In the context of application delivery, Middleware refers to products and services that provide a software layer that connects the operating system to applications, databases, and users.
Middleware sits between the OS and applications to enable interoperability, it handles messaging, data exchange, authentication, and transactions across distributed systems.
Common examples of middleware include:
Common use cases for middleware include:
Some history of the term “middleware”, plus some alternative uses of the term can be found on Wikipedia, see: Middleware - Wikipedia.
Yes, application servers are considered a type of middleware.
The definition of middleware is that it is software that sits between the operating system and end-user applications. Its role is to provide shared services, communication, integration, and runtime capabilities that applications can use without having to implement them from scratch.
Now consider the role of an application server (such as JBoss EAP, IBM WebSphere, Oracle WebLogic, or open-source WildFly), it provides a runtime environment for enterprise applications, typically based on Java EE (Jakarta EE). Application servers supply services such as:
Application servers don’t usually implement business logic directly. Instead, they provide the infrastructure that allows developers to run distributed, scalable, and secure applications. This makes them part of the middleware layer, connecting the OS/network with higher-level applications.
Middleware interacts with APIs and operating systems, but each plays a distinct role in the IT stack. An operating system (OS) is the foundation software layer that manages hardware resources (CPU, memory, storage, networking) and provides basic services so applications can run. Without an OS such as Windows, Linux, or macOS, applications cannot interact directly with hardware.
An API (Application Programming Interface), on the other hand, is a set of rules or protocols that define how and allow one piece of software to communicate with another. APIs are like contracts—they define how developers can request specific services or data from a system or application, but they don’t handle execution or integration logic by themselves.
Middleware sits between applications, databases, and operating systems, enabling reliable communication and integration. While an API exposes functionality, middleware manages the plumbing: message queues, authentication, transaction management, and data transformation. For example, middleware may orchestrate multiple APIs, ensure secure delivery of messages, and maintain system reliability. Middleware can handle failover and retries when an individual call to an API fails.
