Android四步快速实现断点续传

1.导入依赖

implementation 'com.loopj.android:android-async-http:1.5.8'

2.导入权限

<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

3.布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.five.fashion.duandianxuchuan.MainActivity">
<ProgressBar
style="@style/Widget.AppCompat.ProgressBar.Horizontal"
android:layout_width="match_parent"
android:layout_height="100dp"
android:id="@+id/pb"
/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/tv_info"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="下载"
android:id="@+id/bt_download"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="暂停"
android:id="@+id/bt_pause"
/>
</LinearLayout>

4.主要代码

public class MainActivity extends AppCompatActivity {
protected static final String TAG = "OtherActivity";
//下载线程的数量
private final static int threadsize = 3;
protected static final int SET_MAX = 0;
public static final int UPDATE_VIEW = 1;
private ProgressBar pb;
private Button bt_download;
private Button bt_pause;
private TextView tv_info;
//显示进度和更新进度
private Handler mHandler = new Handler(){
public void handleMessage(android.os.Message msg) {
switch (msg.what) {
case SET_MAX://设置进度条的最大值
int filelength = msg.arg1;
pb.setMax(filelength);
break;
case UPDATE_VIEW://更新进度条 和 下载的比率
int len = msg.arg1;//新下载的长度
pb.setProgress(pb.getProgress()+len);//设置进度条的刻度

                int max = pb.getMax();//获取进度的最大值
                int progress = pb.getProgress();//获取已经下载的数据量
                //  下载:30    总:100
                int result = (progress*100)/max;

                tv_info.setText("下载:"+result+"%");

                break;

            default:
                break;
        }
    };
};
String uri = "请放一张图片";放图!!!
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
   //找到控件
    pb = (ProgressBar) findViewById(R.id.pb);
    tv_info = (TextView) findViewById(R.id.tv_info);
    bt_download = (Button) findViewById(R.id.bt_download);
    bt_pause = (Button) findViewById(R.id.bt_pause);
    //数据的回显
    //确定下载的文件
    String name = getFileName(uri);
    File file = new File(Environment.getExternalStorageDirectory(), name);
    if (file.exists()){//文件存在回显
        //获取文件的大小
        int filelength = (int) file.length();
        pb.setMax(filelength);
        try {
            //统计原来所有的下载量
            int count = 0;
            //读取下载记录文件
            for (int threadid = 0; threadid < threadsize; threadid++) {
                //获取原来指定线程的下载记录
                int existDownloadLength = readDownloadInfo(threadid);
                count = count + existDownloadLength;
            }
            //设置进度条的刻度
            pb.setProgress(count);

            //计算比率
            int result = (count * 100) / filelength;
            tv_info.setText("下载:" + result + "%");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    bt_download.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            download(v);
        }
    });
    bt_pause.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            pause(v);
        }
    });
}
//暂停
private boolean flag = false;//是否在下载

public void pause(View v){
    flag = false;
    bt_download.setEnabled(true);
    bt_pause.setEnabled(false);
}

//下载
public void download(View v){
    flag = true; //是在下载
    bt_download.setEnabled(false);//一点击变成不可点击
    bt_pause.setEnabled(true);//一点击变成可点击
    new Thread(){//子线程
        public void run() {
            try {
                //获取服务器上文件的大小
                HttpClient client = new DefaultHttpClient();
                HttpHead request = new HttpHead(uri);
                HttpResponse response = client.execute(request);
                //response  只有响应头  没有响应体
                if(response.getStatusLine().getStatusCode() == 200){
                    Header[] headers = response.getHeaders("Content-Length");
                    String value = headers[0].getValue();
                    //文件大小
                    int filelength = Integer.parseInt(value);
                    Log.i(TAG, "filelength:"+filelength);

                    //设置进度条的最大值
                    Message msg_setmax = Message.obtain(mHandler, SET_MAX, filelength, 0);
                    msg_setmax.sendToTarget();


                    //处理下载记录文件
                    for(int threadid=0;threadid<threadsize;threadid++){
                        //对应的下载记录文件
                        File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
                        //判断文件是否存在
                        if(!file.exists()){
                            //创建文件
                            file.createNewFile();
                        }
                    }

                    //在sdcard创建和服务器大小一样的文件
                    String name = getFileName(uri);
                    File file = new File(Environment.getExternalStorageDirectory(),name);
                    //随机访问文件
                    RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                    //设置文件的大小
                    raf.setLength(filelength);
                    //关闭
                    raf.close();

                    //计算每条线程的下载量
                    int block = (filelength%threadsize == 0)?(filelength/threadsize):(filelength/threadsize+1);
                    //开启三条线程执行下载
                    for(int threadid=0;threadid<threadsize;threadid++){
                        new DownloadThread(threadid, uri, file, block).start();
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        };
    }.start();
}


//线程下载类
private class DownloadThread extends Thread{
    private int threadid;//线程的id
    private String uri;//下载的地址
    private File file;//下载文件
    private int block;//下载的块
    private int start;
    private int end;

    public DownloadThread(int threadid, String uri, File file, int block) {
        super();
        this.threadid = threadid;
        this.uri = uri;
        this.file = file;
        this.block = block;
        //计算下载的开始位置和结束位置
        start = threadid * block;
        end = (threadid + 1)*block -1;

        try {
            //读取该条线程原来的下载记录
            int existDownloadLength = readDownloadInfo(threadid);

            //修改下载的开始位置   从新下载
            start = start + existDownloadLength;
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    //下载   状态码:200是普通的下载      206是分段下载        Range:范围
    @Override
    public void run() {
        super.run();
        try {
            RandomAccessFile raf = new RandomAccessFile(file, "rwd");
            //跳转到起始位置
            raf.seek(start);

            //分段下载
            HttpClient client = new DefaultHttpClient();
            HttpGet request = new HttpGet(uri);
            request.addHeader("Range", "bytes:"+start+"-"+end);//添加请求头
            HttpResponse response = client.execute(request);
            if(response.getStatusLine().getStatusCode() == 200){
                InputStream inputStream = response.getEntity().getContent();
                //把流写入到文件
                byte[] buffer = new byte[1024];
                int len = 0;
                while((len = inputStream.read(buffer)) != -1){
                    //如果暂停下载  点击暂停 false 就直接return 点击下载true接着下载
                    if(!flag){
                        return;//标准线程结束
                    }
                    //写数据
                    raf.write(buffer, 0, len);

                    //读取原来下载的数据量 这里读取是为了更新下载记录
                    int existDownloadLength = readDownloadInfo(threadid);//原来下载的数据量

                    //计算最新的下载
                    int newDownloadLength = existDownloadLength + len;

                    //更新下载记录 从新记录最新下载位置
                    updateDownloadInfo(threadid, newDownloadLength);
                    //更新进度条的显示   下载的百分比
                    Message update_msg = Message.obtain(mHandler, UPDATE_VIEW, len, 0);
                    update_msg.sendToTarget();
                    //模拟  看到进度条动的效果
                    SystemClock.sleep(50);
                }
                inputStream.close();
                raf.close();
                Log.i(TAG, "第"+threadid+"条线程下载完成");
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}


/**
 * 读取指定线程的下载数据量
 * @param threadid  线程的id
 * @return
 * @throws Exception
 */
public int readDownloadInfo(int threadid) throws Exception{
    //下载记录文件
    File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
    BufferedReader br = new BufferedReader(new FileReader(file));
    //读取一行数据
    String content = br.readLine();

    int downlength = 0;
    //如果该文件第一次创建去执行读取操作  文件里面的内容是 null
    if(!TextUtils.isEmpty(content)){
        downlength = Integer.parseInt(content);
    }
    //关闭流
    br.close();
    return downlength;
}


/**
 * 更新下载记录
 * @param threadid
 * @param newDownloadLength
 */
public void updateDownloadInfo(int threadid,int newDownloadLength) throws Exception{
    //下载记录文件
    File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
    FileWriter fw = new FileWriter(file);
    fw.write(newDownloadLength+"");
    fw.close();
}

/**
 * 获取文件的名称
 * @param uri
 * @return
 */
private String getFileName(String uri){
    return uri.substring(uri.lastIndexOf("/")+1);
}

}

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