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How to create Jar library file which automatically creates rest api endpoints to a spring boot application?

I want to create a library jar file. When I bring that to a spring-boot application it should make the application to have Rest API endpoints, without adding any #RestController to the spring-boot application.
For example, I want to create custom-oauth.jar library. When I include the custom-oauth.jar to the spring-boot application, the application should have http://localhost/token and http://localhost/validate ... etc.
I know this is a very common case for spring applications, and there are so many jar files which does this, but I can't find how to implement that in the Spring documentation.
Where should I start reading and what tools I should use?

The most straightforward way to do this in a Boot application is to write your own autoconfiguration module. In short, you create one or more "bootstrap" #Configuration classes and list them in META-INF/spring.factories. They can then do whatever sort of operations you'd normally do (like registering #Beans or #ComponentScans for controller classes included in the jar).

Spring boot basic

Just started exploring spring boot and trying to understand.....
In a normal project scenario, we create multiple projects / modules depending on functionality. Ultimately, package all different jars , wars in .ear and deploy it.
With spring boot, new project are deployed on a separate of instances of tomcat.
But if all these projects are related, it will need reconciliation of proprty files and any other resources differently utilized, before you create .ear.
While I understand the advantages of spring boot while development, is there any thought on how to make this process better when using spring boot?

Modern cloud architectures are moving away from using property files. Your Ops or DevOps teams should appreciate if your app would accept configurations via system properties. Spring Boot is perfectly suited for that.
Older fashioned orchestrators would replace placeholders in your properties files during deployment phase.

Adding spring mvc to a spring java "desktop" application

I have a Java desktop application which uses spring framework and I need to replace the Swing UI with a web front end. I understand that I will need to adapt many things to make things work with the MVC architecture.
My concrete question is the following:
Will my application now have to run entirely in the application server?
I would appreciate if anyone could point me to some documentation that goes through a similar process.
Thanks!

Technically yes, but Spring Boot makes it trivial to set up an embedded servlet container and package your entire application as a runnable jar. This is how we're deploying our applications to production; the only thing we need is a JRE on the server VM, and java -jar takes care of all of it.
I recommend using Maven with the Spring Boot plugin (there's also a Gradle plugin) with the repackage goal, and using the lightweight Undertow servlet engine instead of the default Tomcat.

Adding a web interface (Spring MVC) to existing Java application

I have an existing Java application (Spring based) that currently does NOT have a web interface, nor does it run in a web container. It packages up nicely with a start program and just works.
What I need to do is add an administrative web interface for some administrative type things, retrieving real time metrics, and perhaps some graphs to give the users a warm fuzzy feeling knowing that everything is working. As we are a Spring shop, and some of our web applications already use Spring MVC it only makes sense to us, however, I'm not happy with the suggestions I've had from our internal Spring folks on how I should procede.
What would be the ideal way to bolt on this web interface?
Convert my application to a web application and have a web container launch the application. I not too keen on this approach is the web tier is really secondary to the primary application.
Create a separate project that packages as a war, embed Jetty in my existing app and have it load the war. I think I can use the context loader listener to make the root context of my application the parent to the web application spring context. This would involve breaking up my Maven project into 2 projects I believe. I can't use an existing web technology for communication between the web tier and the primary application as my primary application is not web enabled.
Embed Jetty and put the Spring MVC stuff directly in my app. While I've done this approach before, it does involve some ugliness - for instance exploding the JSP tag libs into my jar.
Any thoughts on some clean separation here?
Also of note, my current jar contains some utility applications which some shell scripts launch. Going a pure WAR route would make this not so easy, since I can't juse point java at my war file and choose a class to execute.
Thanks.

If it's true that web is just a minor addition the application, migrating it to WAR and deploying in servlet container might be an overkill. Embedding web server/servlet container looks much simpler, although it doesn't have to be Jetty or Tomcat. You can use web server built into JDK or write one on top of netty or even raw sockets. But that's a hell to maintain.
Yet another solution to springs to mymind when reading:
web interface for some administrative type things, retrieving real time metrics, and perhaps some graphs
Maybe you don't need an interface, but monitoring infrastructure instead? Check out JMX (Spring has great support for JMX) - and write a second web application that simply connects to your standalone Java app via JMX and displays the metrics in fancy way. Another approach is to expose JMX via Jolokia, which translates JMX to REST services.
This approach has several advantages:
monitoring API is universal, and you get it for free
you don't have to use web client, monitoring application is completely decoupled,
finally changes to your original application are minimal. Check out this proof of concept: 1, 2.

It really depends on the structure of your existing Java/Spring app and how much of an API it provides. I've done something similar to this and I approached it by creating a separate Spring MVC project and then specified the existing Java app as a JAR dependency.
This is easy with Maven (or Ivy, etc) and provides nice decoupling. The trick is to be able to write service classes in the Spring MVC app which then access data via your dependent Spring app via a simple DAO class. That's why I stated at the beginning, that it depends on the structure of your original Java app. It has to be able to provide an API for data access that you can then plug your DAO (impl) into.
If this is not easily done, then the next option I'd suggest is simply converting your Spring app to a Spring MVC app. I've worked on another app where we did this. Using Maven, its possible to specify that the build can create either a war file or a jar file (or both). So it can be deployed as either a webapp (via war) or a normal app (via jar). Yes, the jar version has a bit of bloat but its a worthwhile compromise.
The question of embedding Jetty or using Tomcat via a war file is a completely separate issue that has its pros and cons. It shouldn't affect the approach you take in architecting the web app in the first place.

What do I need to download to start developing apps using the Spring framework?

I need to start developing applications using the Spring framework, and am wondering what tools I need to download to have me up and running.
On the SpringSource website I am seeing all these applications to download and I am wondering, do I really need all this? And what versions should I use, especially for Spring Framework?
Spring Framework
SpringSource dm Server Samples
Spring Security
Spring Web Flow
Spring Web Services
Spring Dynamic Modules
Spring Integration
Spring Batch
Spring.NET
Spring JavaConfig
Spring LDAP
Spring Extensions
Spring IDE
Spring BlazeDS Integration
SpringSource Bundlor
Spring ROO
What other applications do I need to download (eg. Struts, Glassfish, Apache, etc.)?

This depends on what you want to use Spring for. Typically that's Web applications. If so you only need two things:
Spring framework (with minimal dependencies); and
A servlet container (eg Tomcat) or a full-blown application server (eg Glassfish, JBoss).
Everything else is optional. I believe the only required dependency is Apache Commons logging. Depending on what features you use, you may well need more.
If so, here is a [tutorial][1] that creates a barebones Spring MVC project. There are countless others around for that and other topics.
It's entirely possible to use Spring in, say, a Swing application in which case you obviously don't need a servlet container.

All you need from SpringSource is the Spring Framework.
Spring 3.0 is on the way, but for now, use 2.5.6.SEC01, the current production release.
You can get started with a simple servlet container (ie: Tomcat) rather than a full blown application server (eg: JBoss, Glassfish).
The Spring Framework comes bundled with jars for web development - ie: spring-web and spring-webmvc.
See #117535 for a simple example of using Spring MVC.

It mainly dependent on what you need Spring for. Each and every piece of Spring can, actually, be used in separation from the rest. You may use it only for IOC, in this case you don't need, for example, MVC and Servlets, etc...
The easiest way to start is to dowload the main package from http://www.springsource.com/download/community?project=Spring%20Framework
You can use Spring from any IDE

The best way is to use Maven with your project. Basically all you have to do is edit your pom.xml file and tell it that you want to use Spring. Then when you compile your code, Maven will go out and automatically download the Spring libraries you need from their public repository.
Here's an example:
http://pookey.co.uk/blog/archives/63-Getting-started-with-Maven-and-Spring.html