android 多執行緒斷點續傳下載 三
阿新 • • 發佈：2019-01-29
今天跟大家一起分享下android開發中比較難的一個環節,可能很多人看到這個標題就會感覺頭很大,的確如果沒有良好的編碼能力和邏輯思維,這塊是很難搞明白的,前面2次總結中已經為大家分享過有關技術的一些基本要領,我們先一起簡單回顧下它的基本原理。
什麼是多執行緒下載？
多執行緒下載其實就是迅雷,BT一些下載原理,通過多個執行緒同時和伺服器連線,那麼你就可以榨取到較高的帶寬了,大致做法是將檔案切割成N塊,每塊交給單獨一個執行緒去下載,各自下載完成後將檔案塊組合成一個檔案,程式上要完成做切割和組裝的小演算法
什麼是斷點續傳?
斷點續傳,就是當我們下載未結束時候,退出儲存下載進度,當下次開啟繼續下載的時接著上次的進度繼續下載,不用每次下載都重新開始,那麼有關斷點續傳的原理和實現手段,可參考我以前的一篇總結 http://blog.csdn.net/shimiso/article/details/5956314 裡面詳細講解http協議斷點續傳的原理,務必要看懂,否則你無法真正理解本節程式碼
怎麼完成多執行緒斷點續傳?
將兩者合二為一需要程式記住每個檔案塊的下載進度,並儲存入庫,當下載程式啟動時候你需要判斷程式是否已經下載過該檔案,並取出各個檔案塊的儲存記錄,換算出下載進度繼續下載,在這裡你需要掌握java多執行緒的基本知識,handler的使用,以及集合,演算法,檔案操作等基本技能,同時還要解決sqlite資料庫的同步問題,因為它是不太怎麼支援多執行緒操作的,控制不好經常會出現庫被鎖定的異常,同時在android2.3以後就不能activity中直接操作http,否則你將收到系統送上的NetworkOnMainThreadException異常,在UI體驗上一定記住要使用非同步完成,既然大致思路已經清楚,下面我們開始分析程式:
package cn.demo.DBHelper; import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; /** * 建立一個數據庫幫助類 */ public class DBHelper extends SQLiteOpenHelper { //download.db-->資料庫名 public DBHelper(Context context) { super(context, "download.db", null, 1); } /** * 在download.db資料庫下建立一個download_info表儲存下載資訊 */ @Override public void onCreate(SQLiteDatabase db) { db.execSQL("create table download_info(_id integer PRIMARY KEY AUTOINCREMENT, thread_id integer, " + "start_pos integer, end_pos integer, compelete_size integer,url char)"); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { } }
資料庫操作要藉助單例和同步,來保證執行緒的執行順序,以免多個執行緒爭相搶用sqlite資源導致異常出現
package cn.demo.Dao;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import cn.demo.DBHelper.DBHelper;
import cn.demo.entity.DownloadInfo;
/**
*
* 一個業務類
*/
public class Dao {
private static Dao dao=null;
private Context context;
private Dao(Context context) {
this.context=context;
}
public static Dao getInstance(Context context){
if(dao==null){
dao=new Dao(context);
}
return dao;
}
public SQLiteDatabase getConnection() {
SQLiteDatabase sqliteDatabase = null;
try {
sqliteDatabase= new DBHelper(context).getReadableDatabase();
} catch (Exception e) {
}
return sqliteDatabase;
}
/**
* 檢視資料庫中是否有資料
*/
public synchronized boolean isHasInfors(String urlstr) {
SQLiteDatabase database = getConnection();
int count = -1;
Cursor cursor = null;
try {
String sql = "select count(*) from download_info where url=?";
cursor = database.rawQuery(sql, new String[] { urlstr });
if (cursor.moveToFirst()) {
count = cursor.getInt(0);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (null != database) {
database.close();
}
if (null != cursor) {
cursor.close();
}
}
return count == 0;
}
/**
* 儲存 下載的具體資訊
*/
public synchronized void saveInfos(List<DownloadInfo> infos) {
SQLiteDatabase database = getConnection();
try {
for (DownloadInfo info : infos) {
String sql = "insert into download_info(thread_id,start_pos, end_pos,compelete_size,url) values (?,?,?,?,?)";
Object[] bindArgs = { info.getThreadId(), info.getStartPos(),
info.getEndPos(), info.getCompeleteSize(),
info.getUrl() };
database.execSQL(sql, bindArgs);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (null != database) {
database.close();
}
}
}
/**
* 得到下載具體資訊
*/
public synchronized List<DownloadInfo> getInfos(String urlstr) {
List<DownloadInfo> list = new ArrayList<DownloadInfo>();
SQLiteDatabase database = getConnection();
Cursor cursor = null;
try {
String sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";
cursor = database.rawQuery(sql, new String[] { urlstr });
while (cursor.moveToNext()) {
DownloadInfo info = new DownloadInfo(cursor.getInt(0),
cursor.getInt(1), cursor.getInt(2), cursor.getInt(3),
cursor.getString(4));
list.add(info);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (null != database) {
database.close();
}
if (null != cursor) {
cursor.close();
}
}
return list;
}
/**
* 更新資料庫中的下載資訊
*/
public synchronized void updataInfos(int threadId, int compeleteSize, String urlstr) {
SQLiteDatabase database = getConnection();
try {
String sql = "update download_info set compelete_size=? where thread_id=? and url=?";
Object[] bindArgs = { compeleteSize, threadId, urlstr };
database.execSQL(sql, bindArgs);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (null != database) {
database.close();
}
}
}
/**
* 下載完成後刪除資料庫中的資料
*/
public synchronized void delete(String url) {
SQLiteDatabase database = getConnection();
try {
database.delete("download_info", "url=?", new String[] { url });
} catch (Exception e) {
e.printStackTrace();
} finally {
if (null != database) {
database.close();
}
}
}
}package cn.demo.download;
import java.util.List;
import java.util.Map;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.TextView;
public class DownLoadAdapter extends BaseAdapter{
private LayoutInflater mInflater;
private List<Map<String, String>> data;
private Context context;
private OnClickListener click;
public DownLoadAdapter(Context context,List<Map<String, String>> data) {
this.context=context;
mInflater = LayoutInflater.from(context);
this.data=data;
}
public void refresh(List<Map<String, String>> data) {
this.data=data;
this.notifyDataSetChanged();
}
public void setOnclick(OnClickListener click) {
this.click=click;
}
@Override
public int getCount() {
return data.size();
}
@Override
public Object getItem(int position) {
return data.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
final Map<String, String> bean=data.get(position);
ViewHolder holder = null;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_item, null);
holder = new ViewHolder();
holder.resouceName=(TextView) convertView.findViewById(R.id.tv_resouce_name);
holder.startDownload=(Button) convertView.findViewById(R.id.btn_start);
holder.pauseDownload=(Button) convertView.findViewById(R.id.btn_pause);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.resouceName.setText(bean.get("name"));
return convertView;
}
public OnClickListener getClick() {
return click;
}
public void setClick(OnClickListener click) {
this.click = click;
}
private class ViewHolder {
public TextView resouceName;
public Button startDownload;
public Button pauseDownload;
}
}
注意子執行緒不要影響主UI執行緒,靈活運用task和handler,各取所長,保證使用者體驗,handler通常在主執行緒中有利於專門負責處理UI的一些工作
package cn.demo.download;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import android.app.ListActivity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.LinearLayout.LayoutParams;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
import cn.demo.entity.LoadInfo;
import cn.demo.service.Downloader;
public class MainActivity extends ListActivity {
// 固定下載的資源路徑，這裡可以設定網路上的地址
private static final String URL = "http://download.haozip.com/";
// 固定存放下載的音樂的路徑：SD卡目錄下
private static final String SD_PATH = "/mnt/sdcard/";
// 存放各個下載器
private Map<String, Downloader> downloaders = new HashMap<String, Downloader>();
// 存放與下載器對應的進度條
private Map<String, ProgressBar> ProgressBars = new HashMap<String, ProgressBar>();
/**
* 利用訊息處理機制適時更新進度條
*/
private Handler mHandler = new Handler() {
public void handleMessage(Message msg) {
if (msg.what == 1) {
String url = (String) msg.obj;
int length = msg.arg1;
ProgressBar bar = ProgressBars.get(url);
if (bar != null) {
// 設定進度條按讀取的length長度更新
bar.incrementProgressBy(length);
if (bar.getProgress() == bar.getMax()) {
LinearLayout layout = (LinearLayout) bar.getParent();
TextView resouceName=(TextView)layout.findViewById(R.id.tv_resouce_name);
Toast.makeText(MainActivity.this, "["+resouceName.getText()+"]下載完成！", Toast.LENGTH_SHORT).show();
// 下載完成後清除進度條並將map中的資料清空
layout.removeView(bar);
ProgressBars.remove(url);
downloaders.get(url).delete(url);
downloaders.get(url).reset();
downloaders.remove(url);
Button btn_start=(Button)layout.findViewById(R.id.btn_start);
Button btn_pause=(Button)layout.findViewById(R.id.btn_pause);
btn_pause.setVisibility(View.GONE);
btn_start.setVisibility(View.GONE);
}
}
}
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
showListView();
}
// 顯示listView，這裡可以隨便新增
private void showListView() {
List<Map<String, String>> data = new ArrayList<Map<String, String>>();
Map<String, String> map = new HashMap<String, String>();
map.put("name", "haozip_v3.1.exe");
data.add(map);
map = new HashMap<String, String>();
map.put("name", "haozip_v3.1_hj.exe");
data.add(map);
map = new HashMap<String, String>();
map.put("name", "haozip_v2.8_x64_tiny.exe");
data.add(map);
map = new HashMap<String, String>();
map.put("name", "haozip_v2.8_tiny.exe");
data.add(map);
DownLoadAdapter adapter=new DownLoadAdapter(this,data);
setListAdapter(adapter);
}
/**
* 響應開始下載按鈕的點選事件
*/
public void startDownload(View v) {
// 得到textView的內容
LinearLayout layout = (LinearLayout) v.getParent();
String resouceName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();
String urlstr = URL + resouceName;
String localfile = SD_PATH + resouceName;
//設定下載執行緒數為4，這裡是我為了方便隨便固定的
String threadcount = "4";
DownloadTask downloadTask=new DownloadTask(v);
downloadTask.execute(urlstr,localfile,threadcount);
};
class DownloadTask extends AsyncTask<String, Integer, LoadInfo>{
Downloader downloader=null;
View v=null;
String urlstr=null;
public DownloadTask(final View v){
this.v=v;
}
@Override
protected void onPreExecute() {
Button btn_start=(Button)((View)v.getParent()).findViewById(R.id.btn_start);
Button btn_pause=(Button)((View)v.getParent()).findViewById(R.id.btn_pause);
btn_start.setVisibility(View.GONE);
btn_pause.setVisibility(View.VISIBLE);
}
@Override
protected LoadInfo doInBackground(String... params) {
urlstr=params[0];
String localfile=params[1];
int threadcount=Integer.parseInt(params[2]);
// 初始化一個downloader下載器
downloader = downloaders.get(urlstr);
if (downloader == null) {
downloader = new Downloader(urlstr, localfile, threadcount, MainActivity.this, mHandler);
downloaders.put(urlstr, downloader);
}
if (downloader.isdownloading())
return null;
// 得到下載資訊類的個數組成集合
return downloader.getDownloaderInfors();
}
@Override
protected void onPostExecute(LoadInfo loadInfo) {
if(loadInfo!=null){
// 顯示進度條
showProgress(loadInfo, urlstr, v);
// 呼叫方法開始下載
downloader.download();
}
}
};
/**
* 顯示進度條
*/
private void showProgress(LoadInfo loadInfo, String url, View v) {
ProgressBar bar = ProgressBars.get(url);
if (bar == null) {
bar = new ProgressBar(this, null, android.R.attr.progressBarStyleHorizontal);
bar.setMax(loadInfo.getFileSize());
bar.setProgress(loadInfo.getComplete());
ProgressBars.put(url, bar);
LinearLayout.LayoutParams params = new LayoutParams(LayoutParams.FILL_PARENT, 5);
((LinearLayout) ((LinearLayout) v.getParent()).getParent()).addView(bar, params);
}
}
/**
* 響應暫停下載按鈕的點選事件
*/
public void pauseDownload(View v) {
LinearLayout layout = (LinearLayout) v.getParent();
String resouceName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();
String urlstr = URL + resouceName;
downloaders.get(urlstr).pause();
Button btn_start=(Button)((View)v.getParent()).findViewById(R.id.btn_start);
Button btn_pause=(Button)((View)v.getParent()).findViewById(R.id.btn_pause);
btn_pause.setVisibility(View.GONE);
btn_start.setVisibility(View.VISIBLE);
}
}package cn.demo.entity;
/**
*建立一個下載資訊的實體類
*/
public class DownloadInfo {
private int threadId;//下載器id
private int startPos;//開始點
private int endPos;//結束點
private int compeleteSize;//完成度
private String url;//下載器網路標識
public DownloadInfo(int threadId, int startPos, int endPos,
int compeleteSize,String url) {
this.threadId = threadId;
this.startPos = startPos;
this.endPos = endPos;
this.compeleteSize = compeleteSize;
this.url=url;
}
public DownloadInfo() {
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public int getThreadId() {
return threadId;
}
public void setThreadId(int threadId) {
this.threadId = threadId;
}
public int getStartPos() {
return startPos;
}
public void setStartPos(int startPos) {
this.startPos = startPos;
}
public int getEndPos() {
return endPos;
}
public void setEndPos(int endPos) {
this.endPos = endPos;
}
public int getCompeleteSize() {
return compeleteSize;
}
public void setCompeleteSize(int compeleteSize) {
this.compeleteSize = compeleteSize;
}
@Override
public String toString() {
return "DownloadInfo [threadId=" + threadId
+ ", startPos=" + startPos + ", endPos=" + endPos
+ ", compeleteSize=" + compeleteSize +"]";
}
}package cn.demo.entity;
/**
*自定義的一個記載下載器詳細資訊的類
*/
public class LoadInfo {
public int fileSize;//檔案大小
private int complete;//完成度
private String urlstring;//下載器標識
public LoadInfo(int fileSize, int complete, String urlstring) {
this.fileSize = fileSize;
this.complete = complete;
this.urlstring = urlstring;
}
public LoadInfo() {
}
public int getFileSize() {
return fileSize;
}
public void setFileSize(int fileSize) {
this.fileSize = fileSize;
}
public int getComplete() {
return complete;
}
public void setComplete(int complete) {
this.complete = complete;
}
public String getUrlstring() {
return urlstring;
}
public void setUrlstring(String urlstring) {
this.urlstring = urlstring;
}
@Override
public String toString() {
return "LoadInfo [fileSize=" + fileSize + ", complete=" + complete
+ ", urlstring=" + urlstring + "]";
}
}
這是一個核心類,專門用來處理下載的
package cn.demo.service;
import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import cn.demo.Dao.Dao;
import cn.demo.entity.DownloadInfo;
import cn.demo.entity.LoadInfo;
public class Downloader {
private String urlstr;// 下載的地址
private String localfile;// 儲存路徑
private int threadcount;// 執行緒數
private Handler mHandler;// 訊息處理器
private int fileSize;// 所要下載的檔案的大小
private Context context;
private List<DownloadInfo> infos;// 存放下載資訊類的集合
private static final int INIT = 1;//定義三種下載的狀態：初始化狀態，正在下載狀態，暫停狀態
private static final int DOWNLOADING = 2;
private static final int PAUSE = 3;
private int state = INIT;
public Downloader(String urlstr, String localfile, int threadcount,
Context context, Handler mHandler) {
this.urlstr = urlstr;
this.localfile = localfile;
this.threadcount = threadcount;
this.mHandler = mHandler;
this.context = context;
}
/**
*判斷是否正在下載
*/
public boolean isdownloading() {
return state == DOWNLOADING;
}
/**
* 得到downloader裡的資訊
* 首先進行判斷是否是第一次下載，如果是第一次就要進行初始化，並將下載器的資訊儲存到資料庫中
* 如果不是第一次下載，那就要從資料庫中讀出之前下載的資訊（起始位置，結束為止，檔案大小等），並將下載資訊返回給下載器
*/
public LoadInfo getDownloaderInfors() {
if (isFirst(urlstr)) {
Log.v("TAG", "isFirst");
init();
int range = fileSize / threadcount;
infos = new ArrayList<DownloadInfo>();
for (int i = 0; i < threadcount - 1; i++) {
DownloadInfo info = new DownloadInfo(i, i * range, (i + 1)* range - 1, 0, urlstr);
infos.add(info);
}
DownloadInfo info = new DownloadInfo(threadcount - 1,(threadcount - 1) * range, fileSize - 1, 0, urlstr);
infos.add(info);
//儲存infos中的資料到資料庫
Dao.getInstance(context).saveInfos(infos);
//建立一個LoadInfo物件記載下載器的具體資訊
LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);
return loadInfo;
} else {
//得到資料庫中已有的urlstr的下載器的具體資訊
infos = Dao.getInstance(context).getInfos(urlstr);
Log.v("TAG", "not isFirst size=" + infos.size());
int size = 0;
int compeleteSize = 0;
for (DownloadInfo info : infos) {
compeleteSize += info.getCompeleteSize();
size += info.getEndPos() - info.getStartPos() + 1;
}
return new LoadInfo(size, compeleteSize, urlstr);
}
}
/**
* 初始化
*/
private void init() {
try {
URL url = new URL(urlstr);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(5000);
connection.setRequestMethod("GET");
fileSize = connection.getContentLength();
File file = new File(localfile);
if (!file.exists()) {
file.createNewFile();
}
// 本地訪問檔案
RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
accessFile.setLength(fileSize);
accessFile.close();
connection.disconnect();
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 判斷是否是第一次 下載
*/
private boolean isFirst(String urlstr) {
return Dao.getInstance(context).isHasInfors(urlstr);
}
/**
* 利用執行緒開始下載資料
*/
public void download() {
if (infos != null) {
if (state == DOWNLOADING)
return;
state = DOWNLOADING;
for (DownloadInfo info : infos) {
new MyThread(info.getThreadId(), info.getStartPos(),
info.getEndPos(), info.getCompeleteSize(),
info.getUrl()).start();
}
}
}
public class MyThread extends Thread {
private int threadId;
private int startPos;
private int endPos;
private int compeleteSize;
private String urlstr;
public MyThread(int threadId, int startPos, int endPos,
int compeleteSize, String urlstr) {
this.threadId = threadId;
this.startPos = startPos;
this.endPos = endPos;
this.compeleteSize = compeleteSize;
this.urlstr = urlstr;
}
@Override
public void run() {
HttpURLConnection connection = null;
RandomAccessFile randomAccessFile = null;
InputStream is = null;
try {
URL url = new URL(urlstr);
connection = (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(5000);
connection.setRequestMethod("GET");
// 設定範圍，格式為Range：bytes x-y;
connection.setRequestProperty("Range", "bytes="+(startPos + compeleteSize) + "-" + endPos);
randomAccessFile = new RandomAccessFile(localfile, "rwd");
randomAccessFile.seek(startPos + compeleteSize);
// 將要下載的檔案寫到儲存在儲存路徑下的檔案中
is = connection.getInputStream();
byte[] buffer = new byte[4096];
int length = -1;
while ((length = is.read(buffer)) != -1) {
randomAccessFile.write(buffer, 0, length);
compeleteSize += length;
// 更新資料庫中的下載資訊
Dao.getInstance(context).updataInfos(threadId, compeleteSize, urlstr);
// 用訊息將下載資訊傳給進度條，對進度條進行更新
Message message = Message.obtain();
message.what = 1;
message.obj = urlstr;
message.arg1 = length;
mHandler.sendMessage(message);
if (state == PAUSE) {
return;
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
//刪除資料庫中urlstr對應的下載器資訊
public void delete(String urlstr) {
Dao.getInstance(context).delete(urlstr);
}
//設定暫停
public void pause() {
state = PAUSE;
}
//重置下載狀態
public void reset() {
state = INIT;
}
}
以下是些xml檔案
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
<LinearLayout
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="5dip">
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:id="@+id/tv_resouce_name"/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="下載"
android:id="@+id/btn_start"
android:onClick="startDownload"/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="暫停"
android:visibility="gone"
android:id="@+id/btn_pause"
android:onClick="pauseDownload"/>
</LinearLayout>
</LinearLayout><?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/llRoot">
<ListView android:id="@android:id/list"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
</ListView>
</LinearLayout><manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="cn.demo.download"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" android:targetSdkVersion="8" />
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<application android:label="@string/app_name"
android:icon="@drawable/ic_launcher"
android:theme="@style/AppTheme">
<activity
android:name=".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>
執行效果如下
