What does that mean? What does Spring Boot give me that Tomcat doesn't?
Tomcat is a servlet container that implements various Java EE specifications, such as the servlet spec, jsp spec, etc.
Spring encompasses many different libraries. The most widely used is probably Spring MVC, which builds on top of the servlet spec to make building web applications easier. After that Spring Security is probably most widely used, which adds things like auth, CSRF tokens, etc. Spring Data and Spring Cloud are also somewhat popular. There are many more Spring libraries, but I have little to no experience with them.
You can really give or take what you want here. You can use Spring MVC with Spring Data, or Hibernate, or JPA, JDBC, or whatever you want really. One place I worked used Spring MVC with home grown security and ORM layer.
Spring Boot brings "convention over configuration" to Spring. Because Spring is so configurable it can take a lot of boilerplate. Spring Boot removes much of that boilerplate for certain use cases and has, generally speaking, more user friendly defaults.
Spring Boot also runs off a server embedded in the jar. That's why you can "just run" it. You create a "Main" method. You can choose from several embedded servers, including Tomcat. But this isn't exactly special for Spring Boot because you could do this even if you didn't use Spring Boot.
Most of my apps just code against the servlet spec with a JDBC connection to a MYSQL database, sometimes with JSP. Perhaps because most of my business logic lives on the client I've usually found that plain servlets + plain JDBC calls were sufficient
Although I've found it pretty straightforward to configure servlets in Tomcat I can see that Spring MVC makes it a little easier. Maybe the introduction of a framework 'Model' is also an advantage - I'll investigate further.
Regarding Spring security - would I use this package if I was implementing a "Login with Email/Password or Facebook or Google" feature to a website?
Not forgetting that dependency injection -- the original core feature -- is just the bee's knees.
I work for Pivotal, but not on Spring. But I've definitely grown to appreciate it more and more over the years. I deeply miss it when mucking about in Golang.
