18.3. Data Producers

A GeoMesa Kafka data store can act as a Kafka producer and write features to a Kafka topic.

Note

Kafka data stores only meant for writing can disable consuming messages by setting the data store configuration kafka.consumer.count to 0.

First, create the data store:

import org.geotools.data.DataStoreFinder;

String brokers = ...
String zookeepers = ...

// build parameters map
Map<String, Serializable> params = new HashMap<>();
params.put("kafka.brokers", brokers);
params.put("kafka.zookeepers", zookeepers);

// create the data store
KafkaDataStore ds = (KafkaDataStore) DataStoreFinder.getDataStore(params);

Next, create the schema. Each data store can have 0 to many schemas. For example:

SimpleFeatureType sft = ...
ds.createSchema(sft);

Now, you can create or update simple features. Note that the Kafka data store only supports update via feature ID. You may explicitly create a modifying feature writer with an ID filter, or simply use an append feature writer, which will overwrite any existing feature with the same feature ID:

// the name of the simple feature type -  will be the same as sft.getTypeName();
String typeName = sft.getTypeName();

SimpleFeatureWriter fw = ds.getFeatureWriterAppend(typeName, Transaction.AUTO_COMMIT);
SimpleFeature sf = fw.next();
// set properties on sf
fw.write();

Note

When using a modifying feature writer, the features returned will not have the attributes of the actual current features, but will have the correct feature ID.

Warning

To get the Kafka feature writer to use the provided feature ID, the standard GeoTools Hints.USE_PROVIDED_FID or Hints.PROVIDED_FID must be used. Otherwise, a new feature ID will be generated.

Delete simple features:

SimpleFeatureStore store = (SimpleFeatureStore) ds.getFeatureSource(typeName);
FilterFactory2 ff = CommonFactoryFinder.getFilterFactory2();

String id = ...
store.removeFeatures(ff.id(ff.featureId(id)));

And, clear (delete all) features:

store.removeFeatures(Filter.INCLUDE);

Each operation that creates, modifies, deletes, or clears simple features results in a message being sent to a Kafka topic.