Custom Validation in Mule 4 Using Mule SDK

Validators are the operations that validate a Mule message without changing it. Validators can produce the following effects:

• Validator condition is fulfilled: the flow continues and the Mule message remains unchanged
• Validator condition not fulfilled: an error is thrown

Today, we will be creating a custom validation that will indicate whether the currency is valid or not.

Prerequisite

• JDK 1.8 or 11
• Apache Maven (at minimum, 3.3.9)

Steps To Create Custom Validator

• Create Project: Go to your project folder and run the Maven command to generate the project for the mule validator extension: mvn org.mule.extensions:mule-extensions-archetype-maven-plugin:1.2.0:generate

• Remove Connector Configurations: delete the four java classes below. These files will be used for the custom connectors.
  * CurrencyValidatorConfiguration
  * CurrencyValidatorConnection
  * CurrencyValidatorConnectionProvider
  * CurrencyValidatorOperationsTestCase
• Currency Dependency: add the dependency below in pom.xml for currency.

• CurrencyValidatorExtension: this is a currency validator extension class. Add the lines below in this class.

• CurrencyValidatorOperations: the class below adds a validation method that is annotated with @Validator. The method throws an error type that comes from the generic validation error type. Note that you can also annotate the class CurrencyValidatorOperations with @Validator, but if you do, any other operations in it will be flagged as validators.

• CurrencyError: creates the error to throw if the currency validation fails. Notice that it is named according to the validation failure.

• CurrencyErrorsProvider: the validator method needs a ErrorTypeProvider that knows all the error types that the validation can throw. This example creates a ErrorTypeProvider that says that the only error the method can throw is of type CURRENCY-VALIDATOR:INVALID_CURRENCY_CODE .

• Validator Icon: go to the project root directory and create an icon folder. Place an SVG file image in this folder and the icon file name should be icon.svg.
• Maven Build: go to the project directory and run the terminal. Run mvn clean install to build the project.

How to use Custom Validators in a Mule Application

• Create a Mule Application: go to Anypoint Studio and create a Mule application to test the custom validation.
• Add Custom Validator Mule Plugin: go to pom.xml and add the dependency for the custom validator Mule plugin for currency. Make sure you have added the classifier as Mule-plugin. The dependency information will come from the Mule SDK validator.

• HTTP Listener: add an HTTP listener with the default configuration in the test Mule application.
• Currency Validation: drag the currency validation and pass the currency. We are reading the currency from query params.

• Failed Validation Execution: below is the Mule application error logs for invalid currency. Curl command: curl --location --request GET 'localhost:8081/currency?currency=RUPEE' .

• Success Execution: if we pass the correct currency, we will get no validation error and response as currency INR. Curl command: curl --location --request GET 'localhost:8081/currency?currency=INR' .

Here is the Github repository for Mule custom validation.

Conclusion

Today, we have learned how to develop Mule custom validation using Mule JAVA SDK. In the next tutorial, I will cover the Mule SDK for the rest API.