Android 文件断点下载

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)");
    }
}

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：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>

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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);
    }
}

转载于:https://my.oschina.net/u/3407628/blog/1562965