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

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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.

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