Java ANSI轉碼UTF-8

public static void change(String filepath) throws UnsupportedEncodingException, IOException{
    BufferedReader buf = null;
    OutputStreamWriter pw=null;        
    String str = null;
    String allstr="";
        
    //用於輸入換行符的字節碼
    byte[] c=new byte[2];
        c[0]=0x0d;
        c[1]=0x0a;
        String t=new String(c);
        
        buf=new BufferedReader(new InputStreamReader(new FileInputStream(filepath), "GBK"));
        while((str = buf.readLine()) != null){
            allstr=allstr+str+t;
        }
        
        buf.close();        

        pw =new OutputStreamWriter(new FileOutputStream(filepath),"UTF-8");
        pw.write(allstr); 
        pw.close();
    }

　　嘗試用了StringBuffer進行內容的存儲，結果亂碼，原因待查。最后使用String相加的方式解決。