本文將從多個方面詳細闡述okhttp下載文件的用法和特性。
一、下載文件基礎
在使用okhttp下載文件之前，需要了解以下基礎知識：
下載需要使用okhttp的get方法 使用response.body()獲取下載的文件 需要注意進行線程的切換以下是一個簡單的示例：
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder().url(url).build();
client.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
Log.d(TAG, "onFailure: " + e.getMessage());
}
@Override
public void onResponse(Call call, Response response) throws IOException {
InputStream in = response.body().byteStream();
// 獲取文件名
String fileName = url.substring(url.lastIndexOf("/") + 1);
// 獲取目錄路徑
String path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getAbsolutePath();
File file = new File(path, fileName);
FileOutputStream out = new FileOutputStream(file);
byte[] buffer = new byte[2048];
int len = 0;
while ((len = in.read(buffer)) != -1) {
out.write(buffer, 0, len);
}
out.flush();
out.close();
in.close();
}
});二、下載進度監(jiān)聽
在下載文件過程中，可以通過實現(xiàn)ProgressListener接口實時監(jiān)聽下載進度。以下是代碼示例：
public interface ProgressListener {
void onProgress(long currentBytes, long contentLength, boolean done);
}
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;
}
@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 {
long bytesRead = super.read(sink, byteCount);
totalBytesRead += bytesRead != -1 ? bytesRead : 0;
progressListener.onProgress(totalBytesRead, responseBody.contentLength(), bytesRead == -1);
return bytesRead;
}
};
}
}
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder().url(url).build();
client.newCall(request).enqueue(new Callback() {
//...
@Override
public ResponseBody onResponse(Call call, Response response) throws IOException {
ResponseBody responseBody = response.body();
ProgressResponseBody progressResponseBody = new ProgressResponseBody(responseBody, new ProgressListener() {
@Override
public void onProgress(long currentBytes, long contentLength, boolean done) {
float percent = (float)currentBytes / (float)contentLength;
Log.d(TAG, "progress: " + percent);
}
});
return progressResponseBody;
}
});三、下載速度計算
okhttp可以通過下載速度來評估網絡帶寬并優(yōu)化下載的效率。以下是代碼示例：
public class SpeedMonitorRequestBody extends RequestBody {
private RequestBody requestBody;
private ProgressListener listener;
public SpeedMonitorRequestBody(RequestBody requestBody, ProgressListener listener) {
this.requestBody = requestBody;
this.listener = listener;
}
@Override
public MediaType contentType() {
return requestBody.contentType();
}
@Override
public long contentLength() throws IOException {
return requestBody.contentLength();
}
@Override
public void writeTo(BufferedSink sink) throws IOException {
long startTime = System.currentTimeMillis();
long bytesWritten = 0;
long writeTimeout = 0;
long total = contentLength();
long lastScreenTimestamp = 0;
int screenSpan = 1000;//1秒
Buffer buffer = new Buffer();
requestBody.writeTo(buffer);
BufferedSource source = buffer.clone().inputStream().source();
long readCount = 0;
long lastReadCount = 0;
long lastUpdateTime = 0;
while ((readCount = source.read(sink.buffer(), 2048)) != -1) {
sink.flush();
bytesWritten += readCount;
long curTimestamp = System.currentTimeMillis();
long costTime = curTimestamp - startTime;
long speed = (bytesWritten - lastReadCount) / (curTimestamp - lastUpdateTime + 1) * 1000;
if((curTimestamp - lastScreenTimestamp) > screenSpan)
{
lastScreenTimestamp = curTimestamp;
String downloadSpeed = getSpeedString(speed);
//可以把下載速度設置到UI上
}
lastReadCount = bytesWritten;
lastUpdateTime = curTimestamp;
// update progress
listener.onProgress(bytesWritten, total, bytesWritten == total);
if (writeTimeout != 0) {
source.timeout().timeout(writeTimeout, TimeUnit.MILLISECONDS);
}
}
}
Public String getSpeedString(long speed)
{
if(speed > 1024 *1024)
{
float sizeF = (float)speed / (1024.0f*1024.0f);
DecimalFormat df = new DecimalFormat("#.00");
String fileSizeString = df.format(sizeF);
return fileSizeString + " MB/s";
}
else if(speed > 1024)
{
float sizeF = (float)speed / 1024.0f;
DecimalFormat df = new DecimalFormat("#.00");
String fileSizeString = df.format(sizeF);
return fileSizeString + " KB/s";
}
else
{
return Long.toString(speed) + " B/s";
}
}
}
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url(url)
.post(new SpeedMonitorRequestBody(RequestBody.create(MediaType.parse("application/octet-stream"), bytes),
new ProgressListener() {
@Override
public void onProgress(long currentBytes, long totalBytes, boolean done) {
Log.d(TAG, currentBytes + "/" + totalBytes);
}
})
).build();
client.newCall(request).enqueue(new Callback() {
//...
});四、斷點續(xù)傳
okhttp可以通過在請求頭中添加range來實現(xiàn)斷點續(xù)傳。以下是代碼示例：
OkHttpClient client = new OkHttpClient();
Request.Builder builder = new Request.Builder().url(url);
File file = new File("文件路徑");
if (file.exists() && file.length() > 0) {
builder.addHeader("RANGE", "bytes=" + file.length() + "-");
}
Request request = builder.build();
client.newCall(request).enqueue(new Callback() {
//...
@Override
public void onResponse(Call call, Response response) throws IOException {
if (response.code() == 206) {
//斷點續(xù)傳
} else {
//重新下載
}
}
});總結
本文詳細闡述了okhttp下載文件的用法和特性，包括下載基礎、下載進度監(jiān)聽、下載速度計算和斷點續(xù)傳。開發(fā)者可以根據實際需求選取相應的功能實現(xiàn)。總的來說，okhttp下載文件具有簡單易用、下載速度快、資源占用低等優(yōu)點，是一個非常實用的網絡請求框架。
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