Java tutorial
/* * Copyright (c) Ian F. Darwin, http://www.darwinsys.com/, 1996-2002. * All rights reserved. Software written by Ian F. Darwin and others. * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $ * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * * Java, the Duke mascot, and all variants of Sun's Java "steaming coffee * cup" logo are trademarks of Sun Microsystems. Sun's, and James Gosling's, * pioneering role in inventing and promulgating (and standardizing) the Java * language and environment is gratefully acknowledged. * * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for * inventing predecessor languages C and C++ is also gratefully acknowledged. */ // Sun Microsystems Example Code @(#)Grep.java 1.1 01/05/10 //Search a list of files for lines that match a given regular-expression //pattern. Demonstrates NIO mapped byte buffers, charsets, and regular //expressions. import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.nio.CharBuffer; import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; import java.nio.charset.Charset; import java.nio.charset.CharsetDecoder; import java.util.regex.Matcher; import java.util.regex.Pattern; import java.util.regex.PatternSyntaxException; public class GrepSun { // Charset and decoder for ISO-8859-15 private static Charset charset = Charset.forName("ISO-8859-15"); private static CharsetDecoder decoder = charset.newDecoder(); // Pattern used to parse lines private static Pattern linePattern = Pattern.compile(".*\r?\n"); // The input pattern that we're looking for private static Pattern pattern; // Compile the pattern from the command line // private static void compile(String pat) { try { pattern = Pattern.compile(pat); } catch (PatternSyntaxException x) { System.err.println(x.getMessage()); System.exit(1); } } // Use the linePattern to break the given CharBuffer into lines, applying // the input pattern to each line to see if we have a match // private static void grep(File f, CharBuffer cb) { Matcher lm = linePattern.matcher(cb); // Line matcher Matcher pm = null; // Pattern matcher int lines = 0; while (lm.find()) { lines++; CharSequence cs = lm.group(); // The current line if (pm == null) pm = pattern.matcher(cs); else pm.reset(cs); if (pm.find()) System.out.print(f + ":" + lines + ":" + cs); if (lm.end() == cb.limit()) break; } } // Search for occurrences of the input pattern in the given file // private static void grep(File f) throws IOException { // Open the file and then get a channel from the stream FileInputStream fis = new FileInputStream(f); FileChannel fc = fis.getChannel(); // Get the file's size and then map it into memory int sz = (int) fc.size(); MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, sz); // Decode the file into a char buffer CharBuffer cb = decoder.decode(bb); // Perform the search grep(f, cb); // Close the channel and the stream fc.close(); } public static void main(String[] args) { if (args.length < 2) { System.err.println("Usage: java Grep pattern file..."); return; } compile(args[0]); for (int i = 1; i < args.length; i++) { File f = new File(args[i]); try { grep(f); } catch (IOException x) { System.err.println(f + ": " + x); } } } }