执行以下代码时，我得到了输出，但是有些杂乱无章。我该如何清理乱码？

代码：

 protected void doPost(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException {

    StringBuilder buffer = new StringBuilder();
    BufferedReader reader = req.getReader();
    String line;
    while ((line = reader.readLine()) != null) {
        buffer.append(line);
    }}

输出：

7B%22eventType%22%3A%22created%22%2C%22transactionId%22%3A%22573975943%22%2C%22transactionDate%22%3A%222019-11-16+18%3A10%3A39%22%2C%22transactionAmount%22%3A%22162.00%22%2C%22commission%22%3A%2212.96