When comparing Grails vs Slim, the Slant community recommends Slim for most people. In the question“What are the best web frameworks to create a web REST API?” Slim is ranked 12th while Grails is ranked 28th. The most important reason people chose Slim is:
Slim's documentation is well organized and detailed, every concept is thoroughly explained and it is very helpful for both advanced users and beginners.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Grails is highly scalable
Grails is an abstraction over Spring and Hibernate. This makes Grails applications fast and scalable. This is because both Spring and Hibernate are themselves scalable.
Pro More than 900 plugins
Grails is a full-stack web framework, not just MVC. It contains a lot of stuff out of the box, but it doesn’t enforce it. It contains over 900 plugins which provide a Groovy API for a lot of useful and well-known Java libraries. And what is more important is that they are super easy to install!
Pro Very fast setup and scaffolding
Setting up a new project is quite fast and code generation (scaffolding) saves you a lot of time. It also uses a convention over configuration principle which helps you bypass all the configuration trouble.
Grails also comes with a reloading mechanism out of the box.
Pro Easy to use
Grails is designed to be a rapid development framework with a straight learning curve. It advocates convention over configuration. Extensibility is very simple when using plugins (there is a lot of them). One command in the console – and all the dependencies and configurations are managed for you.
Pro Great UI design alternatives
Do you need something advanced in the UI? You can either create it in GSP with an addon of CSS/JavaScript or you can find a plugin that will do the work for you. Plugins include integration with Bootstrap, jQuery, Yeoman and much more.
Pro Great documentation and community
The Documentation section is actually a wiki, which can be modified by any logged in user. It has an official manual, tutorials, screencasts, a sample app and much more. If that does not do it for you, then there are countless third-party tutorials, more than 12k questions on SO and much much more
Pro Well organized and thorough documentation
Slim's documentation is well organized and detailed, every concept is thoroughly explained and it is very helpful for both advanced users and beginners.
Pro A good starting point
Slim is minimal and that is a good thing if you want to start from there. It can be easily extended and even supports popular packages that are used in Laravel (like Illuminate\Database (eloquent)) for example.
Pro REST based
REST fans will love the REST based architecture.
Pro Supports tie-ins for Rack-like middleware
Rack is an interface used in Ruby frameworks used to group and order modules, which most of the time are Ruby classes, and specify between them.
Slim uses a simple concept for it's middleware. By wrapping HTTP requests and responses it unifies the middleware into a single method call.
Pro Useful classes
Contains classes for managing requests, responses, cookies, logging, views, HTTP caching, and more.
Pro Flexible
Slim doesn't demand that you stick to a fixed folder structure. As long as you load Slim the right way you can do anything from there the way you like it.
Pro Extremely lightweight
Paired with swoole it's a micro service powerhouse.
Pro Open source
The Slim Framework is open source and is released under the MIT public license
Pro Extremely customizable
You can add any dependency, package or class that you want to use as a contained dependency.
Pro Supports Php 5.3 and PHP 7
Pro Makes it easy to understand the way some abstract functions and classes are built
In Django most things are abstracted, you just call some function or class without knowing how they were built, but with Slim, you end up understanding the way some abstract functions and classes are built.
Pro Hooks for executing code at different points in its life-cycle
Slim supports code hooks for executing functions at different points in time during the application's lifecycle.
Cons
Con Grails is a fairly complex framework
Grails is a pretty heavy piece of software. It's functionality is covered by GORM (Grails' Object Relational Mapping) which is a facade for hybernate and by Spring MVC.
Everything is glued by core Spring and furthermore, Grails adds another level of abstraction on top of all this. These things may create some trouble down the road when debugging.
Con Too obtuse and JVM centric
If you're a big fan of the JVM and have mastered all its goofy quirks, Grails might be a good choice, but there are other frameworks out there that are more straightforward and easier to use.
Con Very little consistency among different versions
There have been quite some changes that break the compatibility between Slim 2 and Slim 3. Even if you learned how to work with the Slim 2, you will find that Slim 3 requires re-training.
Con Dependency injection is too weak
It is not really dependency injection, but just a configurable container.
Con Needs strong bases to create dependencies
The dependency container schema of Slim is one of the biggest PROS and CONS of the framework. It is true that this schema brings so much flexibility to add anything, but another thing that is true is that you need to have strong bases of patterns, and an extensive knowledge of your libraries to convert it into a Slim dependency.
Con Too minimal
While it's true that Slim is a microframework, it's still too minimal. When used for throwaway projects or simple prototypes, it's perfect. But in the long run, it becomes less and less useful and you end up in implementing a full custom framework in trying to tackle all the missing features.
