Android多线程下载单个文件和断点续传

实现要点：

（1）创建一个线程数组用于多个线程同时开工下载

（2）通过http连接获取文件的大小信息，然后按照线程个数来分配各个线程下载的文件片段

（3）通过http的Range头来请求文件的片段

（4）用一个map表来记录每个线程下载的信息，保存到sqlite数据库里面，用于断点续传的实现，当下载中断，可以从map表的位置开始下载

DBOpenHelper类：数据库操作

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

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) {
// 创建filedownlog表
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);
}
}

FileService类：从数据库读写数据，封装成为map表操作

import java.util.HashMap;
import java.util.Map;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.scofield.oneeng.db.DBOpenHelper;

/**
* 业务bean
*
*/
public class FileService {
private DBOpenHelper openHelper;

public FileService(Context context) {
openHelper = new DBOpenHelper(context);
}

/**
* 获取每条线程已经下载的文件长度
*
* @param path
* @return
*/
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));
}
cursor.close();
db.close();
return data;
}

/**
* 保存每条线程已经下载的文件长度
*
* @param path
* @param map
*/
public void save(String path, Map<Integer, Integer> map) {// int threadid,
// int position
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();
}

/**
* 实时更新每条线程已经下载的文件长度
*
* @param path
* @param map
*/
public void update(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();
}

/**
* 当文件下载完成后，删除对应的下载记录
*
* @param path
*/
public void delete(String path) {
SQLiteDatabase db = openHelper.getWritableDatabase();
db.execSQL("delete from filedownlog where downpath=?",
new Object[] { path });
db.close();
}
}

DownloadThread类：下载线程类，根据下载的位置来下载文件，并且保存到临时文件里面

import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

import android.util.Log;

public class DownloadThread extends Thread {
private static final String TAG = "DownloadThread";
private File saveFile;
private URL downUrl;
private int block;
/* 下载开始位置 */
private int threadId = -1;
private int downLength;
private boolean finish = false;
private FileDownloader downloader;

public DownloadThread(FileDownloader downloader, URL downUrl,
File saveFile, int block, int downLength, int threadId) {
this.downUrl = downUrl;
this.saveFile = saveFile;
this.block = block;
this.downloader = downloader;
this.threadId = threadId;
this.downLength = downLength;
}

@Override
public void run() {
if (downLength < block) {// 未下载完成
try {
HttpURLConnection http = (HttpURLConnection) downUrl.openConnection();
http.setConnectTimeout(5 * 1000); // 设置连接超时
http.setRequestMethod("GET"); // 设置请求方法，这里是“GET”
// 浏览器可接受的MIME类型
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"); // 浏览器所希望的语言种类，当服务器能够提供一种以上的语言版本时要用到
http.setRequestProperty("Referer", downUrl.toString());// 包含一个URL，用户从该URL代表的页面出发访问当前请求的页面。
http.setRequestProperty("Charset", "UTF-8"); // 字符集
int startPos = block * (threadId - 1) + downLength;// 开始位置
int endPos = block * threadId - 1;// 结束位置
http.setRequestProperty("Range", "bytes=" + startPos + "-"
+ endPos);// 设置获取实体数据的范围
// 浏览器类型，如果Servlet返回的内容与浏览器类型有关则该值非常有用。
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"); // 设置为持久连接

// 得到输入流
InputStream inStream = http.getInputStream();
byte[] buffer = new byte[1024];
int offset = 0;
print("Thread " + this.threadId
+ " start download from position " + startPos);
// 随机访问文件
RandomAccessFile threadfile = new RandomAccessFile(
this.saveFile, "rwd");
// 定位到pos位置
threadfile.seek(startPos);
while (!downloader.getExit()
&& (offset = inStream.read(buffer, 0, 1024)) != -1) {
// 写入文件
threadfile.write(buffer, 0, offset);
downLength += offset; // 累加下载的大小
downloader.update(this.threadId, downLength); // 更新指定线程下载最后的位置
downloader.append(offset); // 累加已下载大小
}
threadfile.close();
inStream.close();
print("Thread " + this.threadId + " download finish");
this.finish = true;
} catch (Exception e) {
this.downLength = -1;
print("Thread " + this.threadId + ":" + e);
}
}
}

private static void print(String msg) {
Log.i(TAG, msg);
}

/**
* 下载是否完成
*
* @return
*/
public boolean isFinish() {
return finish;
}

/**
* 已经下载的内容大小
*
* @return 如果返回值为-1,代表下载失败
*/
public long getDownLength() {
return downLength;
}
}

FileDownloader类：文件下载管理器，获取文件大小，分配和启动下载线程，监听下载的结果

import java.io.File;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import android.content.Context;
import android.util.Log;

/**
* 文件下载器
*
*/
public class FileDownloader {
private static final String TAG = "FileDownloader";
private Context context;
private FileService fileService;
/* 停止下载 */
private boolean exit;
/* 已下载文件长度 */
private int downloadSize = 0;
/* 原始文件长度 */
private int fileSize = 0;
/* 线程数 */
private DownloadThread[] threads;
/* 本地保存文件 */
private File saveFile;
/* 缓存各线程下载的长度 */
private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();
/* 每条线程下载的长度 */
private int block;
/* 下载路径 */
private String downloadUrl;

/**
* 获取线程数
*/
public int getThreadSize() {
return threads.length;
}

/**
* 退出下载
*/
public void exit() {
this.exit = true;
}

public boolean getExit() {
return this.exit;
}

/**
* 获取文件大小
*
* @return
*/
public int getFileSize() {
return fileSize;
}

/**
* 累计已下载大小
*
* @param size
*/
protected synchronized void append(int size) {
downloadSize += size;
}

/**
* 更新指定线程最后下载的位置
*
* @param threadId
*            线程id
* @param pos
*            最后下载的位置
*/
protected synchronized void update(int threadId, int pos) {
this.data.put(threadId, pos);
this.fileService.update(this.downloadUrl, threadId, pos);
}

/**
* 构建文件下载器
*
* @param downloadUrl
*            下载路径
* @param fileSaveDir
*            文件保存目录
* @param threadNum
*            下载线程数
*/
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()) // 判断目录是否存在，如果不存在，创建目录
fileSaveDir.mkdirs();
this.threads = new DownloadThread[threadNum];// 实例化线程数组
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(); // 连接
printResponseHeader(conn);
if (conn.getResponseCode() == 200) { // 响应成功
this.fileSize = conn.getContentLength();// 根据响应获取文件大小
if (this.fileSize <= 0)
throw new RuntimeException("Unkown file size ");

String filename = getFileName(conn);// 获取文件名称
this.saveFile = new File(fileSaveDir, filename);// 构建保存文件
Map<Integer, Integer> logdata = fileService
.getData(downloadUrl);// 获取下载记录
if (logdata.size() > 0) {// 如果存在下载记录
for (Map.Entry<Integer, Integer> entry : logdata.entrySet())
data.put(entry.getKey(), entry.getValue());// 把各条线程已经下载的数据长度放入data中
}
if (this.data.size() == this.threads.length) {// 下面计算所有线程已经下载的数据总长度
for (int i = 0; i < this.threads.length; i++) {
this.downloadSize += this.data.get(i + 1);
}
print("已经下载的长度" + this.downloadSize);
}
// 计算每条线程下载的数据长度
this.block = (this.fileSize % this.threads.length) == 0 ? this.fileSize
/ this.threads.length
: this.fileSize / this.threads.length + 1;
} else {
throw new RuntimeException("server no response ");
}
} catch (Exception e) {
print(e.toString());
throw new RuntimeException("don't connection this url");
}
}

/**
* 获取文件名
*/
private String getFileName(HttpURLConnection conn) {
String filename = this.downloadUrl.substring(this.downloadUrl
.lastIndexOf('/') + 1);
if (filename == null || "".equals(filename.trim())) {// 如果获取不到文件名称
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());
if (m.find())
return m.group(1);
}
}
filename = UUID.randomUUID() + ".tmp";// 默认取一个文件名
}
return filename;
}

/**
* 开始下载文件
*
* @param listener
*            监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null
* @return 已下载文件大小
* @throws Exception
*/
public int download(DownloadProgressListener listener) throws Exception {
try {
RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");
if (this.fileSize > 0)
randOut.setLength(this.fileSize); // 预分配fileSize大小
randOut.close();
URL url = new URL(this.downloadUrl);
if (this.data.size() != this.threads.length) {// 如果原先未曾下载或者原先的下载线程数与现在的线程数不一致
this.data.clear();
for (int i = 0; i < this.threads.length; i++) {
this.data.put(i + 1, 0);// 初始化每条线程已经下载的数据长度为0
}
this.downloadSize = 0;
}
for (int i = 0; i < this.threads.length; i++) {// 开启线程进行下载
int downLength = this.data.get(i + 1);
if (downLength < this.block
&& this.downloadSize < this.fileSize) {// 判断线程是否已经完成下载,否则继续下载
this.threads[i] = new DownloadThread(this, url,
this.saveFile, this.block, this.data.get(i + 1),
i + 1);
this.threads[i].setPriority(7); // 设置线程优先级
this.threads[i].start();
} else {
this.threads[i] = null;
}
}
fileService.delete(this.downloadUrl);// 如果存在下载记录，删除它们，然后重新添加
fileService.save(this.downloadUrl, this.data);
boolean notFinish = true;// 下载未完成
while (notFinish) {// 循环判断所有线程是否完成下载
Thread.sleep(900);
notFinish = false;// 假定全部线程下载完成
for (int i = 0; i < this.threads.length; i++) {
if (this.threads[i] != null && !this.threads[i].isFinish()) {// 如果发现线程未完成下载
notFinish = true;// 设置标志为下载没有完成
if (this.threads[i].getDownLength() == -1) {// 如果下载失败,再重新下载
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.downloadSize);// 通知目前已经下载完成的数据长度
}
if (downloadSize == this.fileSize)
fileService.delete(this.downloadUrl);// 下载完成删除记录
} catch (Exception e) {
print(e.toString());
throw new Exception("file download error");
}
return this.downloadSize;
}

/**
* 获取Http响应头字段
*
* @param http
* @return
*/
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;
}

/**
* 打印Http头字段
*
* @param http
*/
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);
}
}