io.nats.examples.NatsDispatch 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.AuthHandler;
import io.nats.client.Connection;
import io.nats.client.Dispatcher;
import io.nats.client.Nats;
import io.nats.client.Options;

public class NatsDispatch {

    static final String usageString =
            "\nUsage: java NatsDispatch [server]  "
            + "\nUse tls:// or opentls:// to require tls, via the Default SSLContext\n"
            + "Set the environment variable NATS_NKEY to use challenge resposne authentication by setting a file containing your seed.\n"
            + "Use the URL for user/pass/token authentication.\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.Builder builder = new Options.Builder().server(server).noReconnect();

            if (System.getenv("NATS_NKEY") != null) {
                AuthHandler handler = new ExampleAuthHandler(System.getenv("NATS_NKEY"));
                builder.authHandler(handler);
            }

            System.out.printf("Trying to connect to %s, and listen to %s for %d messages.\n", server, subject, msgCount);
            Connection nc = Nats.connect(builder.build());
            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\"\n", 
                                        new String(msg.getData(), StandardCharsets.UTF_8), 
                                        msg.getSubject());
                latch.countDown();
            });
            d.subscribe(subject);

            nc.flush(Duration.ZERO);

            latch.await();
            nc.close();
            
        } catch (Exception exp) {
            exp.printStackTrace();
        }
    }

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