[Android实例] Android之断点续传下载
在我们做开发的时候经常遇到的就是下载了,现在下载的方法有很多很多,那么怎么做到断点续传下载呢!很多人都头疼这个问题,如果我们没有很好的逻辑真不是很容易解决啊。我参考了一下前辈们的资料了整理了一个项目,能实现多个文件的同时下载。
断点续传下载,顾名思义,那就是我们在一次下载未结束时,退出下载,第二次下载时会接着第一次下载的进度继续下载。那么怎么记录第一次下载的数据呢,这里肯定就要用到数据库了。下面就是我创建数据库的一个SQLiteOpenHelper类。用来首次运行时创建数据库。
DBHelper.java
- package com.icss.DBHelper;
- import android.content.Context;
- import android.database.sqlite.SQLiteDatabase;
- import android.database.sqlite.SQLiteOpenHelper;
- /**
- * 建立一个数据库帮助类
- */
- public class DBHelper extends SQLiteOpenHelper {
- // download.db-->数据库名
- public DBHelper(Context context) {
- super(context, "download.db", null, 1);
- }
- /**
- * 在download.db数据库下创建一个download_info表存储下载信息
- */
- @Override
- public void onCreate(SQLiteDatabase db) {
- db.execSQL("create table download_info(_id integer PRIMARY KEY AUTOINCREMENT, thread_id integer, "
- + "start_pos integer, end_pos integer, compelete_size integer,url char)");
- }
- @Override
- public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
- }
- }
下面看主界面的布局,在这里,我只设计了一个ListView来显示下载的音乐的名称,和一个开始下载按钮和一个暂停按钮。
布局文件如下:
main.xml:
- <?xml version="1.0" encoding="utf-8"?>
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
- android:orientation="vertical" android:layout_width="fill_parent"
- android:layout_height="fill_parent" android:weightSum="1">
- <ListView android:id="@android:id/list" android:layout_height="wrap_content"
- android:layout_width="match_parent" android:layout_weight="0.70"></ListView>
- </LinearLayout>
list_item.xml:
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
- android:layout_height="fill_parent" android:id="@+id/linearLayout1"
- android:layout_width="fill_parent" android:orientation="vertical">
- <LinearLayout android:layout_width="fill_parent"
- android:id="@+id/linearLayout2" android:layout_height="wrap_content"
- android:orientation="horizontal" android:layout_marginBottom="5dip">
- <TextView android:layout_width="fill_parent"
- android:layout_height="wrap_content" android:layout_weight="1"
- android:id="@+id/tv_resouce_name" />
- <Button android:layout_width="fill_parent"
- android:layout_height="wrap_content" android:layout_weight="1"
- android:text="下载" android:id="@+id/btn_start" android:onClick="startDownload" />
- <Button android:layout_width="fill_parent"
- android:layout_height="wrap_content" android:layout_weight="1"
- android:text="暂停" android:id="@+id/btn_pause" android:onClick="pauseDownload" />
- </LinearLayout>
- </LinearLayout>
我们要定义一个记录在下载时各个时期的数据的类,这里我创建了一个DownloadInfo类来记录。代码如下:
DownloadInfo:
- package com.icss.entity;
- public class DownloadInfo {
- private int threadId;// 下载器id
- private int startPos;// 开始点
- private int endPos;// 结束点
- private int compeleteSize;// 完成度
- private String url;// 下载器网络标识
- public DownloadInfo(int threadId, int startPos, int endPos,
- int compeleteSize, String url) {
- super();
- this.threadId = threadId;
- this.startPos = startPos;
- this.endPos = endPos;
- this.compeleteSize = compeleteSize;
- this.url = url;
- }
- public int getThreadId() {
- return threadId;
- }
- public void setThreadId(int threadId) {
- this.threadId = threadId;
- }
- public int getStartPos() {
- return startPos;
- }
- public void setStartPos(int startPos) {
- this.startPos = startPos;
- }
- public int getEndPos() {
- return endPos;
- }
- public void setEndPos(int endPos) {
- this.endPos = endPos;
- }
- public int getCompeleteSize() {
- return compeleteSize;
- }
- public void setCompeleteSize(int compeleteSize) {
- this.compeleteSize = compeleteSize;
- }
- public String getUrl() {
- return url;
- }
- public void setUrl(String url) {
- this.url = url;
- }
- @Override
- public String toString() {
- return "DownloadInfo [threadId=" + threadId
- + ", startPos=" + startPos + ", endPos=" + endPos
- + ", compeleteSize=" + compeleteSize +"]";
- }
- }
在下载时,我们有进度条来显示进度,怎么确定进度条的进度,大小和起始位置呢?这里我定义了一个LoadInfo类来记录下载器详细信息。代码如下:
LoadInfo:
- package com.icss.entity;
- public class LoadInfo {
- public int fileSize;// 文件大小
- private int complete;// 完成度
- private String urlstring;// 下载器标识
- public LoadInfo() {
- super();
- // TODO Auto-generated constructor stub
- }
- public LoadInfo(int fileSize, int complete, String urlstring) {
- super();
- this.fileSize = fileSize;
- this.complete = complete;
- this.urlstring = urlstring;
- }
- public int getFileSize() {
- return fileSize;
- }
- public void setFileSize(int fileSize) {
- this.fileSize = fileSize;
- }
- public int getComplete() {
- return complete;
- }
- public void setComplete(int complete) {
- this.complete = complete;
- }
- public String getUrlstring() {
- return urlstring;
- }
- public void setUrlstring(String urlstring) {
- this.urlstring = urlstring;
- }
- @Override
- public String toString() {
- return "LoadInfo [fileSize=" + fileSize + ", complete=" + complete
- + ", urlstring=" + urlstring + "]";
- }
- }
下面是最最重要的一步,那就是定义一个下载器来进行下载了,这里我就不多说,具体解释在代码中都有注解,供大家研究参考。
Downloader:
- package com.icss.service;
- import java.io.File;
- import java.io.InputStream;
- import java.io.RandomAccessFile;
- import java.net.HttpURLConnection;
- import java.net.URL;
- import java.util.ArrayList;
- import java.util.List;
- import com.icss.dao.Dao;
- import com.icss.entity.DownloadInfo;
- import com.icss.entity.LoadInfo;
- import android.content.Context;
- import android.os.Handler;
- import android.os.Message;
- import android.util.Log;
- public class Downloader {
- private String urlstr;// 下载的地址
- private String localfile;// 保存路径
- private int threadcount;// 线程数
- private Handler mHandler;// 消息处理器
- private Dao dao;// 工具类
- private int fileSize;// 所要下载的文件的大小
- private List<DownloadInfo> infos;// 存放下载信息类的集合
- 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;
- private int state = INIT;
- public Downloader(String urlstr, String localfile, int threadcount,
- Context context, Handler mHandler) {
- this.urlstr = urlstr;
- this.localfile = localfile;
- this.threadcount = threadcount;
- this.mHandler = mHandler;
- dao = new Dao(context);
- }
- /**
- * 判断是否正在下载
- */
- public boolean isdownloading() {
- return state == DOWNLOADING;
- }
- /**
- * 得到downloader里的信息 首先进行判断是否是第一次下载,如果是第一次就要进行初始化,并将下载器的信息保存到数据库中
- * 如果不是第一次下载,那就要从数据库中读出之前下载的信息(起始位置,结束为止,文件大小等),并将下载信息返回给下载器
- */
- public LoadInfo getDownloaderInfors() {
- if (isFirst(urlstr)) {
- init();
- int range = fileSize / threadcount;
- infos = new ArrayList<DownloadInfo>();
- for (int i = 0; i < threadcount - 1; i++) {
- DownloadInfo info = new DownloadInfo(i, i * range, (i + 1)
- * range - 1, 0, urlstr);
- infos.add(info);
- }
- DownloadInfo info = new DownloadInfo(threadcount - 1,
- (threadcount - 1) * range, fileSize - 1, 0, urlstr);
- infos.add(info);
- // 保存infos中的数据到数据库
- dao.saveInfos(infos);
- // 创建一个LoadInfo对象记载下载器的具体信息
- LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);
- return loadInfo;
- } else {
- // 得到数据库中已有的urlstr的下载器的具体信息
- infos = dao.getInfos(urlstr);
- Log.v("TAG", "not isFirst size=" + infos.size());
- int size = 0;
- int compeleteSize = 0;
- for (DownloadInfo info : infos) {
- compeleteSize += info.getCompeleteSize();
- size += info.getEndPos() - info.getStartPos() + 1;
- }
- return new LoadInfo(size, compeleteSize, urlstr);
- }
- }
- /**
- */
- private void init() {
- try {
- URL url = new URL(urlstr);
- HttpURLConnection connection = (HttpURLConnection) url
- .openConnection();
- connection.setConnectTimeout(5000);
- connection.setRequestMethod("GET");
- fileSize = connection.getContentLength();
- File file = new File(localfile);
- if (!file.exists()) {
- file.createNewFile();
- }
- // 本地访问文件
- RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
- accessFile.setLength(fileSize);
- accessFile.close();
- connection.disconnect();
- } catch (Exception e) {
- e.printStackTrace();
- }
- }
- /**
- * 判断是否是第一次 下载
- */
- private boolean isFirst(String urlstr) {
- return dao.isHasInfors(urlstr);
- }
- /**
- * 114 * 利用线程开始下载数据 115
- */
- public void download() {
- if (infos != null) {
- if (state == DOWNLOADING)
- return;
- state = DOWNLOADING;
- for (DownloadInfo info : infos) {
- new MyThread(info.getThreadId(), info.getStartPos(),
- info.getEndPos(), info.getCompeleteSize(),
- info.getUrl()).start();
- }
- }
- }
- public class MyThread extends Thread {
- private int threadId;
- private int startPos;
- private int endPos;
- private int compeleteSize;
- private String urlstr;
- public MyThread(int threadId, int startPos, int endPos,
- int compeleteSize, String urlstr) {
- this.threadId = threadId;
- this.startPos = startPos;
- this.endPos = endPos;
- this.compeleteSize = compeleteSize;
- this.urlstr = urlstr;
- }
- @Override
- public void run() {
- HttpURLConnection connection = null;
- RandomAccessFile randomAccessFile = null;
- InputStream is = null;
- try {
- URL url = new URL(urlstr);
- connection = (HttpURLConnection) url.openConnection();
- connection.setConnectTimeout(5000);
- connection.setRequestMethod("GET");
- // 设置范围,格式为Range:bytes x-y;
- connection.setRequestProperty("Range", "bytes="
- + (startPos + compeleteSize) + "-" + endPos);
- randomAccessFile = new RandomAccessFile(localfile, "rwd");
- randomAccessFile.seek(startPos + compeleteSize);
- // 将要下载的文件写到保存在保存路径下的文件中
- is = connection.getInputStream();
- byte[] buffer = new byte[4096];
- int length = -1;
- while ((length = is.read(buffer)) != -1) {
- randomAccessFile.write(buffer, 0, length);
- compeleteSize += length;
- // 更新数据库中的下载信息
- dao.updataInfos(threadId, compeleteSize, urlstr);
- // 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 = 1;
- message.obj = urlstr;
- message.arg1 = length;
- mHandler.sendMessage(message);
- if (state == PAUSE) {
- return;
- }
- }
- } catch (Exception e) {
- e.printStackTrace();
- } finally {
- try {
- is.close();
- randomAccessFile.close();
- connection.disconnect();
- dao.closeDb();
- } catch (Exception e) {
- e.printStackTrace();
- }
- }
- }
- }
- // 删除数据库中urlstr对应的下载器信息
- public void delete(String urlstr) {
- dao.delete(urlstr);
- }
- // 设置暂停
- public void pause() {
- state = PAUSE;
- }
- // 重置下载状态
- public void reset() {
- state = INIT;
- }
- }
在这边下载器类的定义中,我们用到了许多关于进行数据库操作的方法,这里我定义了一个数据库工具类,来提供这些方法,代码如下:
Dao:
- package com.icss.dao;
- import java.util.ArrayList;
- import java.util.List;
- import javax.crypto.spec.DESKeySpec;
- import com.icss.DBHelper.DBHelper;
- import com.icss.entity.DownloadInfo;
- import android.content.Context;
- import android.database.Cursor;
- import android.database.sqlite.SQLiteDatabase;
- /**
- *
- * 一个业务类
- */
- public class Dao {
- private DBHelper dbHelper;
- public Dao(Context context) {
- dbHelper = new DBHelper(context);
- }
- /**
- * 查看数据库中是否有数据
- */
- public boolean isHasInfors(String urlstr) {
- SQLiteDatabase database = dbHelper.getReadableDatabase();
- String sql = "select count(*) from download_info where url=?";
- Cursor cursor = database.rawQuery(sql, new String[] { urlstr });
- cursor.moveToFirst();
- int count = cursor.getInt(0);
- cursor.close();
- return count == 0;
- }
- /**
- * 保存 下载的具体信息
- */
- public void saveInfos(List<DownloadInfo> infos) {
- SQLiteDatabase database = dbHelper.getWritableDatabase();
- for (DownloadInfo info : infos) {
- String sql = "insert into download_info(thread_id,start_pos, end_pos,compelete_size,url) values (?,?,?,?,?)";
- Object[] bindArgs = { info.getThreadId(), info.getStartPos(),
- info.getEndPos(), info.getCompeleteSize(), info.getUrl() };
- database.execSQL(sql, bindArgs);
- }
- }
- /**
- * 得到下载具体信息
- */
- public List<DownloadInfo> getInfos(String urlstr) {
- List<DownloadInfo> list = new ArrayList<DownloadInfo>();
- SQLiteDatabase database = dbHelper.getReadableDatabase();
- String sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";
- Cursor cursor = database.rawQuery(sql, new String[] { urlstr });
- while (cursor.moveToNext()) {
- 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;
- }
- /**
- * 更新数据库中的下载信息
- */
- public void updataInfos(int threadId, int compeleteSize, String urlstr) {
- SQLiteDatabase database = dbHelper.getReadableDatabase();
- String sql = "update download_info set compelete_size=? where thread_id=? and url=?";
- Object[] bindArgs = { compeleteSize, threadId, urlstr };
- database.execSQL(sql, bindArgs);
- }
- /**
- * 关闭数据库
- */
- public void closeDb() {
- dbHelper.close();
- }
- /**
- * 下载完成后删除数据库中的数据
- */
- public void delete(String url) {
- SQLiteDatabase database = dbHelper.getReadableDatabase();
- database.delete("download_info", "url=?", new String[] { url });
- database.close();
- }
- }
下面的是程序的主程序,其他的不说了,直接上代码:
- package com.icss;
- import java.util.ArrayList;
- import java.util.HashMap;
- import java.util.List;
- import java.util.Map;
- import android.app.ListActivity;
- import android.os.Bundle;
- import android.os.Handler;
- import android.os.Message;
- import android.view.View;
- import android.widget.LinearLayout;
- import android.widget.LinearLayout.LayoutParams;
- import android.widget.ProgressBar;
- import android.widget.SimpleAdapter;
- import android.widget.TextView;
- import android.widget.Toast;
- import com.icss.entity.LoadInfo;
- import com.icss.service.Downloader;
- public class MainActivity extends ListActivity {
- // 固定下载的资源路径,这里可以设置网络上的地址
- private static final String URL = "http://10.0.0.80:8080/xiangce/";
- // 固定存放下载的音乐的路径:SD卡目录下
- private static final String SD_PATH = "/mnt/sdcard/";
- // 存放各个下载器
- private Map<String, Downloader> downloaders = new HashMap<String, Downloader>();
- // 存放与下载器对应的进度条
- private Map<String, ProgressBar> ProgressBars = new HashMap<String, ProgressBar>();
- /**
- * 31 * 利用消息处理机制适时更新进度条 32
- */
- private Handler mHandler = new Handler() {
- public void handleMessage(Message msg) {
- if (msg.what == 1) {
- String url = (String) msg.obj;
- int length = msg.arg1;
- ProgressBar bar = ProgressBars.get(url);
- if (bar != null) {
- // 设置进度条按读取的length长度更新
- bar.incrementProgressBy(length);
- if (bar.getProgress() == bar.getMax()) {
- Toast.makeText(MainActivity.this, "下载完成!", 0).show();
- // 下载完成后清除进度条并将map中的数据清空
- LinearLayout layout = (LinearLayout) bar.getParent();
- layout.removeView(bar);
- ProgressBars.remove(url);
- downloaders.get(url).delete(url);
- downloaders.get(url).reset();
- downloaders.remove(url);
- }
- }
- }
- }
- };
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- showListView();
- }
- // 显示listView,这里可以随便添加音乐
- private void showListView() {
- List<Map<String, String>> data = new ArrayList<Map<String, String>>();
- Map<String, String> map = new HashMap<String, String>();
- map.put("name", "mm.mp3");
- data.add(map);
- map = new HashMap<String, String>();
- map.put("name", "pp.mp3");
- data.add(map);
- map = new HashMap<String, String>();
- map.put("name", "tt.mp3");
- data.add(map);
- map = new HashMap<String, String>();
- map.put("name", "You.mp3");
- data.add(map);
- SimpleAdapter adapter = new SimpleAdapter(this, data,
- R.layout.list_item, new String[] { "name" },
- new int[] { R.id.tv_resouce_name });
- setListAdapter(adapter);
- }
- /**
- * 83 * 响应开始下载按钮的点击事件 84
- */
- public void startDownload(View v) {
- // 得到textView的内容
- LinearLayout layout = (LinearLayout) v.getParent();
- String musicName = ((TextView) layout
- .findViewById(R.id.tv_resouce_name)).getText().toString();
- String urlstr = URL + musicName;
- String localfile = SD_PATH + musicName;
- // 设置下载线程数为4,这里是我为了方便随便固定的
- int threadcount = 4;
- // 初始化一个downloader下载器
- Downloader downloader = downloaders.get(urlstr);
- if (downloader == null) {
- downloader = new Downloader(urlstr, localfile, threadcount, this,
- mHandler);
- downloaders.put(urlstr, downloader);
- }
- if (downloader.isdownloading())
- return;
- // 得到下载信息类的个数组成集合
- LoadInfo loadInfo = downloader.getDownloaderInfors();
- // 显示进度条
- showProgress(loadInfo, urlstr, v);
- // 调用方法开始下载
- downloader.download();
- }
- /**
- * 显示进度条
- */
- private void showProgress(LoadInfo loadInfo, String url, View v) {
- ProgressBar bar = ProgressBars.get(url);
- if (bar == null) {
- bar = new ProgressBar(this, null,
- android.R.attr.progressBarStyleHorizontal);
- bar.setMax(loadInfo.getFileSize());
- bar.setProgress(loadInfo.getComplete());
- System.out.println(loadInfo.getFileSize()+"--"+loadInfo.getComplete());
- ProgressBars.put(url, bar);
- LinearLayout.LayoutParams params = new LayoutParams(
- LayoutParams.FILL_PARENT, 5);
- ((LinearLayout) ((LinearLayout) v.getParent()).getParent())
- .addView(bar, params);
- }
- }
- /**
- * 响应暂停下载按钮的点击事件
- */
- public void pauseDownload(View v) {
- LinearLayout layout = (LinearLayout) v.getParent();
- String musicName = ((TextView) layout
- .findViewById(R.id.tv_resouce_name)).getText().toString();
- String urlstr = URL + musicName;
- downloaders.get(urlstr).pause();
- }
- }
最后我们需要在android Manifest.xml中添加这两个权限一个是访问internet的权限,另一个是写外存的权限。
- <uses-permission android:name="android.permission.INTERNET"></uses-permission>
- <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
最后运行的效果图:
万事俱备只欠东风啦!哈哈,我需要在我的web工程里放几个音乐文件。
下载后得到的文件可在sdcard下面找到!