在Linux系统下grep指令常见的使用方式有如下两种：
1.grep pattern files – 搜索 files 中匹配 pattern 的内容
2.grep -r pattern dir – 递归搜索 dir 中匹配 pattern 的内容
现有如下方法可实现在Windows系统下通过Java代码实现与第一种使用方法相同的功能：
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;
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 size = (int) fc.size();
MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, size);
//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);
}
}
}
执行java Grep abcd 1.txt 运行效果图如下：
也可以同时搜索多个文件，执行java Grep abcd 1.txt 2.txt 3.txt 4.txt 运行效果如下：
至此，在Windows系统下通过Java代码实现了与Linux系统写grep命令第一种使用方法相同的功能。