使用java实现grep功能(FileChannel, Pattern, MappedByteBuffer 直接字节缓冲区，其内容是文件的内存映射区域)
利用正则表达式查找一系列文件,类似于grep功能. 演示了 NIO mapped byte buffers, charsets, and regular expressions

import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;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;/** * User: wenzhihong * Date: 12-2-23 * Time: 上午10:06 */public class Grep {    private static Charset charset = Charset.forName("utf-8");    private static CharsetDecoder decoder = charset.newDecoder();        private static Pattern linePattern = Pattern.compile(".*\r?\n");    private static Pattern pattern;    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 e) {                System.err.println(f + ":" + e);            }        }    }    private static void grep(File f) throws IOException {        //取得 FileChannel        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);        //把 字节buffer decode 成 charBuffer        CharBuffer cb = decoder.decode(bb);                grep(f, cb);        fc.close();    }    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 curLineCs = lm.group();//the current line            if (pm == null){                pm = pattern.matcher(curLineCs);            } else {                pm.reset(curLineCs);            }                        if (pm.find()){                System.out.println(f + ":" + lines + ":" + curLineCs);            }            if (lm.end() == cb.limit()) { //文件最后                break;            }        }            }    private static void compile(String pat) {        try {            pattern = Pattern.compile(pat);        } catch (PatternSyntaxException e) {            System.err.println(e.getMessage());            System.exit(1);        }    }}