Android入门：通过XML数据与服务器进行通信

一、与服务器通信

类似于浏览器与服务器通信，Android应用也可以与Web服务器通信，比如Android应用可以访问Servlet、JSP、图片等等；

Web服务器通过指定Content-Type可以指定返回的数据的类型，比如text/html表示网页，text/xml表示XML数据，image/jpeg为图片；

二、通过XML让客户端和服务器交流数据

比如Android客户端打开相亲网，则返回的是多个人的序列，包含人的姓名、年龄等信息，而怎么组织这些数据返回给客户端呢？用XML很方便；

三、代码实现

服务器使用了dom4j组织XML数据，并返回给客户端；

代码结构如下：

package org.xiazdong.servlet; import java.io.IOException; import java.util.ArrayList; import java.util.List; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.dom4j.Document; import org.dom4j.DocumentHelper; import org.dom4j.Element; import org.xiazdong.domain.Person; @WebServlet("/ListServlet") public class ListServlet extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request,response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { List list = new ArrayList(); for(int i=0;i<4;i++){ Person person = new Person(i,"xiazdong-"+i,20+i); list.add(person); } Document document = DocumentHelper.createDocument(); Element persons = DocumentHelper.createElement("persons"); document.add(persons); for(int i=0;i<4;i++){ persons.addElement("person").addAttribute("id", list.get(i).getId()+""); persons.addElement("name").addText(list.get(i).getName()); persons.addElement("age").addText(list.get(i).getAge()+""); } String xml = document.asXML(); //用dom4j组织一个XML字符串 response.setContentType("text/xml; charset=UTF-8"); //设置返回值的类型 response.getOutputStream().write(xml.getBytes("UTF-8")); //设置返回值 } }

如果让浏览器访问，效果如下：

（注：Chrome打开总是显示不出XML声明。请用IE打开）

接下来，我们可以开发客户端，目标是用列表显示这些数据；

在AndroidManifest.xml中加入：

每个item的布局如下：

MainActivity.java

package org.xiazdong.personlist; import java.io.InputStream; import java.net.HttpURLConnection; import java.net.URL; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import org.xiazdong.domain.Person; import org.xmlpull.v1.XmlPullParser; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.util.Xml; import android.widget.ListView; import android.widget.SimpleAdapter; public class MainActivity extends Activity { private ListView listView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); listView = (ListView) this.findViewById(R.id.listview); List persons = null; try { persons = getXMLData(); } catch (Exception e) { e.printStackTrace(); } List> maps = new ArrayList>(); for (Person person : persons) { HashMap map = new HashMap(); map.put("id", person.getId()); map.put("name", person.getName()); map.put("age", person.getAge()); maps.add(map); } SimpleAdapter adapter = new SimpleAdapter(this, maps, R.layout.item, new String[] { "id", "name", "age" }, new int[] { R.id.id, R.id.name, R.id.age }); listView.setAdapter(adapter); } //读取XML数据并转为List private List getXMLData() throws Exception { List persons = new ArrayList(); Person person = null; URL url = new URL("http://192.168.0.103:8080/Server/ListServlet"); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); if (conn.getResponseCode() == 200) { InputStream in = conn.getInputStream(); XmlPullParser parser = Xml.newPullParser(); parser.setInput(in, "UTF-8"); int event = parser.getEventType(); while (event != XmlPullParser.END_DOCUMENT) { Log.i("start_document", "start_document"); switch (event) { case XmlPullParser.START_TAG: if ("person".equals(parser.getName())) { person = new Person(); person.setId(Integer.parseInt(parser.getAttributeValue(0))); } if (("name").equals(parser.getName())) { person.setName(parser.nextText()); } if ("age".equals(parser.getName())) { person.setAge(Integer.parseInt(parser.nextText())); } break; case XmlPullParser.END_TAG: if ("person".equals(parser.getName())) { persons.add(person); Log.i("person", person.toString()); } break; } event = parser.next(); } } return persons; } }
效果如下：