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,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,status,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(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,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,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(),1,completeSize,fileStatus.getFileSize()));
dao.updateFileDownStatus(completeSize,url);
}
else
{
list.set(i,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++;
}
},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,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 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,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,downPath);
infos.add(info);
}
DownLoadInfo info = new DownLoadInfo(this.threadCount - 1,(this.threadCount - 1) * range,this.fileSize,downPath);
infos.add(info);
dao.saveInfos(infos,this.context);
//(String urlDownload,int completePercent,int fileSize)
LoadItemInfo loadInfo = new LoadItemInfo(this.downPath,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,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.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,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,buffer.length)) != -1) {
randomAccessFile.write(buffer,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,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编程小技巧。
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