Http download using Java NIO FileChannel

Carvia Tech | December 04, 2019 | 1 min read | 115 views


Java’s Channel should always be preferred for IO related stuff because Channel can utilize OS specific optimization while dealing with the files. An input stream can easily be converted to a FileChannel using Channels.newChannel() static factory method.

RealHttpDownloader
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URI;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.EnumSet;

public class HttpDownloader {

    public File download(URI uri, String fileName) throws IOException {
        Path path = Paths.get(fileName);
        long totalBytesRead = 0L;
        HttpURLConnection con = (HttpURLConnection) uri.resolve(fileName).toURL().openConnection();
        con.setReadTimeout(10000);
        con.setConnectTimeout(10000);
        try (ReadableByteChannel rbc = Channels.newChannel(con.getInputStream());
             FileChannel fileChannel = FileChannel.open(path, EnumSet.of(StandardOpenOption.CREATE, StandardOpenOption.WRITE));) {
            totalBytesRead = fileChannel.transferFrom(rbc, 0, 1 << 22); // download file with max size 4MB
            System.out.println("totalBytesRead = " + totalBytesRead);
            fileChannel.close();
            rbc.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        return path.toFile();
    }
}

FileChannel utilizes OS specific optimization and hence should provide better performance in general compared to any buffered streams.


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