系出名门Android(10) - HTTP 通信, XML 解析, 通过 Hander 实现异步消息处理

系出名门Android(10) - HTTP 通信, XML 解析, 通过 Hander 实现异步消息处理


介绍
在 Android 中与服务端做 HTTP 通信，解析 XML，通过 Handler 实现异步消息处理
HTTP 通信 - 与服务端做 HTTP 通信，分别以 GET 方式和 POST 方式做演示
XML 解析 - 可以用两种方式解析 XML，分别是 DOM 方式和 SAX 方式
异步消息处理 - 通过 Handler 实现异步消息处理，以一个自定义的异步下载类来说明 Handler 的用法 


1、HTTP 通信和 XML 解析的 Demo
MySAXHandler.java

代码 
package com.webabcd.communication;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

// 继承 DefaultHandler 以实现指定 XML 的 SAX 解析器
// DOM - W3C 标准，需要把 xml 数据全部加载完成后才能对其做解析，可对树做任意遍历
// SAX - 流式解析，通过事件模型解析 xml，只能顺序解析
public class MySAXHandler extends DefaultHandler {

    private boolean mIsTitleTag = false;
    private boolean mIsSalaryTag = false;
    private boolean mIsBirthTag = false;
    private String mResult = "";
    
    // 打开 xml 文档的回调函数
    @Override
    public void startDocument() throws SAXException {
        // TODO Auto-generated method stub
        super.startDocument();
    }
    
    // 关闭 xml 文档的回调函数
    @Override
    public void endDocument() throws SAXException {
        // TODO Auto-generated method stub
        super.endDocument();
    }
    
    // 一发现元素开始标记就回调此函数
    @Override
    public void startElement(String uri, String localName, String qName,
            Attributes attributes) throws SAXException {
        if (localName == "title")
            mIsTitleTag = true;
        else if (localName == "salary")
            mIsSalaryTag = true;
        else if (localName == "dateOfBirth")
            mIsBirthTag = true;
        else if (localName == "employee")
            mResult += "\nname:" + attributes.getValue("name");    
    }

    // 一发现元素结束标记就回调此函数
    @Override
    public void endElement(String uri, String localName, String qName)
            throws SAXException {
        if (localName == "title")
            mIsTitleTag = false;
        else if (localName == "salary")
            mIsSalaryTag = false;
        else if (localName == "dateOfBirth")
            mIsBirthTag = false;
    }

    // 一发现元素值或属性值就回调此函数
    @Override
    public void characters(char[] ch, int start, int length)
            throws SAXException {
        if (mIsTitleTag)
            mResult += new String(ch, start, length);
        else if (mIsSalaryTag)
            mResult += " salary:" + new String(ch, start, length);
        else if (mIsBirthTag)
            mResult += " dateOfBirth:" + new String(ch, start, length);
    }
    
    public String getResult(){
        return mResult;
    }
}


Main.java

代码 
package com.webabcd.communication;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.protocol.HTTP;
import org.apache.http.util.ByteArrayBuffer;
import org.apache.http.util.EncodingUtils;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.XMLReader;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class Main extends Activity {
    
    private TextView textView;
    
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        textView = (TextView) this.findViewById(R.id.textView);
        
        Button btn1 = (Button) this.findViewById(R.id.btn1);
        btn1.setText("http get demo");
        btn1.setOnClickListener(new Button.OnClickListener() {
            public void onClick(View v) {
                httpGetDemo();
            }
        });
        
        Button btn2 = (Button) this.findViewById(R.id.btn2);
        btn2.setText("http post demo");
        btn2.setOnClickListener(new Button.OnClickListener() {
            public void onClick(View v) {
                httpPostDemo();
            }
        });
        
        Button btn3 = (Button) this.findViewById(R.id.btn3);
        // DOM - Document Object Model
        btn3.setText("DOM 解析 XML");
        btn3.setOnClickListener(new Button.OnClickListener() {
            public void onClick(View v) {
                DOMDemo();
            }
        });
        
        Button btn4 = (Button) this.findViewById(R.id.btn4);
        // SAX - Simple API for XML
        btn4.setText("SAX 解析 XML");
        btn4.setOnClickListener(new Button.OnClickListener() {
            public void onClick(View v) {
                SAXDemo();
            }
        });
    }
    
    // Android 调用 http 协议的 get 方法
    // 本例：以 http 协议的 get 方法获取远程页面响应的内容
    private void httpGetDemo(){
        try {
            // 模拟器测试时，请使用外网地址
            URL url = new URL("http://xxx.xxx.xxx");
            URLConnection con = url.openConnection();
            
            String result = "http status code: " + ((HttpURLConnection)con).getResponseCode() + "\n";
            // HttpURLConnection.HTTP_OK
            
            InputStream is = con.getInputStream();
            BufferedInputStream bis = new BufferedInputStream(is);
            ByteArrayBuffer bab = new ByteArrayBuffer(32);
            int current = 0;
            while ( (current = bis.read()) != -1 ){
                bab.append((byte)current);
            }
            result += EncodingUtils.getString(bab.toByteArray(), HTTP.UTF_8);
            
            bis.close();
            is.close();

            textView.setText(result);
        } catch (Exception e) {
            textView.setText(e.toString());
        }
    }
    
    // Android 调用 http 协议的 post 方法
    // 本例：以 http 协议的 post 方法向远程页面传递参数，并获取其响应的内容
    private void httpPostDemo(){
        try {
            // 模拟器测试时，请使用外网地址
            String url = "http://5billion.com.cn/post.php";
            Map<String, String> data = new HashMap<String, String>();
            data.put("name", "webabcd");
            data.put("salary", "100");
            
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            ArrayList<BasicNameValuePair> postData = new ArrayList<BasicNameValuePair>();
            for (Map.Entry<String, String> m : data.entrySet()) {
                postData.add(new BasicNameValuePair(m.getKey(), m.getValue()));
            }

            UrlEncodedFormEntity entity = new UrlEncodedFormEntity(postData, HTTP.UTF_8);
            httpPost.setEntity(entity);
            
            HttpResponse response = httpClient.execute(httpPost);
            
            String result = "http status code: " + response.getStatusLine().getStatusCode() + "\n";
            // HttpURLConnection.HTTP_OK
            
            HttpEntity httpEntity = response.getEntity();
            
            InputStream is = httpEntity.getContent();
            result += convertStreamToString(is);
            
            textView.setText(result);
        } catch (Exception e) {
            textView.setText(e.toString());    
        }
    }
    
    // 以 DOM 方式解析 XML（xml 数据详见 res/raw/employee.xml）
    private void DOMDemo(){
        try    {
            DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
            Document doc = docBuilder.parse(this.getResources().openRawResource(R.raw.employee));
            Element rootElement = doc.getDocumentElement();
            NodeList employeeNodeList = rootElement.getElementsByTagName("employee");
            
            textView.setText("DOMDemo" + "\n");
            String title = rootElement.getElementsByTagName("title").item(0).getFirstChild().getNodeValue();
            textView.append(title);
            for (int i=0; i<employeeNodeList.getLength(); i++){
                Element employeeElement = ((Element)employeeNodeList.item(i));
                String name = employeeElement.getAttribute("name");
                String salary = employeeElement.getElementsByTagName("salary").item(0).getFirstChild().getNodeValue();
                String dateOfBirth = employeeElement.getElementsByTagName("dateOfBirth").item(0).getFirstChild().getNodeValue();
                textView.append("\nname: "+name+" salary: "+salary+" dateOfBirth: " + dateOfBirth);
            }
        } catch (Exception e) {
            textView.setText(e.toString());    
        }
    }
    
    // 以 SAX 方式解析 XML（xml 数据详见 res/raw/employee.xml）
    // SAX 解析器的实现详见 MySAXHandler.java
    private void SAXDemo(){
        try    {
            SAXParserFactory saxFactory = SAXParserFactory.newInstance();
            SAXParser parser = saxFactory.newSAXParser();
            XMLReader reader = parser.getXMLReader();
            
            MySAXHandler handler = new MySAXHandler();
            reader.setContentHandler(handler);
            reader.parse(new InputSource(this.getResources().openRawResource(R.raw.employee)));
            String result = handler.getResult();
            textView.setText("SAXDemo" + "\n");
            textView.append(result);
        } catch (Exception e) {
            textView.setText(e.toString());    
        }
    }

    // 辅助方法，用于把流转换为字符串
    private String convertStreamToString(InputStream is) {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();   

        String line = null;
        try {
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }   

        return sb.toString();
    }
}


2、用 Handler 来实现异步消息处理，以一个可以实时汇报下载进度的异步下载类为例
开发一个 Android 类库，本例中此类库名为 webabcd_util

New -> Java Project
项目上点右键 -> Build Path -> Add Libraries -> User Library -> User Libraries -> New -> 为类库起个名字 -> 选中这个类库 -> Add JARs 导入 Android 的 jar 包
项目上点右键 -> Build Path -> Add Libraries -> User Library -> 选择 Android 库

DownloadManagerAsync.java

代码 
package webabcd.util;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;

import org.apache.http.protocol.HTTP;

import android.os.Handler;
import android.os.Message;
import android.util.Log;

// 以一个实例，即异步下载，来演示 Android 的异步消息处理（用 Handler 的方式）
public class DownloadManagerAsync {

    public DownloadManagerAsync() {

    }

    // 实例化自定义的 Handler
    EventHandler mHandler = new EventHandler(this);

    // 按指定 url 地址下载文件到指定路径
    public void download(final String url, final String savePath) {
        new Thread(new Runnable() {
            public void run() {
                try {
                    sendMessage(FILE_DOWNLOAD_CONNECT);
                    URL sourceUrl = new URL(url);
                    URLConnection conn = sourceUrl.openConnection();
                    InputStream inputStream = conn.getInputStream();

                    int fileSize = conn.getContentLength();

                    File savefile = new File(savePath);
                    if (savefile.exists()) {
                        savefile.delete();
                    }
                    savefile.createNewFile();

                    FileOutputStream outputStream = new FileOutputStream(
                            savePath, true);

                    byte[] buffer = new byte[1024];
                    int readCount = 0;
                    int readNum = 0;
                    int prevPercent = 0;
                    while (readCount < fileSize && readNum != -1) {
                        readNum = inputStream.read(buffer);
                        if (readNum > -1) {
                            outputStream.write(buffer);
                            readCount = readCount + readNum;

                            int percent = (int) (readCount * 100 / fileSize);
                            if (percent > prevPercent) {
                                // 发送下载进度信息
                                sendMessage(FILE_DOWNLOAD_UPDATE, percent,
                                        readCount);

                                prevPercent = percent;
                            }
                        }
                    }

                    outputStream.close();
                    sendMessage(FILE_DOWNLOAD_COMPLETE, savePath);

                } catch (Exception e) {
                    sendMessage(FILE_DOWNLOAD_ERROR, e);
                    Log.e("MyError", e.toString());
                }
            }
        }).start();
    }

    // 读取指定 url 地址的响应内容
    public void download(final String url) {
        new Thread(new Runnable() {
            public void run() {
                try {
                    sendMessage(FILE_DOWNLOAD_CONNECT);
                    URL sourceUrl = new URL(url);
                    URLConnection conn = sourceUrl.openConnection();
                    conn.setConnectTimeout(3000);
                    BufferedReader reader = new BufferedReader(
                            new InputStreamReader(conn.getInputStream(),
                                    HTTP.UTF_8));

                    String line = null;
                    StringBuffer content = new StringBuffer();
                    while ((line = reader.readLine()) != null) {
                        content.append(line);
                    }

                    reader.close();

                    sendMessage(FILE_DOWNLOAD_COMPLETE, content.toString());

                } catch (Exception e) {
                    sendMessage(FILE_DOWNLOAD_ERROR, e);
                    Log.e("MyError", e.toString());
                }
            }
        }).start();
    }

    // 向 Handler 发送消息
    private void sendMessage(int what, Object obj) {
        // 构造需要向 Handler 发送的消息
        Message msg = mHandler.obtainMessage(what, obj);
        // 发送消息
        mHandler.sendMessage(msg);
    }

    private void sendMessage(int what) {
        Message msg = mHandler.obtainMessage(what);
        mHandler.sendMessage(msg);
    }

    private void sendMessage(int what, int arg1, int arg2) {
        Message msg = mHandler.obtainMessage(what, arg1, arg2);
        mHandler.sendMessage(msg);
    }

    private static final int FILE_DOWNLOAD_CONNECT = 0;
    private static final int FILE_DOWNLOAD_UPDATE = 1;
    private static final int FILE_DOWNLOAD_COMPLETE = 2;
    private static final int FILE_DOWNLOAD_ERROR = -1;

    // 自定义的 Handler
    private class EventHandler extends Handler {
        private DownloadManagerAsync mManager;

        public EventHandler(DownloadManagerAsync manager) {
            mManager = manager;
        }

        // 处理接收到的消息
        @Override
        public void handleMessage(Message msg) {

            switch (msg.what) {
            case FILE_DOWNLOAD_CONNECT:
                if (mOnDownloadConnectListener != null)
                    mOnDownloadConnectListener.onDownloadConnect(mManager);
                break;
            case FILE_DOWNLOAD_UPDATE:
                if (mOnDownloadUpdateListener != null)
                    mOnDownloadUpdateListener.onDownloadUpdate(mManager,
                            msg.arg1);
                break;
            case FILE_DOWNLOAD_COMPLETE:
                if (mOnDownloadCompleteListener != null)
                    mOnDownloadCompleteListener.onDownloadComplete(mManager,
                            msg.obj);
                break;
            case FILE_DOWNLOAD_ERROR:
                if (mOnDownloadErrorListener != null)
                    mOnDownloadErrorListener.onDownloadError(mManager,
                            (Exception) msg.obj);
                break;
            default:
                break;
            }
        }
    }

    // 定义连接事件
    private OnDownloadConnectListener mOnDownloadConnectListener;
    public interface OnDownloadConnectListener {
        void onDownloadConnect(DownloadManagerAsync manager);
    }
    public void setOnDownloadConnectListener(OnDownloadConnectListener listener) {
        mOnDownloadConnectListener = listener;
    }

    // 定义下载进度更新事件
    private OnDownloadUpdateListener mOnDownloadUpdateListener;
    public interface OnDownloadUpdateListener {
        void onDownloadUpdate(DownloadManagerAsync manager, int percent);
    }
    public void setOnDownloadUpdateListener(OnDownloadUpdateListener listener) {
        mOnDownloadUpdateListener = listener;
    }

    // 定义下载完成事件
    private OnDownloadCompleteListener mOnDownloadCompleteListener;
    public interface OnDownloadCompleteListener {
        void onDownloadComplete(DownloadManagerAsync manager, Object result);
    }
    public void setOnDownloadCompleteListener(
            OnDownloadCompleteListener listener) {
        mOnDownloadCompleteListener = listener;
    }

    // 定义下载异常事件
    private OnDownloadErrorListener mOnDownloadErrorListener;
    public interface OnDownloadErrorListener {
        void onDownloadError(DownloadManagerAsync manager, Exception e);
    }
    public void setOnDownloadErrorListener(OnDownloadErrorListener listener) {
        mOnDownloadErrorListener = listener;
    }
}


调用上面的自定义的 Android 类库

项目上点右键 -> Properties -> Java Build Path -> Projects -> Add 引用上面的类库

Main.java

代码 
package com.webabcd.handler;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

import webabcd.util.DownloadManagerAsync;

public class Main extends Activity implements
        DownloadManagerAsync.OnDownloadCompleteListener,
        DownloadManagerAsync.OnDownloadUpdateListener,
        DownloadManagerAsync.OnDownloadErrorListener {
    
    TextView txt;
    
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        DownloadManagerAsync manager = new DownloadManagerAsync();
        manager.setOnDownloadCompleteListener(this);
        manager.setOnDownloadUpdateListener(this);
        manager.download("http://files.cnblogs.com/webabcd/Android.rar", "/sdcard/Android.rar");
        
        txt = (TextView) this.findViewById(R.id.txt);
        txt.setText("开始下载");
    }

    public void onDownloadComplete(DownloadManagerAsync manager, Object result) {

        txt.setText("下载完成");
    }
    
    public void onDownloadUpdate(DownloadManagerAsync manager, int percent) {

        txt.setText("下载进度：" + String.valueOf(percent) + "%");
    }
    
    public void onDownloadError(DownloadManagerAsync manager, Exception e) {

        txt.setText("下载出错");
    }
}