前言
在rxjava和retrofit日益火热的今天，我们也要给自己定个小目标，比如说利用其来实现支付宝更新app的断点续传下载功能。
基本原理
其实下载文件就是一个get请求，而断点续传则是要把发生异常时，已经下载的位置记录下来，再次下载时从这个位置继续下载。此时就要涉及到两个知识点了，一个Range的请求头字段（有了这个字段就可以读取服务端该文件的字节范围，从而实现从断点处继续下载）。一个RandomAccessFile类，这个类可以通过seek方法设置指针位置，从而来实现从断点处继续写入文件。
效果图
效果图 .gif
代码实现
1、添加依赖
implementation 'io.reactivex.rxjava2:rxjava:2.1.9'
implementation 'io.reactivex.rxjava2:rxandroid:2.0.2'
implementation 'com.squareup.retrofit2:retrofit:2.3.0'
implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
implementation 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'
2、核心代码
RetrofitHttp
基于Retrofit封装的网络请求类，大致流程就是创建一个RetrofitHttp单例，内部使用Retrofit来实现网络请求，执行下载时，可以先创建一个本app默认的文件下载目录，先拿到需要下载文件的下载内容范围然后执行请求，对响应体再进行文件指定位置的写入，同时反馈下载的进度和用sp存储已下载的字节数。这里注意：RandomAccessFile以rwd模式打开时，如果文件不存在，则会创建这个文件。由于是在IntentService的工作线程里调用下载，所以这里不进行线程切换。
public class RetrofitHttp {
private static final int DEFAULT_TIMEOUT = 10;
private static final String TAG = "RetrofitClient";
private ApiService apiService;
private OkHttpClient okHttpClient;
public static String baseUrl = ApiService.BASE_URL;
private static RetrofitHttp sIsntance;
public static RetrofitHttp getInstance() {
if (sIsntance == null) {
synchronized (RetrofitHttp.class) {
if (sIsntance == null) {
sIsntance = new RetrofitHttp();
}
}
}
return sIsntance;
}
private RetrofitHttp() {
okHttpClient = new OkHttpClient.Builder()
.connectTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS)
.build();
Retrofit retrofit = new Retrofit.Builder()
.client(okHttpClient)
.addConverterFactory(GsonConverterFactory.create())
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.baseUrl(baseUrl)
.build();
apiService = retrofit.create(ApiService.class);
}
public void downloadFile(final long range, final String url, final String fileName, final DownloadCallBack downloadCallback) {
//断点续传时请求的总长度
File file = new File(Constant.APP_ROOT_PATH + Constant.DOWNLOAD_DIR, fileName);
String totalLength = "-";
if (file.exists()) {
totalLength += file.length();
}
apiService.executeDownload("bytes=" + Long.toString(range) + totalLength, url)
.subscribe(new Observer<ResponseBody>() {
@Override
public void onSubscribe(Disposable d) {
}
@Override
public void onNext(ResponseBody responseBody) {
RandomAccessFile randomAccessFile = null;
InputStream inputStream = null;
long total = range;
long responseLength = 0;
try {
byte[] buf = new byte[2048];
int len = 0;
responseLength = responseBody.contentLength();
inputStream = responseBody.byteStream();
String filePath = Constant.APP_ROOT_PATH + Constant.DOWNLOAD_DIR;
File file = new File(filePath, fileName);
File dir = new File(filePath);
if (!dir.exists()) {
dir.mkdirs();
}
randomAccessFile = new RandomAccessFile(file, "rwd");
if (range == 0) {
randomAccessFile.setLength(responseLength);
}
randomAccessFile.seek(range);
int progress = 0;
int lastProgress = 0;
while ((len = inputStream.read(buf)) != -1) {
randomAccessFile.write(buf, 0, len);
total += len;
lastProgress = progress;
progress = (int) (total * 100 / randomAccessFile.length());
if (progress > 0 && progress != lastProgress) {
downloadCallback.onProgress(progress);
}
}
downloadCallback.onCompleted();
} catch (Exception e) {
Log.d(TAG, e.getMessage());
downloadCallback.onError(e.getMessage());
e.printStackTrace();
} finally {
try {
SPDownloadUtil.getInstance().save(url, total);
if (randomAccessFile != null) {
randomAccessFile.close();
}
if (inputStream != null) {
inputStream.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
@Override
public void onError(Throwable e) {
downloadCallback.onError(e.toString());
}
@Override
public void onComplete() {
}
});
}
}
ApiService
请求网络的API接口类，@Streaming注解是为了避免将整个文件读进内存，这是在下载大文件时需要注意的地方。在请求头添加Range就可以实现服务器文件的下载内容范围了。至于BASE_URL，这里演示的是下载腾讯视频，所以就用腾讯的了。
public interface ApiService {
public static final String BASE_URL = "http://dldir1.qq.com";
@Streaming
@GET
Observable<ResponseBody> executeDownload(@Header("Range") String range, @Url() String url);
}
DownloadIntentService
后台执行下载的服务，当下载任务完成时调取安装方法进行安装，服务会自己结束。优先会判断要下载的文件是否已经下载完成，如果已下载完，则直接安装。下载的进度会以通知的形式发送出来，这个是仿支付宝的，下载完成和发生异常时自动取消通知。
public class DownloadIntentService extends IntentService {
private static final String TAG = "DownloadIntentService";
private NotificationManager mNotifyManager;
private String mDownloadFileName;
private Notification mNotification;
public DownloadIntentService() {
super("InitializeService");
}
@Override
protected void onHandleIntent(@Nullable Intent intent) {
String downloadUrl = intent.getExtras().getString("download_url");
final int downloadId = intent.getExtras().getInt("download_id");
mDownloadFileName = intent.getExtras().getString("download_file");
Log.d(TAG, "download_url --" + downloadUrl);
Log.d(TAG, "download_file --" + mDownloadFileName);
final File file = new File(Constant.APP_ROOT_PATH + Constant.DOWNLOAD_DIR + mDownloadFileName);
long range = 0;
int progress = 0;
if (file.exists()) {
range = SPDownloadUtil.getInstance().get(downloadUrl, 0);
progress = (int) (range * 100 / file.length());
if (range == file.length()) {
installApp(file);
return;
}
}
Log.d(TAG, "range = " + range);
final RemoteViews remoteViews = new RemoteViews(getPackageName(), R.layout.notify_download);
remoteViews.setProgressBar(R.id.pb_progress, 100, progress, false);
remoteViews.setTextViewText(R.id.tv_progress, "已下载" + progress + "%");
final NotificationCompat.Builder builder =
new NotificationCompat.Builder(this)
.setContent(remoteViews)
.setTicker("正在下载")
.setSmallIcon(R.mipmap.ic_launcher);
mNotification = builder.build();
mNotifyManager = (NotificationManager)
getSystemService(Context.NOTIFICATION_SERVICE);
mNotifyManager.notify(downloadId, mNotification);
RetrofitHttp.getInstance().downloadFile(range, downloadUrl, mDownloadFileName, new DownloadCallBack() {
@Override
public void onProgress(int progress) {
remoteViews.setProgressBar(R.id.pb_progress, 100, progress, false);
remoteViews.setTextViewText(R.id.tv_progress, "已下载" + progress + "%");
mNotifyManager.notify(downloadId, mNotification);
}
@Override
public void onCompleted() {
Log.d(TAG, "下载完成");
mNotifyManager.cancel(downloadId);
installApp(file);
}
@Override
public void onError(String msg) {
mNotifyManager.cancel(downloadId);
Log.d(TAG, "下载发生错误--" + msg);
}
});
}
private void installApp(File file) {
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.setDataAndType(Uri.fromFile(file), "application/vnd.android.package-archive");
startActivity(intent);
}
}
MainActivity
入口activity，只有一个下载按钮，执行下载前判断下载服务是否已运行
public class MainActivity extends AppCompatActivity {
private static final int DOWNLOADAPK_ID = 10;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView tvDownload = findViewById(R.id.tv_download);
tvDownload.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (isServiceRunning(DownloadIntentService.class.getName())) {
Toast.makeText(MainActivity.this, "正在下载", Toast.LENGTH_SHORT).show();
return;
}
//String downloadUrl = http://sqdd.myapp.com/myapp/qqteam/tim/down/tim.apk;
String downloadUrl = "/qqmi/aphone_p2p/TencentVideo_V6.0.0.14297_848.apk";
Intent intent = new Intent(MainActivity.this, DownloadIntentService.class);
Bundle bundle = new Bundle();
bundle.putString("download_url", downloadUrl);
bundle.putInt("download_id", DOWNLOADAPK_ID);
bundle.putString("download_file", downloadUrl.substring(downloadUrl.lastIndexOf('/') + 1));
intent.putExtras(bundle);
startService(intent);
}
});
}
/**
* 用来判断服务是否运行.
*
* @param className 判断的服务名字
* @return true 在运行 false 不在运行
*/
private boolean isServiceRunning(String className) {
boolean isRunning = false;
ActivityManager activityManager = (ActivityManager) this
.getSystemService(Context.ACTIVITY_SERVICE);
List<ActivityManager.RunningServiceInfo> serviceList = activityManager
.getRunningServices(Integer.MAX_VALUE);
if (!(serviceList.size() > 0)) {
return false;
}
for (int i = 0; i < serviceList.size(); i++) {
if (serviceList.get(i).service.getClassName().equals(className) == true) {
isRunning = true;
break;
}
}
return isRunning;
}
}
SPDownloadUtil
记录下载位置的sp工具类
public class SPDownloadUtil {
private static SharedPreferences mSharedPreferences;
private static SPDownloadUtil instance;
private SPDownloadUtil() {
}
public static SPDownloadUtil getInstance() {
if (mSharedPreferences == null || instance == null) {
synchronized (SPDownloadUtil.class) {
if (mSharedPreferences == null || instance == null) {
instance = new SPDownloadUtil();
mSharedPreferences = MainApplication.getInstance().getSharedPreferences(MainApplication.getInstance().getPackageName() + ".downloadSp", Context.MODE_PRIVATE);
}
}
}
return instance;
}
/**
* 清空数据
*
* @return true 成功
*/
public boolean clear() {
return mSharedPreferences.edit().clear().commit();
}
/**
* 保存数据
*
* @param key 键
* @param value 保存的value
*/
public boolean save(String key, long value) {
return mSharedPreferences.edit().putLong(key, value).commit();
}
/**
* 获取保存的数据
*
* @param key 键
* @param defValue 默认返回的value
* @return value
*/
public long get(String key, long defValue) {
return mSharedPreferences.getLong(key, defValue);
}
}
DownloadCallBack
下载回调接口
public interface DownloadCallBack {
void onProgress(int progress);
void onCompleted();
void onError(String msg);
}
Constant
常量类，定义了根目录和下载文件的存放目录
public class Constant {
public final static String APP_ROOT_PATH = Environment.getExternalStorageDirectory().getAbsolutePath() + "/" + MainApplication.getInstance().getPackageName();
public final static String DOWNLOAD_DIR = "/downlaod/";
}
activity_main.xml
首页布局文件
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
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.damon.download.actvity.MainActivity">
<TextView
android:id="@+id/tv_download"
android:layout_width="80dp"
android:layout_height="40dp"
android:background="@color/colorPrimaryDark"
android:gravity="center"
android:text="下载!"
android:textColor="#ffffff"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
</android.support.constraint.ConstraintLayout>
notify_download.xml
通知布局文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#999999"
android:gravity="center"
android:orientation="horizontal"
android:paddingLeft="15dp"
android:paddingRight="10dp">
<ImageView
android:layout_width="40dp"
android:layout_height="40dp"
android:scaleType="fitCenter"
android:src="@mipmap/ic_launcher"/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="12dp"
android:gravity="center"
android:orientation="vertical">
<TextView
android:id="@+id/tv_title"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="我的应用"
android:textColor="#333333"
android:textSize="16sp"
/>
<ProgressBar
android:id="@+id/pb_progress"
style="@style/Widget.AppCompat.ProgressBar.Horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:max="100"
android:progress="0"
android:progressTint="@color/colorPrimary"
/>
<TextView
android:layout_gravity="left"
android:id="@+id/tv_progress"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="已下载"
android:textColor="#333333"
/>
</LinearLayout>
</LinearLayout>
