The document outlines how developers can use the Java transformer in Mule to create custom components or transformers for data transformation. It emphasizes the importance of chaining transformers and using DataWeave for complex scenarios, making it easier to leverage Java for enhanced functionality. It also provides an example of using Java classes to manipulate message properties and payloads within Mule applications.

1. MULE: JAVA TRANSFORMER
ENABLES THE DEVELOPER TO PACKAGE CUSTOM JAVA
CODE

2. BASIC CONSIDERATIONS
• Anypoint Studio provides a set of transformers to
handle the most common data transformation
scenarios
• Developer can chain transformers if a transformer did
not exist for specific needs
• The DataWeave Transform Message component can be
used in place of most other transformers

3. SPECIAL CASES
• Transforming complex data structures
• Applying complex business rules
• The available transformers cannot meet the
requirement
• Simply throw the old lines of code into a component
instead of having to reengineer the code’s behavior
through a series of different Mule components

4. POSSIBLE SOLUTIONS
• Building custom components and/or transformers
• Turning to the most favorite Programming Languages:
o Java
o .NET
o Scripting languages: Groovy, Javascript, Python or Ruby

5. JAVA
• Java is the native language in which Mule is coded
• The Java component enables the developer to package
custom Java code that executes when the component
receives a message
• The Java component can be used to enhance the
functionality and capability of your web-based
applications written in Java

6. JAVA TRANSFORMER (1/2)
• Transforms a message from its original
format to a new, modified format.
• If rather than just changing the
message/payload, trigger a more complex
set of processes coded in Java, use a Java
Component.

7. JAVA TRANSFORMER (2/2)
To configure the Java
Transformer, selecting a
class is the only required
entry:
• Browse for an existing Java
class
• Add a new Java class

8. BASIC JAVA CLASS
• A class must extends:
o org.mule.transformer.AbstractMessageTransformer
Modifies the message and returns it as the output
message of the transformer.
o org.mule.transformer.AbstractTransformer
Modifies the payload and returns it as the output
payload.
• A class must be referenced in a fully-qualified name

9. JAVA CLASS: MESSAGE (1/3)
package com.mulesoft.learning;
import java.util.Map;
import org.mule.api.MuleMessage;
import org.mule.api.transformer.TransformerException;
import org.mule.transformer.AbstractMessageTransformer;
public class MessageTransformer extends AbstractMessageTransformer {
@Override
public Object transformMessage(MuleMessage message, String
outputEncoding) throws TransformerException {
Map<String, String> params =
message.getInboundProperty("http.query.params");
message.setInvocationProperty("myProperty", "Hello, " +
params.get("name"));
return message;
}
}

10. JAVA CLASS: MESSAGE (2/3)
The class has access to Mule Message:
• Inbound Properties
• Outbound Properties
• Payload
• Attachments

11. JAVA CLASS: MESSAGE (3/3)
Run/debug a simple flow
• http://localhost:8081/?name=Max
• It will produce a variable
myProperty, and its value is: Hello,
Max
• It will keep the payload as is

12. JAVA CLASS: PAYLOAD (1/3)
package com.mulesoft.learning;
import org.mule.api.transformer.TransformerException;
import org.mule.transformer.AbstractTransformer;
public class PayloadTransformer extends AbstractTransformer {
@Override
protected Object doTransform(Object src, String enc) throws
TransformerException {
return "Hello, " + src;
}
}

13. JAVA CLASS: PAYLOAD (2/3)
The class has only access to Payload, therefore:
• Add new Byte Array to String Transformer
• Update the custom-transformer class to refer to the new
class

14. JAVA CLASS: PAYLOAD (3/3)
Run/debug the new flow
• Post a raw message: Max
• Send it to http://localhost:8081
• It will produce a new payload: Hello, Max

15. SUMMARY
Mule allows developers to:
• Build their own component and/or transformer
• Simply write their favorite programming language
• Choose the transformation scope

16. RESOURCES:
• https://docs.mulesoft.com/mule-user-guide/v/3.8/java-
transformer-reference