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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.android.systemupdatersample.util;
import android.util.Log;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.net.URLConnection;
/**
* Downloads chunk of a file from given url using {@code offset} and {@code size},
* and saves to a given location.
*
* In real-life application this helper class should download from HTTP Server,
* but in this sample app it will only download from a local file.
*/
public final class FileDownloader {
private String mUrl;
private long mOffset;
private long mSize;
private File mOut;
public FileDownloader(String url, long offset, long size, File out) {
this.mUrl = url;
this.mOffset = offset;
this.mSize = size;
this.mOut = out;
}
/**
* Downloads the file with given offset and size.
*/
public void download() throws IOException {
Log.d("FileDownloader", "downloading " + mOut.getName()
+ " from " + mUrl
+ " to " + mOut.getAbsolutePath());
URL url = new URL(mUrl);
URLConnection connection = url.openConnection();
connection.connect();
// download the file
try (InputStream input = connection.getInputStream()) {
try (OutputStream output = new FileOutputStream(mOut)) {
long skipped = input.skip(mOffset);
if (skipped != mOffset) {
throw new IOException("Can't download file "
+ mUrl
+ " with given offset "
+ mOffset);
}
byte[] data = new byte[4096];
long total = 0;
while (total < mSize) {
int needToRead = (int) Math.min(4096, mSize - total);
int count = input.read(data, 0, needToRead);
if (count <= 0) {
break;
}
output.write(data, 0, count);
total += count;
}
if (total != mSize) {
throw new IOException("Can't download file "
+ mUrl
+ " with given size "
+ mSize);
}
}
}
}
}
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