Grep.java

package jeffaschenk.commons.frameworks.cnxidx.shell;

import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;
import java.util.regex.*;
import java.util.LinkedList;

public class Grep {

    // Charset and decoder for ISO-8859-15
    private static Charset charset = Charset.forName("ISO-8859-15");
    private static CharsetDecoder decoder = charset.newDecoder();

    // Results LinkedLists
    LinkedList<String> gresults = new LinkedList<>();
    LinkedList<String> gcontrol = new LinkedList<>();

    // 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;

    // Default Constructor.
    public Grep() {
    }

    // Compile the pattern from the command line
    //
    private static void compile(String pat) throws PatternSyntaxException {
        pattern = Pattern.compile(pat);
    } // End of compile Method.

    // 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 void grep(File f, CharBuffer cb) throws IOException {
        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()) {
                gcontrol.addLast(f + ":" + lines);
                gresults.addLast(cs.toString());
            } // End of find if.
            if (lm.end() == cb.limit()) {
                break;
            }
        } // End of While Loop.
    } // End of grep method.

    // Search for occurrences of the input pattern in the given file
    //
    public void grep(File f, String _pattern) throws IOException, PatternSyntaxException {

        // 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);

        // Compile the Pattern
        compile(_pattern);

        // Perform the search
        grep(f, cb);

        // Close the channel and the stream
        fc.close();

    } // End of grep Method.

    // Dump Results for a Grep.
    public void dumpResults() {
        // ***************************
        // Iterate through the Results
        for (int i = 0; i < gcontrol.size(); i++) {
            System.out.print(gcontrol.get(i) + ": ");
            System.out.print(gresults.get(i));
        } // End of While Loop.
    } // End of dumpResults Method.

    // Obtain Results from the Grep.
    public LinkedList obtainResults() {
        return (gresults);
    } // End of obtainResults Method.

    // Obtain Control Info from the Grep.
    public LinkedList obtainControl() {
        return (gcontrol);
    } // End of obtainControl Method.

    /**
     * main to provide command line capability.
     */
    public static void main(String[] args) {
        if (args.length < 2) {
            System.err.println("Usage: java Grep pattern file...");
            return;
        }
        for (int i = 1; i < args.length; i++) {
            File f = new File(args[i]);
            try {
                Grep gx = new Grep();
                gx.grep(f, args[0]);
                gx.dumpResults();
            } catch (IOException x) {
                System.err.println(f + ": " + x);
            }
        }
    } // End of Main.

} ///:~ Grep