使用HttpServletRequest获取请求body

可以使用HttpServletRequest的getReader()方法获取请求body，示例代码如下：

HttpServletRequest request = ...;
StringBuilder sb = new StringBuilder();
BufferedReader reader = request.getReader();
char[] buf = new char[1024];
int len;
while ((len = reader.read(buf)) != -1) {
    sb.append(buf, 0, len);
}
String requestBody = sb.toString();