android多线程下载以及断点续传

使用多线程下载文件可以更快完成文件的下载，多线程下载文件之所以快，是因为其抢占的服务器资源多。如：假设服务器同时最多服务100个用户，在服务器中一条线程对应一个用户，100条线程在计算机中并非并发执行，而是由CPU划分时间片轮流执行，如果A应用使用了99条线程下载文件，那么相当于占用了99个用户的资源，假设一秒内CPU分配给每条线程的平均执行时间是10ms，A应用在服务器中一秒内就得到了990ms的执行时间，而其他应用在一秒内只有10ms的执行时间。就如同一个水龙头，每秒出水量相等的情况下，放990毫秒的水
肯定比放10毫秒的水要多。
多线程下载的实现过程：
1>首先得到下载文件的长度，然后设置本地文件
的长度。
HttpURLConnection.getContentLength();
RandomAccessFile file = new RandomAccessFile("QQWubiSetup.exe","rwd");
file.setLength(filesize);//设置本地文件的长度
2>根据文件长度和线程数计算每条线程下载的数据长度和下载位置。如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如上图所示。
3>使用Http的Range头字段指定每条线程从文件的什么位置开始下载，下载到什么位置为止，如：指定从文件的2M位置开始下载，下载到位置(4M-1byte)为止，代码如下：
HttpURLConnection.setRequestProperty("Range", "bytes=2097152-4194303");
4>保存文件，使用RandomAccessFile类指定每条线程从本地文件的什么位置开始写入数据。
RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");
threadfile.seek(2097152);//从文件的什么位置开始写入数据

MulTreadDownload.java

[java]
view plaincopy

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

public class MulThreadDownloadTest {

public static void main(String[] args) throws Exception{
new MulThreadDownloadTest().downlaod();
}

public void downlaod() throws Exception{
String path = "http://net.itcast.cn/QQWubiSetup.exe";
//文件的长度
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection)url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5*1000);
int length = conn.getContentLength();//得到文件的长度
int threadnum = 5;
int block = length%threadnum==0 ? length/threadnum : length/threadnum+1;//计算每条线程下载的数据长度
File file = new File("QQWubiSetup.exe");
RandomAccessFile rfile = new RandomAccessFile(file, "rwd");
rfile.setLength(length);//把本地文件的长度设置为网络文件的长度
rfile.close();
for(int i=0 ; i < threadnum ; i++){
new DownloadThread(block, url, file ,i).start();
}
}

private final class DownloadThread extends Thread{
private int block;//每条线程下载的数据长度
private URL url;//下载路径
private File file;//本地文件
private int threaid;//线程id

public DownloadThread(int block, URL url, File file, int i) {
this.block = block;
this.url = url;
this.file = file;
this.threaid = i;
}

@Override
public void run() {
try {
int startpos = threaid * block;//计算该线程从文件的什么位置开始下载
int endpos = (threaid+1) * block - 1;//计算该线程下载到文件的什么位置结束
HttpURLConnection conn = (HttpURLConnection)url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5*1000);
conn.setRequestProperty("Range", "bytes="+ startpos+"-"+ endpos);
InputStream inputStream = conn.getInputStream();
RandomAccessFile rfile = new RandomAccessFile(file, "rwd");
rfile.seek(startpos);
byte[] buffer = new byte[1024];
int len = 0;
while( (len = inputStream.read(buffer)) != -1){
rfile.write(buffer, 0, len);
}
rfile.close();
inputStream.close();
System.out.println("线程"+ (threaid+1)+ "下载完成");
} catch (Exception e) {
e.printStackTrace();
}
}
}
}

实现断点续传

有两种方式可以保存断点数据：
1.通过文件的形式保存
2 通过数据库的方式保存，如果需要查询的话则要此种方式，即使用Sqllite保存
下面看看如何数据库保存

建立表结构
DBOpenHelper.java

[java]
view plaincopy

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

public class DBOpenHelper extends SQLiteOpenHelper {
private static final String DBNAME = "itcast.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);
}

}

如何操作表，实现对断点数据的一个操作
FileService.java

[java]
view plaincopy

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

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
/**
* 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, 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();
}
/**
* 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();
}

}

实现断点数据的保存

FileDownload.java

[java]
view plaincopy

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 cn.itcast.service.FileService;

import android.content.Context;
import android.util.Log;
/**
* 文件下载器
* @author lihuoming@sohu.com
*/
public class FileDownloader {
private static final String TAG = "FileDownloader";
private Context context;
private FileService fileService;
/* 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;
}
/**
* 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 void update(int threadId, int pos) {
this.data.put(threadId, pos);
}
/**
* 保存记录文件
*/
protected synchronized void saveLogFile() {
this.fileService.update(this.downloadUrl, this.data);
}
/**
* 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()) 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();//根据响应获取文件大小
if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");

String filename = getFileName(conn);
this.saveFile = new File(fileSaveDir, filename);/* 保存文件 */
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());
}
this.block = (this.fileSize % this.threads.length)==0? this.fileSize / this.threads.length : this.fileSize / this.threads.length + 1;
if(this.data.size()==this.threads.length){
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);
}
}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);
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);
}
}
for (int i = 0; i < this.threads.length; i++) {
int downLength = this.data.get(i+1);
if(downLength < this.block && this.downloadSize<this.fileSize){ //该线程未完成下载时,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);
this.threads[i].start();
}else{
this.threads[i] = null;
}
}
this.fileService.save(this.downloadUrl, this.data);
boolean notFinish = true;//下载未完成
while (notFinish) {// 循环判断是否下载完毕
Thread.sleep(900);
notFinish = false;//假定下载完成
for (int i = 0; i < this.threads.length; i++){
if (this.threads[i] != null && !this.threads[i].isFinish()) {
notFinish = true;//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);
}
fileService.delete(this.downloadUrl);
} catch (Exception e) {
print(e.toString());
throw new Exception("file download fail");
}
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);
}

public static void main(String[] args) {
/* FileDownloader loader = new FileDownloader(context, "http://browse.babasport.com/ejb3/ActivePort.exe",
new File("D:\\androidsoft\\test"), 2);
loader.getFileSize();//得到文件总大小
try {
loader.download(new DownloadProgressListener(){
public void onDownloadSize(int size) {
print("已经下载："+ size);
}
});
} catch (Exception e) {
e.printStackTrace();
}*/
}

}

DownloadActivity.java

[java]
view plaincopy

package cn.itcast.download;

import java.io.File;

import cn.itcast.net.download.DownloadProgressListener;
import cn.itcast.net.download.FileDownloader;

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class DownloadActivity extends Activity {
private ProgressBar downloadbar;
private EditText pathText;
private TextView resultView;
private Handler handler = new Handler(){

@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case 1:
int size = msg.getData().getInt("size");
downloadbar.setProgress(size);
float result = (float)downloadbar.getProgress()/ (float)downloadbar.getMax();
int p = (int)(result*100);
resultView.setText(p+"%");
if(downloadbar.getProgress()==downloadbar.getMax())
Toast.makeText(DownloadActivity.this, R.string.success, 1).show();
break;

case -1:
Toast.makeText(DownloadActivity.this, R.string.error, 1).show();
break;
}

}
};

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

Button button = (Button)this.findViewById(R.id.button);
downloadbar = (ProgressBar)this.findViewById(R.id.downloadbar);
pathText = (EditText)this.findViewById(R.id.path);
resultView = (TextView)this.findViewById(R.id.result);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String path = pathText.getText().toString();
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
File dir = Environment.getExternalStorageDirectory();//文件保存目录
download(path, dir);
}else{
Toast.makeText(DownloadActivity.this, R.string.sdcarderror, 1).show();
}
}
});
}
//对于UI控件的更新只能由主线程(UI线程)负责，如果在非UI线程更新UI控件，更新的结果不会反映在屏幕上，某些控件还会出错
private void download(final String path, final File dir){
new Thread(new Runnable() {
@Override
public void run() {
try {
FileDownloader loader = new FileDownloader(DownloadActivity.this, path, dir, 3);
int length = loader.getFileSize();//获取文件的长度
downloadbar.setMax(length);
loader.download(new DownloadProgressListener(){
@Override
public void onDownloadSize(int size) {//可以实时得到文件下载的长度
Message msg = new Message();
msg.what = 1;
msg.getData().putInt("size", size);
handler.sendMessage(msg);
}});
} catch (Exception e) {
Message msg = new Message();
msg.what = -1;
msg.getData().putString("error", "下载失败");
handler.sendMessage(msg);
}
}
}).start();

}
}

注意：//对于UI控件的更新只能由主线程(UI线程)负责，如果在非UI线程更新UI控件，更新的结果不会反映在屏幕上，某些控件还会出错
可以是通过消息队列的方式传递数据到主线程，实现进度更新