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：
[java]
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：
[html]
<uses-permission android:name="android.permission.INTERNET" />
每个item的布局如下：
[html]
<?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
[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<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);
}
//读取XML数据并转为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：
作者：xiazdong