如何XML 字符串获取属性值？

下面的示例 从XML 字符串创建一个 DOM 对象。
然后使用 XPath.selectNodes() 方法应用 XPATH 表达式。

package com.onitroad.xml;
import java.io.IOException;
import java.io.StringReader;
import java.util.ArrayList;
import org.jdom.Document;
import org.jdom.Element;
import org.jdom.JDOMException;
import org.jdom.input.SAXBuilder;
import org.jdom.xpath.XPath;
public class XmlAttributesUsingXPathExample
{
	@SuppressWarnings("unchecked")
	public static void main(String[] args) throws JDOMException, IOException
	{
		Document doc = new SAXBuilder(false).build(new StringReader(new String(
                                               <users>	" +
													<user id='123'>" +
														<firstname>Jack</firstname>" +
													</user>" +
													<user id='456'>" +
														<firstname>Robin</firstname>" +
													</user> " +
													<user id='789'>" +
														<firstname>Tom</firstname>" +
													</user>" +
												</users>")));
		// 构建 xpath 表达式
		XPath xpathExpression = XPath.newInstance("//*[@id]");
		// 应用xpath并获取所有匹配的节点
		ArrayList<Element> userIds =  (ArrayList<Element>) xpathExpression.selectNodes(doc);
		// 遍历所有节点
		for (int i = 0; i < userIds.size(); i++)
        {
        	System.out.println((userIds.get(i)).getAttributeValue("id").trim());
        }
	}
}