java 38 lines · 6 steps

Streaming a file download with Java's HttpClient

A small class fetches a URL and streams the response body straight to disk without buffering it all in memory.

Explained by highlit
Intermediate http-client streaming file-io resource-management
1import java.io.IOException;
2import java.io.InputStream;
3import java.net.URI;
4import java.net.http.HttpClient;
5import java.net.http.HttpRequest;
6import java.net.http.HttpResponse;
7import java.nio.file.Files;
8import java.nio.file.Path;
9import java.nio.file.StandardCopyOption;
10 
11public class RemoteFileDownloader {
12 
13 private final HttpClient httpClient;
14 
15 public RemoteFileDownloader(HttpClient httpClient) {
16 this.httpClient = httpClient;
17 }
18 
19 public long download(URI source, Path destination) throws IOException, InterruptedException {
20 HttpRequest request = HttpRequest.newBuilder(source)
21 .header("Accept", "application/octet-stream")
22 .GET()
23 .build();
24 
25 HttpResponse<InputStream> response =
26 httpClient.send(request, HttpResponse.BodyHandlers.ofInputStream());
27 
28 if (response.statusCode() != 200) {
29 throw new IOException("Unexpected status " + response.statusCode() + " for " + source);
30 }
31 
32 Files.createDirectories(destination.getParent());
33 
34 try (InputStream body = response.body()) {
35 return Files.copy(body, destination, StandardCopyOption.REPLACE_EXISTING);
36 }
37 }
38}
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1Streaming the response body to disk keeps memory use flat regardless of file size.
  2. 2Injecting the HttpClient makes the downloader configurable and testable rather than hardcoding transport details.
  3. 3A try-with-resources block guarantees the network stream closes even when the copy fails.

Related explainers

java 
public class SlidingLogRateLimiter {
 
    private final int maxRequests;
    private final long windowMillis;

How a sliding-log rate limiter works

rate-limiting concurrency sliding-window
Advanced 8 steps
php 
<?php
 
namespace App\Http\Controllers;
 

Streaming a filtered CSV export in Laravel

streaming csv-export query-builder
Intermediate 9 steps
java 
public final class Slugifier {
 
    private static final Pattern NON_LATIN = Pattern.compile("[^\\w-]");
    private static final Pattern WHITESPACE = Pattern.compile("[\\s]+");

Building a URL slugifier in Java

regex unicode-normalization string-processing
Intermediate 8 steps
java 
@Repository
public interface OrderRepository extends JpaRepository<Order, Long> {
 
    @Query("""

Keyset pagination with Spring Data JPA

pagination cursor jpa
Advanced 8 steps
java 
public record FixedWidthField(String name, int start, int end) {
 
    public String extract(String line) {
        int from = Math.min(start, line.length());

Parsing fixed-width text in Java

records parsing streams
Intermediate 7 steps
java 
@RestController
@RequestMapping("/api/quotes")
public class QuoteStreamController {
 

Streaming market quotes with Spring WebFlux

reactive-streams backpressure server-sent-events
Advanced 9 steps

Share this explainer

Here's the card — post it anywhere.

Streaming a file download with Java's HttpClient — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code