Download music from VK

VKDownload.java

import com.sun.istack.internal.Nullable;

import org.apache.commons.lang.StringUtils;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.zip.GZIPInputStream;

public class MainClass
{
	//retrieve access_token here https://vk.com/app35569
	public static final String VK_ACCESS_TOKEN = "";

	//leave empty for self
	public static final String VK_TARGET_USER_ID  = "";

	//set audio id, where need to stop
	public static final long   VK_TARGET_AUDIO_ID = 0;
	public static final int    VK_PAGE_SIZE       = 50;

	public long mOverallBytesLoaded = 0;

	//Mac OS path setup
	public static final String MUSIC_DEST_FOLDER  = System.getProperty("user.home") + "/Desktop/music_result";

	public static void main(String[] args)
	{
		new MainClass().run();
	}

	public static final String VK_API_URL = "https://api.vk.com/method";

	public String joinParams(Map<String, String> params)
	{
		ArrayList<String> pairs = new ArrayList<String>();
		for (String key : params.keySet())
		{
			pairs.add(key + "=" + params.get(key));
		}

		return StringUtils.join(pairs, "&");
	}

	public String constructUrlForPageWithOffset(int offset)
	{
		Map<String, String> params = new HashMap<String, String>();
		params.put("count", "" + VK_PAGE_SIZE);
		params.put("offset", "" + offset);
		params.put("user_id", VK_TARGET_USER_ID);
		params.put("access_token", VK_ACCESS_TOKEN);
		params.put("v", "5.35");

		return String.format(Locale.getDefault(), "%s/%s?%s", VK_API_URL, "audio.get",
		                     joinParams(params));
	}

	@Nullable
	public String loadPage(String pageUrl) {
		try
		{
			URLConnection connection = new URL(pageUrl).openConnection();
			connection.setRequestProperty("Accept-Encoding", "gzip");

			InputStream input = connection.getInputStream();
			if ("gzip".equals(connection.getContentEncoding())) {
				input = new GZIPInputStream(input);
			}

			BufferedReader reader = new BufferedReader(new InputStreamReader(input));
			StringBuilder builder = new StringBuilder("");
			String inputLine;
			while ((inputLine = reader.readLine()) != null)
			{
				builder.append(inputLine);
			}
			reader.close();
			return builder.toString();
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
		return null;
	}


	public boolean saveContentAtUrlToFile(String contentUrl, File targetFile) {
		try
		{
			URLConnection connection = new URL(contentUrl).openConnection();
			InputStream inputStream = connection.getInputStream();
			FileOutputStream outputStream = new FileOutputStream(targetFile);
			int contentLen = connection.getContentLength();

			int maxLevel = 20, level = 1;
			int BUFFER_SIZE = contentLen / maxLevel;
			int bytesRead;
			int totalBytesRead = 0;
			byte[] buffer = new byte[BUFFER_SIZE];
			System.out.println("Start: " + contentUrl);
			System.out.print("0.");
			while ((bytesRead = inputStream.read(buffer)) != -1) {
				outputStream.write(buffer, 0, bytesRead);
				totalBytesRead += bytesRead;
				if (totalBytesRead > BUFFER_SIZE * level)
				{
					System.out.print(".");
					level++;
				}
			}
			mOverallBytesLoaded += totalBytesRead;
			System.out.println("Done (" + humanReadableByteCount(totalBytesRead, true) + ")");
			inputStream.close();
			outputStream.close();
			return true;
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
		return false;
	}

	public static String humanReadableByteCount(long bytes, boolean si) {
		int unit = si ? 1000 : 1024;
		if (bytes < unit) return bytes + " B";
		int exp = (int) (Math.log(bytes) / Math.log(unit));
		String pre = (si ? "kMGTPE" : "KMGTPE").charAt(exp-1) + (si ? "" : "i");
		return String.format("%.1f %sB", bytes / Math.pow(unit, exp), pre);
	}

	public void run() {
		int currentOffset = 0;
		int totalSongsLoaded = 0;
		boolean canLoadNextPage = true;
		JSONParser parser=new JSONParser();
		File targetDir = new File(MUSIC_DEST_FOLDER);
		boolean b = targetDir.mkdirs();
		if (b) {
			System.out.println("Directory prepared");
		}
		do {
			System.out.println("Loading page for user: " + VK_TARGET_USER_ID + " with offset: " + currentOffset);
			String request = constructUrlForPageWithOffset(currentOffset);
			String rawJson = loadPage(request);
			if (rawJson == null) {
				System.out.println("Can't load request: " + request);
				break;
			}

			try
			{
				JSONObject wholeResponse = (JSONObject)parser.parse(rawJson);

				Object response = wholeResponse.get("response");
				if (response == null) {
					System.out.println("Failed to parse response: " + rawJson);
					break;
				}
				JSONObject responseData = (JSONObject)response;
				JSONArray items = (JSONArray)responseData.get("items");
				if (items == null) {
					System.out.println("Failed to receive items: " + rawJson);
					break;
				}

				int size = items.size();
				for (Object item : items) {
					VKAudio audio = new VKAudio((JSONObject) item);

					canLoadNextPage = VK_TARGET_AUDIO_ID != audio.id;

					String fileName = String.format("%s - %s.mp3", audio.artist, audio.title);
					File targetFile = new File(targetDir + File.separator + fileName);

					System.out.println("Downloading: " + audio.toString());
					if (!saveContentAtUrlToFile(audio.url, targetFile)) {
						System.out.println("Failed to load audio: " + audio.toString());
					} else {
						totalSongsLoaded++;
					}

					System.out.println();

					if (!canLoadNextPage) {
						System.out.println("Target song reached");
						break;
					}

				}
				currentOffset += size;

			}
			catch (ParseException e)
			{
				e.printStackTrace();
			}
		} while (canLoadNextPage);

		System.out.println("Finished loading. Songs loaded: " + totalSongsLoaded + ". Bytes loaded: " + humanReadableByteCount(mOverallBytesLoaded, true));
	}

	public static class VKAudio {
		public Long id;
		public String artist;
		public String title;
		public String url;

		public VKAudio(JSONObject data)
		{
			this.id = (Long) data.get("id");
			this.artist = ((String) data.get("artist")).trim();
			this.title  = ((String) data.get("title")).trim();
			this.url = (String) data.get("url");
		}

		@Override
		public String toString()
		{
			return String.format("Audio(id %d): %s - %s", id, artist, title);
		}
	}
}