Here you can find the source of readLines(File file)
public static List<String> readLines(File file)
//package com.java2s; /*/*from w w w . j av a2s . c om*/ * $Id$ * * Copyright (C) 2003-2015 JNode.org * * This library is free software; you can redistribute it and/or modify it * under the terms of the GNU Lesser General Public License as published * by the Free Software Foundation; either version 2.1 of the License, or * (at your option) any later version. * * This library is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public * License for more details. * * You should have received a copy of the GNU Lesser General Public License * along with this library; If not, write to the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. */ import java.io.BufferedReader; import java.io.Closeable; import java.io.File; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.Flushable; import java.io.IOException; import java.io.Reader; import java.util.List; import java.util.LinkedList; public class Main { private static final int BUFFER_SIZE = 4096; private static final String ex_null_param = "A required paramater is null"; public static List<String> readLines(File file) { BufferedReader reader = openBufferedReader(file); if (reader == null) { return null; } try { return readLines(reader); } finally { close(reader); } } public static List<String> readLines(Reader reader) { return readLines(new BufferedReader(reader, BUFFER_SIZE), -1); } public static List<String> readLines(BufferedReader reader) { return readLines(reader, -1); } /** * Read all of the lines from a Reader. * * Calling this is the same as readLines(new BufferedReader(reader), max) * * @param reader the source to read from * @param max the max number of lines to read, if this is -1 Integer.MAX_VALUE is used * @return a list of strings, possibly empty, or null if there was an exception. * @throws NullPointerException if reader is null */ public static List<String> readLines(Reader reader, int max) { return readLines(new BufferedReader(reader, BUFFER_SIZE), max); } /** * Read all of the lines from a Reader. * * If there are no lines to read, an empty List will be returned. * * If there was an exception while reading, null will be returned. * * @param reader the source to read from * @param max the max number of lines to read, if this is -1 Integer.MAX_VALUE is used * @return a list of strings, possibly empty, or null if there was an exception. * @throws NullPointerException if reader is null */ public static List<String> readLines(BufferedReader reader, int max) { checkNull(reader); List<String> ret = new LinkedList<String>(); String line; int count = 0; try { if (max > 0) { while ((count++ < max) && (line = reader.readLine()) != null) { ret.add(line); } } else { while ((line = reader.readLine()) != null) { ret.add(line); } } } catch (IOException e) { return null; } return ret; } /** * Opens a BufferedReader on a file. * * This method will not throw a FileNotFoundException like the FileReader * constructor would. * * @param file the file to open the reader on * @return the reader, or null if the file could not be opened * @throws NullPointerException if file is null */ public static BufferedReader openBufferedReader(File file) { return openBufferedReader(file, BUFFER_SIZE); } /** * Opens a BufferedReader on a file. * * This method will not throw a FileNotFoundException like the FileReader * constructor would. * * @param file the file to open the reader on * @param bufferSize the buffer size to use for this reader * @return the reader, or null if the file could not be opened * @throws NullPointerException if file is null */ public static BufferedReader openBufferedReader(File file, int bufferSize) { Reader reader = openReader(file); if (reader != null) { return new BufferedReader(reader, bufferSize); } return null; } /** * Wraps a {@code Reader} with a {@code BufferedReader}. * * @param reader the reader to wrap * @return a {@code BufferedReader} * @throws NullPointerException if reader is null */ public static BufferedReader openBufferedReader(Reader reader) { return openBufferedReader(reader, BUFFER_SIZE); } /** * Wraps a {@code Reader} with a {@code BufferedReader}. * * @param reader the reader to wrap * @param bufferSize the size of buffer to use * @return a {@code BufferedReader} * @throws NullPointerException if reader is null */ public static BufferedReader openBufferedReader(Reader reader, int bufferSize) { checkNull(reader); return new BufferedReader(reader, bufferSize); } /** * Call the close method of a list of Closeable objects. * * This will not throw a NullPointerException if any of the objects are null. * * This is a convenience method that traps the exception from various * stream close() methods. * * @param objs one or more Closeable objects. */ public static void close(Closeable... objs) { close(false, objs); } /** * Call the close method of a list of Closeable objects. * * If the flush parameter is set to true, and an object implements * the Flushable interface, then the flush method will be called before * the close method is called. * * This will not throw a NullPointerException if any of the objects are null. * * This will not throw an IOException if either the close or flush methods throw * an IOException. * * If calling flush causes an IOException, close will still be called. * * @param flush if true, check if the object is Flushable * @param objs one or more Closeable objects */ public static void close(boolean flush, Closeable... objs) { for (Closeable obj : objs) { if (obj != null) { if (flush && (obj instanceof Flushable)) { try { ((Flushable) obj).flush(); } catch (IOException _) { // ignore } } try { obj.close(); } catch (IOException _) { // ignore } } } } /** * Check for null objects in a list of objects. */ private static void checkNull(Object... objs) { for (Object obj : objs) { if (obj == null) throw new NullPointerException(ex_null_param); } } /** * Opens a Reader on a file. * * This method will not throw a FileNotFoundException like the FileReader * constructor would. * * @param file the file to open the reader on * @return the reader, or null if the file could not be opened * @throws NullPointerException if file is null */ public static Reader openReader(File file) { checkNull(file); try { return new FileReader(file); } catch (FileNotFoundException e) { // fall through } return null; } /** * Call the flush method of a list of Flushable objects. * * This method will not throw a NullPointerException if any of the objects are null. * * This method will trap the IOException from flush. * * @param objs one or more Flushable objects */ public static void flush(Flushable... objs) { for (Flushable obj : objs) { if (obj != null) { try { obj.flush(); } catch (IOException e) { // ignore } } } } }