java基础----过滤文件中不需要的字符

今天在一个讨论群中有人问了一个问题，要去掉文件中的汉字等特殊字符，只保留数字，写了个小程序实现这个功能

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.List;
/**
 * 读取一个txt文件，去掉其中的汉字，剩下每个数字串存储成一行，存到新文件中
 * @author huangqun
 */
public class KeepNumber {
	public static void main(String[] args) {
		String regExp = "[^0-9]*";//正则表达式   非数字
    	List<String> cacheList = new ArrayList<String>();  //缓存list 用于存放处理后的字符串  每行是一个字符串放到list中   
    	try {
    		//1.读取文件
			String readStr = null;  
			File file = new File("E:/1.txt");//要处理的文件路径   FIXME
    		InputStream is = new FileInputStream(file);
			InputStreamReader isr = new InputStreamReader(is);
			BufferedReader br = new BufferedReader(isr);
			while(null != (readStr = br.readLine())) {
				if("".equals(readStr.trim())) continue;
				readStr = readStr.replaceAll(regExp, "");//替换操作
				cacheList.add(readStr);
			}
			br.close();isr.close();is.close();
			
			//2.把cacheList写到新文件中
			String outPath = file.getAbsolutePath();
			/**
			 * 组装新生成的备份文件路径
			 */
		    outPath = outPath.substring(0, outPath.indexOf(".")) + "bak." + outPath.substring(outPath.indexOf(".")+1, outPath.length());
			File outFile = new File(outPath);
			if (!outFile.exists()) {
				outFile.createNewFile();
			}
			OutputStream os = new FileOutputStream(outFile);
			OutputStreamWriter osw = new OutputStreamWriter(os);
			BufferedWriter bw = new BufferedWriter(osw);
			for (String str : cacheList) {
				System.out.print(str + "\r\n");
				bw.write(str + "\r\n");
			}
			bw.flush();osw.close();os.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}