Android入门：多线程断点下载详细介绍

本案例在于实现文件的多线程断点下载，即文件在下载一部分中断后，可继续接着已有进度下载，并通过进度条显示进度。也就是说在文件开始下载的同时，自动创建每个线程的下载进度的本地文件，下载中断后，重新进入应用点击下载，程序检查有没有本地文件的存在，若存在，获取本地文件中的下载进度，继续进行下载。当下载完成后，自动删除本地文件。

一、多线程断点下载介绍

所谓的多线程断点下载就是利用多线程下载，并且可被中断，如果突然没电了，重启手机后可以继续下载，而不需要重新下载；

利用的技术有：SQLite存储各个线程的下载量，HTTP请求获得下载数据；

二、辅助类介绍

为了完成多线程断点下载我们需要预先编写一些辅助类：

(1)DBOpenHelper

(2)FileService：
-Map getData(String path); 根据URL获得各个线程的下载量
-save(String path, Map map);存储URL对应的各个线程下载量，此函数为刚刚开始时调用
-update(String path, Map map);更新数据库中URL对应的各个线程的下载量；
-delete(String path);删除URL对应的数据；

(3)FileDownloader:
-getFileSize()；获得下载文件的大小
-download(DownloadProgressListener listener);下载文件，并设置监听器

(4)DownloadThread:此类在FileDownloader的download中执行；

先将辅助类列出：
DBOpenHelper.Java

package service; 
 
import android.content.Context; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
 
public class DBOpenHelper extends SQLiteOpenHelper { 
  private static final String DBNAME = "download.db"; 
  private static final int VERSION = 1; 
   
  public DBOpenHelper(Context context) { 
    super(context, DBNAME, null, VERSION); 
  } 
   
  @Override 
  public void onCreate(SQLiteDatabase db) { 
    db.execSQL("CREATE TABLE IF NOT EXISTS filedownlog (id integer primary key autoincrement, downpath varchar(100), threadid INTEGER, downlength INTEGER)"); 
  } 
 
  @Override 
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    db.execSQL("DROP TABLE IF EXISTS filedownlog"); 
    onCreate(db); 
  } 
 
} 

FileService.java

package service; 
 
import java.util.HashMap; 
import java.util.Map; 
 
import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
 
public class FileService { 
  private DBOpenHelper openHelper; 
 
  public FileService(Context context) { 
    openHelper = new DBOpenHelper(context); 
  } 
   
  public Map getData(String path){ 
    SQLiteDatabase db = openHelper.getReadableDatabase(); 
    Cursor cursor = db.rawQuery("select threadid, downlength from filedownlog where downpath=?", new String[]{path}); 
    Map data = new HashMap(); 
    while(cursor.moveTonext()){ 
      data.put(cursor.getInt(0), cursor.getInt(1)); 
    } 
    cursor.close(); 
    db.close(); 
    return data; 
  } 
   
  public void save(String path, Map map){//int threadid, int position 
    SQLiteDatabase db = openHelper.getWritableDatabase(); 
    db.beginTransaction(); 
    try{ 
      for(Map.Entry entry : map.entrySet()){ 
 db.execSQL("insert into filedownlog(downpath, threadid, downlength) values(?,?,?)", 
     new Object[]{path, entry.getKey(), entry.getValue()}); 
      } 
      db.setTransactionSuccessful(); 
    }finally{ 
      db.endTransaction(); 
    } 
    db.close(); 
  } 
   
  public void update(String path, Map map){ 
    SQLiteDatabase db = openHelper.getWritableDatabase(); 
    db.beginTransaction(); 
    try{ 
      for(Map.Entry entry : map.entrySet()){ 
 db.execSQL("update filedownlog set downlength=? where downpath=? and threadid=?", 
     new Object[]{entry.getValue(), path, entry.getKey()}); 
      } 
      db.setTransactionSuccessful(); 
    }finally{ 
      db.endTransaction(); 
    } 
    db.close(); 
  } 
   
  public void delete(String path){ 
    SQLiteDatabase db = openHelper.getWritableDatabase(); 
    db.execSQL("delete from filedownlog where downpath=?", new Object[]{path}); 
    db.close(); 
  } 
   
} 

FileDownloader.java

package net.download; 
 
import java.io.File; 
import java.io.RandomAccessFile; 
import java.net.HttpURLConnection; 
import java.net.URL; 
import java.util.linkedHashMap; 
import java.util.Map; 
import java.util.UUID; 
import java.util.concurrent.ConcurrentHashMap; 
import java.util.regex.Matcher; 
import java.util.regex.Pattern; 
 
import service.FileService; 
import android.content.Context; 
import android.util.Log; 
 
public class FileDownloader { 
  private static final String TAG = "FileDownloader"; 
  private Context context; 
  private FileService fileService;   
   
  private int downloadSize = 0; 
   
  private int fileSize = 0; 
   
  private DownloadThread[] threads; 
   
  private File saveFile; 
   
  private Map data = new ConcurrentHashMap(); 
   
  private int block; 
   
  private String downloadUrl; 
   
  public int getThreadSize() { 
    return threads.length; 
  } 
   
  public int getFileSize() { 
    return fileSize; 
  } 
   
  protected synchronized void append(int size) { 
    downloadSize += size; 
  } 
   
  protected synchronized void update(int threadId, int pos) { 
    this.data.put(threadId, pos); 
    this.fileService.update(this.downloadUrl, this.data); 
  } 
   
  public FileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum) { 
    try { 
      this.context = context; 
      this.downloadUrl = downloadUrl; 
      fileService = new FileService(this.context); 
      URL url = new URL(this.downloadUrl); 
      if(!fileSaveDir.exists()) fileSaveDir.mkdirs(); 
      this.threads = new DownloadThread[threadNum]; 
      //1.获得文件大小 
      HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
      conn.setConnectTimeout(5*1000); 
      conn.setRequestMethod("GET"); 
      conn.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, * 
  private String getFileName(HttpURLConnection conn) { 
    String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1); 
    if(filename==null || "".equals(filename.trim())){//如果获取不到文件名称 
      for (int i = 0;; i++) { 
 String mine = conn.getHeaderField(i); 
 if (mine == null) break; 
 if("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())){ 
   Matcher m = Pattern.compile(".*filename=(.*)").matcher(mine.toLowerCase()); 
   if(m.find()) return m.group(1); 
 } 
      } 
      filename = UUID.randomUUID()+ ".tmp";//默认取一个文件名 
    } 
    return filename; 
  } 
   
   
  public int download(DownloadProgressListener listener) throws Exception{ 
    try { 
      RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw"); 
      if(this.fileSize>0) randOut.setLength(this.fileSize); 
      randOut.close(); 
      URL url = new URL(this.downloadUrl); 
      //如果线程数与以前不一样，则重新开始下 
      if(this.data.size() != this.threads.length){ 
 this.data.clear(); 
 for (int i = 0; i < this.threads.length; i++) { 
   this.data.put(i+1, 0);//初始化每条线程已经下载的数据长度为0 
 } 
      } 
      for (int i = 0; i < this.threads.length; i++) {//开启线程进行下载 
 int downLength = this.data.get(i+1); 
 if(downLength < this.block && this.downloadSize getHttpResponseHeader(HttpURLConnection http) { 
    Map header = new linkedHashMap(); 
    for (int i = 0;; i++) { 
      String mine = http.getHeaderField(i); 
      if (mine == null) break; 
      header.put(http.getHeaderFieldKey(i), mine); 
    } 
    return header; 
  } 
   
  public static void printResponseHeader(HttpURLConnection http){ 
    Map header = getHttpResponseHeader(http); 
    for(Map.Entry entry : header.entrySet()){ 
      String key = entry.getKey()!=null ? entry.getKey()+ ":" : ""; 
      print(key+ entry.getValue()); 
    } 
  } 
 
  private static void print(String msg){ 
    Log.i(TAG, msg); 
  } 
} 

DownloadThread.java

package net.download; 
 
import java.io.File; 
import java.io.InputStream; 
import java.io.RandomAccessFile; 
import java.net.HttpURLConnection; 
import java.net.URL; 
 
import android.util.Log; 
 
public class DownloadThread extends Thread { 
  private static final String TAG = "DownloadThread"; 
  private File saveFile; 
  private URL downUrl; 
  private int block; 
   
  private int threadId = -1;  
  private int downLength; 
  private boolean finish = false; 
  private FileDownloader downloader; 
 
  public DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downLength, int threadId) { 
    this.downUrl = downUrl; 
    this.saveFile = saveFile; 
    this.block = block; 
    this.downloader = downloader; 
    this.threadId = threadId; 
    this.downLength = downLength; 
  } 
   
  @Override 
  public void run() { 
    if(downLength < block){//未下载完成 
      try { 
 HttpURLConnection http = (HttpURLConnection) downUrl.openConnection(); 
 http.setConnectTimeout(5 * 1000); 
 http.setRequestMethod("GET"); 
 http.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, * 
  public boolean isFinish() { 
    return finish; 
  } 
   
  public long getDownLength() { 
    return downLength; 
  } 
} 
DownloadProgressListener.java
package net.download; 
 
//下载监听器 
public interface DownloadProgressListener { 
  public void onDownloadSize(int size); 
} 

三、具体代码

效果如下：

实现代码：

package org.xiazdong.download; 
 
import java.io.File; 
 
import net.download.DownloadProgressListener; 
import net.download.FileDownloader; 
import android.app.Activity; 
import android.os.Bundle; 
import android.os.Environment; 
import android.os.Handler; 
import android.os.Message; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.ProgressBar; 
import android.widget.TextView; 
import android.widget.Toast; 
 
public class MainActivity extends Activity { 
  private Button downloadButton; 
  private EditText urlpathEditText; 
  private TextView percentTextView; 
  private ProgressBar progressBar; 
  private Handler handler; 
  //主线程 
  private class UIHandler extends Handler{ 
    @Override 
    public void handleMessage(Message msg) { 
      int downloadsize = msg.getData().getInt("downloadsize"); 
      int percent = msg.getData().getInt("percent"); 
      progressBar.setProgress(downloadsize); 
      percentTextView.setText(percent+"%"); 
    } 
  } 
  private onClickListener listener = new onClickListener() { 
    DownloadThread thread; 
    class DownloadThread extends Thread{ 
      private String url ; 
      private File saveDir; 
      private FileDownloader download; 
      public DownloadThread(String url, File saveDir) { 
 this.url = url; 
 this.saveDir = saveDir; 
      } 
      //子线程 
      @Override 
      public void run() { 
 download = new FileDownloader(MainActivity.this,url, saveDir, 3); 
 progressBar.setMax(download.getFileSize()); //设置最大刻度 
 try { 
   download.download(downListener); 
 } catch (Exception e) { 
   e.printStackTrace(); 
 } 
      } 
    } 
    //由子线程调用 
    private DownloadProgressListener downListener = new DownloadProgressListener() { 
      @Override 
      public void onDownloadSize(int size) { 
 //实时跟踪下载的情况 
 int percent = (int)(((double)size)/progressBar.getMax()*100); 
 Message msg = new Message(); 
 msg.what = 1;  //设置id 
 System.out.println(percent+"%"); 
 System.out.println(size+"k"); 
 msg.getData().putInt("percent", percent); 
 msg.getData().putInt("downloadsize",size); 
 handler.sendMessage(msg); 
  
      } 
    }; 
     
    @Override 
    public void onClick(View v) { 
      if(v==downloadButton){ 
 if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){ 
   String url = urlpathEditText.getText().toString(); 
   File saveDir = Environment.getExternalStorageDirectory(); 
   download(url,saveDir); 
 } 
 else{ 
   Toast.makeText(MainActivity.this, "SDCARD不存在", Toast.LENGTH_SHORT).show(); 
 } 
      } 
    } 
 
    private void download(String url, File saveDir) { 
      thread = new DownloadThread(url,saveDir); 
      thread.start(); 

    } 
  }; 
  @Override 
  public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    downloadButton = (Button)findViewById(R.id.download); 
    urlpathEditText = (EditText)findViewById(R.id.path); 
    percentTextView = (TextView)findViewById(R.id.textView); 
    progressBar = (ProgressBar)findViewById(R.id.progressBar);  
    downloadButton.setonClickListener(listener); 
    handler = new UIHandler(); 
  } 
} 

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