本文出自：https://blog.csdn.net/dt235201314/article/details/80911932
一丶概述
斷點(diǎn)續(xù)傳是IO章節(jié)的練習(xí)泌豆，顯然實(shí)現(xiàn)斷點(diǎn)續(xù)傳知識(shí)點(diǎn)不僅僅是IO相關(guān)知識(shí)，RandomAccessFile倒是主要環(huán)節(jié)
二丶效果圖
image.png
三丶RandomAccessFile
1.簡介
image
我們可以看到它的父類是Object吏饿，沒有繼承字節(jié)流踪危、字符流家族中任何一個(gè)類蔬浙。并且它實(shí)現(xiàn)了DataInput、DataOutput這兩個(gè)接口贞远，也就意味著這個(gè)類既可以讀也可以寫畴博。
RandomAccessFile既可以讀取文件內(nèi)容，也可以向文件輸出數(shù)據(jù)蓝仲。同時(shí)支持“隨機(jī)訪問”的方式绎晃，可以直接跳轉(zhuǎn)到文件的任意地方來讀寫數(shù)據(jù)。
與OutputStream杂曲、Writer等輸出流不同的是，RandomAccessFile允許自由定義文件記錄指針袁余，RandomAccessFile可以不從開始的地方開始輸出擎勘，因此RandomAccessFile可以向已存在的文件后追加內(nèi)容。如果程序需要向已存在的文件后追加內(nèi)容颖榜，則應(yīng)該使用RandomAccessFile棚饵。
RandomAccessFile的一個(gè)重要使用場景就是網(wǎng)絡(luò)請(qǐng)求中的多線程下載及斷點(diǎn)續(xù)傳。
2.構(gòu)造方法
RandomAccessFile類有兩個(gè)構(gòu)造函數(shù)掩完，其實(shí)這兩個(gè)構(gòu)造函數(shù)基本相同噪漾，只不過是指定文件的形式不同——一個(gè)需要使用String參數(shù)來指定文件名，一個(gè)使用File參數(shù)來指定文件本身且蓬。除此之外欣硼，創(chuàng)建RandomAccessFile對(duì)象時(shí)還需要指定一個(gè)mode參數(shù)，該參數(shù)指定RandomAccessFile的訪問模式恶阴，一共有4種模式：
"r": 以只讀方式打開诈胜。調(diào)用結(jié)果對(duì)象的任何 write 方法都將導(dǎo)致拋出 IOException。
"rw": 打開以便讀取和寫入冯事。
"rws": 打開以便讀取和寫入焦匈。相對(duì)于 "rw"，"rws" 還要求對(duì)“文件的內(nèi)容”或“元數(shù)據(jù)”的每個(gè)更新都同步寫入到基礎(chǔ)存儲(chǔ)設(shè)備昵仅。
"rwd" : 打開以便讀取和寫入缓熟，相對(duì)于 "rw"，"rwd" 還要求對(duì)“文件的內(nèi)容”的每個(gè)更新都同步寫入到基礎(chǔ)存儲(chǔ)設(shè)備摔笤。
3.重要方法
RandomAccessFile對(duì)象包含了一個(gè)記錄指針够滑，用以標(biāo)識(shí)當(dāng)前讀寫處的位置囊颅，當(dāng)程序新創(chuàng)建一個(gè)RandomAccessFile對(duì)象時(shí)皮璧，該對(duì)象的文件指針記錄位于文件頭（也就是0處），當(dāng)讀/寫了n個(gè)字節(jié)后姻锁，文件記錄指針將會(huì)后移n個(gè)字節(jié)寞冯。除此之外渴析，RandomAccessFile還可以自由移動(dòng)該記錄指針晚伙。下面就是RandomAccessFile具有的兩個(gè)特殊方法，來操作記錄指針俭茧，實(shí)現(xiàn)隨機(jī)訪問：
long getFilePointer( )：返回文件記錄指針的當(dāng)前位置
void seek(long pos )：將文件指針定位到pos位置
4.demo案例
public static void main(String[] args)
{
try
{
insert("d:/out.txt",5,"插入的內(nèi)容");
}
catch (IOException e)
{
e.printStackTrace();
}
}
private static void insert(String fileName,long pos,String content) throws IOException
{
//創(chuàng)建臨時(shí)空文件
File tempFile = File.createTempFile("temp",null);
//在虛擬機(jī)終止時(shí)咆疗，請(qǐng)求刪除此抽象路徑名表示的文件或目錄
tempFile.deleteOnExit();
FileOutputStream fos = new FileOutputStream(tempFile);
RandomAccessFile raf = new RandomAccessFile(fileName,"rw");
raf.seek(pos);
byte[] buffer = new byte[4];
int num = 0;
while(-1 != (num = raf.read(buffer)))
{
fos.write(buffer,0,num);
}
raf.seek(pos);
raf.write(content.getBytes());
FileInputStream fis = new FileInputStream(tempFile);
while(-1 != (num = fis.read(buffer)))
{
raf.write(buffer,0,num);
}
}
image
一個(gè)漢字=2個(gè)英文字母=2字節(jié) 杭州G=5個(gè)字節(jié)
四丶斷點(diǎn)續(xù)傳實(shí)現(xiàn)原理
其實(shí)斷點(diǎn)續(xù)傳的原理很簡單，從字面上理解母债，所謂斷點(diǎn)續(xù)傳就是從停止的地方重新下載午磁。
斷點(diǎn)：線程停止的位置。
續(xù)傳：從停止的位置重新下載毡们。
用代碼解析就是：
斷點(diǎn) ==> 當(dāng)前線程已經(jīng)下載完成的數(shù)據(jù)長度迅皇。
續(xù)傳 ==> 向服務(wù)器請(qǐng)求上次線程停止位置之后的數(shù)據(jù)。
原理知道了衙熔，功能實(shí)現(xiàn)起來也簡單登颓。每當(dāng)線程停止時(shí)就把已下載的數(shù)據(jù)長度寫入記錄文件，當(dāng)重新下載時(shí)红氯，從記錄文件讀取已經(jīng)下載了的長度框咙。而這個(gè)長度就是所需要的斷點(diǎn)。
續(xù)傳的實(shí)現(xiàn)也簡單痢甘，可以通過設(shè)置網(wǎng)絡(luò)請(qǐng)求參數(shù)喇嘱，請(qǐng)求服務(wù)器從指定的位置開始讀取數(shù)據(jù)。
而要實(shí)現(xiàn)這兩個(gè)功能只需要使用到httpURLconnection里面的setRequestProperty方法便可以實(shí)現(xiàn).
public void setRequestProperty(String field, String newValue)
如下所示塞栅，便是向服務(wù)器請(qǐng)求500-1000之間的500個(gè)byte：
conn.setRequestProperty("Range", "bytes=" + 500 + "-" + 1000);
以上只是續(xù)傳的一部分需求者铜，當(dāng)我們獲取到下載數(shù)據(jù)時(shí)，還需要將數(shù)據(jù)寫入文件放椰，而普通發(fā)File對(duì)象并不提供從指定位置寫入數(shù)據(jù)的功能王暗，這個(gè)時(shí)候，就需要使用到RandomAccessFile來實(shí)現(xiàn)從指定位置給文件寫入數(shù)據(jù)的功能庄敛。
public void seek(long offset)
如下所示俗壹，便是從文件的的第100個(gè)byte后開始寫入數(shù)據(jù)。
raFile.seek(100);
而開始寫入數(shù)據(jù)時(shí)還需要用到RandomAccessFile里面的另外一個(gè)方法
public void write(byte[] buffer, int byteOffset, int byteCount)
該方法的使用和OutputStream的write的使用一模一樣...
而多線程斷點(diǎn)續(xù)傳便是在單線程的斷點(diǎn)續(xù)傳上延伸的藻烤，而多線程斷點(diǎn)續(xù)傳是把整個(gè)文件分割成幾個(gè)部分绷雏，每個(gè)部分由一條線程執(zhí)行下載，而每一條下載線程都要實(shí)現(xiàn)斷點(diǎn)續(xù)傳功能怖亭。
為了實(shí)現(xiàn)文件分割功能涎显，我們需要使用到httpURLconnection的另外一個(gè)方法：
public int getContentLength()
當(dāng)請(qǐng)求成功時(shí)，可以通過該方法獲取到文件的總長度兴猩。
每一條線程下載大小 = fileLength / THREAD_NUM
在多線程斷點(diǎn)續(xù)傳下載中期吓，有一點(diǎn)需要特別注意：
由于文件是分成多個(gè)部分是被不同的線程的同時(shí)下載的，這就需要倾芝，每一條線程都分別需要有一個(gè)斷點(diǎn)記錄讨勤，和一個(gè)線程完成狀態(tài)的記錄箭跳；
只有所有線程的下載狀態(tài)都處于完成狀態(tài)時(shí)，才能表示文件已經(jīng)下載完成潭千。
五丶核心代碼實(shí)現(xiàn)
主Activity
public class DownLoadActivity extends Activity {
private static final int PROCESSING = 1;
private static final int FAILURE = -1;
private EditText pathText;
private Button downloadButton;
private Button stopButton;
private ProgressBar progressBar;
private Context context;
Handler handler = new UIHandler(this);
private static class UIHandler extends Handler {
private final WeakReference<DownLoadActivity> mActivity;
//弱引用谱姓，避免內(nèi)存泄露
UIHandler(DownLoadActivity activity) {
mActivity = new WeakReference<>(activity);
}
@Override
public void handleMessage(Message msg) {
DownLoadActivity activity = mActivity.get();
if (activity != null) {
switch (msg.what) {
case PROCESSING:
ProgressBar progressBar = (ProgressBar) activity.findViewById(R.id.progressBar);
TextView resultView = (TextView) activity.findViewById(R.id.resultView);
progressBar.setProgress(msg.getData().getInt("size"));
float num = (float) progressBar.getProgress() / (float) progressBar.getMax();
int result = (int) (num * 100);
resultView.setText(result + "%");
if (progressBar.getProgress() == progressBar.getMax()) {
Toast.makeText(activity, R.string.success, Toast.LENGTH_LONG).show();
}
break;
case FAILURE:
Toast.makeText(activity, R.string.error, Toast.LENGTH_LONG).show();
break;
default:
}
}
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.down_load_activity);
context = this;
pathText = (EditText) findViewById(R.id.path);
downloadButton = (Button) findViewById(R.id.downloadbutton);
stopButton = (Button) findViewById(R.id.stopbutton);
progressBar = (ProgressBar) findViewById(R.id.progressBar);
ButtonClickListener listener = new ButtonClickListener();
downloadButton.setOnClickListener(listener);
stopButton.setOnClickListener(listener);
}
private class ButtonClickListener implements View.OnClickListener {
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.downloadbutton:
String path = pathText.getText().toString();
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
//外部存儲(chǔ)
//File savDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES);
//File savDir = Environment.getExternalStorageDirectory();
//內(nèi)部存儲(chǔ)
File savDir = new File(context.getCacheDir(), "/cache/exe");
download(path, savDir);
} else {
Toast.makeText(getApplicationContext(), R.string.sdcarderror, Toast.LENGTH_LONG).show();
}
downloadButton.setEnabled(false);
stopButton.setEnabled(true);
break;
case R.id.stopbutton:
exit();
Toast.makeText(getApplicationContext(), "Now thread is Stopping!!", Toast.LENGTH_LONG).show();
downloadButton.setEnabled(true);
stopButton.setEnabled(false);
break;
default:
}
}
private DownloadTask task;
private void exit() {
if (task != null) {
task.exit();
}
}
private void download(String path, File savDir) {
task = new DownloadTask(path, savDir);
new Thread(task).start();
}
class DownloadTask implements Runnable {
private String path;
private File saveDir;
private FileDownloader loader;
DownloadTask(String path, File saveDir) {
this.path = path;
this.saveDir = saveDir;
}
void exit() {
if (loader != null) {
loader.exit();
}
}
//進(jìn)度監(jiān)聽，通過message機(jī)制把傳送進(jìn)度
DownloadProgressListener downloadProgressListener = new DownloadProgressListener() {
@Override
public void onDownloadSize(int size) {
Message msg = new Message();
msg.what = PROCESSING;
msg.getData().putInt("size", size);
handler.sendMessage(msg);
}
};
@Override
public void run() {
try {
//固定三個(gè)線程
loader = new FileDownloader(getApplicationContext(), path, saveDir, 3);
progressBar.setMax(loader.getFileSize());
loader.download(downloadProgressListener);
} catch (Exception e) {
e.printStackTrace();
handler.sendMessage(handler.obtainMessage(FAILURE));
}
}
}
}
}
下載線程類
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 downloadedLength;
private boolean finished = false;
private FileDownloader downloader;
DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downloadedLength, int threadId) {
this.downUrl = downUrl;
this.saveFile = saveFile;
this.block = block;
this.downloader = downloader;
this.threadId = threadId;
this.downloadedLength = downloadedLength;
}
@Override
public void run() {
if(downloadedLength < block){
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, */*");
http.setRequestProperty("Accept-Language", "zh-CN");
http.setRequestProperty("Referer", downUrl.toString());
http.setRequestProperty("Charset", "UTF-8");
int startPos = block * (threadId - 1) + downloadedLength;
int endPos = block * threadId -1;
http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);
http.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");
http.setRequestProperty("Connection", "Keep-Alive");
InputStream inStream = http.getInputStream();
byte[] buffer = new byte[1024];
int offset = 0;
print("Thread " + this.threadId + " starts to download from position "+ startPos);
RandomAccessFile threadFile = new RandomAccessFile(this.saveFile, "rwd");
threadFile.seek(startPos);
while (!downloader.getExited() && (offset = inStream.read(buffer, 0, 1024)) != -1) {
threadFile.write(buffer, 0, offset);
downloadedLength += offset;
downloader.update(this.threadId, downloadedLength);
downloader.append(offset);
}
threadFile.close();
inStream.close();
if(downloader.getExited())
print("Thread " + this.threadId + " has been paused");
else
print("Thread " + this.threadId + " download finish");
this.finished = true;
} catch (Exception e) {
this.downloadedLength = -1;
print("Thread "+ this.threadId+ ":"+ e);
}
}
}
private static void print(String msg){
Log.i(TAG, msg);
}
public boolean isFinished() {
return finished;
}
public long getDownloadedLength() {
return downloadedLength;
}
}
文件下載類
public class FileDownloader {
private static final String TAG = "FileDownloader";
private Context context;
private FileService fileService;
private boolean exited;
private int downloadedSize = 0;
private int fileSize = 0;
private DownloadThread[] threads;
private File saveFile;
private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();
private int block;
private String downloadUrl;
public int getThreadSize() {
return threads.length;
}
public void exit() {
this.exited = true;
}
public boolean getExited() {
return this.exited;
}
public int getFileSize() {
return fileSize;
}
protected synchronized void append(int size) {
downloadedSize += size;
}
protected synchronized void update(int threadId, int pos) {
this.data.put(threadId, pos);
this.fileService.update_tyc(this.downloadUrl, 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];
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, */*");
conn.setRequestProperty("Accept-Language", "zh-CN");
conn.setRequestProperty("Referer", downloadUrl);
conn.setRequestProperty("Charset", "UTF-8");
conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");
conn.setRequestProperty("Connection", "Keep-Alive");
conn.connect();
printResponseHeader(conn);
if (conn.getResponseCode() == 200) {
this.fileSize = conn.getContentLength();
if (this.fileSize <= 0)
throw new RuntimeException("Unkown file size ");
String filename = getFileName(conn);
this.saveFile = new File(fileSaveDir, filename);
Map<Integer, Integer> logdata = fileService.getData(downloadUrl);
if (logdata.size() > 0) {
for (Map.Entry<Integer, Integer> entry : logdata.entrySet())
data.put(entry.getKey(), entry.getValue());
}
if (this.data.size() == this.threads.length) {
for (int i = 0; i < this.threads.length; i++) {
this.downloadedSize += this.data.get(i + 1);
}
print("已經(jīng)下載的長度" + this.downloadedSize + "個(gè)字節(jié)");
}
this.block = (this.fileSize % this.threads.length) == 0 ? this.fileSize / this.threads.length : this.fileSize / this.threads.length + 1;
} else {
print("服務(wù)器響應(yīng)錯(cuò)誤:" + conn.getResponseCode() + conn.getResponseMessage());
throw new RuntimeException("server response error ");
}
} catch (Exception e) {
print(e.toString());
throw new RuntimeException("Can't connection this url");
}
}
private String getFileName(HttpURLConnection conn) {
String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);
if (filename == null || "".equals(filename.trim())) {
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(Locale.getDefault()));
if (m.find())
return m.group(1);
}
}
filename = UUID.randomUUID() + ".tmp";
}
return filename;
}
public int download(DownloadProgressListener listener) throws Exception {
try {
RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rwd");
if (this.fileSize > 0)
randOut.setLength(this.fileSize);
randOut.close();
URL url = new URL(this.downloadUrl);
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);
}
this.downloadedSize = 0;
}
for (int i = 0; i < this.threads.length; i++) {
int downloadedLength = this.data.get(i + 1);
if (downloadedLength < this.block && this.downloadedSize < this.fileSize) {
this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i + 1), i + 1);
this.threads[i].setPriority(7);
this.threads[i].start();
} else {
this.threads[i] = null;
}
}
this.fileService.delete(this.downloadUrl);
this.fileService.save(this.downloadUrl, this.data);
boolean notFinished = true;
while (notFinished) {
Thread.sleep(900);
notFinished = false;
for (int i = 0; i < this.threads.length; i++) {
if (this.threads[i] != null && !this.threads[i].isFinished()) {
notFinished = true;
if (this.threads[i].getDownloadedLength() == -1) {
this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i + 1), i + 1);
this.threads[i].setPriority(7);
this.threads[i].start();
}
}
}
if (listener != null)
listener.onDownloadSize(this.downloadedSize);
}
if (downloadedSize == this.fileSize)
this.fileService.delete(this.downloadUrl);
} catch (Exception e) {
print(e.toString());
throw new Exception("File downloads error");
}
return this.downloadedSize;
}
public static Map<String, String> getHttpResponseHeader(HttpURLConnection http) {
Map<String, String> header = new LinkedHashMap<String, String>();
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<String, String> header = getHttpResponseHeader(http);
for (Map.Entry<String, String> entry : header.entrySet()) {
String key = entry.getKey() != null ? entry.getKey() + ":" : "";
print(key + entry.getValue());
}
}
private static void print(String msg) {
Log.i(TAG, msg);
}
}
Android內(nèi)存處理類
public class FileService {
private DBOpenHelper openHelper;
public FileService(Context context) {
openHelper = new DBOpenHelper(context);
}
@SuppressLint("UseSparseArrays")
public Map<Integer, Integer> getData(String path) {
SQLiteDatabase db = openHelper.getReadableDatabase();
Cursor cursor = db.rawQuery("select threadid, downlength from filedownlog where downpath=?", new String[]{path});
Map<Integer, Integer> data = new HashMap<Integer, Integer>();
while (cursor.moveToNext()) {
data.put(cursor.getInt(0), cursor.getInt(1));
data.put(cursor.getInt(cursor.getColumnIndexOrThrow("threadid")), cursor.getInt(cursor.getColumnIndexOrThrow("downlength")));
}
cursor.close();
db.close();
return data;
}
public void save(String path, Map<Integer, Integer> map) {
SQLiteDatabase db = openHelper.getWritableDatabase();
db.beginTransaction();
try {
for (Map.Entry<Integer, Integer> 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_tyc(String path, int threadId, int pos) {
SQLiteDatabase db = openHelper.getWritableDatabase();
db.execSQL("update filedownlog set downlength=? where downpath=? and threadid=?", new Object[]{pos, path, threadId});
db.close();
}
public void update(String path, Map<Integer, Integer> map) {
SQLiteDatabase db = openHelper.getWritableDatabase();
db.beginTransaction();
try {
for (Map.Entry<Integer, Integer> 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();
}
}
數(shù)據(jù)輔助類
public class DBOpenHelper extends SQLiteOpenHelper {
private static final String DBNAME = "eric.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);
}
}
六丶提升學(xué)習(xí)
這里只是入門簡單的用HttpURLConnection實(shí)現(xiàn)刨晴，現(xiàn)在流行的RxRetrofit大神封裝見
RxRetrofit - 終極封裝 - 深入淺出 & 斷點(diǎn)續(xù)傳
七丶參考文章
深入理解JAVA I/O系列四：RandomAccessFile
源碼下載：
https://github.com/JinBoy23520/CoderToDeveloperByTCLer
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