使用dom4j和xpath

使用dom4j和XPath
配置开发包
dom4j-1.6.1.jar
jaxen-1.1-beta-6.jar（XPath必备）

取某一节点
Element root = (Element) document.selectSingleNode("//root");

取某一节点的属性
Attribute attribute = (Attribute) document.selectSingleNode("//root/cell/@value");

使用经验
我们在做系统间交互时，通常通过自定义的xml文件进行数据交换。例如：系统A需要向系统B传输一个xml字串的条件如下：

   <?xml version="1.0" encoding="gb2312"?>  
   <root systemid="Darenkou" userid="admin" default="DA" icon="0000">  
         <cell value=""/>  
   </root>

系统A只需填充cell节点的value属性值，我的建议是将这段xml写成本地文件，每次传输时首先读取xml文件，再置cell节点的 value属性值，然后将xml对象转变成字串传给系统B。这样的优点是：一般systemid="Darenkou" userid="admin" default="DA" icon="0000" 是传输参数，当有所变动时只需修改本地文件即可。

详细例程
test.xml



            <?xml version="1.0" encoding="gb2312"?>;
            <root id="TK12" name="管理员" value=""/>;



XmlTest.java

import java.io.File;
            import java.io.IOException;
            import java.io.StringWriter;
            import java.io.UnsupportedEncodingException;
            import java.util.HashMap;
            import java.util.Iterator;
            
            import org.dom4j.Document;
            import org.dom4j.DocumentException;
            import org.dom4j.Element;
            import org.dom4j.io.OutputFormat;
            import org.dom4j.io.SAXReader;
            import org.dom4j.io.XMLWriter;
            
            public class XmlTest {
                   public static String generateXml(HashMap map) {
                          String strXml = null;
            
                          if (map != null) {
            
                                 SAXReader reader = new SAXReader();
                                 Document document = null;
            
                                 try {
                                        document = reader.read(new File("D:/test.xml"));
                                 } catch (DocumentException e) {
                                        e.printStackTrace();
            
                                 }
            
                                 Element root = (Element) document.selectSingleNode("//root");
                                 root.attribute("value").setValue("分布");
            
                                 Iterator iter = map.keySet().iterator();
                                 while (iter.hasNext()) {
                                        String key = (String) iter.next();
                                        String value = (String) map.get(key);
            
                                        Element element = root.addElement("cell").addAttribute("value",
                                                      key);
                                        element.addElement("element").addAttribute("type", "数值")
                                                      .addAttribute("name", "人数").addText(value);
            
                                 }
            
                                 strXml = encodeXml(document, "gb2312");
                          }
            
                          return strXml;
                   }
            
                   private static String encodeXml(Document document, String aEncode) {
                          // 进行编码转换
                          StringWriter sw = new StringWriter();
            
                          OutputFormat format = OutputFormat.createPrettyPrint();
                          format.setEncoding(aEncode);
            
                          try {
                                 XMLWriter writer = new XMLWriter(format);
                                 writer.setWriter(sw);
                                 writer.write(document);
                          } catch (UnsupportedEncodingException e) {
                                 e.printStackTrace();
                          } catch (IOException e) {
                                 e.printStackTrace();
                          }
            
                          return sw.toString();
                   }
            
                   public static void main(String[] args) {
                          HashMap map = new HashMap();
                          map.put("上海", "200");
                          map.put("北京", "300");
                          map.put("天津", "300");
            
                          System.out.println(generateXml(map));
            
                   }
            }

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