Question

我无法找到使用java从pub / sub读取消息的方法。

我在我的pom中使用这个maven依赖

<dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-pubsub</artifactId>
  <version>0.17.2-alpha</version>
</dependency>

我实现了这个主要方法来创建一个新主题：

public static void main(String... args) throws Exception {

        // Your Google Cloud Platform project ID
        String projectId = ServiceOptions.getDefaultProjectId();

        // Your topic ID
        String topicId = "my-new-topic-1";
        // Create a new topic
        TopicName topic = TopicName.create(projectId, topicId);
        try (TopicAdminClient topicAdminClient = TopicAdminClient.create()) {
            topicAdminClient.createTopic(topic); 
        }
}

以上代码效果很好，实际上，我可以看到使用Google云端控制台创建的新主题。

我实现了以下主要方法来向我的主题写一条消息：

public static void main(String a[]) throws InterruptedException, ExecutionException{
        String projectId = ServiceOptions.getDefaultProjectId(); 
        String topicId = "my-new-topic-1";

        String payload = "Hellooooo!!!";
        PubsubMessage pubsubMessage =
                  PubsubMessage.newBuilder().setData(ByteString.copyFromUtf8(payload)).build();

        TopicName topic = TopicName.create(projectId, topicId);

        Publisher publisher;
        try {
            publisher = Publisher.defaultBuilder(
                    topic)
                    .build();
            publisher.publish(pubsubMessage);

            System.out.println("Sent!");
        } catch (IOException e) {
            System.out.println("Not Sended!");
            e.printStackTrace();
        }
}

现在我无法验证此消息是否真的已发送。我想使用订阅我的主题来实现一个消息阅读器。有人能告诉我一个关于从主题阅读消息的正确且有效的java示例吗？

任何人都可以帮助我吗？提前谢谢！

Answer 1

Cloud Pub/Sub Pull Subscriber Guide包含用于阅读主题消息的示例代码。

Answer 2

这里是使用Google云客户端库的版本。


package com.techm.data.client;

import com.google.cloud.pubsub.v1.AckReplyConsumer;
import com.google.cloud.pubsub.v1.MessageReceiver;
import com.google.cloud.pubsub.v1.Subscriber;
import com.google.cloud.pubsub.v1.SubscriptionAdminClient;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.pubsub.v1.ProjectSubscriptionName;
import com.google.pubsub.v1.ProjectTopicName;
import com.google.pubsub.v1.PubsubMessage;
import com.google.pubsub.v1.PushConfig;

/**
 * A snippet for Google Cloud Pub/Sub showing how to create a Pub/Sub pull
 * subscription and asynchronously pull messages from it.
 */
public class CreateSubscriptionAndConsumeMessages {

    private static String projectId = "projectId";
    private static String topicId = "topicName";
    private static String subscriptionId = "subscriptionName";

    public static void createSubscription() throws Exception {
        ProjectTopicName topic = ProjectTopicName.of(projectId, topicId);
        ProjectSubscriptionName subscription = ProjectSubscriptionName.of(projectId, subscriptionId);

        try (SubscriptionAdminClient subscriptionAdminClient = SubscriptionAdminClient.create()) {
            subscriptionAdminClient.createSubscription(subscription, topic, PushConfig.getDefaultInstance(), 0);
        }
    }

    public static void main(String... args) throws Exception {
        ProjectSubscriptionName subscription = ProjectSubscriptionName.of(projectId, subscriptionId);       

        createSubscription();


        MessageReceiver receiver = new MessageReceiver() {
            @Override
            public void receiveMessage(PubsubMessage message, AckReplyConsumer consumer) {
                System.out.println("Received message: " + message.getData().toStringUtf8());
                consumer.ack();
            }
        };
        Subscriber subscriber = null;
        try {
            subscriber = Subscriber.newBuilder(subscription, receiver).build();
            subscriber.addListener(new Subscriber.Listener() {
                @Override
                public void failed(Subscriber.State from, Throwable failure) {
                    // Handle failure. This is called when the Subscriber encountered a fatal error
                    // and is
                    // shutting down.
                    System.err.println(failure);
                }
            }, MoreExecutors.directExecutor());
            subscriber.startAsync().awaitRunning();         

            // In this example, we will pull messages for one minute (60,000ms) then stop.
            // In a real application, this sleep-then-stop is not necessary.
            // Simply call stopAsync().awaitTerminated() when the server is shutting down,
            // etc.
            Thread.sleep(60000);
        } finally {
            if (subscriber != null) {
                subscriber.stopAsync().awaitTerminated();
            }
        }
    }
}

这对我来说很好。

Answer 3

消息阅读器注入订阅者。 code的这一部分将处理消息：

MessageReceiver receiver =
    new MessageReceiver() {
      @Override
      public void receiveMessage(PubsubMessage message, AckReplyConsumer consumer) {
        // handle incoming message, then ack/nack the received message
        System.out.println("Id : " + message.getMessageId());
        System.out.println("Data : " + message.getData().toStringUtf8());
        consumer.ack();
      }
    };

Answer 4

我没有使用过Google Cloud客户端库，但是使用了api客户端库。这是我创建订阅的方式。

package com.techm.datapipeline.client;

import java.io.IOException;
import java.security.GeneralSecurityException;

import com.google.api.client.googleapis.json.GoogleJsonResponseException;
import com.google.api.client.http.HttpStatusCodes;
import com.google.api.services.pubsub.Pubsub;
import com.google.api.services.pubsub.Pubsub.Projects.Subscriptions.Create;
import com.google.api.services.pubsub.Pubsub.Projects.Subscriptions.Get;
import com.google.api.services.pubsub.Pubsub.Projects.Topics;
import com.google.api.services.pubsub.model.ExpirationPolicy;
import com.google.api.services.pubsub.model.Subscription;
import com.google.api.services.pubsub.model.Topic;
import com.techm.datapipeline.factory.PubsubFactory;

public class CreatePullSubscriberClient {

    private final static String PROJECT_NAME = "yourProjectId";
    private final static String TOPIC_NAME = "yourTopicName";
    private final static String SUBSCRIPTION_NAME = "yourSubscriptionName";

    public static void main(String[] args) throws IOException, GeneralSecurityException {
        Pubsub pubSub = PubsubFactory.getService();

        String topicName = String.format("projects/%s/topics/%s", PROJECT_NAME, TOPIC_NAME);
        String subscriptionName = String.format("projects/%s/subscriptions/%s", PROJECT_NAME, SUBSCRIPTION_NAME);

        Topics.Get listReq = pubSub.projects().topics().get(topicName);
        Topic topic = listReq.execute();

        if (topic == null) {
            System.err.println("Topic doesn't exist...run CreateTopicClient...to create the topic");
            System.exit(0);
        }

        Subscription subscription = null;
        try {
            Get getReq = pubSub.projects().subscriptions().get(subscriptionName);
            subscription = getReq.execute();
        } catch (GoogleJsonResponseException e) {
            if (e.getStatusCode() == HttpStatusCodes.STATUS_CODE_NOT_FOUND) {
                System.out.println("Subscription " + subscriptionName + " does not exist...will create it");
            }
        }

        if (subscription != null) {
            System.out.println("Subscription already exists ==> " + subscription.toPrettyString());
            System.exit(0);
        }

        subscription = new Subscription();

        subscription.setTopic(topicName);
        subscription.setPushConfig(null); // indicating a pull

        ExpirationPolicy expirationPolicy = new ExpirationPolicy();
        expirationPolicy.setTtl(null); // never expires;
        subscription.setExpirationPolicy(expirationPolicy);

        subscription.setAckDeadlineSeconds(null); // so defaults to 10 sec

        subscription.setRetainAckedMessages(true);

        Long _week = 7L * 24 * 60 * 60;
        subscription.setMessageRetentionDuration(String.valueOf(_week)+"s");

        subscription.setName(subscriptionName);

        Create createReq = pubSub.projects().subscriptions().create(subscriptionName, subscription);
        Subscription createdSubscription = createReq.execute();

        System.out.println("Subscription created ==> " + createdSubscription.toPrettyString());
    }

}

创建订阅（拉式）后，这就是从主题中提取消息的方式。

package com.techm.datapipeline.client;

import java.io.IOException;
import java.security.GeneralSecurityException;
import java.util.ArrayList;
import java.util.List;

import com.google.api.client.googleapis.json.GoogleJsonResponseException;
import com.google.api.client.http.HttpStatusCodes;
import com.google.api.client.util.Base64;
import com.google.api.services.pubsub.Pubsub;
import com.google.api.services.pubsub.Pubsub.Projects.Subscriptions.Acknowledge;
import com.google.api.services.pubsub.Pubsub.Projects.Subscriptions.Get;
import com.google.api.services.pubsub.Pubsub.Projects.Subscriptions.Pull;
import com.google.api.services.pubsub.model.AcknowledgeRequest;
import com.google.api.services.pubsub.model.Empty;
import com.google.api.services.pubsub.model.PullRequest;
import com.google.api.services.pubsub.model.PullResponse;
import com.google.api.services.pubsub.model.ReceivedMessage;
import com.techm.datapipeline.factory.PubsubFactory;

public class PullSubscriptionsClient {

    private final static String PROJECT_NAME = "yourProjectId";
    private final static String SUBSCRIPTION_NAME = "yourSubscriptionName";

    private final static String SUBSCRIPTION_NYC_NAME = "test";


    public static void main(String[] args) throws IOException, GeneralSecurityException {
        Pubsub pubSub = PubsubFactory.getService();

        String subscriptionName = String.format("projects/%s/subscriptions/%s", PROJECT_NAME, SUBSCRIPTION_NAME);
        //String subscriptionName = String.format("projects/%s/subscriptions/%s", PROJECT_NAME, SUBSCRIPTION_NYC_NAME);

        try {
            Get getReq = pubSub.projects().subscriptions().get(subscriptionName);
            getReq.execute();
        } catch (GoogleJsonResponseException e) {
            if (e.getStatusCode() == HttpStatusCodes.STATUS_CODE_NOT_FOUND) {
                System.out.println("Subscription " + subscriptionName
                        + " does not exist...run CreatePullSubscriberClient to create");
            }
        }

        PullRequest pullRequest = new PullRequest();
        pullRequest.setReturnImmediately(false); // wait until you get a message
        pullRequest.setMaxMessages(1000);

        Pull pullReq = pubSub.projects().subscriptions().pull(subscriptionName, pullRequest);
        PullResponse pullResponse = pullReq.execute();

        List<ReceivedMessage> msgs = pullResponse.getReceivedMessages();
        List<String> ackIds = new ArrayList<String>();
        int i = 0;
        if (msgs != null) {
            for (ReceivedMessage msg : msgs) {
                ackIds.add(msg.getAckId());
                //System.out.println(i++ + ":===:" + msg.getAckId());
                String object = new String(Base64.decodeBase64(msg.getMessage().getData()));
                System.out.println("Decoded object String ==> " + object );
            }

            //acknowledge all the received messages
            AcknowledgeRequest content = new AcknowledgeRequest();
            content.setAckIds(ackIds);
            Acknowledge ackReq = pubSub.projects().subscriptions().acknowledge(subscriptionName, content);
            Empty empty = ackReq.execute();
        }

    }

}

注意：此客户端仅等待，直到收到至少一条消息，并且如果一次接收到一条消息（最多为MaxMessages中设置的最大值），则终止。

让我知道是否有帮助。我将很快尝试使用云客户端库，一旦接触它们，它将发布更新。

这是缺少的工厂类...如果您打算运行它...

package com.techm.datapipeline.factory;


import java.io.IOException;
import java.security.GeneralSecurityException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.logging.Level;
import java.util.logging.Logger;

import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.services.pubsub.Pubsub;
import com.google.api.services.pubsub.PubsubScopes;

public class PubsubFactory {

    private static Pubsub instance = null;
    private static final Logger logger = Logger.getLogger(PubsubFactory.class.getName());

    public static synchronized Pubsub getService() throws IOException, GeneralSecurityException {
        if (instance == null) {
            instance = buildService();
        }
        return instance;
    }

    private static Pubsub buildService() throws IOException, GeneralSecurityException {
        logger.log(Level.FINER, "Start of buildService");
        HttpTransport transport = GoogleNetHttpTransport.newTrustedTransport();
        JsonFactory jsonFactory = new JacksonFactory();
        GoogleCredential credential = GoogleCredential.getApplicationDefault(transport, jsonFactory);

        // Depending on the environment that provides the default credentials (for
        // example: Compute Engine, App Engine), the credentials may require us to
        // specify the scopes we need explicitly. 
        if (credential.createScopedRequired()) {
            Collection<String> scopes = new ArrayList<>();
            scopes.add(PubsubScopes.PUBSUB);
            credential = credential.createScoped(scopes);
        }

        logger.log(Level.FINER, "End of buildService");

        // TODO - Get the application name from outside.
        return new Pubsub.Builder(transport, jsonFactory, credential).setApplicationName("Your Application Name/Version")
                .build();
    }

}

Google Pub / Sub Java示例

4 个答案: