httpUrlConnection中文亂碼

public void getFeiInfo(String sessionId) throws IOException{
   //發送的請求參數，發送的格式也是Json的
   String requestString = getJsonString();
   try {
      //請求的地址
      URL url = new URL("http://182.92.204.151/openInvoice/api/invoice/fpkj");
      HttpURLConnection conn = (HttpURLConnection) url.openConnection();
      //發送Post請求，開啟其讀寫的功能
      conn.setDoOutput(true);
      conn.setDoInput(true);
      conn.setRequestProperty("accpt", "        text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");
      conn.setRequestProperty("User-Agent", "        Mozilla/5.0 (Windows NT 6.1; rv:27.0) Gecko/20100101 Firefox/27.0");
      conn.setRequestProperty("X-Requested-With", "XMLHttpRequest");
      conn.setRequestProperty("Connection", "        keep-alive");
      conn.setRequestProperty("Cookie", sessionId);
      conn.setRequestMethod("POST");
      //發送Post請求
      conn.connect();
      OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());
      //發送參數
      writer.write("data="+requestString);
      writer.flush();
      ByteArrayOutputStream baos=new ByteArrayOutputStream();
      byte[] buf = new byte[1024];
      int len = 0;
      InputStream is = conn.getInputStream();
      while((len=is.read(buf))!=-1){
         baos.write(buf, 0, len);
      }
      baos.flush();
      System.out.println(baos.toString("utf8"));
      baos.close();
      is.close();
   } catch (MalformedURLException ex) {
      ex.printStackTrace();
   } catch (IOException ex) {
      ex.printStackTrace();
   }
}