How to access PubSub using java client

[BabaHere]

Hi folks,

I want to use GCP PubSub using custom java client but I`m unable to connect.

I have use below code to connect - 

TopicName topicName = TopicName.of(projectId, topicId);

Publisher publisher = null;

publisher = Publisher.newBuilder(topicName).build();

ByteString data = ByteString.copyFromUtf8(sampleJsonMessage);

PubsubMessage pubSubMessage = PubsubMessage.newBuilder().setData(data).build();

ApiFuture<String> messageIdFuture = publisher.publish(pubSubMessage);

But Its not working. Any suggestion to achieve this.

Also I have tried https://cloud.google.com/pubsub/docs/publish-receive-messages-client-library this example as well, but getting below exception -

Thanks