Middleware enables developers to build applications without creating a custom integration whenever they need to connect to application components (services or microservices), data sources, computing resources or devices.

Middleware does this by providing services that enable different applications and services to communicate through common messaging frameworks, such as JavaScript object notation (JSON), representational state transfer (REST), extensible markup language (XML), simple object access protocol (SOAP) or web services. Typically, middleware also provides services that enable components written in multiple languages—such as Java, C++, PHP and Python—to talk with each other.

Standard middleware architectural components include the following:

• Middleware management console: The management console gives developers an overview of middleware events, activities, configurations and so on.

• Client interface: The client interface on the front-end communicates with back-end applications, databases microservices or other services.

• Middleware internal interface: The middleware internal interface allows middleware instances to communicate with each other using a special middleware protocol.

• Platform interface: The platform interface connects to back-end servers and different operating systems (OSs), ensuring middleware functions across platforms.

• Contract manager: The contract manager defines the data exchange rules that applications must follow.

• Session manager: The session manager ensures secure communication between middleware and applications and ensures they are not timed out.  

• Database manager: The database manager provides integration with different databases based on specific requirements (for example, on-prem or cloud-based data).

• Runtime monitor: The runtime monitor keeps track of all middleware data movements and provides activity reports for software developers.

There are many different types of middleware. Some focus on specific types of connectivity, others on particular applications, application components and devices. Some combine middleware capabilities for a specific software development task. Some of the best-known and most commonly used types of middleware software include the following:

• Message-oriented middleware (MOM)

• Remote procedure call (RPC) middleware

• Data or database middleware

• Application programming interface (API) middleware

• Object request broker (ORB) middleware

• Transactional middleware

• Asynchronous data streaming middleware

• Device middleware

• Portal middleware

• Robotics middleware

• Enterprise application integration middleware

Message-oriented middleware (MOM) enables application components that use different messaging protocols to communicate and exchange messages. In addition to translating or transforming messages between applications, MOM manages the routing of the messages, so they always get to the proper components in the appropriate order. Examples of MOM include message queues and message brokers.

Remote procedure call (RPC) middleware enables one application to trigger a procedure in another application—running on the same computer or a different computer or network—as if both were part of the same application on the same computer.

Data or database middleware simplifies access to and interaction with back-end databases. Typically, database middleware is some form of SQL database server.

Application programming interface (API) middleware provides tools developers can use to create, expose and manage APIs for their applications so that other developers can connect to them.

Some API middleware includes tools for monetizing APIs, enabling different organizations to use them, at cost. Examples of API middleware include API management platforms, API gateways and API developer portals.

Object request broker (ORB) middleware acts as a broker between a request from one application object or component and the fulfillment of that request by another object or component on the distributed network.

ORBs operate with the Common Object Request Broker Architecture (CORBA), which enables one software component to make a request of another without knowing where the other is hosted or what its user interface (UI) looks like—the "brokering" handles this information during the exchange.

Transactional middleware provides services to support the execution of data transactions across a distributed network. The best-known transactional middleware is transaction processing monitors (TPMs), which drive transactions from one step to the next—running the data exchange and adding, changing or deleting data where needed, among others—through to completion.

Asynchronous data streaming middleware replicates a data stream in an intermediate store, enabling data sharing between multiple applications. Apache Kafka is one of the best-known examples of middleware open source platforms for real-time event streaming.

Device middleware provides a focused set of integration and connectivity capabilities for developing apps for a specific mobile operating system (OS).

Portal middleware provides tools and resources for integrating content and capabilities from various related applications 'at the glass' or on a single screen to create a single composite application.

Robotics middleware simplifies the integration of robotic hardware, firmware and software from multiple manufacturers and locations.

There are two basic classes of middleware: enterprise application middleware and platform middleware.

Enterprise application integration middleware enables an organization to establish an enterprise integration hub. This provides a standardized way to connect all applications, application components, business processes and back-end data sources throughout the extended enterprise.

Until about a decade ago, the most prevalent enterprise application integration middleware was the enterprise service bus (ESB), which served as the integration hub within a service-oriented architecture (SOA).

Today, integration platform as a service (iPaaS) allows an organization to connect applications, data, processes and services across a hybrid cloud—the combination of on-premises, private cloud and public cloud environments. This helps organizations avoid the work and expense of purchasing, installing, managing and maintaining the integration middleware (and the hardware it runs on) within its own data center. Major cloud service providers (CSPs)—Microsoft Azure, Google Cloud, Amazon Web Services (AWS) or IBM Cloud—all offer iPaaS solutions.

Platform middleware (or application platform middleware) supports application development. It accelerates application delivery by providing a runtime hosting environment—such as a Java runtime environment (Java RE), containers or both—for application or business logic. Platform middleware can include or combine enterprise application servers, web servers, content management systems (CMSs) and other middleware types listed above.