How can I download and save a file from the Internet using Java?

java

file-transfer

nio

try-with-resources

byNikita Barsukov·Aug 29, 2024

Jump right into the download action with Java NIO for fuss-free file downloading:

import java.net.URL;
import java.nio.file.Paths;
import java.nio.file.Files;

public class QuickFileDownloader {
    public static void main(String[] args) throws IOException {
        URL downloadUrl = new URL("http://example.com/file.zip");  // Hello beautiful file I am coming for you!
        Files.copy(downloadUrl.openStream(), Paths.get("localfile.zip"));  // And... you're now mine!
    }
}

This code snippet allows you to snatch files in the blink of an eye by calling Files.copy() to download the data directly to a file.

Stingy with dependencies? No worries!

For the folks who like to keep the number of dependencies low or just hate dealing with pesky libraries, stay tuned as we explore these neat Java NIO and utility tricks.

Byte Channel: Rapid fire transfer

With Java NIO channels, transferring bytes is like firing rapid rounds of a laser gun! The code below uses the transferFrom() method to pull off a swift and efficient transfer.

import java.net.URL;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.FileChannel;
import java.nio.file.StandardOpenOption;
import java.io.IOException;

public class EnhancedFileDownloader {
    public static void downloadFile(String fileURL, Path outputFile) throws IOException {
        try (ReadableByteChannel readableByteChannel = Channels.newChannel(new URL(fileURL).openStream());
             FileChannel fileChannel = FileChannel.open(outputFile, StandardOpenOption.WRITE, StandardOpenOption.CREATE)) {
            
            long transferred = 0L;
            long position = 0L;
            long count = Long.MAX_VALUE;
            // fingers crossed! Will transfer bandwidth allow me to do this?
            while (transferred < count) {
                transferred += fileChannel.transferFrom(readableByteChannel, position, count);
                position += transferred;  // Hey FileChannel, how about those bytes, huh?
            }
        }
    }

    public static void main(String[] args) throws IOException {
        downloadFile("http://example.com/bigfile.iso", Paths.get("localbigfile.iso"));  // Nerd alert: Who has big .iso files these days?
    }
}

The savior try-with-resources

Here's where try-with-resources comes into play, making sure the streams are properly closed, preventing any unexpected leaks - remember, you're also saving the planet!


import java.net.URL;
import java.io.InputStream;
import java.io.FileOutputStream;

public class TryWithResourcesDownloader {
    public static void main(String[] args) {
        try (InputStream in = new URL("http://example.com/document.pdf").openStream();
             FileOutputStream out = new FileOutputStream("localdocument.pdf")) {  // Do you feel the stream flowing?

            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = in.read(buffer)) != -1) {
                out.write(buffer, 0, bytesRead);  // Bartender, keep 'em coming!
            }
        } catch (IOException e) {
            System.out.println("What's the matter, couldn't catch your stream?");  // Dry humor, huh?
        }
    }
}

Extra perks from Java

In this section, we explore a handful of additional features from Java that give you more control over your file download.

Stream and network efficiency

For more power in handling large files, consider the chunk method where your downloads are split into byte-sized pieces for more seamless and stable transfers.

Pattern usage

Parameterizing your Java methods makes your process more dynamic - like changing weapons during a boss fight!

Resource management

To win in any game, managing resources efficiently is important and this holds true here. Always be extra careful with your streams using try-with-resources!