详解Android使用OKHttp3实现下载(断点续传、显示进度)

2019-12-12 03:50:46

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OKHttp3是如今非常流行的Android网络请求框架,那么如何利用Android实现断点续传呢,今天写了个Demo尝试了一下,感觉还是有点意思

准备阶段

我们会用到OKHttp3来做网络请求,使用RxJava来实现线程的切换,并且开启Java8来启用Lambda表达式,毕竟RxJava实现线程切换非常方便,而且数据流的形式也非常舒服,同时Lambda和RxJava配合食用味道更佳

打开我们的app Module下的build.gradle,代码如下

apply plugin: 'com.android.application'  android {   compileSdkVersion 24   buildToolsVersion "24.0.3"    defaultConfig {     applicationId "com.lanou3g.downdemo"     minSdkVersion 15     targetSdkVersion 24     versionCode 1     versionName "1.0"     testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"     //为了开启Java8     jackOptions{       enabled true;     }   }   buildTypes {     release {       minifyEnabled false       proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'     }   }    //开启Java1.8 能够使用lambda表达式   compileOptions{     sourceCompatibility JavaVersion.VERSION_1_8     targetCompatibility JavaVersion.VERSION_1_8   } }  dependencies {   compile fileTree(dir: 'libs', include: ['*.jar'])   androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {     exclude group: 'com.android.support', module: 'support-annotations'   })   compile 'com.android.support:appcompat-v7:24.1.1'   testCompile 'junit:junit:4.12'    //OKHttp   compile 'com.squareup.okhttp3:okhttp:3.6.0'   //RxJava和RxAndroid 用来做线程切换的   compile 'io.reactivex.rxjava2:rxandroid:2.0.1'   compile 'io.reactivex.rxjava2:rxjava:2.0.1' }

OKHttp和RxJava,RxAndroid使用的都是最新的版本,并且配置开启了Java8

布局文件

接着开始书写布局文件

<?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:paddingBottom="@dimen/activity_vertical_margin"   android:paddingLeft="@dimen/activity_horizontal_margin"   android:paddingRight="@dimen/activity_horizontal_margin"   android:paddingTop="@dimen/activity_vertical_margin"   android:orientation="vertical"   tools:context="com.lanou3g.downdemo.MainActivity">    <LinearLayout     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:orientation="horizontal">     <ProgressBar       android:id="@+id/main_progress1"       android:layout_width="0dp"       android:layout_weight="1"       android:layout_height="match_parent"       style="@style/Widget.AppCompat.ProgressBar.Horizontal" />     <Button       android:id="@+id/main_btn_down1"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:text="下载1"/>     <Button       android:id="@+id/main_btn_cancel1"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:text="取消1"/>   </LinearLayout>   <LinearLayout     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:orientation="horizontal">     <ProgressBar       android:id="@+id/main_progress2"       android:layout_width="0dp"       android:layout_weight="1"       android:layout_height="match_parent"       style="@style/Widget.AppCompat.ProgressBar.Horizontal" />     <Button       android:id="@+id/main_btn_down2"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:text="下载2"/>     <Button       android:id="@+id/main_btn_cancel2"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:text="取消2"/>   </LinearLayout>   <LinearLayout     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:orientation="horizontal">     <ProgressBar       android:id="@+id/main_progress3"       android:layout_width="0dp"       android:layout_weight="1"       android:layout_height="match_parent"       style="@style/Widget.AppCompat.ProgressBar.Horizontal" />     <Button       android:id="@+id/main_btn_down3"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:text="下载3"/>     <Button       android:id="@+id/main_btn_cancel3"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:text="取消3"/>   </LinearLayout> </LinearLayout>

大概是这个样子的

3个ProgressBar就是为了显示进度的,每个ProgressBar对应2个Button,一个是开始下载,一个是暂停(取消)下载,这里需要说明的是,对下载来说暂停和取消没有什么区别,除非当取消的时候,会顺带把临时文件都删除了,在本例里是不区分他俩的.

Application

我们这里需要用到一些文件路径,有一个全局Context会比较方便, 而Application也是Context的子类,使用它的是最方便的,所以我们写一个类来继承Application

package com.lanou3g.downdemo;  import android.app.Application; import android.content.Context;  /**  * Created by 陈丰尧 on 2017/2/2.  */  public class MyApp extends Application {   public static Context sContext;//全局的Context对象    @Override   public void onCreate() {     super.onCreate();     sContext = this;   } }

可以看到,我们就是要获得一个全局的Context对象的

我们在AndroidManifest中注册一下我们的Application,同时再把我们所需要的权限给上

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"   package="com.lanou3g.downdemo">      <!--网络权限-->   <uses-permission android:name="android.permission.INTERNET"/>    <application     android:allowBackup="true"     android:icon="@mipmap/ic_launcher"     android:label="@string/app_name"     android:supportsRtl="true"     android:name=".MyApp"     android:theme="@style/AppTheme">     <activity android:name=".MainActivity">       <intent-filter>         <action android:name="android.intent.action.MAIN" />          <category android:name="android.intent.category.LAUNCHER" />       </intent-filter>     </activity>   </application>  </manifest>

我们只需要一个网络权限,在application标签下,添加name属性,来指向我们的Application

DownloadManager

接下来是核心代码了,就是我们的DownloadManager,先上代码

package com.lanou3g.downdemo;  import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.util.HashMap; import java.util.concurrent.atomic.AtomicReference;  import io.reactivex.Observable; import io.reactivex.ObservableEmitter; import io.reactivex.ObservableOnSubscribe; import io.reactivex.android.schedulers.AndroidSchedulers; import io.reactivex.schedulers.Schedulers; import okhttp3.Call; import okhttp3.OkHttpClient; import okhttp3.Request; import okhttp3.Response;  /**  * Created by 陈丰尧 on 2017/2/2.  */  public class DownloadManager {    private static final AtomicReference<DownloadManager> INSTANCE = new AtomicReference<>();   private HashMap<String, Call> downCalls;//用来存放各个下载的请求   private OkHttpClient mClient;//OKHttpClient;    //获得一个单例类   public static DownloadManager getInstance() {     for (; ; ) {       DownloadManager current = INSTANCE.get();       if (current != null) {         return current;       }       current = new DownloadManager();       if (INSTANCE.compareAndSet(null, current)) {         return current;       }     }   }    private DownloadManager() {     downCalls = new HashMap<>();     mClient = new OkHttpClient.Builder().build();   }    /**    * 开始下载    *    * @param url       下载请求的网址    * @param downLoadObserver 用来回调的接口    */   public void download(String url, DownLoadObserver downLoadObserver) {     Observable.just(url)         .filter(s -> !downCalls.containsKey(s))//call的map已经有了,就证明正在下载,则这次不下载         .flatMap(s -> Observable.just(createDownInfo(s)))         .map(this::getRealFileName)//检测本地文件夹,生成新的文件名         .flatMap(downloadInfo -> Observable.create(new DownloadSubscribe(downloadInfo)))//下载         .observeOn(AndroidSchedulers.mainThread())//在主线程回调         .subscribeOn(Schedulers.io())//在子线程执行         .subscribe(downLoadObserver);//添加观察者    }    public void cancel(String url) {     Call call = downCalls.get(url);     if (call != null) {       call.cancel();//取消     }     downCalls.remove(url);   }    /**    * 创建DownInfo    *    * @param url 请求网址    * @return DownInfo    */   private DownloadInfo createDownInfo(String url) {     DownloadInfo downloadInfo = new DownloadInfo(url);     long contentLength = getContentLength(url);//获得文件大小     downloadInfo.setTotal(contentLength);     String fileName = url.substring(url.lastIndexOf("/"));     downloadInfo.setFileName(fileName);     return downloadInfo;   }    private DownloadInfo getRealFileName(DownloadInfo downloadInfo) {     String fileName = downloadInfo.getFileName();     long downloadLength = 0, contentLength = downloadInfo.getTotal();     File file = new File(MyApp.sContext.getFilesDir(), fileName);     if (file.exists()) {       //找到了文件,代表已经下载过,则获取其长度       downloadLength = file.length();     }     //之前下载过,需要重新来一个文件     int i = 1;     while (downloadLength >= contentLength) {       int dotIndex = fileName.lastIndexOf(".");       String fileNameOther;       if (dotIndex == -1) {         fileNameOther = fileName + "(" + i + ")";       } else {         fileNameOther = fileName.substring(0, dotIndex)             + "(" + i + ")" + fileName.substring(dotIndex);       }       File newFile = new File(MyApp.sContext.getFilesDir(), fileNameOther);       file = newFile;       downloadLength = newFile.length();       i++;     }     //设置改变过的文件名/大小     downloadInfo.setProgress(downloadLength);     downloadInfo.setFileName(file.getName());     return downloadInfo;   }    private class DownloadSubscribe implements ObservableOnSubscribe<DownloadInfo> {     private DownloadInfo downloadInfo;      public DownloadSubscribe(DownloadInfo downloadInfo) {       this.downloadInfo = downloadInfo;     }      @Override     public void subscribe(ObservableEmitter<DownloadInfo> e) throws Exception {       String url = downloadInfo.getUrl();       long downloadLength = downloadInfo.getProgress();//已经下载好的长度       long contentLength = downloadInfo.getTotal();//文件的总长度       //初始进度信息       e.onNext(downloadInfo);        Request request = new Request.Builder()           //确定下载的范围,添加此头,则服务器就可以跳过已经下载好的部分           .addHeader("RANGE", "bytes=" + downloadLength + "-" + contentLength)           .url(url)           .build();       Call call = mClient.newCall(request);       downCalls.put(url, call);//把这个添加到call里,方便取消       Response response = call.execute();        File file = new File(MyApp.sContext.getFilesDir(), downloadInfo.getFileName());       InputStream is = null;       FileOutputStream fileOutputStream = null;       try {         is = response.body().byteStream();         fileOutputStream = new FileOutputStream(file, true);         byte[] buffer = new byte[2048];//缓冲数组2kB         int len;         while ((len = is.read(buffer)) != -1) {           fileOutputStream.write(buffer, 0, len);           downloadLength += len;           downloadInfo.setProgress(downloadLength);           e.onNext(downloadInfo);         }         fileOutputStream.flush();         downCalls.remove(url);       } finally {         //关闭IO流         IOUtil.closeAll(is, fileOutputStream);        }       e.onComplete();//完成     }   }    /**    * 获取下载长度    *    * @param downloadUrl    * @return    */   private long getContentLength(String downloadUrl) {     Request request = new Request.Builder()         .url(downloadUrl)         .build();     try {       Response response = mClient.newCall(request).execute();       if (response != null && response.isSuccessful()) {         long contentLength = response.body().contentLength();         response.close();         return contentLength == 0 ? DownloadInfo.TOTAL_ERROR : contentLength;       }     } catch (IOException e) {       e.printStackTrace();     }     return DownloadInfo.TOTAL_ERROR;   }   }

代码稍微有点长,关键部位我都加了注释了,我们挑关键地方看看

首先我们这个类是单例类,我们下载只需要一个OKHttpClient就足够了,所以我们让构造方法私有,而单例类的获取实例方法就是这个getInstance();当然大家用别的方式实现单例也可以的,然后我们在构造方法里初始化我们的HttpClient,并且初始化一个HashMap,用来放所有的网络请求的,这样当我们取消下载的时候,就可以找到url对应的网络请求然后把它取消掉就可以了

接下来就是核心的download方法了,首先是参数,第一个参数url不用多说,就是请求的网址,第二个参数是一个Observer对象,因为我们使用的是RxJava,并且没有特别多复杂的方法,所以就没单独写接口,而是谢了一个Observer对象来作为回调,接下来是DownLoadObserver的代码

package com.lanou3g.downdemo;  import io.reactivex.Observer; import io.reactivex.disposables.Disposable;  /**  * Created by 陈丰尧 on 2017/2/2.  */  public abstract class DownLoadObserver implements Observer<DownloadInfo> {   protected Disposable d;//可以用于取消注册的监听者   protected DownloadInfo downloadInfo;   @Override   public void onSubscribe(Disposable d) {     this.d = d;   }    @Override   public void onNext(DownloadInfo downloadInfo) {     this.downloadInfo = downloadInfo;   }    @Override   public void onError(Throwable e) {     e.printStackTrace();   }   }

在RxJava2中这个Observer有点变化,当注册观察者的时候,会调用onSubscribe方法,而该方法参数就是用来取消注册的,这样的改动可以更灵活的有监听者来取消监听了,我们的进度信息会一直的传送的onNext方法里,这里将下载所需要的内容封了一个类叫DownloadInfo

package com.lanou3g.downdemo;  /**  * Created by 陈丰尧 on 2017/2/2.  * 下载信息  */  public class DownloadInfo {   public static final long TOTAL_ERROR = -1;//获取进度失败   private String url;   private long total;   private long progress;   private String fileName;      public DownloadInfo(String url) {     this.url = url;   }    public String getUrl() {     return url;   }    public String getFileName() {     return fileName;   }    public void setFileName(String fileName) {     this.fileName = fileName;   }    public long getTotal() {     return total;   }    public void setTotal(long total) {     this.total = total;   }    public long getProgress() {     return progress;   }    public void setProgress(long progress) {     this.progress = progress;   } }

这个类就是一些基本信息,total就是需要下载的文件的总大小,而progress就是当前下载的进度了,这样就可以计算出下载的进度信息了

接着看DownloadManager的download方法,首先通过url生成一个Observable对象,然后通过filter操作符过滤一下,如果当前正在下载这个url对应的内容,那么就不下载它,

接下来调用createDownInfo重新生成Observable对象,这里应该用map也是可以的,createDownInfo这个方法里会调用getContentLength来获取服务器上的文件大小,可以看一下这个方法的代码,

/**   * 获取下载长度   *   * @param downloadUrl   * @return   */   private long getContentLength(String downloadUrl) {     Request request = new Request.Builder()         .url(downloadUrl)         .build();     try {       Response response = mClient.newCall(request).execute();       if (response != null && response.isSuccessful()) {         long contentLength = response.body().contentLength();         response.close();         return contentLength == 0 ? DownloadInfo.TOTAL_ERROR : contentLength;       }     } catch (IOException e) {       e.printStackTrace();     }     return DownloadInfo.TOTAL_ERROR;   }

可以看到,其实就是在通过OK进行了一次网络请求,并且从返回的头信息里拿到文件的大小信息,一般这个信息都是可以拿到的,除非下载网址不是直接指向资源文件的,而是自己手写的Servlet,那就得跟后台人员沟通好了.注意,这次网络请求并没有真正的去下载文件,而是请求个大小就结束了,具体原因会在后面真正请求数据的时候解释

接着download方法

获取完文件大小后,就可以去硬盘里找文件了,这里调用了getRealFileName方法

private DownloadInfo getRealFileName(DownloadInfo downloadInfo) {     String fileName = downloadInfo.getFileName();     long downloadLength = 0, contentLength = downloadInfo.getTotal();     File file = new File(MyApp.sContext.getFilesDir(), fileName);     if (file.exists()) {       //找到了文件,代表已经下载过,则获取其长度       downloadLength = file.length();     }     //之前下载过,需要重新来一个文件     int i = 1;     while (downloadLength >= contentLength) {       int dotIndex = fileName.lastIndexOf(".");       String fileNameOther;       if (dotIndex == -1) {         fileNameOther = fileName + "(" + i + ")";       } else {         fileNameOther = fileName.substring(0, dotIndex)             + "(" + i + ")" + fileName.substring(dotIndex);       }       File newFile = new File(MyApp.sContext.getFilesDir(), fileNameOther);       file = newFile;       downloadLength = newFile.length();       i++;     }     //设置改变过的文件名/大小     downloadInfo.setProgress(downloadLength);     downloadInfo.setFileName(file.getName());     return downloadInfo;   }

这个方法就是看本地是否有已经下载过的文件,如果有,再判断一次本地文件的大小和服务器上数据的大小,如果是一样的,证明之前下载全了,就再成一个带(1)这样的文件,而如果本地文件大小比服务器上的小的话,那么证明之前下载了一半断掉了,那么就把进度信息保存上,并把文件名也存上,看完了再回到download方法

之后就开始真正的网络请求了,这里写了一个内部类来实现ObservableOnSubscribe接口,这个接口也是RxJava2的,东西和之前一样,好像只改了名字,看一下代码

private class DownloadSubscribe implements ObservableOnSubscribe<DownloadInfo> {     private DownloadInfo downloadInfo;      public DownloadSubscribe(DownloadInfo downloadInfo) {       this.downloadInfo = downloadInfo;     }      @Override     public void subscribe(ObservableEmitter<DownloadInfo> e) throws Exception {       String url = downloadInfo.getUrl();       long downloadLength = downloadInfo.getProgress();//已经下载好的长度       long contentLength = downloadInfo.getTotal();//文件的总长度       //初始进度信息       e.onNext(downloadInfo);        Request request = new Request.Builder()           //确定下载的范围,添加此头,则服务器就可以跳过已经下载好的部分           .addHeader("RANGE", "bytes=" + downloadLength + "-" + contentLength)           .url(url)           .build();       Call call = mClient.newCall(request);       downCalls.put(url, call);//把这个添加到call里,方便取消       Response response = call.execute();        File file = new File(MyApp.sContext.getFilesDir(), downloadInfo.getFileName());       InputStream is = null;       FileOutputStream fileOutputStream = null;       try {         is = response.body().byteStream();         fileOutputStream = new FileOutputStream(file, true);         byte[] buffer = new byte[2048];//缓冲数组2kB         int len;         while ((len = is.read(buffer)) != -1) {           fileOutputStream.write(buffer, 0, len);           downloadLength += len;           downloadInfo.setProgress(downloadLength);           e.onNext(downloadInfo);         }         fileOutputStream.flush();         downCalls.remove(url);       } finally {         //关闭IO流         IOUtil.closeAll(is, fileOutputStream);        }       e.onComplete();//完成     }   }

主要看subscribe方法

首先拿到url,当前进度信息和文件的总大小,然后开始网络请求,注意这次网络请求的时候需要添加一条头信息

.addHeader("RANGE", "bytes=" + downloadLength + "-" + contentLength)

这条头信息的意思是下载的范围是多少,downloadLength是从哪开始下载,contentLength是下载到哪,当要断点续传的话必须添加这个头,让输入流跳过多少字节的形式是不行的,所以我们要想能成功的添加这条信息那么就必须对这个url请求2次,一次拿到总长度,来方便判断本地是否有下载一半的数据,第二次才开始真正的读流进行网络请求,我还想了一种思路,当文件没有下载完成的时候添加一个自定义的后缀,当下载完成再把这个后缀取消了,应该就不需要请求两次了.

接下来就是正常的网络请求,向本地写文件了,而写文件到本地这,网上大多用的是RandomAccessFile这个类,但是如果不涉及到多个部分拼接的话是没必要的,直接使用输出流就好了,在输出流的构造方法上添加一个true的参数,代表是在原文件的后面添加数据即可,而在循环里,不断的调用onNext方法发送进度信息,当写完了之后别忘了关流,同时把call对象从hashMap中移除了.这里写了一个IOUtil来关流

package com.lanou3g.downdemo;  import java.io.Closeable; import java.io.IOException;  /**  * Created by 陈丰尧 on 2017/2/2.  */  public class IOUtil {   public static void closeAll(Closeable... closeables){     if(closeables == null){       return;     }     for (Closeable closeable : closeables) {       if(closeable!=null){         try {           closeable.close();         } catch (IOException e) {           e.printStackTrace();         }       }     }   } }

其实就是挨一个判断是否为空,并关闭罢了

这样download方法就完成了,剩下的就是切换线程,注册观察者了

MainActivity

最后是aty的代码

package com.lanou3g.downdemo;  import android.net.Uri; import android.support.annotation.IdRes; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.ProgressBar; import android.widget.Toast;  public class MainActivity extends AppCompatActivity implements View.OnClickListener {   private Button downloadBtn1, downloadBtn2, downloadBtn3;   private Button cancelBtn1, cancelBtn2, cancelBtn3;   private ProgressBar progress1, progress2, progress3;   private String url1 = "http://192.168.31.169:8080/out/dream.flac";   private String url2 = "http://192.168.31.169:8080/out/music.mp3";   private String url3 = "http://192.168.31.169:8080/out/code.zip";   @Override   protected void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     setContentView(R.layout.activity_main);      downloadBtn1 = bindView(R.id.main_btn_down1);     downloadBtn2 = bindView(R.id.main_btn_down2);     downloadBtn3 = bindView(R.id.main_btn_down3);      cancelBtn1 = bindView(R.id.main_btn_cancel1);     cancelBtn2 = bindView(R.id.main_btn_cancel2);     cancelBtn3 = bindView(R.id.main_btn_cancel3);      progress1 = bindView(R.id.main_progress1);     progress2 = bindView(R.id.main_progress2);     progress3 = bindView(R.id.main_progress3);      downloadBtn1.setOnClickListener(this);     downloadBtn2.setOnClickListener(this);     downloadBtn3.setOnClickListener(this);      cancelBtn1.setOnClickListener(this);     cancelBtn2.setOnClickListener(this);     cancelBtn3.setOnClickListener(this);   }    @Override   public void onClick(View v) {     switch (v.getId()) {       case R.id.main_btn_down1:         DownloadManager.getInstance().download(url1, new DownLoadObserver() {           @Override           public void onNext(DownloadInfo value) {             super.onNext(value);             progress1.setMax((int) value.getTotal());             progress1.setProgress((int) value.getProgress());           }            @Override           public void onComplete() {             if(downloadInfo != null){               Toast.makeText(MainActivity.this,                   downloadInfo.getFileName() + "-DownloadComplete",                   Toast.LENGTH_SHORT).show();             }           }         });         break;       case R.id.main_btn_down2:         DownloadManager.getInstance().download(url2, new DownLoadObserver() {           @Override           public void onNext(DownloadInfo value) {             super.onNext(value);             progress2.setMax((int) value.getTotal());             progress2.setProgress((int) value.getProgress());           }            @Override           public void onComplete() {             if(downloadInfo != null){               Toast.makeText(MainActivity.this,                   downloadInfo.getFileName() + Uri.encode("下载完成"),                   Toast.LENGTH_SHORT).show();             }           }         });         break;       case R.id.main_btn_down3:         DownloadManager.getInstance().download(url3, new DownLoadObserver() {           @Override           public void onNext(DownloadInfo value) {             super.onNext(value);             progress3.setMax((int) value.getTotal());             progress3.setProgress((int) value.getProgress());           }            @Override           public void onComplete() {             if(downloadInfo != null){               Toast.makeText(MainActivity.this,                   downloadInfo.getFileName() + "下载完成",                   Toast.LENGTH_SHORT).show();             }           }         });         break;       case R.id.main_btn_cancel1:         DownloadManager.getInstance().cancel(url1);         break;       case R.id.main_btn_cancel2:         DownloadManager.getInstance().cancel(url2);         break;       case R.id.main_btn_cancel3:         DownloadManager.getInstance().cancel(url3);         break;     }   }      private <T extends View> T bindView(@IdRes int id){     View viewById = findViewById(id);     return (T) viewById;   } }

Activity里没什么了,就是注册监听,开始下载,取消下载这些了,下面我们来看看效果吧

运行效果