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>
在EOE的论坛上看到，拿到这里跟大家分享，有时间我自己也实践一下。
注明：QQ技术交流群：108614806 感兴趣的加一下。