Java client#

Starting from version 3.9.0-RC13, HSFS provides a pure Java client. This guide explains how to use the client to connect to Hopsworks and read or write feature data.

Generate an API key#

For instructions on how to generate an API key follow this user guide. For the Java client to work correctly make sure you add the following scopes to your API key:

1. featurestore
2. project
3. job
4. kafka

Add the HSFS dependency to your project:#

The HSFS library is available on the Hopsworks' Maven repository. If you are using Maven as build tool, you can add the following in your pom.xml file:

<repositories>
    <repository>
        <id>Hops</id>
        <name>Hops Repository</name>
        <url>https://archiva.hops.works/repository/Hops/</url>
        <releases>
            <enabled>true</enabled>
        </releases>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
    </repository>
</repositories>

The artifactId for the HSFS Java build is hsfs, if you are using Maven as build tool, you can add the following dependency:

<dependency>
    <groupId>com.logicalclocks</groupId>
    <artifactId>hsfs</artifactId>
    <version>${hsfs.version}</version>
</dependency>

Connecting to the Feature Store#

You are now ready to connect to the Hopsworks Feature Store from a Java client:

//Import necessary classes
import com.logicalclocks.hsfs.FeatureStore;
import com.logicalclocks.hsfs.FeatureView;
import com.logicalclocks.hsfs.HopsworksConnection;

//Establish connection with Hopsworks.
HopsworksConnection hopsworksConnection = HopsworksConnection.builder()
  .host("my_instance")                      // DNS of your Feature Store instance
  .port(443)                                // Port to reach your Hopsworks instance, defaults to 443
  .project("my_project")                    // Name of your Hopsworks Feature Store project 
  .apiKeyValue("api_key")                   // The API key to authenticate with the feature store
  .hostnameVerification(false)               // Disable for self-signed certificates
  .build();

//get feature store handle
FeatureStore fs = hopsworksConnection.getFeatureStore();

//get feature view handle
FeatureView fv = fs.getFeatureView(fvName, fvVersion);

// get feature vector
List<Object> singleVector = fv.getFeatureVector(new HashMap<String, Object>() {{
        put("id", 100);
        }});

Update feature data#

The Java client allows you to update data on existing feature groups using the streaming interface. You can provide a list of POJO objects to the insertStream method.

The feature group should exists already (can be created using the Python client) and the POJO objects should be serializable with the feature group's AVRO schema.

Please see the tutorial for a code example on how to write data.

Limitations#

Currently using the Java client to retrieve feature vectors have the following limitations:

• Only the SQL interface is supported. It is not possible to retrieve feature vectors using the REST API Interface
• Feature Views with model dependent transformations attached are not applied. If your feature view has model dependent transformations, please use the Python client.

Next Steps#

You can find more information on how to interact from Java client in the JavaDoc or this tutorial