Retrofit下載檔案進度
預設情況下,Retrofit在處理結果前會將整個Server Response讀進記憶體,這在JSON或者XML等Response上表現還算良好,但如果是一個非常大的檔案,就可能造成OutofMemory異常。因此我們在進行下載大檔案時需要使用@Streaming註解,使用@Streaming主要作用是把實時下載的位元組就立馬寫入磁碟,而不用把整個檔案讀入記憶體。
final ExecutorService executorService = Executors.newFixedThreadPool(1);
Retrofit.Builder retrofitBuilder = new Retrofit.Builder ()
.addConverterFactory(GsonConverterFactory.create())
.callbackExecutor(executorService) android.os.NetworkOnMainThreadException
.baseUrl("https://raw.githubusercontent.com/");
在Retrofit中callback回撥預設在主執行緒,使用@Streaming必須把callback回撥放在子執行緒中,這裡增加callbackExecutor(executorService) 表示把callback回撥放在核心執行緒為1的執行緒池中執行。
實現進度監聽首先需要建立一個監聽進度的回撥介面:
/**
* progress表示當前已經下載的檔案大小
* total表示檔案大小
* speed表示下載速度
* done表示是否下載完成
* Created by 1013369768 on 2017/10/20.
*/
public interface ProgressListener {
void onProgress(long progress,long total,long speed,boolean done);
}
重寫ResponseBody類的某些方法:
public class ProgressResponseBody extends ResponseBody {
private final ResponseBody responseBody;
private final ProgressListener progressListener;
private BufferedSource bufferedSource;
public ProgressResponseBody(ResponseBody responseBody, ProgressListener progressListener) {
this.responseBody = responseBody;
this.progressListener = progressListener;
}
@Nullable
@Override
public MediaType contentType() {
return responseBody.contentType();
}
@Override
public long contentLength() {
return responseBody.contentLength();
}
@Override
public BufferedSource source() {
if (bufferedSource == null) {
bufferedSource = Okio.buffer(source(responseBody.source()));
}
return bufferedSource;
}
private Source source(Source source) {
return new ForwardingSource(source) {
long totalBytesRead = 0L;
@Override
public long read(Buffer sink, long byteCount) throws IOException {
//當前讀取位元組數
long bytesRead = super.read(sink, byteCount);
//增加當前讀取的位元組數,如果讀取完成了bytesRead會返回-1
totalBytesRead += bytesRead != -1 ? bytesRead : 0;
//回撥,如果contentLength()不知道長度,會返回-1
progressListener.onProgress(totalBytesRead, responseBody.contentLength(),bytesRead,bytesRead == -1);
return bytesRead;
}
};
}
}
在ProgressResponseBody類中,把已經讀取的位元組數totalBytesRead,檔案的總大小responseBody.contentLength(),讀取的速度bytesRead,bytesRead==-1表示讀取到檔案結尾返回true,未讀取到檔案結尾返回false;得到這些數值後傳入到ProgressListener介面,所以這個ProgressListener介面是在子執行緒中執行的。
public class ProgressHelper {
private static ProgressBean progressBean = new ProgressBean();
private static ProgressHandler mProgressHandler;
public static OkHttpClient.Builder addProgress(OkHttpClient.Builder builder){
if (builder == null){
builder = new OkHttpClient.Builder();
}
final ProgressListener progressListener = new ProgressListener() {
//該方法在子執行緒中執行
@Override
public void onProgress(long progress, long total,long speed, boolean done) {
if (mProgressHandler == null){
return;
}
progressBean.setBytesRead(progress);
progressBean.setContentLength(total);
progressBean.setSpeed(speed);
progressBean.setDone(done);
mProgressHandler.sendMessage(progressBean);
}
};
//新增攔截器,自定義ResponseBody,新增下載進度
builder.networkInterceptors().add(new Interceptor() {
@Override
public okhttp3.Response intercept(Chain chain) throws IOException {
okhttp3.Response originalResponse = chain.proceed(chain.request());
return originalResponse.newBuilder().body(
new ProgressResponseBody(originalResponse.body(), progressListener))
.build();
}
});
return builder;
}
public static void setProgressHandler(ProgressHandler progressHandler){
mProgressHandler = progressHandler;
}
}
我們通過為OkhttpClient新增一個攔截器來使用我們自定義的ProgressResponseBody。並且在ProgressHelper類中把long progress, long total,long speed, boolean done引數儲存在progressBean類中。
public class ProgressBean {
private long bytesRead;
private long contentLength;
private long speed;
private boolean done;
public long getSpeed() {
return speed;
}
public void setSpeed(long speed) {
this.speed = speed;
}
public long getBytesRead() {
return bytesRead;
}
public void setBytesRead(long bytesRead) {
this.bytesRead = bytesRead;
}
public long getContentLength() {
return contentLength;
}
public void setContentLength(long contentLength) {
this.contentLength = contentLength;
}
public boolean isDone() {
return done;
}
public void setDone(boolean done) {
this.done = done;
}
}
由於onProgress方法回撥在子執行緒中,所以需要使用handler進行更新UI
public abstract class ProgressHandler {
private static final int DOWNLOAD_PROGRESS = 1;
protected abstract void onProgress(long progress, long total,long speed, boolean done);
private final Handler mHandler = new UIHandler(Looper.getMainLooper(),this);
protected void sendMessage(ProgressBean progressBean){
mHandler.obtainMessage(DOWNLOAD_PROGRESS,progressBean).sendToTarget();
}
static class UIHandler extends Handler{
private final WeakReference<ProgressHandler> mProgressHandler;
public UIHandler(Looper looper,ProgressHandler progressHandler) {
super(looper);
mProgressHandler = new WeakReference<ProgressHandler>(progressHandler);
}
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case DOWNLOAD_PROGRESS:
ProgressHandler progressHandler = mProgressHandler.get();
if(progressHandler!=null) {
ProgressBean progressBean = (ProgressBean)msg.obj;
progressHandler.onProgress(progressBean.getBytesRead(),progressBean.getContentLength(),progressBean.getSpeed(),progressBean.isDone());
}
break;
default:
break;
}
}
}
}
涉及到訊息機制就涉及到Handler類,在Handler的子類中維護一個弱引用指向外部類(用到了static防止記憶體洩露,但是需要呼叫外部類的一個非靜態函式,所以將外部類引用直接由建構函式傳入,在內部通過呼叫該引用的方法去實現),然後將主執行緒的Looper傳入,呼叫父類建構函式,在handleMessage函式中回撥我們的抽象方法。