public static void main(String[] args) throws IOException {
　　　　　//源文件为gbk编码
        /*FileReader fr=new FileReader("a.txt");
        OutputStreamWriter osw=new OutputStreamWriter(new FileOutputStream("b.txt"),"utf-8");

        int i;
        while((i=fr.read())!=-1){
            osw.write(i);
        }
        fr.close();
        osw.close();*/

　　　　　//源文件为utf-8编码
        InputStreamReader isr=new InputStreamReader(new FileInputStream("b.txt"),"utf-8");
        FileWriter fw=new FileWriter("a.txt");
        int j;
        while((j=isr.read())!=-1){
            fw.write(j);
        }
        isr.close();
        fw.close();
    }