效果圖
白話分析:
多線程:肯定是多個線程咯
斷點:線程停止下載的位置
續傳:線程從停止下載的位置上繼續下載，直到完成任務為止。
核心分析:
斷點:
當前線程已經下載的數據長度
續傳:
向服務器請求上次線程停止下載位置的數據
con.setRequestProperty("Range", "bytes=" + start + "-" + end);分配線程:
int currentPartSize = fileSize / mThreadNum;
定義位置
定義線程開始下載的位置和結束的位置
for (int i = 0; i < mThreadNum; i++) {int start = i * currentPartSize;//計算每條線程下載的開始位置 int end = start + currentPartSize-1;//線程結束的位置 if(i==mThreadNum-1){ end=fileSize; }}創建數據庫:
由于每一個文件要分成多個部分，要被不同的線程同時進行下載。當然要創建線程表，保存當前線程下載開始的位置和結束的位置，還有完成進度等。創建file表，保存當前下載的文件信息，比如：文件名，url，下載進度等信息
線程表:
public static final String CREATE_TABLE_SQL="create table "+TABLE_NAME+"(_id integer primary " +"key autoincrement, threadId, start , end, completed, url)";
file表：
public static final String CREATE_TABLE_SQL="create table "+TABLE_NAME+"(_id integer primary" + " key autoincrement ,fileName, url, length, finished)";
創建線程類
無非就2個類，一個是線程管理類DownLoadManager.Java，核心方法：start(),stop(),restart(),addTask().clear()。另一個是線程任務類
DownLoadTask.java，就是一個線程類，用于下載線程分配好的任務。后面會貼出具體代碼。
創建數據庫方法類
無非就是單例模式，封裝一些增刪改查等基礎數據庫方法，后面會貼出具體代碼。
創建實體類
也就是創建ThreadInfo和FileInfo這2個實體類，把下載文件信息和線程信息暫時存儲起來。
引入的第三方開源庫
NumberProgressBar是一個關于進度條的開源庫，挺不錯的。直達鏈接
代碼具體分析
1.首先是創建實體類，文件的實體類FileInfo，肯定有fileName,url,length,finised,isStop,isDownloading這些屬性。線程的實體類ThreadInfo肯定有threadId,start,end,completed,url這些屬性。這些都很簡單
//ThredInfo.java public class FileInfo { private String fileName; //文件名 private String url; //下載地址 private int length; //文件大小 private int finished; //下載已完成進度 private boolean isStop=false; //是否暫停下載 private boolean isDownloading=false; //是否正在下載 public FileInfo(){ } public FileInfo(String fileName,String url){ this.fileName=fileName; this.url=url; } public String getFileName() { return fileName; } public void setFileName(String fileName) { this.fileName = fileName; } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public int getLength() { return length; } public void setLength(int length) { this.length = length; } public int getFinished() { return finished; } public void setFinished(int finished) { this.finished = finished; } public boolean isStop() { return isStop; } public void setStop(boolean stop) { isStop = stop; } public boolean isDownloading() { return isDownloading; } public void setDownloading(boolean downloading) { isDownloading = downloading; } @Override public String toString() { return "FileInfo{" + "fileName='" + fileName + '/'' + ", url='" + url + '/'' + ", length=" + length + ", finished=" + finished + ", isStop=" + isStop + ", isDownloading=" + isDownloading + '}'; }} //FileInfo.java public class FileInfo { private String fileName; //文件名 private String url; //下載地址 private int length; //文件大小 private int finished; //下載已完成進度 private boolean isStop=false; //是否暫停下載 private boolean isDownloading=false; //是否正在下載 public FileInfo(){ } public FileInfo(String fileName,String url){ this.fileName=fileName; this.url=url; } public String getFileName() { return fileName; } public void setFileName(String fileName) { this.fileName = fileName; } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public int getLength() { return length; } public void setLength(int length) { this.length = length; } public int getFinished() { return finished; } public void setFinished(int finished) { this.finished = finished; } public boolean isStop() { return isStop; } public void setStop(boolean stop) { isStop = stop; } public boolean isDownloading() { return isDownloading; } public void setDownloading(boolean downloading) { isDownloading = downloading; } @Override public String toString() { return "FileInfo{" + "fileName='" + fileName + '/'' + ", url='" + url + '/'' + ", length=" + length + ", finished=" + finished + ", isStop=" + isStop + ", isDownloading=" + isDownloading + '}'; }}2.實體類寫完了，那么接下來寫創建一個類，繼承SQLiteOpenHelper類，來管理數據庫連接，主要作用：管理數據庫的初始化，并允許應用程序通過該類獲取SQLiteDatabase對象。
public class ThreadHelper extends SQLiteOpenHelper{ public static final String TABLE_NAME="downthread"; public static final String CREATE_TABLE_SQL="create table "+TABLE_NAME+"(_id integer primary " +"key autoincrement, threadId, start , end, completed, url)"; public ThreadHelper(Context context, String name, int version) { super(context, name, null, version); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(CREATE_TABLE_SQL); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { }}3.接下來封裝一些數據庫的增刪改查操作，用的單例模式，用雙重檢驗鎖實現單例。好處:既能很大程度上確保線程安全，又能實現延遲加載。 缺點:使用volatile關鍵字會使JVM對該代碼的優化喪失，影響性能。并且在一些高并發的情況，仍然可能會創建多個實例，這稱為雙重檢驗鎖定失效。單例模式
public class Thread { private SQLiteDatabase db; public static final String DB_NAME="downthread.db3"; public static final int VERSION=1; private Context mContext; private volatile static Thread t=null; private Thread(){ mContext= BaseApplication.getContext(); db=new ThreadHelper(mContext,DB_NAME,VERSION).getReadableDatabase(); } public static Thread getInstance(){ if(t==null){ synchronized (Thread.class){ if(t==null){ t=new Thread(); } } } return t; } public SQLiteDatabase getDb(){ return db; } //保存當前線程下載進度 public synchronized void insert(ThreadInfo threadInfo){ ContentValues values=new ContentValues(); values.put("threadId",threadInfo.getThreadId()); values.put("start",threadInfo.getStart()); values.put("end",threadInfo.getEnd()); values.put("completed",threadInfo.getCompeleted()); values.put("url",threadInfo.getUrl()); long rowId=db.insert(ThreadHelper.TABLE_NAME,null,values); if(rowId!=-1){ UtilsLog.i("插入線程記錄成功"); }else{ UtilsLog.i("插入線程記錄失敗"); } } //查詢當前線程 下載的進度 public synchronized ThreadInfo query(String threadId,String queryUrl){ Cursor cursor=db.query(ThreadHelper.TABLE_NAME,null,"threadId= ? and url= ?",new String[]{threadId,queryUrl},null,null,null); ThreadInfo info=new ThreadInfo(); if(cursor!=null){ while (cursor.moveToNext()){ int start=cursor.getInt(2); int end=cursor.getInt(3); int completed=cursor.getInt(4); String url=cursor.getString(5); info.setThreadId(threadId); info.setStart(start); info.setEnd(end); info.setCompeleted(completed); info.setUrl(url); } cursor.close(); } return info; } //更新當前線程下載進度 public synchronized void update(ThreadInfo info){ ContentValues values=new ContentValues(); values.put("start",info.getStart()); values.put("completed",info.getCompeleted()); db.update(ThreadHelper.TABLE_NAME,values,"threadId= ? and url= ?",new String[]{info.getThreadId(),info.getUrl()}); } //關閉db public void close(){ db.close(); } //判斷多線程任務下載 是否第一次創建線程 public boolean isExist(String url){ Cursor cursor=db.query(ThreadHelper.TABLE_NAME,null,"url= ?",new String[]{url},null,null,null); boolean isExist=cursor.moveToNext(); cursor.close(); return isExist; } public synchronized void delete(ThreadInfo info){ long rowId=db.delete(ThreadHelper.TABLE_NAME,"url =? and threadId= ?",new String[]{info.getUrl(),info.getThreadId()}); if(rowId!=-1){ UtilsLog.i("刪除下載線程記錄成功"); }else{ UtilsLog.i("刪除下載線程記錄失敗"); } } public synchronized void delete(String url){ long rowId=db.delete(ThreadHelper.TABLE_NAME,"url =? ",new String[]{url}); if(rowId!=-1){ UtilsLog.i("刪除下載線程記錄成功"); }else{ UtilsLog.i("刪除下載線程記錄失敗"); } }}4.基本的準備操作我們已經完成了，那么開始寫關于下載的類吧。首先寫的肯定是DownLoadManager類，就是管理任務下載的類。不多說，直接看代碼。
public class DownLoadManager { private Map<String, FileInfo> map = new HashMap<>(); private static int mThreadNum; private int fileSize; private boolean flag = false; //true第一次下載 false不是第一次下載 private List<DownLoadTask> threads; private static FileInfo mInfo; private static ResultListener mlistener; public static ExecutorService executorService = Executors.newCachedThreadPool(); public static File file; private int totalComleted; private DownLoadManager() { threads = new ArrayList<>(); } public static DownLoadManager getInstance(FileInfo info, int threadNum,ResultListener listener) { mlistener = listener; mThreadNum = threadNum; mInfo = info; return DownLoadManagerHolder.dlm; } private static class DownLoadManagerHolder { private static final DownLoadManager dlm = new DownLoadManager(); } public void start() { totalComleted=0; clear(); final FileInfo newInfo = DownLoad.getInstance().queryData(mInfo.getUrl()); newInfo.setDownloading(true); map.put(mInfo.getUrl(),newInfo); prepare(newInfo); } //停止下載任務 public void stop() { map.get(mInfo.getUrl()).setDownloading(false); map.get(mInfo.getUrl()).setStop(true); } public void clear(){ if(threads.size()>0){ threads.clear(); } } //重新下載任務 public void restart() { stop(); try { File file = new File(com.cmazxiaoma.downloader.download.DownLoadManager.FILE_PATH, map.get(mInfo.getUrl()).getFileName()); if (file.exists()) { file.delete(); } java.lang.Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } DownLoad.getInstance().resetData(mInfo.getUrl()); start(); } //獲取當前任務狀態, 是否在下載 public boolean getCurrentState() { return map.get(mInfo.getUrl()).isDownloading(); } //添加下載任務 public void addTask(FileInfo info) { //判斷數據庫是否已經存在此下載信息 if (!DownLoad.getInstance().isExist(info)) { DownLoad.getInstance().insertData(info); map.put(info.getUrl(), info); } else { DownLoad.getInstance().delete(info); DownLoad.getInstance().insertData(info); UtilsLog.i("map已經更新"); map.remove(info.getUrl()); map.put(info.getUrl(), info); } } private void prepare(final FileInfo newInfo) { new java.lang.Thread(){ @Override public void run() { HttpURLConnection con = null; RandomAccessFile raf=null; try { //連接資源 URL url = new URL(newInfo.getUrl()); UtilsLog.i("url=" + url); con = (HttpURLConnection) url.openConnection(); con.setConnectTimeout(2 * 1000); con.setRequestMethod("GET"); int length = -1; UtilsLog.i("responseCode=" + con.getResponseCode()); if (con.getResponseCode() == 200) { length = con.getContentLength(); UtilsLog.i("文件大小=" + length); } if (length <= 0) { return; } //創建文件保存路徑 File dir = new File(com.cmazxiaoma.downloader.download.DownLoadManager.FILE_PATH); if (!dir.exists()) { dir.mkdirs();//建立多級文件夾 } newInfo.setLength(length); fileSize = length; UtilsLog.i("當前線程Id=" + java.lang.Thread.currentThread().getId() + ",name=" + java.lang.Thread.currentThread().getName()); int currentPartSize = fileSize / mThreadNum; file = new File(com.cmazxiaoma.downloader.download.DownLoadManager.FILE_PATH, newInfo.getFileName()); raf = new RandomAccessFile(file, "rwd"); raf.setLength(fileSize); if (Thread.getInstance().isExist(newInfo.getUrl())) { flag = false; } else { flag = true; } for (int i = 0; i < mThreadNum; i++) { if (flag) { UtilsLog.i("第一次多線程下載"); int start = i * currentPartSize;//計算每條線程下載的開始位置 int end = start + currentPartSize-1;//線程結束的位置 if(i==mThreadNum-1){ end=fileSize; } String threadId = "xiaoma" + i; ThreadInfo threadInfo = new ThreadInfo(threadId, start, end, 0,newInfo.getUrl()); Thread.getInstance().insert(threadInfo); DownLoadTask thread = new DownLoadTask(threadInfo,newInfo, threadId, start, end, 0); DownLoadManager.executorService.execute(thread); threads.add(thread); } else { UtilsLog.i("不是第一次多線程下載"); ThreadInfo threadInfo = Thread.getInstance().query("xiaoma" + i, newInfo.getUrl()); DownLoadTask thread = new DownLoadTask(threadInfo,newInfo,threadInfo.getThreadId(),threadInfo.getStart(),threadInfo.getEnd(),threadInfo.getCompeleted());//這里出現過問題 DownLoadManager.executorService.execute(thread); threads.add(thread); } } boolean isCompleted=false; while(!isCompleted){ isCompleted=true; for(DownLoadTask thread:threads){ totalComleted+=thread.completed; if(!thread.isCompleted){ isCompleted=false; } } if(newInfo.isStop()){ totalComleted=0; return; } Message message=new Message(); message.what=0x555; message.arg1=fileSize; message.arg2=totalComleted; handler.sendMessage(message); if(isCompleted){ totalComleted=0; //任務線程全部完成，清空集合 clear(); handler.sendEmptyMessage(0x666); return; } totalComleted=0; java.lang.Thread.sleep(1000); } }catch (Exception e) { e.printStackTrace(); }finally { try { if (con != null) { con.disconnect(); } if(raf!=null){ raf.close(); } } catch (IOException e) { e.printStackTrace(); } } } }.start(); } private Handler handler=new Handler(){ @Override public void handleMessage(Message msg) { super.handleMessage(msg); switch (msg.what){ case 0x555: if(mlistener!=null){ mlistener.progress(msg.arg1,msg.arg2); } break; case 0x666: if(mlistener!=null){ mlistener.comleted(); } break; } } };}5.接下來呢，就是DownLoadTask類了，就是一個線程下載類。
public class DownLoadTask extends java.lang.Thread{ private int start;//當前線程的開始下載位置 private int end;//當前線程結束下載的位置 private RandomAccessFile raf;//當前線程負責下載的文件大小 public int completed=0;//當前線程已下載的字節數 private String threadId;//自己定義的線程Id private FileInfo info; private ThreadInfo threadInfo; public boolean isCompleted=false; //true為當前線程完成任務,false為當前線程未完成任務 //保存新的start public int finshed=0; public int newStart=0; public DownLoadTask(ThreadInfo threadInfo,FileInfo info,String threadId, int start, int end,int completed){ this.threadInfo=threadInfo; this.info=info; this.threadId=threadId; this.start=start; this.end=end; this.completed=completed; } @Override public void run() { HttpURLConnection con = null; try { UtilsLog.i("start="+start+",end="+end+",completed="+completed+",threadId="+getThreadId()); URL url = new URL(info.getUrl()); con = (HttpURLConnection) url.openConnection(); con.setConnectTimeout(2 * 1000); con.setRequestMethod("GET"); con.setRequestProperty("Range", "bytes=" + start + "-"+end);//重點 raf=new RandomAccessFile(DownLoadManager.file,"rwd"); //從文件的某一位置寫入 raf.seek(start); if (con.getResponseCode() == 206) { //文件部分下載 返回碼是206 InputStream is = con.getInputStream(); byte[] buffer = new byte[4096]; int hasRead = 0; while ((hasRead = is.read(buffer)) != -1) { //寫入文件 raf.write(buffer, 0, hasRead); //單個文件的完成程度 completed += hasRead; threadInfo.setCompeleted(completed); //保存新的start finshed=finshed+hasRead;//這里出現過問題，嘻嘻 newStart=start+finshed; threadInfo.setStart(newStart); //UtilsLog.i("Thread:"+getThreadId()+",completed=" + completed); //停止下載 if (info.isStop()) { UtilsLog.i("isStop="+info.isStop()); //保存下載進度 UtilsLog.i("現在Thread:"+getThreadId()+",completed=" + completed); Thread.getInstance().update(threadInfo); return; } } //刪除該線程下載記錄 Thread.getInstance().delete(threadInfo); isCompleted=true; Thread.getInstance().update(threadInfo); UtilsLog.i("thread:"+getThreadId()+"已經完成任務!--"+"completed="+completed); } } catch (Exception e) { if (con != null) { con.disconnect(); } try { if (raf != null) { raf.close(); } } catch (IOException e1) { e1.printStackTrace(); } } } public String getThreadId() { return threadId; }}6.接口，就是一個監聽下載進度的接口，也是很簡單。
public interface ResultListener{ void progress(int max, int progress); void comleted();}結束
大致操作就是這樣，其實多線程也挺簡單的。
以上所述是小編給大家介紹的Android多線程+單線程+斷點續傳+進度條顯示下載功能，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對VEVB武林網網站的支持！
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