各位父老乡亲，我单汉三又回来了，今天为大家带来一个用原生的安卓写的多线程断点下载Demo。
通过本文你可以学习到：
- SQLite的基本使用，数据库的增删改查。 Handler的消息处理与更新UI。 Service（主要用于下载）的进阶与使用。 原生的json文件解析（多层嵌套）。 RandomAccessFile的基本使用，可以将文件分段。 基于HttpURLConnection的大文件下载。 上面内容结合，实现多线程，断点下载。
Demo是在TV上运行的，图片显示的问题不要纠结了。
文件下载的Demo已完成，没时间上传与讲解，今天为您展示并讲解一下，纯原生的东西来下载文件，希望可以帮你理解更多安卓比较基础的问题。
我们的思路：建立一个数据库，两个表，一个用来保存网络数据，一个保存本地下载的进度等等。在点击下载按钮的时候启动DownloadService，进行比对之后下载
先看一下Demo的目录结构：
所有的步骤在代码里有非常详细的讲解，一定要看代码（下面是抽取的几个重要的类讲解）！
数据库的建立与DAO
/** * Created by Administrator on 2017/3/6 0006. */public class DownLoadDBHelper extends SQLiteOpenHelper { /** * DownLoadDBHelper用于创建数据库，如果不会使用原生的建库的话 * * 跟随小司机我的脚步来一起练一练 * 建两个表： * download_info表存储下载信息 * localdownload_info表存储本地下载信息 * 之后对比两个表进行继续下载等等 */ public static String DATABASE_NAME = "downloadFILES.db"; public static String TABLE_DOWNLOAD_INFO = "download_info"; public static String TABLE_LOCALDOWNLOAD_INFO = "localdownload_info"; private static int version = 1; public DownLoadDBHelper(Context context) { super(context, DATABASE_NAME, null, version); } @Override public void onCreate(SQLiteDatabase db) { /*在此进行创建数据库和表格,来一起动手写一遍,就是两个sqlite语句*/ db.execSQL("create table " + TABLE_DOWNLOAD_INFO + "(" + "id integer PRIMARY KEY AUTOINCREMENT," + "thread_id integer," + "start_position integer," + "end_position integer," + " completed_size integer," + "url varchar(100))"); db.execSQL("create table " + TABLE_LOCALDOWNLOAD_INFO + "(" + "id integer PRIMARY KEY AUTOINCREMENT," + "name varchar(50)," + "url varchar(100)," + "completedSize integer," + "fileSize integer," + "status integer)"); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { /*数据库更新升级，检测到版本的变化，发现版本号不一样，就会自动调用onUpgrade函数 * 新版本号和老版本号都会作为onUpgrade函数的参数传进来，便于开发者知道数据库应该从哪个版本升级到哪个版本。 * */ String sql = "drop table if exists " + TABLE_DOWNLOAD_INFO + ""; String sqlOne = "drop table if exists " + TABLE_LOCALDOWNLOAD_INFO + ""; db.execSQL(sql); db.execSQL(sqlOne); onCreate(db);//删除数据库，重新创建。这里只是简单的，并没有添加或者减少数据库中的其他字段 }}
DAO对数据库进行增删改查
/** * Created by ShanCanCan on 2017/3/6 0006. */public class Dao { /* * DAO层主要是做数据持久层的工作，负责与数据库进行联络的一些任务都封装在此。 * DAO层所定义的接口里的方法都大同小异，这是由我们在DAO层对数据库访问的操作来决定的， * 对数据库的操作，我们基本要用到的就是新增，更新，删除，查询等方法。 * 因而DAO层里面基本上都应该要涵盖这些方法对应的操作。 * */ private static Dao dao; private static DownLoadDBHelper dbHelper; public static final byte[] Lock = new byte[0]; //新建两个字节作为对象锁 public static final byte[] file_Lock = new byte[0]; public Dao() {//空构造方法， } public static synchronized Dao getInstance(Context context) {//本demo用单例模式中的懒汉模式+线程不安全 线程安全的代价是效率变低 if (dao == null) { dao = new Dao(); dbHelper = new DownLoadDBHelper(context); } return dao; } /* public static synchronized Dao getInstance(Context context) {//本demo用单例模式中的懒汉模式+线程安全 线程安全的代价是效率变低，99%情况下不需要同步 if (dao == null) { //你可以在这两个方法中随便选择一个 dao = new Dao(); dbHelper = new DownLoadDBHelper(context); } return dao; }*/ /*************************************** 下方Dao层中对数据库的增、删、改、查 *********************************************************/ /** * 检查本地下载记录，是否下载过 * * @param url * @return */ public boolean isExist(String url) { SQLiteDatabase database = dbHelper.getReadableDatabase(); //获取本app所创建的数据库 String sql = "select count(*) from " + TABLE_LOCALDOWNLOAD_INFO + " where url=?"; //查询语句,查询总共有多少条的语句 Cursor cursor = database.rawQuery(sql, new String[]{url}); /** * * @Cursor * Cursor 是每行的集合。 * 使用 moveToFirst() 定位第一行。 * 你必须知道每一列的名称。 * 你必须知道每一列的数据类型。 * Cursor 是一个随机的数据源。 * 所有的数据都是通过下标取得。 * Cursor按照我的理解就是一个箭头，指到哪一行就是那一行的集合 * 比较重要的方法有：close(),moveToFirst(),moveToNext(),moveToLast(),moveToPrevious(),getColumnCount()等。 * * @rawQuery * rawQuery是直接使用SQL语句进行查询的，也就是第一个参数字符串， * 在字符串内的“？”会被后面的String[]数组逐一对换掉 * cursor用完之后要关闭，cursor用完之后要关闭，cursor用完之后要关闭。重要的事情说三遍！！！ * * */ cursor.moveToFirst(); int count = cursor.getInt(0); cursor.close(); return count > 0; } /** * 是否为首次下载 * * @param url * @return */ public boolean isFirstDownload(String url) { SQLiteDatabase database = dbHelper.getReadableDatabase(); String sql = "select count(*) from " + TABLE_DOWNLOAD_INFO + " where url=?"; Cursor cursor = database.rawQuery(sql, new String[]{url}); cursor.moveToFirst(); int count = cursor.getInt(0); cursor.close(); return count == 0; } /** * 保存下载的具体信息 保存所下载的list集合中的数据 * * @param infos * @param context */ public void saveInfos(List<DownLoadInfo> infos, Context context) { /** * 事务（Transaction）是并发控制的单位，是用户定义的一个操作序列。 * 这些操作要么都做，要么都不做，是一个不可分割的工作单位。 * 通过事务，SQL Server能将逻辑相关的一组操作绑定在一起， * 以便保持数据的完整性。 * * 事务具有四个特征：原子性（ Atomicity ）、一致性（ Consistency ）、 * 隔离性（ Isolation ）和持续性（ Durability ）。这四个特性简称为 ACID 特性。 * * */ synchronized (Lock) { SQLiteDatabase database = dbHelper.getWritableDatabase(); database.beginTransaction();//开启事务 try {//如果有异常，在这里捕获 for (DownLoadInfo info : infos) {//for循环将数据存入数据库 String sql = "insert into " + TABLE_DOWNLOAD_INFO + "(thread_id,start_position, end_position, completed_size, url) values (?,?,?,?,?)"; Object[] bindArgs = {info.getThreadId(), info.getStartPosition(), info.getEndPosition(), info.getCompletedSize(), info.getUrl()}; database.execSQL(sql, bindArgs); } database.setTransactionSuccessful();//结束事务 } catch (SQLException e) { e.printStackTrace(); } finally { database.endTransaction();//关闭事务 } } } /** * 得到下载具体信息 * * @param urlstr * @return List<DownloadInfo> 一个下载器信息集合器,里面存放了每条线程的下载信息 */ public List<DownLoadInfo> getInfos(String urlstr) { List<DownLoadInfo> list = new ArrayList<DownLoadInfo>(); SQLiteDatabase database = dbHelper.getReadableDatabase(); String sql = "select thread_id, start_position, end_position, completed_size, url from " + TABLE_DOWNLOAD_INFO + " where url=?"; Cursor cursor = database.rawQuery(sql, new String[]{urlstr}); while (cursor.moveToNext()) {//通过cursor取到下载器信息，循环遍历，得到下载器集合 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; } /** * 本地下载列表添加记录,添加本地数据库信息，完成度等等 * * @param fileStatus **/ public void insertFileStatus(FileStatus fileStatus) { synchronized (file_Lock) {//异步加开启事务，保证数据的完整性 SQLiteDatabase database = dbHelper.getWritableDatabase(); database.beginTransaction(); try { String sql = "insert into " + TABLE_LOCALDOWNLOAD_INFO + " (name,url,completedSize,fileSize,status) values(?,?,?,?,?)"; Object[] bindArgs = {fileStatus.getName(), fileStatus.getUrl(), fileStatus.getCompletedSize(), fileStatus.getFileSize(), fileStatus.getStatus()}; database.execSQL(sql, bindArgs); database.setTransactionSuccessful(); } catch (SQLException e) { e.printStackTrace(); } finally { database.endTransaction(); } } } /** * @param context * @param compeletedSize * @param threadId * @param urlstr 这里是更新数据库，建议在保存一个表格的时候就对另一个表格数据库进行更新 */ public void updataInfos(int threadId, int compeletedSize, String urlstr, Context context) { synchronized (Lock) { String sql = "update " + TABLE_DOWNLOAD_INFO + "set completed_size = ? where thread_id =? and url=?"; String localSql = "update " + TABLE_LOCALDOWNLOAD_INFO + "set completedSize = (select sum(completed_size) from " + TABLE_DOWNLOAD_INFO + "where url=? group by url ) where url=?"; Object[] bindArgs = {compeletedSize, threadId, urlstr}; Object[] localArgs = {urlstr, urlstr}; SQLiteDatabase database = dbHelper.getWritableDatabase(); database.beginTransaction(); try { database.execSQL(sql, bindArgs); database.execSQL(localSql, localArgs); database.setTransactionSuccessful(); } catch (SQLException e) { e.printStackTrace(); } finally { database.endTransaction(); } } } /** * @param url 更新文件的状态，0为正在下载，1为已经下载完成,2为下载出错 **/ public void updateFileStatus(String url) { synchronized (file_Lock) { String sql = "update " + TABLE_LOCALDOWNLOAD_INFO + " set status = ? where url = ?"; Object[] bindArgs = {1, url}; SQLiteDatabase database = dbHelper.getWritableDatabase(); database.beginTransaction(); try { database.execSQL(sql, bindArgs); database.setTransactionSuccessful(); } catch (SQLException e) { e.printStackTrace(); } finally { database.endTransaction(); } } } /** * @return List<FileStatus> * 取出本地下载列表数据，如在重新进入应用时，要重新把进度之类的设置好 **/ public List<FileStatus> getFileStatus() { List<FileStatus> list = new ArrayList<FileStatus>(); SQLiteDatabase database = dbHelper.getReadableDatabase(); //String sql = "slect * from " + TABLE_LOCALDOWNLOAD_INFO + ""; //不能用，需要哪些条件就在语句中写出哪些条件 String sql = "select name, url, status, completedSize, fileSize from " + TABLE_LOCALDOWNLOAD_INFO + ""; Cursor cursor = database.rawQuery(sql, null); while (cursor.moveToNext()) { FileStatus fileState = new FileStatus(cursor.getString(0), cursor.getString(1), cursor.getInt(2), cursor.getInt(3), cursor.getInt(4)); list.add(fileState); } cursor.close(); return list; } /** * @param url * @param completeSize * @param status 更新文件的下载状态 **/ public void updateFileDownStatus(int completeSize, int status, String url) { synchronized (file_Lock) { String sql = "update " + TABLE_LOCALDOWNLOAD_INFO + " set completedSize = ?,status = ? where url = ?"; SQLiteDatabase database = dbHelper.getWritableDatabase(); database.beginTransaction(); try { Object[] bindArgs = {completeSize, status, url}; database.execSQL(sql, bindArgs); database.delete(TABLE_DOWNLOAD_INFO, "url = ?", new String[]{url}); database.setTransactionSuccessful(); } catch (SQLException e) { e.printStackTrace(); } finally { database.endTransaction(); } } } /** * @param url 获取文件名称 **/ public String getFileName(String url) { String result = ""; String sql = "select name from " + TABLE_LOCALDOWNLOAD_INFO + " where url = ?"; SQLiteDatabase database = dbHelper.getReadableDatabase(); Cursor cursor = database.rawQuery(sql, new String[]{url}); if (cursor.moveToNext()) { result = cursor.getString(0); } cursor.close(); return result; } /** * 删除文件之后，要删除下载的数据，一个是用户可以重新下载 * 另一个是表再次添加一条数据的时候不出现错误 * * @param url */ public void deleteFile(String url) { SQLiteDatabase database = dbHelper.getWritableDatabase(); database.beginTransaction(); try { database.delete(TABLE_DOWNLOAD_INFO, " url = ?", new String[]{url}); database.delete(TABLE_LOCALDOWNLOAD_INFO, " url = ?", new String[]{url}); database.setTransactionSuccessful(); } catch (Exception e) { e.printStackTrace(); } finally { database.endTransaction(); } } /** * 关闭数据库 * * @close */ public void closeDB() { dbHelper.close(); }}
DownloadService 主要代码
@SuppressLint("HandlerLeak")public class DownloadService extends Service{ public IBinder binder = new MyBinder(); public class MyBinder extends Binder { public DownloadService getService() { return DownloadService.this; } } @Override public IBinder onBind(Intent intent) { return binder; } public static int number = 0; // 文件保存地址 public final String savePath = "/mnt/sdcard/MultiFileDownload/"; // 存放下载列表的引用 public static List<FileStatus> list = new ArrayList<FileStatus>(); public static Map<String, String> localDownList = new HashMap<String, String>(); // 保存每个文件下载的下载器 public static Map<String, Downloader> downloaders = new HashMap<String, Downloader>(); // 每个下载文件完成的长度 private Map<String, Integer> completeSizes = new HashMap<String, Integer>(); // 每个下载文件的总长度 private Map<String, Integer> fileSizes = new HashMap<String, Integer>(); private Downloader downloader; private int threadCount = 5; private Dao dao; private DownLoadCallback loadCallback; private FileStatus mFileStatus = null; private Handler handler = new Handler() { @Override public void handleMessage(Message msg) { super.handleMessage(msg); if (msg.what == 1) { String url = (String) msg.obj; int length = msg.arg1; int completeSize = completeSizes.get(url); int fileSize = fileSizes.get(url); completeSize += length; completeSizes.put(url, completeSize); synchronized (list) { for (int i = 0; i < list.size(); i++) { FileStatus fileStatus = list.get(i); if (fileStatus.getUrl().equals(url)) { if (completeSize == fileStatus.getFileSize()) { System.out.println("-----------下载完成:"+fileStatus.getName()+":"+completeSize+"-----"+fileStatus.getFileSize()); list.set(i, new FileStatus(fileStatus.getName(), fileStatus.getUrl(), 1, completeSize, fileStatus.getFileSize())); dao.updateFileDownStatus(completeSize, 1, url); } else { list.set(i, new FileStatus(fileStatus.getName(), fileStatus.getUrl(), 0, completeSize, fileStatus.getFileSize())); } mFileStatus = list.get(i); } } this.postDelayed(new Runnable() { @Override public void run() { if (loadCallback != null && mFileStatus != null) { loadCallback.refreshUI(mFileStatus); } } }, 1000); } } } }; @Override public void onCreate() { super.onCreate(); dao = Dao.getInstance(this); list = dao.getFileStatus(); for (FileStatus fileStatus : list) { localDownList.put(fileStatus.getUrl(), fileStatus.getUrl()); } Timer timer = new Timer(); timer.schedule(new TimerTask() { @Override public void run() { number++; } }, 0, 1000); } public void download(final Button button, final String url, final String name, final Handler mHandler) { if (dao.isExist(url)) { Toast.makeText(this, "别点了，已经在下载了", Toast.LENGTH_SHORT).show(); return; } final String fileName = name + url.substring(url.lastIndexOf(".")); new Thread(new Runnable() { @Override public void run() { downloader = downloaders.get(url); if (downloader == null) { downloader = new Downloader(url, savePath, fileName, threadCount, DownloadService.this, handler); downloaders.put(url, downloader); } if (downloader.isDownloading()) return; LoadInfo loadInfo = downloader.getDownloaderInfors(); if(loadInfo != null) { FileStatus fileStatus = new FileStatus(fileName, url, 0, loadInfo.getComplete(), loadInfo.getFileSize()); dao.insertFileStatus(fileStatus); completeSizes.put(url, loadInfo.getComplete()); fileSizes.put(url, fileStatus.getFileSize()); list.add(fileStatus); localDownList.put(url, url); downloader.download(); Message msg = new Message(); msg.what = 1; msg.obj = button; mHandler.sendMessage(msg); } else { Message msg = new Message(); msg.what = 2; msg.obj = button; mHandler.sendMessage(msg); } } }).start(); } //暂停下载 public void Pause(Downloader downloader) { downloader.pause(); } //继续下载 public void reDownload(final Button button, final String url, final String name, final Handler mHandler) { new Thread(new Runnable() { @Override public void run() { String fileName = dao.getFileName(url); downloader = downloaders.get(url); if (downloader == null) { downloader = new Downloader(url, savePath, fileName, threadCount, DownloadService.this, handler); downloaders.put(url, downloader); } if (downloader.isDownloading()) return; LoadInfo loadInfo = downloader.getDownloaderInfors(); if(loadInfo != null && !fileName.equals("")) { if(!completeSizes.containsKey(url)) { completeSizes.put(url, loadInfo.getComplete()); } if(!fileSizes.containsKey(url)) { fileSizes.put(url, loadInfo.getFileSize()); } downloader.download(); Message msg = new Message(); msg.what = 1; msg.obj = button; mHandler.sendMessage(msg); } else { Message msg = new Message(); msg.what = 2; msg.obj = button; mHandler.sendMessage(msg); } } }).start(); } public void delete(final String url) { Downloader down = downloaders.get(url); if(down != null) { down.pause(); } handler.postDelayed(new Runnable() { @Override public void run() { dao.deleteFile(url); for (int i = 0; i < list.size(); i++) { FileStatus fileStatus = list.get(i); if (fileStatus.getUrl().equals(url)) { list.remove(i); } } localDownList.remove(url); downloaders.remove(url); completeSizes.remove(url); fileSizes.remove(url); if(loadCallback != null) { loadCallback.deleteFile(url); } } }, 1000); } public interface DownLoadCallback { public void refreshUI(FileStatus fileStatus); public void deleteFile(String url); } public void setLoadCallback(DownLoadCallback loadCallback) { this.loadCallback = loadCallback; }}
下载工具类DownLoadUtil
/** * Created by ShanCanCan on 2017/3/7 0007. */public class DownLoadUtil { /** * 此类的主要功能 * 1、检查是否下载 * 2、下载文件,文件的下载采用httpurlconnection */ private String downPath;// 下载路径 private String savePath;// 保存路径 private String fileName;// 文件名称 private int threadCount;// 线程数 private Handler mHandler; private Dao dao; private Context context; private int fileSize;// 文件大小 private int range; private List<DownLoadInfo> infos;// 存放下载信息类的集合 private int state = INIT; private static final int INIT = 1;// 定义三种下载的状态：初始化状态，正在下载状态，暂停状态 private static final int DOWNLOADING = 2; private static final int PAUSE = 3; /** * 构造方法，获取dao的对象 * * @param downPath * @param savePath * @param fileName * @param threadCount * @param context * @param mHandler */ public DownLoadUtil(String downPath, String savePath, String fileName, int threadCount, Handler mHandler, Context context) { this.downPath = downPath; this.savePath = savePath; this.fileName = fileName; this.threadCount = threadCount; this.mHandler = mHandler; this.context = context; dao = Dao.getInstance(context); } /** * 判断是否PAUSE **/ public boolean isPause() { return state == PAUSE; } /** * 判断是否DOWNLOADING */ public boolean isDownloading() { return state == DOWNLOADING; } /** * @param url 判断是否是第一次下载，利用dao查询数据库中是否有下载这个地址的记录 */ private boolean isFirst(String url) { return dao.isFirstDownload(url); } /** * 获取要下载的东西 */ public LoadItemInfo getDownloadInfos() { if (isFirst(downPath)) { if (initFirst()) {//如果是第一次下载的话，要进行初始化,1.获得下载文件的长度 2.创建文件,设置文件的大小 range = this.fileSize / this.threadCount; infos = new ArrayList<DownLoadInfo>(); //这里就是启动多线程下载，看出来了吗？配合RandomAccessFile。每一个DownLoadInfo就是RandomAccessFile文件的一部分 for (int i = 0; i < this.threadCount - 1; i++) { DownLoadInfo info = new DownLoadInfo(i, i * range, (i + 1) * range - 1, 0, downPath); infos.add(info); } DownLoadInfo info = new DownLoadInfo(this.threadCount - 1, (this.threadCount - 1) * range, this.fileSize, 0, downPath); infos.add(info); dao.saveInfos(infos, this.context); //(String urlDownload, int completePercent, int fileSize) LoadItemInfo loadInfo = new LoadItemInfo(this.downPath, 0, this.fileSize); return loadInfo; } else { return null; } } else { //不是第一次下载，我们应该怎么做呢？从数据库里面取回来 infos = dao.getInfos(this.downPath); if (infos != null && infos.size() > 0) { int size = 0; int completeSize = 0; for (DownLoadInfo info : infos) { completeSize += info.getCompletedSize(); size += info.getEndPosition() - info.getStartPosition() + this.threadCount - 1; } LoadItemInfo loadInfo = new LoadItemInfo(this.downPath, completeSize, size); return loadInfo; } else { return null; } } } // 设置暂停 public void pause() { state = PAUSE; } // 重置下载状态,将下载状态设置为init初始化状态 public void reset() { state = INIT; } /** * 基本上，RandomAccessFile的工作方式是，把DataInputStream和DataOutputStream结合起来，再加上它自己的一些方法， * 比如定位用的getFilePointer( )，在文件里移动用的seek( )，以及判断文件大小的length( )、skipBytes()跳过多少字节数。 * 此外，它的构造函数还要一个表示以只读方式("r")，还是以读写方式("rw")打开文件的参数 (和C的fopen( )一模一样)。它不支持只写文件。 */ private boolean initFirst() { boolean result = true; HttpURLConnection conn = null; RandomAccessFile randomFile = null; URL url = null; try { url = new URL(downPath); conn = (HttpURLConnection) url.openConnection(); conn.setConnectTimeout(5 * 1000); conn.setRequestMethod("GET"); // 如果http返回的代码是200或者206则为连接成功 if (conn.getResponseCode() == 200 || conn.getResponseCode() == 206) //状态码(206)，表示服务器已经执行完部分对资源的GET请求 { fileSize = conn.getContentLength();// 得到文件的大小 if (fileSize <= 0) { //("网络故障,无法获取文件大小"); return false; } File dir = new File(savePath); // 如果文件目录不存在,则创建 if (!dir.exists()) { if (dir.mkdirs()) { //("mkdirs success."); } } File file = new File(this.savePath, this.fileName); randomFile = new RandomAccessFile(file, "rwd"); randomFile.setLength(fileSize);// 设置保存文件的大小 randomFile.close(); conn.disconnect(); } } catch (Exception e) { e.printStackTrace(); result = false; } finally { if (randomFile != null) { try { randomFile.close(); } catch (IOException e) { e.printStackTrace(); } } if (conn != null) { conn.disconnect(); } } return result; } /** * 下面的这个方法就是开启多线程进行下载了数据了 */ public void downLoad() { if (infos != null) { if (state == DOWNLOADING) { return; } state = DOWNLOADING;// 把状态设置为正在下载 for (DownLoadInfo info : infos) {//为什么说我们是多线程呢？因为我们分别用新线程去下载刚才分割好的一个RandomAccessFile文件 new DownLoadThread(info.getThreadId(), info.getStartPosition(), info.getEndPosition(), info.getCompletedSize(), info.getUrl(), this.context).start(); } } } /** * 现在要创建线程用来下载了，这里采用内部类 */ public class DownLoadThread extends Thread { private int threadId; private int startPostion; private int endPostion; private int compeletedSize; private String url; private Context context; public static final int PROGRESS = 1; public DownLoadThread(int threadId, int startPostion, int endPostion, int compeletedSize, String url, Context context) {//构造方法，传入特定的参数 this.threadId = threadId; this.startPostion = startPostion; this.endPostion = endPostion; this.compeletedSize = compeletedSize; this.url = url; this.context = context; } //开始下载 @Override public void run() { HttpURLConnection conn = null; RandomAccessFile randomAccessFile = null; InputStream inStream = null; File file = new File(savePath, fileName); URL url = null; try { url = new URL(this.url); conn = (HttpURLConnection) url.openConnection(); constructConnection(conn); if (conn.getResponseCode() == 200 || conn.getResponseCode() == 206) { randomAccessFile = new RandomAccessFile(file, "rwd"); randomAccessFile.seek(this.startPostion + this.compeletedSize);//RandomAccessFile移动指针，到需要下载的块 inStream = conn.getInputStream(); byte buffer[] = new byte[4096];//这个4096为么子呢？我也不知道，就是看阿里的人下载apk的时候都用4096，我也用 int length = 0; while ((length = inStream.read(buffer, 0, buffer.length)) != -1) { randomAccessFile.write(buffer, 0, length); compeletedSize += length; // 更新数据库中的下载信息 dao.updataInfos(threadId, compeletedSize, this.url, this.context); // 用消息将下载信息传给进度条，对进度条进行更新 Message message = Message.obtain(); message.what = PROGRESS; message.obj = this.url; message.arg1 = length; mHandler.sendMessage(message);// 给DownloadService发送消息 if (state == PAUSE) { //("-----pause-----"); return; } } // ("------------线程:" + this.threadId + "下载完成"); } } catch (IOException e) { e.printStackTrace(); //("-----下载异常-----"); 这里下载异常我就不处理了，你可以发一条重新下载的消息 } finally {//用完只后流要关闭，不然容易造成资源抢占，内存泄漏 try { if (inStream != null) { inStream.close(); } if (randomAccessFile != null) { randomAccessFile.close(); } if (conn != null) { conn.disconnect(); } } catch (IOException e) { e.printStackTrace(); } } } /** * 构建请求连接时的参数 返回开始下载的位置 * * @param conn */ private void constructConnection(HttpURLConnection conn) throws IOException { conn.setConnectTimeout(5 * 1000);// 设置连接超时5秒 conn.setRequestMethod("GET");// GET方式提交，如果你是用post请求必须添加 conn.setDoOutput(true); conn.setDoInput(true); 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", this.url); conn.setRequestProperty("Charset", "UTF-8"); int startPositionNew = this.startPostion + this.compeletedSize; // 设置获取实体数据的范围 conn.setRequestProperty("Range", "bytes=" + startPositionNew + "-" + this.endPostion); 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(); } }}
Github地址：https://github.com/Shanlovana/DownLoadFiles/
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。
当你感到悲哀痛苦时，最好是去学些什么东西。
