Java 11 introduces a new package, java.net.http, for making HTTP requests. For general usage, it's pretty straight forward.
My question is: how do I use java.net.http to handle chunked responses as each chunk is received by the client?
java.http.net contains a reactive BodySubscriber which appears to be what I want, but I can't find an example of how it's used.
Below is a python implementation that prints chunks as they arrive, I'd like to the same thing with java.net.http:
import argparse
import requests
def main(url: str):
with requests.get(url, stream=True) as r:
for c in r.iter_content(chunk_size=1):
print(c.decode("UTF-8"), end="")
if __name__ == "__main__":
parser = argparse.ArgumentParser(
description="Read from a URL and print as text as chunks arrive")
parser.add_argument('url', type=str, help="A URL to read from")
args = parser.parse_args()
main(args.url)
Just for completeness, here's a simple example of making a blocking request using java.net.http:
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpResponse;
import java.net.http.HttpRequest;
public class HttpGetDemo {
public static void main(String[] args) throws Exception {
var request = HttpRequest.newBuilder()
.uri(URI.create(args[0]))
.build();
var bodyHandler = HttpResponse.BodyHandlers
.ofString();
var client = HttpClient.newHttpClient();
var response = client.send(request, bodyHandler);
System.out.println(response.body());
}
}
And here's the example making an non-blocking/async request:
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpResponse;
import java.net.http.HttpRequest;
/**
* ReadChunked
*/
public class HttpAsyncGetDemo {
public static void main(String[] args) throws Exception {
var request = HttpRequest.newBuilder()
.uri(URI.create(args[0]))
.build();
var bodyHandler = HttpResponse.BodyHandlers
.ofString();
var client = HttpClient.newHttpClient();
client.sendAsync(request, bodyHandler)
.thenApply(HttpResponse::body)
.thenAccept(System.out::println)
.join();
}
}
Thanks to @pavel and @chegar999 for their partial answers. They led me to my solution.
The solution I came up with is below. Basically, the solution is to use a custom java.net.http.HttpResponse.BodySubscriber. A BodySubscriber contains reactive methods (onSubscribe, onNext, onError, and onComplete) and a getBody method that basically returns a java CompletableFuture that will eventually produce the body of the HTTP request. Once you have your BodySubscriber in hand you can use it like:
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create(uri))
.build();
return client.sendAsync(request, responseInfo -> new StringSubscriber())
.whenComplete((r, t) -> System.out.println("--- Status code " + r.statusCode()))
.thenApply(HttpResponse::body);
Note the line:
client.sendAsync(request, responseInfo -> new StringSubscriber())
That's where we register our custom BodySubscriber; in this case, my custom class is named StringSubscriber.
This is a complete working example. Using Java 11, you can run it without compiling it. Just past it into a file named CustomSubscriber.java, then run the command java CustomSubscriber <some url>. It prints the contents of each chunk as it arrives. It also collects them and returns them as the body when the response has completed.
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.net.http.HttpResponse.BodyHandlers;
import java.net.http.HttpResponse.BodySubscriber;
import java.net.URI;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.Flow;
import java.util.stream.Collectors;
import java.util.List;
public class CustomSubscriber {
public static void main(String[] args) {
CustomSubscriber cs = new CustomSubscriber();
String body = cs.get(args[0]).join();
System.out.println("--- Response body:\n: ..." + body + "...");
}
public CompletableFuture<String> get(String uri) {
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create(uri))
.build();
return client.sendAsync(request, responseInfo -> new StringSubscriber())
.whenComplete((r, t) -> System.out.println("--- Status code " + r.statusCode()))
.thenApply(HttpResponse::body);
}
static class StringSubscriber implements BodySubscriber<String> {
final CompletableFuture<String> bodyCF = new CompletableFuture<>();
Flow.Subscription subscription;
List<ByteBuffer> responseData = new CopyOnWriteArrayList<>();
@Override
public CompletionStage<String> getBody() {
return bodyCF;
}
@Override
public void onSubscribe(Flow.Subscription subscription) {
this.subscription = subscription;
subscription.request(1); // Request first item
}
@Override
public void onNext(List<ByteBuffer> buffers) {
System.out.println("-- onNext " + buffers);
try {
System.out.println("\tBuffer Content:\n" + asString(buffers));
}
catch (Exception e) {
System.out.println("\tUnable to print buffer content");
}
buffers.forEach(ByteBuffer::rewind); // Rewind after reading
responseData.addAll(buffers);
subscription.request(1); // Request next item
}
@Override
public void onError(Throwable throwable) {
bodyCF.completeExceptionally(throwable);
}
@Override
public void onComplete() {
bodyCF.complete(asString(responseData));
}
private String asString(List<ByteBuffer> buffers) {
return new String(toBytes(buffers), StandardCharsets.UTF_8);
}
private byte[] toBytes(List<ByteBuffer> buffers) {
int size = buffers.stream()
.mapToInt(ByteBuffer::remaining)
.sum();
byte[] bs = new byte[size];
int offset = 0;
for (ByteBuffer buffer : buffers) {
int remaining = buffer.remaining();
buffer.get(bs, offset, remaining);
offset += remaining;
}
return bs;
}
}
}
To test this solution, you'll need a server that sends a response that uses Transfer-encoding: chunked and sends it slow enough to watch the chunks arrive. I've created one at https://github.com/hohonuuli/demo-chunk-server but you can spin it up using Docker like so:
docker run -p 8080:8080 hohonuuli/demo-chunk-server
Then run the CustomSubscriber.java code using java CustomSubscriber.java http://localhost:8080/chunk/10