Android——断点续传（下载）

朴灿烈づ我的快乐病毒、 2022-06-02 01:23 394阅读 0赞

**断点续传的原理：**  
断点续传和断点下载都是用的RandomAccessFile, 它具有移动指定的文件大小的位置的功能seek 。

断点续传是由服务器给客户端一个已经上传的位置标记position，然后客户端再将文件指针移动到相应的position，通过输入流将文件剩余部分读出来传输给服务器断点下载 是由客户端告诉服务器已经下载的大小，然后服务器会将指针移动到相应的position，继续读出，把文件返回给客户端。 当然为了下载的更快一下，也可以多线程下载，那么基本实现就是给每个线程分配固定的字节的文件，分别去读。

**DownloadUtils**

public class DownloadUtils {
        private static final String TAG = "DownloadUtils";
        private static volatile DownloadUtils instance;
        private File file;
        private String filePath;
    
        private OkHttpClient client;
        private File downloadFile;
        private long startPosition;
        private Call call;
    
        private DownloadUtils() {
            client = new OkHttpClient();
        }
    
        private DownloadListener listener;
    
        public void setListener(DownloadListener listener) {
            this.listener = listener;
        }
    
        /** * 初始化下载父路径 * * @param path */ public void initDownload(String path) {
            file = new File(path);
            if (!file.getParentFile().exists()) {
                file.getParentFile().mkdir();
            }
            if (!file.exists()) {
                file.mkdir();
            }
            filePath = file.getAbsolutePath();
            Log.i(TAG, "initDownload: " + filePath);
        }
    
        public static DownloadUtils getInstance() {
            if (null == instance) {
                synchronized (DownloadUtils.class) {
                    if (instance == null) {
                        instance = new DownloadUtils();
                    }
                }
            }
            return instance;
        }
    
        public void startDownload(String url) {
            if (TextUtils.isEmpty(url)) {
                return;
            }
    
    
            if (url.contains(".")) {
                String typeName = url.substring(url.lastIndexOf(".") + 1);
                if (url.contains("/")) {
                    String name = url.substring(url.lastIndexOf("/") + 1, url.lastIndexOf("."));
                    String fn = name + "." + typeName;
    
                    downloadFile = new File(file, fn);
                }
            }
            startPosition = 0;
            if (downloadFile.exists()) {
                startPosition = downloadFile.length();
            }
    
            Request request = new Request.Builder()
                    .addHeader("RANGE", "bytes=" + startPosition + "-")
                    .url(url)
                    .build();
    
            call = client.newCall(request);
            call.enqueue(new Callback() {
                @Override public void onFailure(Call call, IOException e) {
    
                }
    
                @Override public void onResponse(Call call, Response response) throws IOException {
                    listener.startDownload();
                    ResponseBody body = response.body();
                    long totalLength = body.contentLength() + startPosition;
                    Log.i(TAG, "totalLength: " + totalLength + "----");
                    InputStream is = body.byteStream();
                    byte[] buf = new byte[2048];
                    int length = 0;
                    long totalNum = startPosition;
                    RandomAccessFile raf = new RandomAccessFile(downloadFile, "rw");
                    raf.seek(totalNum);
                    while ((length = is.read(buf, 0, buf.length)) != -1) {
                        raf.write(buf, 0, length);
                        totalNum += length;
                        listener.downloadProgress(totalNum * 100 / totalLength);
    
                    }
                    Log.i(TAG, "totalNum==" + totalNum + "---");
                    listener.finishDownload(downloadFile.getAbsolutePath());
                    body.close();
                }
            });
    
    
        }
    
        public void pauseDownload() {
            listener.pauseDownload();
            if (call != null && call.isExecuted()) {
                call.cancel();
            }
        }
    }

DownloadListener

public interface DownloadListener {
        void startDownload();
    
        void pauseDownload();
    
        void finishDownload(String path);
    
        void downloadProgress(long progress);
    }

MainActivity

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    
        private TextView tv_pro;
        private ProgressBar progressBar;
        private Button btn_start;
        private Button btn_pause;
        private String downloadUrl = "http://acj3.pc6.com/pc6_soure/2017-12/com.yek.android.kfc.activitys_3820.apk";
    
        @Override protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            tv_pro = findViewById(R.id.tv_pro);
            progressBar = findViewById(R.id.progressbar);
            btn_start = findViewById(R.id.start);
            btn_pause = findViewById(R.id.pause);
            btn_start.setOnClickListener(this);
            btn_pause.setOnClickListener(this);
            if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
                File storageDirectory = Environment.getExternalStorageDirectory();
                String absolutePath = storageDirectory.getAbsolutePath();
                final String path = absolutePath + "/Download/";
                Log.i("zzz", "下载路径 " + path);
                DownloadUtils.getInstance().initDownload(path);
                DownloadUtils.getInstance().setListener(new DownloadListener() {
                    @Override public void startDownload() {
    
                    }
    
                    @Override public void pauseDownload() {
    
                    }
    
                    @Override public void finishDownload(String path) {
                        installApk(new File(path));
                    }
    
    
                    @Override public void downloadProgress(final long progress) {
                        runOnUiThread(new Runnable() {
                            @Override public void run() {
                                tv_pro.setText((int)progress + "%");
                                progressBar.setProgress((int) progress);
                            }
                        });
                    }
                });
            }
        }
    
        @Override public void onClick(View view) {
            switch (view.getId()) {
                case R.id.start:
                    DownloadUtils.getInstance().startDownload(downloadUrl);
                    break;
                case R.id.pause:
                    DownloadUtils.getInstance().pauseDownload();
                    break;
            }
        }
        /** * 安装apk * * @param file */ private void installApk(File file) {
            Intent intent = new Intent();
            intent.setAction(Intent.ACTION_VIEW);
            intent.addCategory("android.intent.category.DEFAULT");
            intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            intent.setDataAndType(Uri.fromFile(file), "application/vnd.android.package-archive");
            startActivity(intent);
            android.os.Process.killProcess(android.os.Process.myPid());
        }
    }

activity\_main.xml

<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout 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"
        tools:context="com.bwie.com.wangruixin20171227.MainActivity">
    
        <TextView android:id="@+id/tv_pro"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:text="0%" />
    
        <ProgressBar android:id="@+id/progressbar"
            style="?android:attr/progressBarStyleHorizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_below="@+id/tv_pro"
            android:layout_marginTop="12dp"
            android:max="100"
            android:progress="0" />
    
        <Button android:id="@+id/start"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_below="@+id/progressbar"
            android:layout_marginTop="15dp"
            android:text="开始下载" />
    
        <Button android:id="@+id/pause"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_below="@+id/start"
            android:layout_marginTop="26dp"
            android:text="暂停下载" />
    
    
    </RelativeLayout>