io.nats.examples.jetstream.simple.IterableConsumerExample 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.
The newest version!
// Copyright 2023 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.simple;

import io.nats.client.*;
import io.nats.client.api.ConsumerConfiguration;
import io.nats.examples.jetstream.ResilientPublisher;

import java.io.IOException;

import static io.nats.examples.jetstream.NatsJsUtils.createOrReplaceStream;

/**
 * This example will demonstrate simplified IterableConsumer where the developer calls nextMessage.
 */
public class IterableConsumerExample {
    private static final String STREAM = "iterable-stream";
    private static final String SUBJECT = "iterable-subject";
    private static final String CONSUMER_NAME = "iterable-consumer";
    private static final String MESSAGE_PREFIX = "iterable";
    private static final int STOP_COUNT = 500;
    private static final int REPORT_EVERY = 50;

    private static final String SERVER = "nats://localhost:4222";

    public static void main(String[] args) {
        Options options = Options.builder().server(SERVER).build();
        try (Connection nc = Nats.connect(options)) {
            JetStreamManagement jsm = nc.jetStreamManagement();
            createOrReplaceStream(jsm, STREAM, SUBJECT);

            // get stream context, create consumer, get the consumer context, get an IterableConsumer
            StreamContext streamContext;
            ConsumerContext consumerContext;
            try {
                streamContext = nc.getStreamContext(STREAM);
                consumerContext = streamContext.createOrUpdateConsumer(ConsumerConfiguration.builder().durable(CONSUMER_NAME).build());
            }
            catch (JetStreamApiException | IOException e) {
                // JetStreamApiException:
                //      1. the stream or consumer did not exist
                //      2. api calls under the covers theoretically this could fail, but practically it won't.
                // IOException:
                //      likely a connection problem
                return;
            }

            System.out.println("Starting publish...");
            ResilientPublisher publisher = new ResilientPublisher(nc, jsm, STREAM, SUBJECT).basicDataPrefix(MESSAGE_PREFIX).jitter(10);
            Thread pubThread = new Thread(publisher);
            pubThread.start();

            // set up the iterable consumer
            Thread consumeThread = new Thread(() -> {
                int count = 0;
                long start = System.currentTimeMillis();
                try (IterableConsumer consumer = consumerContext.iterate()) {
                    System.out.println("Starting main loop.");
                    while (count < STOP_COUNT) {
                        Message msg = consumer.nextMessage(1000);
                        if (msg != null) {
                            msg.ack();
                            if (++count % REPORT_EVERY == 0) {
                                report("Main loop running", System.currentTimeMillis() - start, count);
                            }
                        }
                    }
                    report("Main loop stopped", System.currentTimeMillis() - start, count);

                    // The consumer has at least 1 pull request active. When stop is called,
                    // no more pull requests will be made, but messages already requested
                    // will still come across the wire to the client.
                    consumer.stop();

                    System.out.println("Starting post-stop loop.");
                    while (!consumer.isFinished()) {
                        Message msg = consumer.nextMessage(1000);
                        if (msg != null) {
                            msg.ack();
                            if (++count % REPORT_EVERY == 0) {
                                report("Post-stop loop running", System.currentTimeMillis() - start, ++count);
                            }
                        }
                    }
                    report("Post-stop loop stopped", System.currentTimeMillis() - start, count);
                }
                catch (JetStreamStatusCheckedException | InterruptedException | IOException | JetStreamApiException e) {
                    // JetStreamStatusCheckedException:
                    //      Either the consumer was deleted in the middle
                    //      of the pull or there is a new status from the
                    //      server that this client is not aware of
                    // InterruptedException:
                    //      developer interrupted this thread?
                    System.err.println("Exception should be handled properly, just exiting here.");
                    System.exit(-1);
                }
                catch (Exception e) {
                    // this is from the FetchConsumer being AutoCloseable, but should never be called
                    // as work inside the close is already guarded by try/catch
                    System.err.println("Exception should be handled properly, just exiting here.");
                    System.exit(-1);
                }
                report("Done", System.currentTimeMillis() - start, count);
            });
            consumeThread.start();
            consumeThread.join();

            publisher.stop(); // otherwise it will complain when the connection goes away
            pubThread.join();
        }
        catch (IOException | InterruptedException ioe) {
            // IOException:
            //      problem making the connection
            // InterruptedException:
            //      thread interruption in the body of the example
        }
    }

    private static void report(String label, long ms, int count) {
        System.out.println(label + ": Received " + count + " messages in " + ms + "ms.");
    }
}