What is Spring?

Spring is usually described as a lightweight framework for building applications on Java, but there are two interesting points associated with this formulation:

First, Spring can be used to build any application in Java (for example, standalone, web, or enterprise (JEE) applications on Java), unlike many other frameworks, and in particular the Apache Struts framework, which is designed only for creating web applications.

Secondly, a simple framework Spring does not really mean the number of classes or the size of the distribution, but the main principle of the entire philosophy Spring - minimal impact.

Source: Book "Spring 5 For professionals" Fifth Edition

Why use Spring in Java?

When writing code on Java, you need to use Spring to make the code beautiful, correct.
Spring is a framework that provides good programming patterns.
For example, the main patern Spring is to manage objects using IoC (Inversion of Control) Spring ...    DI (Dependency Injection) Spring ...

Source: youtube (Евгений Борисов Java Developer)