就一个秘密。ANSI其实就是GBK。

/**
     * 向文件中写入内容
     * @param filepath 文件路径与名称
     * @param newstr  写入的内容
     *              以ansi的编码格式打开文件
     * @return
     * @throws IOException
     */
    private static  boolean writeFileContent2(String filepath,String newstr) throws IOException{
        Boolean bool = false;
        String filein = newstr;//新写入的行
        String temp  = "";

        FileInputStream fis = null;
        InputStreamReader isr = null;
        BufferedReader br = null;
        FileOutputStream fos  = null;
        OutputStreamWriter pw = null;
        try {
            File file = new File(filepath);//文件路径(包括文件名称)
            //将文件读入输入流
            fis = new FileInputStream(file);
            isr = new InputStreamReader(fis);
            br = new BufferedReader(isr);
            StringBuffer buffer = new StringBuffer();

            //文件原有内容
            for(int i=0;(temp =br.readLine())!=null;i++){
                buffer.append(temp);
                // 行与行之间的分隔符 相当于“\n”
                buffer = buffer.append(System.getProperty("line.separator"));
            }
            buffer.append(filein);

            fos = new FileOutputStream(file);
            pw = new OutputStreamWriter(fos,"GBK");
            pw.write(buffer.toString().toCharArray());
            pw.flush();
            bool = true;
        } catch (Exception e) {
            logger.error(e.getMessage());
        }finally {
            //不要忘记关闭
            if (pw != null) {
                pw.close();
            }
            if (fos != null) {
                fos.close();
            }
            if (br != null) {
                br.close();
            }
            if (isr != null) {
                isr.close();
            }
            if (fis != null) {
                fis.close();
            }
        }
        return bool;
    }