要解析的string爲response
1.將字符串轉換城數據流對象InputStream
ByteArrayInputStream in=new ByteArrayInputStream(response.getBytes());
2.將數據流轉化成document對象
Document document =DocumentBuilderFactory.newInstance().newDocumentBuilder.Parse(in);
3.將document對象轉化城url
Element root=document.getDocumetElement();
NodeList nodes=root.getElementsByTagName("node");
Node node=nodes.item(0);
String url=node.getFirstChild().getNodeValue();
return url;