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Client library for working with the NATS messaging system.
// 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.Iterator;
import java.util.List;
import java.util.concurrent.TimeoutException;
import static io.nats.examples.ExampleUtils.sleep;
import static io.nats.examples.jetstream.NatsJsUtils.createStreamExitWhenExists;
import static io.nats.examples.jetstream.NatsJsUtils.publish;
/**
* This example will demonstrate miscellaneous uses cases of a pull subscription of:
* iterate pull: iterate(int batchSize, Duration or millis maxWait),
* no manual handling of null or status.
*/
public class NatsJsPullSubIterateUseCases {
static final String usageString =
"\nUsage: java -cp NatsJsPullSubIterateUseCases [-s server] [-strm stream] [-sub subject] [-dur durable]"
+ "\n\nDefault Values:"
+ "\n [-strm] iterate-uc-stream"
+ "\n [-sub] iterate-uc-subject"
+ "\n [-dur] iterate-uc-durable"
+ "\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 Iterate, Use Cases", args, usageString)
.defaultStream("iterate-uc-stream")
.defaultSubject("iterate-uc-subject")
.defaultDurable("iterate-uc-durable")
.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();
// 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();
// 0.1 Initialize. subscription
// 0.2 Flush outgoing communication with/to the server, useful when app is both publishing and subscribing.
System.out.println("\n----------\n0. Initialize the subscription and pull.");
JetStreamSubscription sub = js.subscribe(exArgs.subject, pullOptions);
nc.flush(Duration.ofSeconds(1));
// 1. iterate, but there are no messages yet.
// - Read the messages, get them all (0)
System.out.println("----------\n1. There are no messages yet");
Iterator iterator = sub.iterate(10, Duration.ofSeconds(3));
List messages = NatsJsUtils.reportFetch(iterator);
messages.forEach(Message::ack);
System.out.println("We should have received 0 total messages, we received: " + messages.size());
// 2. Publish 10 messages
// - iterate messages, get 10
System.out.println("----------\n2. Publish 10 which satisfies the batch");
publish(js, exArgs.subject, "A", 10);
iterator = sub.iterate(10, Duration.ofSeconds(3));
messages = NatsJsUtils.reportFetch(iterator);
messages.forEach(Message::ack);
System.out.println("We should have received 10 total messages, we received: " + messages.size());
// 3. Publish 20 messages
// - iterate messages, only get 10
System.out.println("----------\n3. Publish 20 which is larger than the batch size.");
publish(js, exArgs.subject, "B", 20);
iterator = sub.iterate(10, Duration.ofSeconds(3));
messages = NatsJsUtils.reportFetch(iterator);
messages.forEach(Message::ack);
System.out.println("We should have received 10 total messages, we received: " + messages.size());
// 4. There are still messages left from the last
// - iterate messages, get 10
System.out.println("----------\n4. Get the rest of the publish.");
iterator = sub.iterate(10, Duration.ofSeconds(3));
messages = NatsJsUtils.reportFetch(iterator);
messages.forEach(Message::ack);
System.out.println("We should have received 10 total messages, we received: " + messages.size());
// 5. Publish 5 messages
// - iterate messages, get 5
// - Since there are less than batch size we only get what the server has.
System.out.println("----------\n5. Publish 5 which is less than batch size.");
publish(js, exArgs.subject, "C", 5);
iterator = sub.iterate(10, Duration.ofSeconds(3));
messages = NatsJsUtils.reportFetch(iterator);
messages.forEach(Message::ack);
System.out.println("We should have received 5 total messages, we received: " + messages.size());
// 6. Publish 15 messages
// - iterate messages, only get 10
System.out.println("----------\n6. Publish 15 which is more than the batch size.");
publish(js, exArgs.subject, "D", 15);
iterator = sub.iterate(10, Duration.ofSeconds(3));
messages = NatsJsUtils.reportFetch(iterator);
messages.forEach(Message::ack);
System.out.println("We should have received 10 total messages, we received: " + messages.size());
// 7. There are 5 messages left
// - iterate messages, only get 5
System.out.println("----------\n7. There are 5 messages left.");
iterator = sub.iterate(10, Duration.ofSeconds(3));
messages = NatsJsUtils.reportFetch(iterator);
messages.forEach(Message::ack);
System.out.println("We should have received 5 messages, we received: " + messages.size());
// 8. Read but don't ack.
// - iterate messages, get 10, but either take too long to ack them or don't ack them
System.out.println("----------\n8. iterate but don't ack.");
publish(js, exArgs.subject, "E", 10);
iterator = sub.iterate(10, Duration.ofSeconds(3));
messages = NatsJsUtils.reportFetch(iterator);
System.out.println("We should have received 10 message, we received: " + messages.size());
sleep(3000); // longer than the ackWait
// 9. iterate messages,
// - get the 10 messages we didn't ack
System.out.println("----------\n9. iterate, get the messages we did not ack.");
iterator = sub.iterate(10, Duration.ofSeconds(3));
messages = NatsJsUtils.reportFetch(iterator);
messages.forEach(Message::ack);
System.out.println("We should have received 10 message, we received: " + messages.size());
System.out.println("----------\n");
// 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);
}
}
}
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