io.nats.examples.jetstream.NatsJsPullSubFetch Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of jnats Show documentation
Client library for working with the NATS messaging system.
There is a newer version: 2.20.5
// Copyright 2020 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at:
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package io.nats.examples.jetstream;

import io.nats.client.*;
import io.nats.client.api.ConsumerConfiguration;
import io.nats.examples.ExampleArgs;
import io.nats.examples.ExampleUtils;

import java.io.IOException;
import java.time.Duration;
import java.util.List;
import java.util.concurrent.TimeoutException;

import static io.nats.examples.jetstream.NatsJsUtils.createStreamExitWhenExists;
import static io.nats.examples.jetstream.NatsJsUtils.publishInBackground;

/**
 * This example will demonstrate basic use of a pull subscription of:
 * fetch pull: fetch(int batchSize, Duration or millis maxWait),
 */
public class NatsJsPullSubFetch {
    static final String usageString =
        "\nUsage: java -cp  NatsJsPullSubFetch [-s server] [-strm stream] [-sub subject] [-dur durable] [-mcnt msgCount]"
            + "\n\nDefault Values:"
            + "\n   [-strm] fetch-stream"
            + "\n   [-sub]  fetch-subject"
            + "\n   [-dur]  fetch-durable-not-required"
            + "\n   [-mcnt] 15"
            + "\n\nUse tls:// or opentls:// to require tls, via the Default SSLContext\n"
            + "\nSet the environment variable NATS_NKEY to use challenge response authentication by setting a file containing your private key.\n"
            + "\nSet the environment variable NATS_CREDS to use JWT/NKey authentication by setting a file containing your user creds.\n"
            + "\nUse the URL in the -s server parameter for user/pass/token authentication.\n";

    public static void main(String[] args) {
        ExampleArgs exArgs = ExampleArgs.builder("Pull Subscription using macro Fetch", args, usageString)
                .defaultStream("fetch-stream")
                .defaultSubject("fetch-subject")
                .defaultDurable("fetch-durable-not-required")
                .defaultMsgCount(15)
                .build();

        try (Connection nc = Nats.connect(ExampleUtils.createExampleOptions(exArgs.server))) {
            // Create a JetStreamManagement context.
            JetStreamManagement jsm = nc.jetStreamManagement();

            // Use the utility to create a stream stored in memory.
            createStreamExitWhenExists(jsm, exArgs.stream, exArgs.subject);

            // Create our JetStream context.
            JetStream js = nc.jetStream();

            // start publishing the messages, don't wait for them to finish, simulating an outside producer
            publishInBackground(js, exArgs.subject, "fetch-message", exArgs.msgCount);

            // Build our consumer configuration and subscription options.
            // make sure the ack wait is sufficient to handle the reading and processing of the batch.
            ConsumerConfiguration cc = ConsumerConfiguration.builder()
                .ackWait(Duration.ofMillis(2500))
                .build();
            PullSubscribeOptions pullOptions = PullSubscribeOptions.builder()
                .durable(exArgs.durable)
                .configuration(cc)
                .build();

            JetStreamSubscription sub = js.subscribe(exArgs.subject, pullOptions);
            nc.flush(Duration.ofSeconds(1));

            int red = 0;
            while (red < exArgs.msgCount) {
                List list = sub.fetch(10, Duration.ofSeconds(1));
                for (Message m : list) {
                    red++; // process message
                    System.out.println("" + red + ". " + m);
                    m.ack();
                }
            }

            // delete the stream since we are done with it.
            jsm.deleteStream(exArgs.stream);
        }
        catch (RuntimeException e) {
            // Synchronous pull calls, including raw calls, fetch, iterate and reader
            // can throw JetStreamStatusException, although it is rare.
            // It also can happen if a new server version introduces a status the client does not understand.
            // The two current statuses that cause this are:
            // 1. 409 "Consumer Deleted" - The consumer was deleted externally in the middle of a pull request.
            // 2. 409 "Consumer is push based" - The consumer was modified externally and changed into a push consumer
            System.err.println(e);
        }
        catch (JetStreamApiException | IOException | TimeoutException | InterruptedException e) {
            System.err.println(e);
        }
    }
}