我要生成的xml结构是
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <a id="1">
    <b>xxx</b>
    <c>xxx</c>
  </a>
结果却是
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <a id="1"><b>xxx</b><c>xxx</c></a>
谁有解决办法