import java.io.*;
import java.util.regex.*;
import org.apache.commons.io.IOUtils;

public class Test{

	static String toString(File f) throws Exception{
		String text=null;

		InputStream fin=new FileInputStream(f);
		text=IOUtils.toString(fin,"UTF-8");
		fin.close();

		return text;
	}

	static String replace(String text){
		Pattern pat=Pattern.compile("(fire)fex");

		StringBuffer sb=new StringBuffer();
		
		Matcher m=pat.matcher(text);
		while( m.find() ){
			String g1=m.group(1);
			m.appendReplacement(sb, g1+"fox");
		}
		m.appendTail(sb);
		
		return sb.toString();
	}


	public static void main(String[] args){
		try{
			File f=new File("firefox.txt");
			String text=toString(f);
			System.out.print("src   :"+text);

			String result=replace(text);
			System.out.print("result:"+result);
		}
		catch(Exception ex){
			ex.printStackTrace();
		}
	}

}