You can use the Unified API to specify the metadata structure that describes the byte data content of a message.

1. Define the metadata structure.
   1. Import com.pushtechnology.diffusionclient.Diffusion and the following classes from the com.pushtechnology.diffusion.content.metadata package:
      • MetadataFactory
      • MContent
      • MRecord
      • MField
      • MString
      • MIntegerString
      • MDecimalString
      • MCustomString
   2. Use the Diffusion.metadata method to get a MetadataFactory.

      private final MetadataFactory factory = Diffusion.metadata();

   3. Use the methods on the MetadataFactory to specify the content, record, and field definitions that make up the metadata structure.
      For example, the following code uses a content builder to create content metadata with a single record type that can occur zero to n times.

      public MContent createContentRepeating() {
          return
              factory.contentBuilder("Content").
                  add(
                      factory.record(
                          "Rec1",
                          factory.string("A"),
                          factory.string("B")),
                      0,
                      -1).
                  build();
      
      }

      For more information, see Java Unified API documentation.

2. Create a record topic and apply the metadata definition to it.
   1. Import the TopicControl feature, Session class, and RecordTopicDetails class.

      import com.pushtechnology.diffusion.client.features.control.topics.TopicControl;
      import com.pushtechnology.diffusion.client.session.Session;
      import com.pushtechnology.diffusion.client.topics.details.RecordTopicDetails;

   2. Create a Session instance and use it to get the TopicControl feature.

      final Session session = Diffusion.sessions().open("ws://diffusion.example.com:80");
      final TopicControl tc = session.feature(TopicControl.class);

   3. Get a topic builder for a record topic from the TopicControl feature.

      final RecordTopicDetails.Builder builder =
                  tc.newDetailsBuilder(RecordTopicDetails.Builder.class);

   4. Use the metadata method of the topic builder to create the topic definition.

      tc.addTopic(
                  TOPIC_NAME,
                  builder.metadata(metadata).build(),
                  new TopicControl.AddCallback.Default() {
                      @Override
                      public void onTopicAdded(String topic) {
                          theTopic = topic;
                      }
      
                  });

package com.example.metadata;

import com.pushtechnology.diffusion.client.Diffusion;
import com.pushtechnology.diffusion.client.content.metadata.MContent;
import com.pushtechnology.diffusion.client.content.metadata.MDecimalString;
import com.pushtechnology.diffusion.client.content.metadata.MField;
import com.pushtechnology.diffusion.client.content.metadata.MRecord;
import com.pushtechnology.diffusion.client.content.metadata.MetadataFactory;
import com.pushtechnology.diffusion.client.topics.details.TopicType;
import com.pushtechnology.diffusion.client.features.control.topics.TopicControl;
import com.pushtechnology.diffusion.client.session.Session;
import com.pushtechnology.diffusion.client.topics.details.RecordTopicDetails;
import com.pushtechnology.diffusion.client.types.UpdateOptions;


/**
 * An example of a client creating metadata definition and using it when creating a 
 * topic definition. 
 */
public class ControlClient {

    private final static String TOPIC_NAME = "foo/record";
    private String theTopic;
    private final MetadataFactory factory = Diffusion.metadata();

    /**
     * Creates control client instance.
     */
    public ControlClient() {
        
        // Create the Session
        final Session session = Diffusion.sessions()
                .open("ws://diffusion.example.com:80");

        // Add the TopicControl feature
        final TopicControl tc = session.feature(TopicControl.class);

        // Create metadata for the topic
        final MContent metadata = defineMetadata();
        
        // Get a topic builder
        final RecordTopicDetails.Builder builder =
            tc.newDetailsBuilder(RecordTopicDetails.Builder.class);

        // Create the topic with metadata 
        tc.addTopic(
            TOPIC_NAME,
            builder.metadata(metadata).build(),
            new TopicControl.AddCallback.Default() {
                @Override
                public void onTopicAdded(String topic) {
                    theTopic = topic;
                }

            });

    }
    
    
    /**
     * A simple example of creating content metadata with two records.
     *
     * @return content metadata
     */
    public MContent defineMetadata() {
        return factory.content(
            "Content",
            createNameAndAddressRecord(),
            createMultipleRateCurrencyRecord("Exchange Rates", 5));
    }
    
    /**
     * Creates a simple name and address record with fixed name single
     * multiplicity fields.
     *
     * @return record definition.
     */
    public MRecord createNameAndAddressRecord() {
        return factory.record(
            "NameAndAddress",
            factory.string("FirstName"),
            factory.string("Surname"),
            factory.string("HouseNumber"),
            factory.string("Street"),
            factory.string("Town"),
            factory.string("State"),
            factory.string("PostCode"));
    }

    /**
     * This creates a record with two fields, a string called "Currency" and a
     * decimal string called "Rate" with a default value of 1.00 which repeats a
     * specified number of times.
     *
     * @param name the record name
     * @param occurs the number of occurrences of the "Rate" field
     * @return the metadata record
     */
    public MRecord createMultipleRateCurrencyRecord(String name, int occurs) {
        return factory.recordBuilder(name).
            add(factory.string("Currency")).
            add(factory.decimal("Rate", "1.00"), occurs).
            build();
    }

}