Porting Kettle Plugins

Change maven dependencies

You no longer need a Pentaho specific $HOME/.m2/settings.xml

  • Change group pentaho-kettle to org.hop

  • Change dependency kettle-core to hop-core

  • Change dependency kettle-engine to hop-engine

  • Change dependency kettle-ui-swt to hop-ui-swt

API changes

Interface naming

All interface classes have changed from <Name>Interface to I<Name>. For example: RowMetaInterface → IRowMeta


Transformations are now called Pipelines. This means that the corresponding classes have changed.

For example: - TransMeta is now called PipelineMeta - Trans is now called Pipeline


Steps are now called Transforms. For example:

  • StepMeta is now called TransformMeta

  • StepMetaInterface is now called ITransformMeta

  • BaseStep is now called BaseTransform

  • StepDataInterface is now called ITransformData

…​and so on

Transform Generics

ITransform no longer expects you to pass ITransformMeta and ITransformData classes in the following methods:

  • processRow()

  • init()

  • dispose()

  • stopRunning()

This greatly simplifies the code. Your need to let Hop know what the relationship is between your implementation of ITransform, ITransformMeta, ITransformData, for example:

public class Sample extends BaseTransform<SampleMeta, SampleData> implements ITransform<SampleMeta, SampleData> {



The same is true for your implementation of ITransformMeta:

public class SampleMeta extends BaseTransformMeta implements ITransformMeta<Sample, SampleData> {




Any references to Repository, including parameters and the saveRep() and loadRep() methods in Transforms and Actions can be safely removed


VariableSpace was renamed to IVariables The API has also been cleaned up and simplified. For example, environmentSubstitute() is now called resolve() Please note that metadata objects (TransMeta, JobMeta, DatabaseMeta, …​) no longer implement VariableSpace (or IVariables). Only runtime objects like Pipeline, Workflow, ITransform and so on have a state in Hop.

Extension point plugins

If you’re porting classes implementing an Extension Point plugin by implementing ExtensionPointInterface please note that you’ll receive an extra parameter which is IVariables. It aims to contain the variables of the parent object in the XP context. Obviously the interface name changed to IExtensionPoint. You can also use generics to specify the expected class of the receiving subject.

Slave Servers and Database Connections

These objects are no longer stored in a Pipeline or a Workflow, they are now fully shared objects so any references of those in the interface methods of Transforms and Actions can be safely removed:

  • List<DatabaseMeta> databases

  • List<SlaveServer> slaveServers

MetaStore → HopMetadata

The MetaStore code is unfortunately LGPL licensed and for that reason removed from the project. It was replaced by the general IHopMetadataProvider instead of the IMetaStore references. At any given time you can ask the current IHopMetadataProvider to give you a serializer for a metadata class. This IHopMetadataSerializer can then be used to CRUD objects as well as list and so on.

For more information on how to implement Hop Metadata plugins, see: Metadata Plugins.

MetaStore elements can now be managed in a standard way. In your transform dialogs you can use the widget:

MetaSelectionLine<T extends IHopMetadata>

This will take care of adding label, tooltip, combo box and a few buttons to manage the metastore elements.