io.nats.examples.NatsReply 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: 2.20.2
// Copyright 2015-2018 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;

import java.nio.charset.StandardCharsets;
import java.time.Duration;
import java.util.concurrent.CountDownLatch;

import io.nats.client.Connection;
import io.nats.client.Dispatcher;
import io.nats.client.Nats;
import io.nats.client.Options;

public class NatsReply {

    static final String usageString =
            "\nUsage: java NatsReply [server]  "
                    + "\n\nUse tls:// or opentls:// to require tls, via the Default SSLContext\n";

    public static void main(String args[]) {
        String subject;
        int msgCount;
        String server;

        if (args.length == 3) {
            server = args[0];
            subject = args[1];
            msgCount = Integer.parseInt(args[2]);
        } else if (args.length == 2) {
            server = Options.DEFAULT_URL;
            subject = args[0];
            msgCount = Integer.parseInt(args[1]);
        } else {
            usage();
            return;
        }

        try {
            
            Options options = new Options.Builder().server(server).noReconnect().build();
            Connection nc = Nats.connect(options);
            CountDownLatch latch = new CountDownLatch(msgCount); // dispatcher runs callback in another thread
            
            Dispatcher d = nc.createDispatcher((msg) -> {
                System.out.printf("Received message \"%s\" on subject \"%s\", replying to %s\n", 
                                        new String(msg.getData(), StandardCharsets.UTF_8), 
                                        msg.getSubject(), msg.getReplyTo());
                nc.publish(msg.getReplyTo(), msg.getData());
                latch.countDown();
            });
            d.subscribe(subject);

            nc.flush(Duration.ZERO);

            latch.await();

            nc.closeDispatcher(d); // This isn't required, closing the connection will do it
            nc.close();
            
        } catch (Exception exp) {
            exp.printStackTrace();
        }
    }

    static void usage() {
        System.err.println(usageString);
        System.exit(-1);
    }
}