通常在操作xml的时候，都是通过inputstream（很多情况下是FileInputStream）来读入xml并转为dom的，很多人会遇到这种情况数据不是从文件读入的而是从String中取得的
于是会使用
InputStream in = new ByteArrayInputStream (str.getBytes());来取得inputstream ，但是这种InputStream中数据被转成了byte数组，所以转dom的时候就会报错
可以通过一下思路来解决
// 字符串转XML
String xmlStr = \"......\";
StringReader sr = new StringReader(xmlStr);
InputSource is = new InputSource(sr);
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder=factory.newDocumentBuilder();
Document doc = builder.parse(is);
//XML转字符串
TransformerFactory tf = TransformerFactory.newInstance();
Transformer t = tf.newTransformer();
t.setOutputProperty(\"encoding\",\"GB23121\");//解决中文问题，试过用GBK不行
ByteArrayOutputStream bos = new ByteArrayOutputStream();
t.transform(new DOMSource(doc), new StreamResult(bos));
String xmlStr = bos.toString();
<!-- xml 格式
<books>
<book id='1001'>
<author>andylin</author>
<title>c language</title>
<publisher id="aaa">O'Reilly</publisher>
</book>
<book id='1002'>
<author>congfeng</author>
<t ......
