# Transformers

A transformer, as the name suggests, is a component which transforms a message. For example, a transformer could modify the body of a message or add or remove properties. Both diverts and core bridges support.

A transformer is simply a class which implements the interface `org.apache.activemq.artemis.core.server.transformer.Transformer`:

    public interface Transformer {

       default void init(Map<String, String> properties) { }

       Message transform(Message message);
    }

The `init` method is called immediately after the broker instantiates the class. There is a default method implementation so implementing `init` is optional. However, if the transformer needs any configuration properties it should implement `init` and the broker will pass the configured key/value pairs to the transformer using a `java.util.Map`.

## Configuration

The most basic configuration requires only specifying the transformer's class name, e.g.:

    <transformer-class-name>
       org.foo.MyTransformer
    </transformer-class-name>

However, if the transformer needs any configuration properties those can be specified using a slightly different syntax, e.g.:

    <transformer>
       <class-name>org.foo.MyTransformerWithProperties</class-name>
       <property key="transformerKey1" value="transformerValue1"/>
       <property key="transformerKey2" value="transformerValue2"/>
    </transformer>

Any transformer implementation needs to be added to the broker's classpath. See the documentation on adding runtime dependencies to understand how to make your transformer available to the broker.

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