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