Mule 3 to Mule 4 Cheat Sheet

Configuration Properties: There’s a new way of handling configuration properties in Mule 4

Using Secure Properties: Secure placeholders are now a Runtime feature and no longer part of the Security Module

Using the HTTP Connector: The new HTTP connector has some differences with Mule 3, especially when it comes to handling multipart and form requests.

From MEL to DataWeave: DataWeave 2.0 is now the expression language. Here’s how to adapt your MEL expressions to DataWeave.

From DataWeave 1.0 to DataWeave 2.0: A new version of DataWeave is available in Mule 4

Where are the explicit transformers?: Transformers like <object-to-string /> or <object-to-json> are no longer necessary. Mule handles this automatically under the covers

Define a custom Object Store: Custom Object Stores are now defined through the new connector

Use watermarks: Watermarks have been simplified. You can also do it manually now allowing for more complex use cases.

Accessing the Mule Message: The Mule Message has a new structure and it’s accessed differently. Here’s a quick overview.

Using Java: Interoperability with Java is now done through the Java module. Optionally you can also try the Scripting module or the Mule SDK

Using Spring: Instead of defining Spring beans directly in your application, you can now use the Spring Module.

Using reconnection strategies: There are some small but important differences around reconnection in Mule 4.

Classloading isolation: Classloading isolation changes the way resources and classes are shared. Read this article to learn more.

Core Components Migration: A comprehensive list of the changes that were made to the core language elements

Using the new connectors: A comprehensive list of the changes that were made to the main connectors.

Using the Security Module (AES): Anypoint Enterprise Security module was split into different modules explained here.

Migrating Gateways: This section covers the migration of API Gateway related features.

Migrating ApiKit apps: Covers the necessary steps to successfully migrate APIkit-based applications.

Migrating custom components: You can use the Mule SDK to create your own reusable components

Migrating DevKit based components: There’s a DevKit Migration Tool that helps to migrate DevKit projects for Mule 3 into Mule SDK ones.

Transport service overrides: Covers how to migrate from generic transports.