#####效果圖
#####白話分析: 多執行緒:肯定是多個執行緒咯 斷點:執行緒停止下載的位置 續傳:執行緒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: 當前執行緒已經下載的資料長度
######續傳: 向伺服器請求上次執行緒停止下載位置的資料
con.setRequestProperty("Range", "bytes=" + start + "-" + end);
複製程式碼######分配執行緒:
int currentPartSize = fileSize / mThreadNum;
複製程式碼######定義位置
定義執行緒開始下載的位置和結束的位置
for (int i = 0; i < mThreadNum; i++) {
int start = i * currentPartSize;//計算每條執行緒下載的開始位置
int end = start + currentPartSize-1;//執行緒結束的位置
if(i==mThreadNum-1){
end=fileSize;
}}
複製程式碼######建立資料庫: 由於每一個檔案要分成多個部分，要被不同的執行緒同時進行下載。當然要建立執行緒表，儲存當前執行緒下載開始的位置和結束的位置，還有完成進度等。建立file表，儲存當前下載的檔案資訊，比如：檔名，url，下載進度等資訊 ######執行緒表:
public static final String CREATE_TABLE_SQL="create table "+TABLE_NAME+"(_id integer primary "
+"key autoincrement, threadId, start , end, completed, url)";
複製程式碼######file表：
public static final String CREATE_TABLE_SQL="create table "+TABLE_NAME+"(_id integer primary" +
" key autoincrement ,fileName, url, length, finished)";
複製程式碼######建立執行緒類
無非就2個類，一個是執行緒管理類DownLoadManager.java，核心方法：start(),stop(),restart(),addTask().clear()。另一個是執行緒任務類
DownLoadTask.java，就是一個執行緒類，用於下載執行緒分配好的任務。後面會貼出具體程式碼。
######建立資料庫方法類
無非就是單例模式，封裝一些增刪改查等基礎資料庫方法，後面會貼出具體程式碼。
######建立實體類
也就是建立ThreadInfo和FileInfo這2個實體類，把下載檔案資訊和執行緒資訊暫時儲存起來。
######引入的第三方開源庫
NumberProgressBar是一個關於進度條的開源庫，挺不錯的。直達連結
#####程式碼具體分析
1.首先是建立實體類，檔案的實體類FileInfo，肯定有fileName,url,length,finised,isStop,isDownloading這些屬性。執行緒的實體類ThreadInfo肯定有threadId,start,end,completed,url這些屬性。這些都很簡單
//ThreadInfo.java
public class ThreadInfo {
private String threadId;
private int start;
private int end;
private int compeleted;
private String url;
public ThreadInfo(){
}
public ThreadInfo(String threadId, int start, int end, int compeleted, String url) {
this.threadId = threadId;
this.start = start;
this.end = end;
this.compeleted = compeleted;
this.url = url;
}
public String getThreadId() {
return threadId;
}
public void setThreadId(String threadId) {
this.threadId = threadId;
}
public int getStart() {
return start;
}
public void setStart(int start) {
this.start = start;
}
public int getEnd() {
return end;
}
public void setEnd(int end) {
this.end = end;
}
public int getCompeleted() {
return compeleted;
}
public void setCompeleted(int compeleted) {
this.compeleted = compeleted;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
複製程式碼}
//FileInfo.java
public class FileInfo {
private String fileName; //檔名
private String url; //下載地址
private int length; //檔案大小
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 +
'}';
}}
複製程式碼2.實體類寫完了，那麼接下來寫建立一個類，繼承SQLiteOpenHelper類，來管理資料庫連線，主要作用：管理資料庫的初始化，並允許應用程式通過該類獲取SQLiteDatabase物件。
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) {
}}
複製程式碼3.接下來封裝一些資料庫的增刪改查操作，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執行緒安全，又能實現延遲載入。 缺點:使用volatile關鍵字會使JVM對該程式碼的優化喪失，影響效能。並且在一些高併發的情況，仍然可能會建立多個例項，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;
}
//儲存當前執行緒下載進度
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("插入執行緒記錄成功");
}else{
UtilsLog.i("插入執行緒記錄失敗");
}
}
//查詢當前執行緒 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;
}
//更新當前執行緒下載進度
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();
}
//判斷多執行緒任務下載 是否第一次建立執行緒
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("刪除下載執行緒記錄成功");
}else{
UtilsLog.i("刪除下載執行緒記錄失敗");
}
}
public synchronized void delete(String url){
long rowId=db.delete(ThreadHelper.TABLE_NAME,"url =? ",new String[]{url});
if(rowId!=-1){
UtilsLog.i("刪除下載執行緒記錄成功");
}else{
UtilsLog.i("刪除下載執行緒記錄失敗");
}
}}
複製程式碼4.基本的準備操作我們已經完成了，那麼開始寫關於下載的類吧。首先寫的肯定是DownLoadManager類，就是管理任務下載的類。不多說，直接看程式碼。
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();
}
//新增下載任務
public void addTask(FileInfo info) {
//判斷資料庫是否已經存在此下載資訊
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 {
//連線資源
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("檔案大小=" + length);
}
if (length <= 0) {
return;
}
//建立檔案儲存路徑
File dir = new File(com.cmazxiaoma.downloader.download.DownLoadManager.FILE_PATH);
if (!dir.exists()) {
dir.mkdirs();//建立多級資料夾
}
newInfo.setLength(length);
fileSize = length;
UtilsLog.i("當前執行緒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("第一次多執行緒下載");
int start = i * currentPartSize;//計算每條執行緒下載的開始位置
int end = start + currentPartSize-1;//執行緒結束的位置
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("不是第一次多執行緒下載");
ThreadInfo threadInfo = Thread.getInstance().query("xiaoma" + i, newInfo.getUrl());
DownLoadTask thread = new DownLoadTask(threadInfo,newInfo,threadInfo.getThreadId(),threadInfo.getStart(),threadInfo.getEnd(),threadInfo.getCompeleted());//這裡出現過問題
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;
//任務執行緒全部完成，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;
}
}
};}
複製程式碼5.接下來呢，就是DownLoadTask類了，就是一個執行緒下載類。
public class DownLoadTask extends java.lang.Thread{
private int start;//當前執行緒的開始下載位置
private int end;//當前執行緒結束下載的位置
private RandomAccessFile raf;//當前執行緒負責下載的檔案大小
public int completed=0;//當前執行緒已下載的位元組數
private String threadId;//自己定義的執行緒Id
private FileInfo info;
private ThreadInfo threadInfo;
public boolean isCompleted=false; //true為當前執行緒完成任務,false為當前執行緒未完成任務
//儲存新的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");
//從檔案的某一位置寫入
raf.seek(start);
if (con.getResponseCode() == 206) { //檔案部分下載 返回碼是206
InputStream is = con.getInputStream();
byte[] buffer = new byte[4096];
int hasRead = 0;
while ((hasRead = is.read(buffer)) != -1) {
//寫入檔案
raf.write(buffer, 0, hasRead);
//單個檔案的完成程度
completed += hasRead;
threadInfo.setCompeleted(completed);
//儲存新的start
finshed=finshed+hasRead;//這裡出現過問題，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());
//儲存下載進度
UtilsLog.i("現在Thread:"+getThreadId()+",completed=" + completed);
Thread.getInstance().update(threadInfo);
return;
}
}
//刪除該執行緒下載記錄
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;
}}
複製程式碼6.介面，就是一個監聽下載進度的介面，也是很簡單。
public interface ResultListener{
void progress(int max, int progress);
void comleted();}
複製程式碼######結束 大致操作就是這樣，其實多執行緒也挺簡單的。