curator-examples/src/main/java/discovery/DiscoveryExample.java

/*
 * Copyright 2012 Netflix, Inc.
 *
 *    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 discovery;

import com.google.common.base.Predicate;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.common.io.Closeables;
import com.netflix.curator.framework.CuratorFramework;
import com.netflix.curator.framework.CuratorFrameworkFactory;
import com.netflix.curator.retry.ExponentialBackoffRetry;
import com.netflix.curator.test.TestingServer;
import com.netflix.curator.x.discovery.ServiceDiscovery;
import com.netflix.curator.x.discovery.ServiceDiscoveryBuilder;
import com.netflix.curator.x.discovery.ServiceInstance;
import com.netflix.curator.x.discovery.ServiceProvider;
import com.netflix.curator.x.discovery.details.JsonInstanceSerializer;
import com.netflix.curator.x.discovery.strategies.RandomStrategy;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.Map;

public class DiscoveryExample
{
    private static final String     PATH = "/discovery/example";

    public static void main(String[] args) throws Exception
    {
        // This method is scaffolding to get the example up and running

        TestingServer                                   server = new TestingServer();
        CuratorFramework                                client = null;
        ServiceDiscovery<InstanceDetails>               serviceDiscovery = null;
        Map<String, ServiceProvider<InstanceDetails>>   providers = Maps.newHashMap();
        try
        {
            client = CuratorFrameworkFactory.newClient(server.getConnectString(), new ExponentialBackoffRetry(1000, 3));
            client.start();

            JsonInstanceSerializer<InstanceDetails> serializer = new JsonInstanceSerializer<InstanceDetails>(InstanceDetails.class);
            serviceDiscovery = ServiceDiscoveryBuilder.builder(InstanceDetails.class).client(client).basePath(PATH).serializer(serializer).build();
            serviceDiscovery.start();

            processCommands(serviceDiscovery, providers, client);
        }
        finally
        {
            for ( ServiceProvider<InstanceDetails> cache : providers.values() )
            {
                Closeables.closeQuietly(cache);
            }

            Closeables.closeQuietly(serviceDiscovery);
            Closeables.closeQuietly(client);
            Closeables.closeQuietly(server);
        }
    }

    private static void processCommands(ServiceDiscovery<InstanceDetails> serviceDiscovery, Map<String, ServiceProvider<InstanceDetails>> providers, CuratorFramework client) throws Exception
    {
        // More scaffolding that does a simple command line processor

        printHelp();

        List<ExampleServer>     servers = Lists.newArrayList();
        try
        {
            BufferedReader          in = new BufferedReader(new InputStreamReader(System.in));
            boolean                 done = false;
            while ( !done )
            {
                System.out.print("> ");

                String      command = in.readLine().trim();
                String[]    parts = command.split("\\s");
                if ( parts.length == 0 )
                {
                    continue;
                }
                String      operation = parts[0];
                String      args[] = Arrays.copyOfRange(parts, 1, parts.length);

                if ( operation.equalsIgnoreCase("help") || operation.equalsIgnoreCase("?") )
                {
                    printHelp();
                }
                else if ( operation.equalsIgnoreCase("q") || operation.equalsIgnoreCase("quit") )
                {
                    done = true;
                }
                else if ( operation.equals("add") )
                {
                    addInstance(args, client, command, servers);
                }
                else if ( operation.equals("delete") )
                {
                    deleteInstance(args, command, servers);
                }
                else if ( operation.equals("random") )
                {
                    listRandomInstance(args, serviceDiscovery, providers, command);
                }
                else if ( operation.equals("list") )
                {
                    listInstances(serviceDiscovery);
                }
            }
        }
        finally
        {
            for ( ExampleServer server : servers )
            {
                Closeables.closeQuietly(server);
            }
        }
    }

    private static void listRandomInstance(String[] args, ServiceDiscovery<InstanceDetails> serviceDiscovery, Map<String, ServiceProvider<InstanceDetails>> providers, String command) throws Exception
    {
        // this shows how to use a ServiceProvider
        // in a real application you'd create the ServiceProvider early for the service(s) you're interested in

        if ( args.length != 1 )
        {
            System.err.println("syntax error (expected random <name>): " + command);
            return;
        }

        String                              serviceName = args[0];
        ServiceProvider<InstanceDetails>    provider = providers.get(serviceName);
        if ( provider == null )
        {
            provider = serviceDiscovery.serviceProviderBuilder().serviceName(serviceName).providerStrategy(new RandomStrategy<InstanceDetails>()).build();
            providers.put(serviceName, provider);
            provider.start();

            Thread.sleep(2500); // give the provider time to warm up - in a real application you wouldn't need to do this
        }

        ServiceInstance<InstanceDetails>    instance = provider.getInstance();
        if ( instance == null )
        {
            System.err.println("No instances named: " + serviceName);
        }
        else
        {
            outputInstance(instance);
        }
    }

    private static void listInstances(ServiceDiscovery<InstanceDetails> serviceDiscovery) throws Exception
    {
        // This shows how to query all the instances in service discovery

        try
        {
            Collection<String>  serviceNames = serviceDiscovery.queryForNames();
            System.out.println(serviceNames.size() + " type(s)");
            for ( String serviceName : serviceNames )
            {
                Collection<ServiceInstance<InstanceDetails>> instances = serviceDiscovery.queryForInstances(serviceName);
                System.out.println(serviceName);
                for ( ServiceInstance<InstanceDetails> instance : instances )
                {
                    outputInstance(instance);
                }
            }
        }
        finally
        {
            Closeables.closeQuietly(serviceDiscovery);
        }
    }

    private static void outputInstance(ServiceInstance<InstanceDetails> instance)
    {
        System.out.println("\t" + instance.getPayload().getDescription() + ": " + instance.buildUriSpec());
    }

    private static void deleteInstance(String[] args, String command, List<ExampleServer> servers)
    {
        // simulate a random instance going down
        // in a real application, this would occur due to normal operation, a crash, maintenance, etc.

        if ( args.length != 1 )
        {
            System.err.println("syntax error (expected delete <name>): " + command);
            return;
        }

        final String    serviceName = args[0];
        ExampleServer   server = Iterables.find
        (
            servers,
            new Predicate<ExampleServer>()
            {
                @Override
                public boolean apply(ExampleServer server)
                {
                    return server.getThisInstance().getName().endsWith(serviceName);
                }
            },
            null
        );
        if ( server == null )
        {
            System.err.println("No servers found named: " + serviceName);
            return;
        }

        servers.remove(server);
        Closeables.closeQuietly(server);
        System.out.println("Removed a random instance of: " + serviceName);
    }

    private static void addInstance(String[] args, CuratorFramework client, String command, List<ExampleServer> servers) throws Exception
    {
        // simulate a new instance coming up
        // in a real application, this would be a separate process

        if ( args.length < 2 )
        {
            System.err.println("syntax error (expected add <name> <description>): " + command);
            return;
        }

        StringBuilder   description = new StringBuilder();
        for ( int i = 1; i < args.length; ++i )
        {
            if ( i > 1 )
            {
                description.append(' ');
            }
            description.append(args[i]);
        }

        String          serviceName = args[0];
        ExampleServer   server = new ExampleServer(client, PATH, serviceName, description.toString());
        servers.add(server);
        server.start();

        System.out.println(serviceName + " added");
    }

    private static void printHelp()
    {
        System.out.println("An example of using the ServiceDiscovery APIs. This example is driven by entering commands at the prompt:\n");
        System.out.println("add <name> <description>: Adds a mock service with the given name and description");
        System.out.println("delete <name>: Deletes one of the mock services with the given name");
        System.out.println("list: Lists all the currently registered services");
        System.out.println("random <name>: Lists a random instance of the service with the given name");
        System.out.println("quit: Quit the example");
        System.out.println();
    }
}