android HTTP 通信, XML 解析, 通过 Hander 实现异步消息处理（2）

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2010-02-03 10:56

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");
}
}