Android入門：通過XML資料與伺服器進行通訊

一、與伺服器通訊

類似於瀏覽器與伺服器通訊，Android應用也可以與Web伺服器通訊，比如Android應用可以訪問Servlet、JSP、圖片等等；

Web伺服器通過指定Content-Type可以指定返回的資料的類型，比如text/html表示網頁，text/xml表示XML資料，image/jpeg為圖片；

二、通過XML讓用戶端和伺服器交流資料比如Android用戶端開啟相親網，則返回的是多個人的序列，包含人的姓名、年齡等資訊，而怎麼組織這些資料返回給用戶端呢？用XML很方便；三、代碼實現伺服器使用了dom4j組織XML資料，並返回給用戶端；代碼結構如下：

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<Person> list = new ArrayList<Person>();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組織一個XML字串response.setContentType("text/xml; charset=UTF-8");//設定傳回值的類型response.getOutputStream().write(xml.getBytes("UTF-8"));//設定傳回值}}

如果讓瀏覽器訪問，效果如下：（註：Chrome開啟總是顯示不出XML聲明。請用IE開啟）接下來，我們可以開發用戶端，目標是用列表顯示這些資料；在AndroidManifest.xml中加入：

<uses-permission android:name="android.permission.INTERNET" />

每個item的布局如下：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="horizontal" >    <TextView        android:layout_width="50dp"        android:layout_height="wrap_content"         android:id="@+id/id"        />    <TextView        android:layout_width="100dp"        android:layout_height="wrap_content"         android:id="@+id/name"        /><TextView        android:layout_width="50dp"        android:layout_height="wrap_content"         android:id="@+id/age"        /></LinearLayout>

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;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);listView = (ListView) this.findViewById(R.id.listview);List<Person> persons = null;try {persons = getXMLData();} catch (Exception e) {e.printStackTrace();}List<Map<String, Object>> maps = new ArrayList<Map<String, Object>>();for (Person person : persons) {HashMap<String, Object> map = new HashMap<String, Object>();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);}//讀取XML資料並轉為List<Person>private List<Person> getXMLData() throws Exception {List<Person> persons = new ArrayList<Person>();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：