java 41 lines · 8 steps

Enforcing HTTP timeouts with a Future

A thread pool runs each fetch off-thread so the caller can bound it with Future.get and cancel on timeout.

Explained by highlit
Intermediate concurrency timeouts thread-pool exception-handling cancellation
1public class TimedFetchService {
2 
3 private final ExecutorService executor = Executors.newFixedThreadPool(8);
4 private final HttpClient httpClient = HttpClient.newHttpClient();
5 
6 public String fetchWithTimeout(URI uri, Duration timeout) {
7 Future<String> future = executor.submit(() -> {
8 HttpRequest request = HttpRequest.newBuilder(uri).GET().build();
9 HttpResponse<String> response =
10 httpClient.send(request, HttpResponse.BodyHandlers.ofString());
11 return response.body();
12 });
13 
14 try {
15 return future.get(timeout.toMillis(), TimeUnit.MILLISECONDS);
16 } catch (TimeoutException e) {
17 future.cancel(true);
18 throw new FetchTimeoutException(
19 "Request to " + uri + " exceeded " + timeout.toMillis() + "ms", e);
20 } catch (ExecutionException e) {
21 throw new FetchFailedException("Request to " + uri + " failed", e.getCause());
22 } catch (InterruptedException e) {
23 future.cancel(true);
24 Thread.currentThread().interrupt();
25 throw new FetchFailedException("Interrupted while fetching " + uri, e);
26 }
27 }
28 
29 @PreDestroy
30 public void shutdown() {
31 executor.shutdown();
32 try {
33 if (!executor.awaitTermination(5, TimeUnit.SECONDS)) {
34 executor.shutdownNow();
35 }
36 } catch (InterruptedException e) {
37 executor.shutdownNow();
38 Thread.currentThread().interrupt();
39 }
40 }
41}
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1Wrapping blocking work in a Future lets you impose a wall-clock deadline the underlying call may not support.
  2. 2Each checked exception from Future.get maps to a distinct failure mode that deserves its own handling.
  3. 3A pooled executor needs an explicit lifecycle so its threads shut down cleanly with the owning component.

Related explainers

java 
@Component
@Converter
public class EncryptedStringConverter implements AttributeConverter<String, String> {
 

Transparent column encryption in Spring & JPA

encryption aes-gcm jpa-converter
Advanced 10 steps
java 
package com.acme.billing.config;
 
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.ConfigurationProperties;

Feature-flagged beans with Spring @ConditionalOnProperty

feature-flags conditional-beans strategy-pattern
Intermediate 5 steps
go 
func (w *Watcher) resetDebounce(d time.Duration) {
	if !w.timer.Stop() {
		select {
		case <-w.timer.C:

Debouncing a stream of events in Go

debounce timers channels
Advanced 7 steps
java 
public static Map<String, String> parseCookieHeader(String header) {
    Map<String, String> cookies = new LinkedHashMap<>();
    if (header == null || header.isBlank()) {
        return cookies;

Parsing an HTTP Cookie header in Java

string-parsing http url-decoding
Intermediate 6 steps
rust 
use std::collections::VecDeque;
use std::sync::{Arc, Condvar, Mutex};
use std::time::{Duration, Instant};
 

Building a counting semaphore in Rust

concurrency synchronization condition-variable
Advanced 9 steps
java 
public class TimedSocketReader {
 
    private static final int READ_TIMEOUT_MS = 5_000;
    private static final int CONNECT_TIMEOUT_MS = 3_000;

Reading a socket with connect and read timeouts

sockets timeouts io
Intermediate 8 steps

Share this explainer

Here's the card — post it anywhere.

Enforcing HTTP timeouts with a Future — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code