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
public class DownLoadDBHelper extends SQLiteOpenHelper {
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) {
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) {
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
public class Dao {
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 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.moveToFirst();
int count = cursor.getInt(0);
cursor.close();
return count > 0;
}
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;
}
public void saveInfos(List infos, Context context) {
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
}
}
}
public List getInfos(String urlstr) {
List list = new ArrayList();
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;
}
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();
}
}
}
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();
}
}
}
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();
}
}
}
public List getFileStatus() {
List list = new ArrayList();
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;
}
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();
}
}
}
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;
}
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();
}
}
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 list = new ArrayList();
public static Map localDownList = new HashMap();
// 保存每个文件下载的下载器
public static Map downloaders = new HashMap();
// 每个下载文件完成的长度
private Map completeSizes = new HashMap();
// 每个下载文件的总长度
private Map fileSizes = new HashMap();
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
public class DownLoadUtil {
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 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;
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);
}
public boolean isPause() {
return state == PAUSE;
}
public boolean isDownloading() {
return state == DOWNLOADING;
}
private boolean isFirst(String url) {
return dao.isFirstDownload(url);
}
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();
//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;
}
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;
}
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();
}
}
}
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();
}
}
}
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考高分网。
