Mule application building blocks are separated into categories in the Mule 3 Palette:

Add modules in Mule 4

Search from Exchange and Add in Mule 4

Now lets discuss about components

Message Sources :

The first building block of most flows is a receiver that receives new messages and places them in the queue for processing.

• Message sources are usually Anypoint Connectors.
• Connectors provide connectivity to external resources, such as:
• Databases, protocols, or APIs.
• Standard protocols like HTTP, FTP, SMTP, AMQP.
• Third-party APIs like Salesforce, Twitter, or MongoDB.

Anypoint Connectors :

• There are 2 main types:
• Endpoint-based connectors
• Operation-based connectors

Endpoint-Based Connectors :

• Are either inbound or outbound endpoints in a flow.
• Inbound endpoints serve as a message source for a flow.
• Outbound endpoints send information to external systems.

Operation-Based Connectors :

• These connectors require the specification of an operation in order to perform.
• This category includes most connectors not based on a standard communication protocol

Connector vs Endpoint :

• A connector is a Mule-specific connection to an external resource of any kind.
• An endpoint is a flow-level element that is configured to receive and/or send messages from and/or to external resources.
• When you drag a connector from the Mule Palette, an endpoint is created.
• Connectors and endpoints are global elements.

Creating Mule Applications With Anypoint Studio

Anypoint Studio is an Eclipse-based integration development environment that provides:

• Two-way editing between graphical and XML views.
• Visual debugging (EE).
• A data transformation framework and language (EE).
• One-click deployment of applications.
• Templates for common integration patterns (EE).
• Integration with Maven for continuous build processes.

Sample Flow: Visual

Anypoint Studio View: 

Running an Application:

Anypoint Studio comes with an embedded Mule runtime to test applications without leaving it.
The console outputs application logs and information:

Introducing Mule Flows and Message

Mule Flows

Mule applications accept and process messages through a series of message processors plugged together in the flow.

A typical flow has:

Message Source  – Accepts a message from an external source, triggering the execution of the flow.
Message Processors – Transforms, filters, enrichs, and processes messages.
An application can consist of:

• A single flow.
• Multiple flows/subflows connected together to create more complex applications.

Anatomy of  a Flow : 

artifacts-json: In Mule 4

Pom.xml: 

Pom file is now required for Mule 4 app build. All mule app in mule4 is packaging as mule-application 

Project Explorer: 

Below Project explorer shows how the structure of Mule 4 App will look like:

Runtime Selection: 

You can select your required runtime by selecting through Run/Debug as configuration

Quick Access: 

Munit Coverage View: 

Testing Applications: For testing Mule Application

Some options:
• A browser.
• A cURL command-line utility.
• A browser extension like Postman (for Google Chrome).