/* * Copyright (c) 2000 David Flanagan.  All rights reserved. * This code is from the book Java Examples in a Nutshell, 2nd 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. * You may distribute it non-commercially as long as you retain this notice. * For a commercial use license, or to purchase the book (recommended), * visit http://www.davidflanagan.com/javaexamples2. */package com.davidflanagan.examples.io;import java.io.*;/** * This class is a BufferedReader that filters out all lines that * do not contain the specified pattern. **/public class GrepReader extends BufferedReader {    String pattern;  // The string we are going to be matching.        /** Pass the stream to our superclass, and remember the pattern ourself */    public GrepReader(Reader in, String pattern) {        super(in);        this.pattern = pattern;    }        /**     * This is the filter: call our superclass's readLine() to get the     * actual lines, but only return lines that contain the pattern.     * When the superclass readLine() returns null (EOF), we return null.     **/    public final String readLine() throws IOException {        String line;        do { line = super.readLine(); }        while ((line != null)&& line.indexOf(pattern) == -1);        return line;    }        /**     * This class demonstrates the use of the GrepReader class.     * It prints the lines of a file that contain a specified substring.     **/    public static class Test {        public static void main(String args[]) {            try {                if (args.length != 2)                     throw new IllegalArgumentException("Wrong number of args");                GrepReader in=new GrepReader(new FileReader(args[1]), args[0]);                String line;                while((line = in.readLine()) != null) System.out.println(line);                in.close();            }            catch (Exception e) {                 System.err.println(e);                System.out.println("Usage: java GrepReader$Test" +				   " <pattern> <file>");            }        }    }}