Android多线程下载示例详解

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
 xmlns:tools="http://schemas.android.com/tools" 
 android:layout_width="match_parent" 
 android:layout_height="match_parent" 
 android:paddingBottom="@dimen/activity_vertical_margin" 
 android:paddingLeft="@dimen/activity_horizontal_margin" 
 android:paddingRight="@dimen/activity_horizontal_margin" 
 android:paddingTop="@dimen/activity_vertical_margin" 
 android:orientation="vertical" 
 tools:context=".MainActivity" > 
 
 <TextView 
 android:layout_width="match_parent" 
 android:layout_height="wrap_content" 
 android:text="下载路径" /> 
 
 <EditText 
 android:id="@+id/ed_path" 
 android:layout_width="match_parent" 
 android:layout_height="wrap_content" 
 android:text="http://192.168.0.170:8080/web/youdao.exe"/> 
 <Button 
 android:layout_width="wrap_content" 
 android:layout_height="wrap_content" 
 android:text="下载" 
 android:onClick="download"/> 
 
 <ProgressBar 
 android:id="@+id/pb" 
 android:layout_width="match_parent" 
 android:layout_height="wrap_content" 
 style="@android:style/Widget.ProgressBar.Horizontal"/> 
 
 <TextView 
 android:id="@+id/tv_info" 
 android:layout_width="match_parent" 
 android:layout_height="wrap_content" 
 android:gravity="center" 
 android:text="下载:0%"/> 
 
</LinearLayout> 

package com.example.inter; 
 
/** 
 * 自定义进度条监听器 
 * @author liuyazhuang 
 * 
 */ 
public interface ProgressBarListener { 
 /** 
 * 获取文件的长度 
 * @param length 
 */ 
 void getMax(int length); 
 /** 
 * 获取每次下载的长度 
 * @param length 
 */ 
 void getDownload(int length); 
} 

package com.example.download; 
 
import java.io.File; 
import java.io.FileOutputStream; 
import java.io.InputStream; 
import java.io.RandomAccessFile; 
import java.net.HttpURLConnection; 
import java.net.URL; 
 
import com.example.inter.ProgressBarListener; 
 
/** 
 * 自定义线程类 
 * @author liuyazhuang 
 * 
 */ 
public class DownloadThread extends Thread { 
 //下载的线程id 
 private int threadId; 
 //下载的文件路径 
 private String path; 
 //保存的文件 
 private File file; 
 //下载的进度条更新的监听器 
 private ProgressBarListener listener; 
 //每条线程下载的数据量 
 private int block; 
 //下载的开始位置 
 private int startPosition; 
 //下载的结束位置 
 private int endPosition; 
 
 public DownloadThread(int threadId, String path, File file, ProgressBarListener listener, int block) { 
 this.threadId = threadId; 
 this.path = path; 
 this.file = file; 
 this.listener = listener; 
 this.block = block; 
  
 this.startPosition = threadId * block; 
 this.endPosition = (threadId + 1) * block - 1; 
 } 
 
 @Override 
 public void run() { 
 super.run(); 
 try { 
  //创建RandomAccessFile对象 
  RandomAccessFile accessFile = new RandomAccessFile(file, "rwd"); 
  //跳转到开始位置 
  accessFile.seek(startPosition); 
  URL url = new URL(path); 
  //打开http链接 
  HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
  //设置超时时间 
  conn.setConnectTimeout(5000); 
  //指定请求方式为GET方式 
  conn.setRequestMethod("GET"); 
  //指定下载的位置 
  conn.setRequestProperty("Range", "bytes="+startPosition + "-" + endPosition); 
  //不用再去判断状态码是否为200 
  InputStream in = conn.getInputStream(); 
  byte[] buffer = new byte[1024]; 
  int len = 0; 
  while((len = in.read(buffer)) != -1){ 
  accessFile.write(buffer, 0, len); 
  //更新下载进度 
  listener.getDownload(len); 
  } 
  accessFile.close(); 
  in.close(); 
 } catch (Exception e) { 
  // TODO: handle exception 
  e.printStackTrace(); 
 } 
 } 
} 

package com.example.download; 
 
import java.io.File; 
import java.io.RandomAccessFile; 
import java.net.HttpURLConnection; 
import java.net.URL; 
 
import android.os.Environment; 
 
import com.example.inter.ProgressBarListener; 
 
/** 
 * 文件下载管理器 
 * @author liuyazhuang 
 * 
 */ 
public class DownloadManager { 
 //下载线程的数量 
 private static final int TREAD_SIZE = 3; 
 private File file; 
 /** 
 * 下载文件的方法 
 * @param path：下载文件的路径 
 * @param listener：自定义的下载文件监听接口 
 * @throws Exception 
 */ 
 public void download(String path, ProgressBarListener listener) throws Exception{ 
 URL url = new URL(path); 
 HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
 conn.setConnectTimeout(5000); 
 conn.setRequestMethod("GET"); 
 if(conn.getResponseCode() == 200){ 
  int filesize = conn.getContentLength(); 
  //设置进度条的最大长度 
  listener.getMax(filesize); 
  //创建一个和服务器大小一样的文件 
  file = new File(Environment.getExternalStorageDirectory(), this.getFileName(path)); 
  RandomAccessFile accessFile = new RandomAccessFile(file, "rwd"); 
  accessFile.setLength(filesize); 
  //要关闭RandomAccessFile对象 
  accessFile.close(); 
  
  //计算出每条线程下载的数据量 
  int block = filesize % TREAD_SIZE == 0 ? (filesize / TREAD_SIZE) : (filesize / TREAD_SIZE +1 ); 
  
  //开启线程下载 
  for(int i = 0; i < TREAD_SIZE; i++){ 
  new DownloadThread(i, path, file, listener, block).start(); 
  } 
 } 
 } 
 
 /** 
 * 截取路径中的文件名称 
 * @param path:要截取文件名称的路径 
 * @return:截取到的文件名称 
 */ 
 private String getFileName(String path){ 
 return path.substring(path.lastIndexOf("/") + 1); 
 } 
} 

package com.example.multi; 
 
import android.app.Activity; 
import android.os.Bundle; 
import android.os.Handler; 
import android.os.Message; 
import android.view.Menu; 
import android.view.View; 
import android.widget.EditText; 
import android.widget.ProgressBar; 
import android.widget.TextView; 
import android.widget.Toast; 
 
import com.example.download.DownloadManager; 
import com.example.inter.ProgressBarListener; 
 
/** 
 * MainActivity整个应用程序的入口 
 * @author liuyazhuang 
 * 
 */ 
public class MainActivity extends Activity { 
 
 protected static final int ERROR_DOWNLOAD = 0; 
 protected static final int SET_PROGRESS_MAX = 1; 
 protected static final int UPDATE_PROGRESS = 2; 
 
 private EditText ed_path; 
 private ProgressBar pb; 
 private TextView tv_info; 
 private DownloadManager manager; 
 //handler操作 
 private Handler mHandler = new Handler(){ 
  
 public void handleMessage(android.os.Message msg) { 
  switch (msg.what) { 
  case ERROR_DOWNLOAD: 
  //提示用户下载失败 
  Toast.makeText(MainActivity.this, "下载失败", Toast.LENGTH_SHORT).show(); 
  break; 
  case SET_PROGRESS_MAX: 
  //得到最大值 
  int max = (Integer) msg.obj; 
  //设置进度条的最大值 
  pb.setMax(max); 
  break; 
  case UPDATE_PROGRESS: 
  //获取当前下载的长度 
  int currentprogress = pb.getProgress(); 
  //获取新下载的长度 
  int len = (Integer) msg.obj; 
  //计算当前总下载长度 
  int crrrentTotalProgress = currentprogress + len; 
  pb.setProgress(crrrentTotalProgress); 
   
  //获取总大小 
  int maxProgress = pb.getMax(); 
  //计算百分比 
  float value = (float)currentprogress / (float)maxProgress; 
  int percent = (int) (value * 100); 
  //显示下载的百分比 
  tv_info.setText("下载:"+percent+"%"); 
  break; 
  default: 
  break; 
  } 
 }; 
 }; 
 @Override 
 protected void onCreate(Bundle savedInstanceState) { 
 super.onCreate(savedInstanceState); 
 setContentView(R.layout.activity_main); 
 this.ed_path = (EditText) super.findViewById(R.id.ed_path); 
 this.pb = (ProgressBar) super.findViewById(R.id.pb); 
 this.tv_info = (TextView) super.findViewById(R.id.tv_info); 
 this.manager = new DownloadManager(); 
  
 } 
 
 @Override 
 public boolean onCreateOptionsMenu(Menu menu) { 
 // Inflate the menu; this adds items to the action bar if it is present. 
 getMenuInflater().inflate(R.menu.main, menu); 
 return true; 
 } 
 
 public void download(View v){ 
 final String path = ed_path.getText().toString(); 
 //下载 
 new Thread(new Runnable() { 
  @Override 
  public void run() { 
  // TODO Auto-generated method stub 
  try { 
   manager.download(path, new ProgressBarListener() { 
   @Override 
   public void getMax(int length) { 
    // TODO Auto-generated method stub 
    Message message = new Message(); 
    message.what = SET_PROGRESS_MAX; 
    message.obj = length; 
    mHandler.sendMessage(message); 
   } 
    
   @Override 
   public void getDownload(int length) { 
    // TODO Auto-generated method stub 
    Message message = new Message(); 
    message.what = UPDATE_PROGRESS; 
    message.obj = length; 
    mHandler.sendMessage(message); 
   } 
   }); 
  } catch (Exception e) { 
   // TODO: handle exception 
   e.printStackTrace(); 
   Message message = new Message(); 
   message.what = ERROR_DOWNLOAD; 
   mHandler.sendMessage(message); 
  } 
  } 
 }).start(); 
 } 
} 

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
 package="com.example.multi" 
 android:versionCode="1" 
 android:versionName="1.0" > 
 
 <uses-sdk 
 android:minSdkVersion="8" 
 android:targetSdkVersion="18" /> 
 <uses-permission android:name="android.permission.INTERNET"/> 
 <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/> 
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> 
 <application 
 android:allowBackup="true" 
 android:icon="@drawable/ic_launcher" 
 android:label="@string/app_name" 
 android:theme="@style/AppTheme" > 
 <activity 
  android:name="com.example.multi.MainActivity" 
  android:label="@string/app_name" > 
  <intent-filter> 
  <action android:name="android.intent.action.MAIN" /> 
 
  <category android:name="android.intent.category.LAUNCHER" /> 
  </intent-filter> 
 </activity> 
 </application> 
 
</manifest>