Another Example of Grep

package com.darwinsys;
 
/*
 * 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);
	    }
	}
    }
 
}