BGrep: a regular expression search utility, like Unix grep
/*
* Copyright (c) 2004 David Flanagan. All rights reserved.
* This code is from the book Java Examples in a Nutshell, 3nd Edition.
* It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
* You may study, use, and modify it for any non-commercial purpose,
* including teaching and use in open-source projects.
* You may distribute it non-commercially as long as you retain this notice.
* For a commercial use license, or to purchase the book,
* please visit http://www.davidflanagan.com/javaexamples3.
*/
//package je3.nio;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.UnsupportedCharsetException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;
/**
* BGrep: a regular expression search utility, like Unix grep, but
* block-oriented instead of line-oriented. For any match found, the filename
* and character position within the file (note: not the line number) are
* printed along with the text that matched.
*
* Usage: java je3.nio.BGrep [options] <pattern> <files>...
*
* Options: -e <encoding> specifies and encoding. UTF-8 is the default -i
* enables case-insensitive matching. Use -s also for non-ASCII text -s enables
* strict (but slower) processing of non-ASCII characters
*
* This program requires that each file to be searched fits into main memory,
* and so does not work with extremely large files.
*/
public class BGrep {
public static void main(String[] args) {
String encodingName = "UTF-8"; // Default to UTF-8 encoding
int flags = Pattern.MULTILINE; // Default regexp flags
try { // Fatal exceptions are handled after this try block
// First, process any options
int nextarg = 0;
while (args[nextarg].charAt(0) == '-') {
String option = args[nextarg++];
if (option.equals("-e")) {
encodingName = args[nextarg++];
} else if (option.equals("-i")) { // case-insensitive matching
flags |= Pattern.CASE_INSENSITIVE;
} else if (option.equals("-s")) { // Strict Unicode processing
flags |= Pattern.UNICODE_CASE; // case-insensitive Unicode
flags |= Pattern.CANON_EQ; // canonicalize Unicode
} else {
System.err.println("Unknown option: " + option);
usage();
}
}
// Get the Charset for converting bytes to chars
Charset charset = Charset.forName(encodingName);
// Next argument must be a regexp. Compile it to a Pattern object
Pattern pattern = Pattern.compile(args[nextarg++], flags);
// Require that at least one file is specified
if (nextarg == args.length)
usage();
// Loop through each of the specified filenames
while (nextarg < args.length) {
String filename = args[nextarg++];
CharBuffer chars; // This will hold complete text of the file
try { // Handle per-file errors locally
// Open a FileChannel to the named file
FileInputStream stream = new FileInputStream(filename);
FileChannel f = stream.getChannel();
// Memory-map the file into one big ByteBuffer. This is
// easy but may be somewhat inefficient for short files.
ByteBuffer bytes = f.map(FileChannel.MapMode.READ_ONLY, 0, f.size());
// We can close the file once it is is mapped into memory.
// Closing the stream closes the channel, too.
stream.close();
// Decode the entire ByteBuffer into one big CharBuffer
chars = charset.decode(bytes);
} catch (IOException e) { // File not found or other problem
System.err.println(e); // Print error message
continue; // and move on to the next file
}
// This is the basic regexp loop for finding all matches in a
// CharSequence. Note that CharBuffer implements CharSequence.
// A Matcher holds state for a given Pattern and text.
Matcher matcher = pattern.matcher(chars);
while (matcher.find()) { // While there are more matches
// Print out details of the match
System.out.println(filename + ":" + // file name
matcher.start() + ": " + // character pos
matcher.group()); // matching text
}
}
}
// These are the things that can go wrong in the code above
catch (UnsupportedCharsetException e) { // Bad encoding name
System.err.println("Unknown encoding: " + encodingName);
} catch (PatternSyntaxException e) { // Bad pattern
System.err.println("Syntax error in search pattern:\n" + e.getMessage());
} catch (ArrayIndexOutOfBoundsException e) { // Wrong number of arguments
usage();
}
}
/** A utility method to display invocation syntax and exit. */
public static void usage() {
System.err.println("Usage: java BGrep [-e <encoding>] [-i] [-s]" + " <pattern> <filename>...");
System.exit(1);
}
}
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