@Android网络编程之——文件断点下载
一：关于断点下载所涉及到的知识点
1.对SQLite的增删改查(主要用来保存当前任务的一些信息)
2.HttpURLConnection的请求配置
HttpURLConnection connection = null;
//设置下载请求属性
connection.setRequestProperty();3.RandomAccessFile 对文件进行写入
RandomAccessFile rwd = null;
//从文件的某一位置写入
rwd.seek();4.基本的I/O流操作，以及逻辑处理
二：第一步我们先来创建一张表用来保存我们的下载信息
public class DbHelper extends SQLiteOpenHelper {
public static String TABLE = "file";//表名
public DbHelper(Context context) {
super(context, "download.db", null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
//文件名，下载地址，下载文件的总长度，当前下载完成长度
db.execSQL("create table file(fileName varchar,url varchar,length integer,finished integer)");
}
}三：第二步同时既然是对数据库的操作，那我们在DbHelper.class中来写好几个公用方法
/**
* 插入一条下载信息
*/
public void insertData(SQLiteDatabase db, FileInfo info) {
ContentValues values = new ContentValues();
values.put("fileName", info.getFileName());
values.put("url", info.getUrl());
values.put("length", info.getLength());
values.put("finished", info.getFinished());
db.insert(TABLE, null, values);
}
/**
* 是否已经插入这条数据
*/
public boolean isExist(SQLiteDatabase db, FileInfo info) {
Cursor cursor = db.query(TABLE, null, "url = ?", new String[]{info.getUrl()}, null, null, null, null);
boolean exist = cursor.moveToNext();
cursor.close();
return exist;
}
/**
* 查询已经存在的一条信息
*/
public FileInfo queryData(SQLiteDatabase db, String url) {
Cursor cursor = db.query(TABLE, null, "url = ?", new String[]{url}, null, null, null, null);
FileInfo info = new FileInfo();
if (cursor != null) {
while (cursor.moveToNext()) {
String fileName = cursor.getString(cursor.getColumnIndex("fileName"));
int length = cursor.getInt(cursor.getColumnIndex("length"));
int finished = cursor.getInt(cursor.getColumnIndex("finished"));
info.setStop(false);
info.setFileName(fileName);
info.setUrl(url);
info.setLength(length);
info.setFinished(finished);
}
cursor.close();
}
return info;
}
/**
* 恢复一条下载信息
*/
public void resetData(SQLiteDatabase db, String url) {
ContentValues values = new ContentValues();
values.put("finished", 0);
values.put("length", 0);
db.update(TABLE, values, "url = ?", new String[]{url});
}3.从上面方法中可以看出来还有一个FileInfo对象，没错这是自己创建的一个下载任务实体类一起来看看吧
//保存下载任务信息
public class FileInfo {
private String fileName;//文件名
private String url;//下载地址
private int length;//文件大小
private int finished;//下载以已完成进度
private boolean isStop = false;//是否暂停下载
private boolean isDownLoading = false;//是否正在下载
//......
//剩下的都是对应的get and set 方法就不贴出来了，自动生成就好了四：第三步我们创建一个类DownLoaderManger来管理我们的下载任务包括、添加下载任务、开始下载、暂停下载、重新下载
public class DownLoaderManger {
public static String FILE_PATH = Environment.getExternalStorageDirectory() + "/azhong";//文件下载保存路径
private DbHelper helper;//数据库帮助类
private SQLiteDatabase db;
private OnProgressListener listener;//进度回调监听
private Map<String, FileInfo> map = new HashMap<>();//保存正在下载的任务信息
private static DownLoaderManger manger;
private DownLoaderManger(DbHelper helper, OnProgressListener listener) {
this.helper = helper;
this.listener = listener;
db = helper.getReadableDatabase();
}
/**
* 单例模式
*
* @param helper 数据库帮助类
* @param listener 下载进度回调接口
* @return
*/
public static synchronized DownLoaderManger getInstance(DbHelper helper, OnProgressListener listener) {
if (manger == null) {
synchronized (DownLoaderManger.class) {
if (manger == null) {
manger = new DownLoaderManger(helper, listener);
}
}
}
return manger;
}
/**
* 开始下载任务
*/
public void start(String url) {
db = helper.getReadableDatabase();
FileInfo info = helper.queryData(db, url);
map.put(url, info);
//开始任务下载
new DownLoadTask(map.get(url), helper, listener).start();
}
/**
* 停止下载任务
*/
public void stop(String url) {
map.get(url).setStop(true);
}
/**
* 重新下载任务
*/
public void restart(String url) {
stop(url);
try {
File file = new File(FILE_PATH, map.get(url).getFileName());
if (file.exists()) {
file.delete();
}
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
db = helper.getWritableDatabase();
helper.resetData(db, url);
start(url);
}
/**
* 获取当前任务状态
*/
public boolean getCurrentState(String url) {
return map.get(url).isDownLoading();
}
/**
* 添加下载任务
*
* @param info 下载文件信息
*/
public void addTask(FileInfo info) {
//判断数据库是否已经存在这条下载信息
if (!helper.isExist(db, info)) {
db = helper.getWritableDatabase();
helper.insertData(db, info);
map.put(info.getUrl(), info);
} else {
//从数据库获取最新的下载信息
db = helper.getReadableDatabase();
FileInfo o = helper.queryData(db, info.getUrl());
if (!map.containsKey(info.getUrl())) {
map.put(info.getUrl(), o);
}
}
}
}五：上面代码中OnProgressListener接口，当然还有一个最最重要的DownLoadTask了这里面就是实现了如何断点下载的，下面来一起看下里面的实现逻辑吧。。。
//下载进度接口
public interface OnProgressListener {
void updateProgress(int max, int progress);
}六：重点–下载线程
/**
* 下载文件线程
* 从服务器获取需要下载的文件大小
*/
public class DownLoadTask extends Thread {
private FileInfo info;
private SQLiteDatabase db;
private DbHelper helper;//数据库帮助类
private int finished = 0;//当前已下载完成的进度
private OnProgressListener listener;//进度回调监听
public DownLoadTask(FileInfo info, DbHelper helper, OnProgressListener listener) {
this.info = info;
this.helper = helper;
this.db = helper.getReadableDatabase();
this.listener = listener;
info.setDownLoading(true);
}
@Override
public void run() {
getLength();
HttpURLConnection connection = null;
RandomAccessFile rwd = null;
try {
URL url = new URL(info.getUrl());
connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(3000);
//从上次下载完成的地方下载
int start = info.getFinished();
//设置下载位置(从服务器上取要下载文件的某一段)
connection.setRequestProperty("Range", "bytes=" + start + "-" + info.getLength());//设置下载范围
//设置文件写入位置
File file = new File(DownLoaderManger.FILE_PATH, info.getFileName());
rwd = new RandomAccessFile(file, "rwd");
//从文件的某一位置开始写入
rwd.seek(start);
finished += info.getFinished();
if (connection.getResponseCode() == 206) {//文件部分下载，返回码为206
InputStream is = connection.getInputStream();
byte[] buffer = new byte[1024 * 4];
int len;
while ((len = is.read(buffer)) != -1) {
//写入文件
rwd.write(buffer, 0, len);
finished += len;
info.setFinished(finished);
//更新界面显示
Message msg = new Message();
msg.what = 0x123;
msg.arg1 = info.getLength();
msg.arg2 = info.getFinished();
handler.sendMessage(msg);
//停止下载
if (info.isStop()) {
info.setDownLoading(false);
//保存此次下载的进度
helper.updateData(db, info);
db.close();
return;
}
}
//下载完成
info.setDownLoading(false);
helper.updateData(db, info);
db.close();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
try {
if (rwd != null) {
rwd.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 首先开启一个线程去获取要下载文件的大小（长度）
*/
private void getLength() {
HttpURLConnection connection = null;
try {
//连接网络
URL url = new URL(info.getUrl());
connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(3000);
int length = -1;
if (connection.getResponseCode() == 200) {//网络连接成功
//获得文件长度
length = connection.getContentLength();
}
if (length <= 0) {
//连接失败
return;
}
//创建文件保存路径
File dir = new File(DownLoaderManger.FILE_PATH);
if (!dir.exists()) {
dir.mkdirs();
}
info.setLength(length);
} catch (Exception e) {
e.printStackTrace();
} finally {
//释放资源
try {
if (connection != null) {
connection.disconnect();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
/**
* 更新进度
*/
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case 0x123:
if (listener != null) {
listener.updateProgress(msg.arg1, msg.arg2);
}
break;
}
}
};
}七：下载流程—>首先获取要下载文件的总长度—>然后指定从上次结束的位置开始下载文件。客官阅读需仔细哦，精华都在注释里面哦！个人认为重点部分如下两个：
//设置下载位置(从服务器上取要下载文件的某一段)
connection.setRequestProperty("Range", "bytes=" + start + "-" + info.getLength());//设置下载范围
RandomAccessFile rwd = new RandomAccessFile(file, "rwd");
//从文件的某一位置开始写入
rwd.seek(start);八：上面做了一系列准备工作之后，就可以正式开始下载了让我们一起来瞧瞧
1.给主布局界面放两个按钮，来开始/暂停/重新下载
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.azhong.downloader.MainActivity">
<com.azhong.downloader.view.NumberProgressBar
android:id="@+id/pb"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<Button
android:id="@+id/start"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="16dp"
android:text="开始下载" />
<Button
android:id="@+id/restart"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
android:text="重新下载" />
</LinearLayout>2.关于NumberProgressBar的使用可以移驾至这里
3.记得在清单文件中加入 网络访问和内存读写权限哦！
4.既然我们封装了那么久，那肯定用起来就会很简单了
public class MainActivity extends AppCompatActivity implements OnProgressListener {
private NumberProgressBar pb;//进度条
private DownLoaderManger downLoader = null;
private FileInfo info;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pb = (NumberProgressBar) findViewById(R.id.pb);
final Button start = (Button) findViewById(R.id.start);//开始下载
final Button restart = (Button) findViewById(R.id.restart);//重新下载
final DbHelper helper = new DbHelper(this);
downLoader = DownLoaderManger.getInstance(helper, this);
info = new FileInfo("Kuaiya482.apk", "http://downloadz.dewmobile.net/Official/Kuaiya482.apk");
downLoader.addTask(info);
start.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (downLoader.getCurrentState(info.getUrl())) {
downLoader.stop(info.getUrl());
start.setText("开始下载");
} else {
downLoader.start(info.getUrl());
start.setText("暂停下载");
}
}
});
restart.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
downLoader.restart(info.getUrl());
start.setText("暂停下载");
}
});
}
@Override
public void updateProgress(final int max, final int progress) {
pb.setMax(max);
pb.setProgress(progress);
}
}
