本案例在于实现文件的多线程断点下载，即文件在下载一部分中断后，可继续接着已有进度下载，并通过进度条显示进度。也就是说在文件开始下载的同时，自动创建每个线程的下载进度的本地文件，下载中断后，重新进入应用点击下载，程序检查有没有本地文件的存在，若存在，获取本地文件中的下载进度，继续进行下载。当下载完成后，自动删除本地文件。
一、多线程断点下载介绍
所谓的多线程断点下载就是利用多线程下载，并且可被中断，如果突然没电了，重启手机后可以继续下载，而不需要重新下载；
利用的技术有：SQLite存储各个线程的下载量，HTTP请求获得下载数据；
二、辅助类介绍
为了完成多线程断点下载我们需要预先编写一些辅助类：
(1)DBOpenHelper
(2)FileService：
-Map<Integer,Integer> getData(String path); 根据URL获得各个线程的下载量
-save(String path, Map<Integer, Integer> map);存储URL对应的各个线程下载量，此函数为刚刚开始时调用
-update(String path, Map<Integer, Integer> map);更新数据库中URL对应的各个线程的下载量；
-delete(String path);删除URL对应的数据；
(3)FileDownloader:
-getFileSize()；获得下载文件的大小
-download(DownloadProgressListener listener);下载文件，并设置监听器
(4)DownloadThread:此类在FileDownloader的download中执行；
先将辅助类列出：
DBOpenHelper.Java
package service;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DBOpenHelper extends SQLiteOpenHelper {
private static final String DBNAME = "download.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);
}
}
FileService.java
package service;
import java.util.HashMap;
import java.util.Map;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
public class FileService {
private DBOpenHelper openHelper;
public FileService(Context context) {
openHelper = new DBOpenHelper(context);
}
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;
}
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();
}
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();
}
public void delete(String path){
SQLiteDatabase db = openHelper.getWritableDatabase();
db.execSQL("delete from filedownlog where downpath=?", new Object[]{path});
db.close();
}
}
FileDownloader.java
package net.download;
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 service.FileService;
import android.content.Context;
import android.util.Log;
public class FileDownloader {
private static final String TAG = "FileDownloader";
private Context context;
private FileService fileService;
private int downloadSize = 0;
private int fileSize = 0;
private DownloadThread[] threads;
private File saveFile;
private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();
private int block;
private String downloadUrl;
public int getThreadSize() {
return threads.length;
}
public int getFileSize() {
return fileSize;
}
protected synchronized void append(int size) {
downloadSize += size;
}
protected synchronized void update(int threadId, int pos) {
this.data.put(threadId, pos);
this.fileService.update(this.downloadUrl, this.data);
}
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];
//1.获得文件大小
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, *
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;
}
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);
//如果线程数与以前不一样，则重新开始下
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);//初始化每条线程已经下载的数据长度为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);
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
}
fileService.delete(this.downloadUrl);
} catch (Exception e) {
print(e.toString());
throw new Exception("file download fail");
}
return this.downloadSize;
}
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;
}
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);
}
}
DownloadThread.java
package net.download;
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;
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);
http.setRequestMethod("GET");
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, *
public boolean isFinish() {
return finish;
}
public long getDownLength() {
return downLength;
}
}
DownloadProgressListener.java
package net.download;
//下载监听器
public interface DownloadProgressListener {
public void onDownloadSize(int size);
}
三、具体代码
效果如下：
实现代码：
package org.xiazdong.download;
import java.io.File;
import net.download.DownloadProgressListener;
import 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.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
private Button downloadButton;
private EditText urlpathEditText;
private TextView percentTextView;
private ProgressBar progressBar;
private Handler handler;
//主线程
private class UIHandler extends Handler{
@Override
public void handleMessage(Message msg) {
int downloadsize = msg.getData().getInt("downloadsize");
int percent = msg.getData().getInt("percent");
progressBar.setProgress(downloadsize);
percentTextView.setText(percent+"%");
}
}
private OnClickListener listener = new OnClickListener() {
DownloadThread thread;
class DownloadThread extends Thread{
private String url ;
private File saveDir;
private FileDownloader download;
public DownloadThread(String url, File saveDir) {
this.url = url;
this.saveDir = saveDir;
}
//子线程
@Override
public void run() {
download = new FileDownloader(MainActivity.this,url, saveDir, 3);
progressBar.setMax(download.getFileSize()); //设置最大刻度
try {
download.download(downListener);
} catch (Exception e) {
e.printStackTrace();
}
}
}
//由子线程调用
private DownloadProgressListener downListener = new DownloadProgressListener() {
@Override
public void onDownloadSize(int size) {
//实时跟踪下载的情况
int percent = (int)(((double)size)/progressBar.getMax()*100);
Message msg = new Message();
msg.what = 1; //设置id
System.out.println(percent+"%");
System.out.println(size+"k");
msg.getData().putInt("percent", percent);
msg.getData().putInt("downloadsize",size);
handler.sendMessage(msg);
}
};
@Override
public void onClick(View v) {
if(v==downloadButton){
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
String url = urlpathEditText.getText().toString();
File saveDir = Environment.getExternalStorageDirectory();
download(url,saveDir);
}
else{
Toast.makeText(MainActivity.this, "SDCARD不存在", Toast.LENGTH_SHORT).show();
}
}
}
private void download(String url, File saveDir) {
thread = new DownloadThread(url,saveDir);
thread.start();
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
downloadButton = (Button)findViewById(R.id.download);
urlpathEditText = (EditText)findViewById(R.id.path);
percentTextView = (TextView)findViewById(R.id.textView);
progressBar = (ProgressBar)findViewById(R.id.progressBar);
downloadButton.setOnClickListener(listener);
handler = new UIHandler();
}
}
