Chapter 114: HTTP Methods in Java

HTTP methods (verbs) tell intermediaries and clients what kind of action you intend. java.net.http.HttpRequest exposes .GET(), .POST(BodyPublisher), .PUT, .DELETE, and a generic .method(name, publisher) for PATCH and custom verbs.

1. Topic title

Methods: vocabulary for intent—GET reads, POST submits, PUT replaces, DELETE removes

2. What it means

Safe methods — GET, HEAD, OPTIONS should not change server state in ways that matter—caches assume this.

Idempotent methods — PUT, DELETE, GET, HEAD should leave the system in the same end state if repeated (network retries).

POST — creates resources or triggers non-idempotent work—duplicate POST may create two rows—design dedup tokens when needed.

PATCH — partial update—support varies; some APIs use POST for partial updates for simplicity.

3. Why it is used

CDNs and browser caches rely on correct GET usage.

Clients auto-retry idempotent calls after timeouts—wrong verb choice duplicates payments.

4. Mental sketch

GET is looking at a museum exhibit behind glass. POST is dropping a coin into a donation box—each drop is a new event. PUT is replacing the whole painting in the frame. PATCH is touching up one corner.

5. Java code example

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.charset.StandardCharsets;
 
public class HttpMethodsDemo {
    public static void main(String[] args) throws Exception {
        HttpClient client = HttpClient.newHttpClient();
 
        HttpRequest get = HttpRequest.newBuilder(URI.create("https://httpbin.org/get")).GET().build();
        System.out.println("GET -> " + client.send(get, HttpResponse.BodyHandlers.ofString()).statusCode());
 
        String json = "{\"name\":\"ada\"}";
        HttpRequest post = HttpRequest.newBuilder(URI.create("https://httpbin.org/post"))
                .header("Content-Type", "application/json")
                .POST(HttpRequest.BodyPublishers.ofString(json, StandardCharsets.UTF_8))
                .build();
        System.out.println("POST -> " + client.send(post, HttpResponse.BodyHandlers.ofString()).statusCode());
 
        HttpRequest del = HttpRequest.newBuilder(URI.create("https://httpbin.org/delete")).DELETE().build();
        System.out.println("DELETE -> " + client.send(del, HttpResponse.BodyHandlers.ofString()).statusCode());
    }
}

httpbin echoes payloads—use it to see headers and bodies your client sent.

6. Explanation of code

BodyPublishers.ofString streams UTF-8 text—match Content-Type to actual bytes (JSON is text with a convention).

7. Common mistakes

Side-effecting GET — breaks prefetch, crawler, and human expectations.

PUT without full body when your contract says “replace entire resource”—clients wipe unspecified fields accidentally.

8. Best practices

Document which operations are idempotent and how retries should behave.

Prefer HEAD when you only need headers (length, ETag) without body cost.

9. Small practice task

Send OPTIONS to https://httpbin.org/get with .method("OPTIONS", HttpRequest.BodyPublishers.noBody())—print Allow (if present) from response headers.

Beginner tip

If corporate proxies block httpbin, run the same calls against localhost once Chapter 117’s tiny server is up.