java，把文本中的所有“。”都替换成“，”

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;

public class Test {
public static void main(String[] args) {
try {
replaceTxt("D:\\a.txt", "D:\\b.txt");
} catch (Exception e) {
e.printStackTrace();
}
}

public static void replaceTxt(String s, String d) throws Exception {
File sFile = new File(s);
File dFile = new File(d);
BufferedReader bReader = new BufferedReader(new FileReader(sFile));
BufferedWriter bWriter = new BufferedWriter(new FileWriter(dFile));
String string = "";
while ((string = bReader.readLine()) != null) {
bWriter.write(string.replace("。", "，")+"\r\n");
}
bWriter.close();
bReader.close();
}
}

BufferedInputStream is=new Bu