/
NextExample.java
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/
NextExample.java
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// 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 java.io.IOException;
import static io.nats.examples.jetstream.NatsJsUtils.createOrReplaceStream;
/**
* This example will demonstrate simplified next
*/
public class NextExample {
private static final String STREAM = "next-stream";
private static final String SUBJECT = "next-subject";
private static final String CONSUMER_NAME = "next-consumer";
public static String SERVER = "nats://localhost:4222";
public static void main(String[] args) {
Options options = Options.builder().server(SERVER).build();
try (Connection nc = Nats.connect(options)) {
JetStream js = nc.jetStream();
createOrReplaceStream(nc.jetStreamManagement(), STREAM, SUBJECT);
// get stream context, create consumer and get the consumer context
StreamContext streamContext;
ConsumerContext consumerContext;
try {
streamContext = nc.getStreamContext(STREAM);
consumerContext = streamContext.createOrUpdateConsumer(ConsumerConfiguration.builder().durable(CONSUMER_NAME).build());
}
catch (JetStreamApiException | IOException e) {
// JetStreamApiException:
// the stream or consumer did not exist
// IOException:
// likely a connection problem
return;
}
int count = 20;
// Simulate messages coming in
Thread t = new Thread(() -> {
int sleep = 2000;
boolean down = true;
for (int x = 1; x <= count; x++) {
try {
Thread.sleep(sleep);
if (down) {
sleep -= 200;
down = sleep > 0;
}
else {
sleep += 200;
}
js.publish(SUBJECT, ("message-" + x).getBytes());
}
catch (JetStreamApiException | IOException | InterruptedException e) {
// JetStreamApiException:
// The "publish" somehow was rejected by the server.
// Unlikely w/o publish option expectations.
// IOException:
// likely a connection problem
// InterruptedException:
// developer interrupted this thread?
throw new RuntimeException(e);
}
}
});
t.start();
int received = 0;
while (received < count) {
try {
long start = System.currentTimeMillis();
Message m = consumerContext.next(1000);
long elapsed = System.currentTimeMillis() - start;
if (m == null) {
System.out.println("Waited " + elapsed + "ms for message, got null");
}
else {
++received;
m.ack();
System.out.println("Waited " + elapsed + "ms for message, got " + new String(m.getData()));
}
}
catch (JetStreamApiException | JetStreamStatusCheckedException | IOException | InterruptedException e) {
// JetStreamApiException:
// api calls under the covers theoretically this could fail, but practically it won't.
// 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
// IOException:
// likely a connection problem
// InterruptedException:
// developer interrupted this thread?
return;
}
}
t.join();
}
catch (IOException | InterruptedException ioe) {
// IOException:
// problem making the connection
// InterruptedException:
// thread interruption in the body of the example
}
}
}