斷點續傳
1. 原理：新建數據庫幫助類dbhelper
public class DBHelper extends SQLiteOpenHelper {
public DBHelper(Context context) {
super(context, "download.db", null, 1);
}
/**
* 數據庫下載表download_info
* 開始節點，結束節點，文件的總大小，訪問的網址
*/
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
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) {
// TODO Auto-generated method stub
}
}- 數據庫中的數據所對應的實體類DownloadInfo
package com.example.test006.entity;
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;// 下載器網絡標識
public DownloadInfo(int threadId, int startPos, int endPos,
int compeleteSize, String url) {
super();
this.threadId = threadId;
this.startPos = startPos;
this.endPos = endPos;
this.compeleteSize = compeleteSize;
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;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
@Override
public String toString() {
return "DownloadInfo [threadId=" + threadId
+ ", startPos=" + startPos + ", endPos=" + endPos
+ ", compeleteSize=" + compeleteSize +"]";
}
}- 由於是多線程下載，需要新建一個實體類，代表總的下載進度。
package com.example.test006.entity;
public class LoadInfo {
public int fileSize;// 文件大小
private int complete;// 完成度
private String urlstring;// 下載器標識
public LoadInfo() {
super();
// TODO Auto-generated constructor stub
}
public LoadInfo(int fileSize, int complete, String urlstring) {
super();
this.fileSize = fileSize;
this.complete = complete;
this.urlstring = urlstring;
}
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 + "]";
}
}4．dao層，與數據庫直接交互
/**
*
* 一個業務類
*/
public class Dao {
private DBHelper dbHelper;
public Dao(Context context) {
dbHelper = new DBHelper(context);
}
/**
* 查看數據庫中是否有數據
*/
public boolean isHasInfors(String urlstr) {
SQLiteDatabase database = dbHelper.getReadableDatabase();
String sql = "select count(*) from download_info where url=?";
Cursor cursor = database.rawQuery(sql, new String[] { urlstr });
cursor.moveToFirst();
int count = cursor.getInt(0);
cursor.close();
return count == 0;
}
/**
* 保存 下載的具體信息
*/
public void saveInfos(List<DownloadInfo> infos) {
SQLiteDatabase database = dbHelper.getWritableDatabase();
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);
}
}
/**
* 得到下載具體信息
*/
public List<DownloadInfo> getInfos(String urlstr) {
List<DownloadInfo> list = new ArrayList<DownloadInfo>();
SQLiteDatabase database = dbHelper.getReadableDatabase();
String sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";
Cursor 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);
}
cursor.close();
return list;
}
/**
* 更新數據庫中的下載信息
*/
public void updataInfos(int threadId, int compeleteSize, String urlstr) {
SQLiteDatabase database = dbHelper.getReadableDatabase();
String sql = "update download_info set compelete_size=? where thread_id=? and url=?";
Object[] bindArgs = { compeleteSize, threadId, urlstr };
database.execSQL(sql, bindArgs);
}
/**
* 關閉數據庫
*/
public void closeDb() {
dbHelper.close();
}
/**
* 下載完成後刪除數據庫中的數據
*/
public void delete(String url) {
SQLiteDatabase database = dbHelper.getReadableDatabase();
database.delete("download_info", "url=?", new String[] { url });
database.close();
}
}- dao層與activity層 之間的幫助層。
public class DownLoader {
private String urlstr;// 下載的地址
private String localfile;// 保存路徑
private int threadcount;// 線程數
private Handler mHandler;// 消息處理器
private Dao dao;// 工具類
private int fileSize;// 所要下載的文件的大小
private List<DownloadInfo> infos;// 存放下載信息類的集合
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;
dao = new Dao(context);
}
/**
* 判斷是否正在下載
*/
public boolean isdownloading() {
return state == DOWNLOADING;
}
/**
* 得到downloader裏的信息 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，並將下載器的信息保存到數據庫中
* 如果不是第一次下載，那就要從數據庫中讀出之前下載的信息（起始位置，結束爲止，文件大小等），並將下載信息返回給下載器
*/
public LoadInfo getDownloaderInfors() {
if (isFirst(urlstr)) {
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);
// 保存infos中的數據到數據庫
dao.saveInfos(infos);
// 創建一個LoadInfo對象記載下載器的具體信息
LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);
return loadInfo;
} else {
// 得到數據庫中已有的urlstr的下載器的具體信息
infos = dao.getInfos(urlstr);
Log.v("TAG", "not isFirst size=" + infos.size());
int size = 0;
int compeleteSize = 0;
for (DownloadInfo info : infos) {
//
compeleteSize += info.getCompeleteSize();
//剩下的總大小
size += info.getEndPos() - info.getStartPos() + 1;
}
return new LoadInfo(size, compeleteSize, urlstr);
}
}
/**
* 初始化網絡
*/
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();
}
// 本地訪問文件
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.isHasInfors(urlstr);
}
/**
* 114 * 利用線程開始下載數據 115
*/
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");
// 設置範圍，格式爲Range：bytes x-y;
connection.setRequestProperty("Range", "bytes="
+ (startPos + compeleteSize) + "-" + endPos);
//跳過前邊的所有字節數
randomAccessFile = new RandomAccessFile(localfile, "rwd");
randomAccessFile.seek(startPos + compeleteSize);
// 將要下載的文件寫到保存在保存路徑下的文件中
is = connection.getInputStream();
byte[] buffer = new byte[4096];
int length = -1;
while ((length = is.read(buffer)) != -1) {
randomAccessFile.write(buffer, 0, length);
compeleteSize += length;
// 更新數據庫中的下載信息
dao.updataInfos(threadId, compeleteSize, urlstr);
// 用消息將下載信息傳給進度條，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();
} finally {
try {
is.close();
randomAccessFile.close();
connection.disconnect();
dao.closeDb();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
// 刪除數據庫中urlstr對應的下載器信息
public void delete(String urlstr) {
dao.delete(urlstr);
}
// 設置暫停
public void pause() {
state = PAUSE;
}
// 重置下載狀態
public void reset() {
state = INIT;
}
}- activity中的實現
public class MainActivity extends ListActivity {
// 固定下載的資源路徑，這裏可以設置網絡上的地址
private static final String URL = "http://10.0.3.2:8080/TomcatTest/xiangce/";
// 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>();
/**
* 31 * 利用消息處理機制適時更新進度條 32
*/
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) {
// 設置進度條按讀取的length長度更新
bar.incrementProgressBy(length);
if (bar.getProgress() == bar.getMax()) {
Toast.makeText(MainActivity.this, "下載完成！", 0).show();
// 下載完成後清除進度條並將map中的數據清空
LinearLayout layout = (LinearLayout) bar.getParent();
layout.removeView(bar);
ProgressBars.remove(url);
downloaders.get(url).delete(url);
downloaders.get(url).reset();
downloaders.remove(url);
}
}
}
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
showListView();
}
// 顯示listView，這裏可以隨便添加音樂
private void showListView() {
List<Map<String, String>> data = new ArrayList<Map<String, String>>();
Map<String, String> map = new HashMap<String, String>();
map.put("name", "pic1.jpg");
data.add(map);
map = new HashMap<String, String>();
map.put("name", "pic2.jpg");
data.add(map);
map = new HashMap<String, String>();
map.put("name", "pic3.jpg");
data.add(map);
map = new HashMap<String, String>();
map.put("name", "pic4.jpg");
data.add(map);
map = new HashMap<String, String>();
map.put("name", "pic5.jpg");
data.add(map);
SimpleAdapter adapter = new SimpleAdapter(this, data,
R.layout.list_item, new String[] { "name" },
new int[] { R.id.tv_resouce_name });
setListAdapter(adapter);
}
/**
* 83 * 響應開始下載按鈕的點擊事件 84
*/
public void startDownload(View v) {
// 得到textView的內容
LinearLayout layout = (LinearLayout) v.getParent();
String musicName = ((TextView) layout
.findViewById(R.id.tv_resouce_name)).getText().toString();
String urlstr = URL + musicName;
String localfile = SD_PATH + musicName;
// 設置下載線程數爲4，這裏是我爲了方便隨便固定的
int threadcount = 4;
// 初始化一個downloader下載器
DownLoader downloader = downloaders.get(urlstr);
if (downloader == null) {
downloader = new DownLoader(urlstr, localfile, threadcount, this,
mHandler);
downloaders.put(urlstr, downloader);
}
//如果正在下載，不再往下執行。
if (downloader.isdownloading())
return;
// 得到下載信息類的個數組成集合
LoadInfo loadInfo = downloader.getDownloaderInfors();
// 顯示進度條
showProgress(loadInfo, urlstr, v);
// 調用方法開始下載
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());
System.out.println(loadInfo.getFileSize()+"--"+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擊事件
*/
public void pauseDownload(View v) {
LinearLayout layout = (LinearLayout) v.getParent();
String musicName = ((TextView) layout
.findViewById(R.id.tv_resouce_name)).getText().toString();
String urlstr = URL + musicName;
downloaders.get(urlstr).pause();
}
}
