.google.common.annotations.GwtIncompatible; 22 import com.google.errorprone.annotations.CanIgnoreReturnValue; 23 import java.io.IOException; 24 import java.io.Reader; 25 import java.nio.CharBuffer; 26 import java.util.ArrayDeque; 27 import java.util.Queue; 28 import javax.annotation.CheckForNull; 29 30 /** 31 * A class for reading lines of text. Provides the same functionality as {@link 32 * java.io.BufferedReader#readLine()} but for all {@link Readable} objects, not just instances of 33 * {@link Reader}. 34 * 35 * @author Chris Nokleberg 36 * @since 1.0 37 */ 38 @Beta 39 @GwtIncompatible 40 @ElementTypesAreNonnullByDefault 41 public final class LineReader { 42 private final Readable readable; 43 @CheckForNull private final Reader reader; 44 private final CharBuffer cbuf = createBuffer(); 45 private final char[] buf = cbuf.array(); 46 47 private final Queue<String> lines = new ArrayDeque<>(); 48 private final LineBuffer lineBuf = 49 new LineBuffer() { 50 @Override 51 protected void handleLine(String line, String end) { 52 lines.add(line); 53 } 54 }; 55 56 /** Creates a new instance that will read lines from the given {@code Readable} object. */ LineReader(Readable readable)57 public LineReader(Readable readable) { 58 this.readable = checkNotNull(readable); 59 this.reader = (readable instanceof Reader) ? (Reader) readable : null; 60 } 61 62 /** 63 * Reads a line of text. A line is considered to be terminated by any one of a line feed ({@code 64 * '\n'}), a carriage return ({@code '\r'}), or a carriage return followed immediately by a 65 * linefeed ({@code "\r\n"}). 66 * 67 * @return a {@code String} containing the contents of the line, not including any 68 * line-termination characters, or {@code null} if the end of the stream has been reached. 69 * @throws IOException if an I/O error occurs 70 */ 71 @CanIgnoreReturnValue // to skip a line 72 @CheckForNull readLine()73 public String readLine() throws IOException { 74 while (lines.peek() == null) { 75 Java8Compatibility.clear(cbuf); 76 // The default implementation of Reader#read(CharBuffer) allocates a 77 // temporary char[], so we call Reader#read(char[], int, int) instead. 78 int read = (reader != null) ? reader.read(buf, 0, buf.length) : readable.read(cbuf); 79 if (read == -1) { 80 lineBuf.finish(); 81 break; 82 } 83 lineBuf.add(buf, 0, read); 84 } 85 return lines.poll(); 86 } 87 } 88