Integration is important because applications are intended to interact with each other. Forcing them to work in isolation makes them useless.

It's common to find companies that have their own software, developed in-house, to solve their specific business requirements; but, since certain scenarios tend to be common for more than one company, there are third-party services that can fulfill these needs. Since the functionality offered by these systems is ready to use, we have to find a way to make these applications work as a single system, and that's where Enterprise Integration Patterns (EIP) come into play.

EIPs provide proven solutions to recurring problems that can be applied in different contexts with slight modifications, depending on particular business needs. There is a vast catalog of these patterns available on the internet, and a must-read within this field is the book Enterprise Integration Patterns, by Gregor Hohpe and Bobby Woolf. This book explains a large list of patterns, along with example scenarios, by using a technology agnostic approach.

Once you understand the theory around EIPs, you will find Spring Integration pretty handy for implementing them; it will have all of the benefits inherent to the Spring Framework, as discussed previously.

When we discuss integration, we can consider the concept using a three-step approach. Let's start reviewing the following diagram which shows these three steps:

The following is a list of steps that are executed as a part of the preceding process:

1. There is a data source where the information is extracted; a poll is sometimes needed, in order to ask for data.
2. The ingested data is filtered, transformed, composed, decomposed, routed, and so on, depending on what's required. It's here that the EIPs are used.
3. The processed data is ready to be delivered or stored, depending on what is needed.

Spring Integration provides built-in support for retrieving or sending information from or to queues, databases, system files, FTP servers, and many other options. Moreover, if needed, you can write your own implementation and plug it in, in order to make it work as a part of your process. The DSL provided by Spring makes it easy to read and implement the EIPs.