Java Methods in Mule 4 Using DataWeave

In this blog, we will discuss how to import Java classes, call Java functions, instantiate Java classes that are present in our Mule project through DataWeave. We can only call Static methods via DataWeave (methods that belong to a Java class, not methods that belong to a specific instance of a class).

Note- The Listener configuration we’ll be using in all the examples is:

1. Calling a Java static method through DataWeave:

Step 1: Create a Mule project named call-static-method-from-java-class.

Step 2: Create a Java class named NumberToBaseThirtySixString under base.thirtysix.string package inside src/main/java folder.

Step 3: Create a mule flow in which we will actually call the static function present inside our Java class.

Listener Path:

Transform Message Configuration:

Before calling the static function in our DataWeave code, we need to import the Java class in which that function is present. For importing a Java class in our DataWeave code, we use the syntax –
import java! followed by a fully-qualified class name. For example, here we will import our Java class with import java!base::thirtysix::string::NumberToBaseThirtySixString.

Postman Output:

2. Calling a Java static method through DataWeave in a single line:

Listener Path:

Transform Message Configuration:
In this method, there is no need to import the java class separately and then call the static method. We can call the static method through a single line.

Postman Output:

3. Instantiate a Java class in DataWeave:

Step 1: Create a Mule project named instantiate-a-java-class-in-DataWeave
Step 2: Create a Java class named Student under com.student package inside src/main/java folder.

Step 3: Create a mule flow in which we will instantiate our Java class.

Listener Path:

Transform Message Configuration:

In this DataWeave code, we are instantiating the Student class. The instances of the java classes created in our DataWeave code can refer to the instance variables but not instance methods. To instantiate our Java class, we need to follow these steps:

Step 1:  Import our class in the DataWeave code.

Step 2: Create its instance using the ‘new’ keyword.

Postman Output:

 4. Call instance methods through DataWeave:

Listener Path:

Transform Message Configuration:

Postman Output:

Hence this output shows that we can’t access instance methods in DataWeave.