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how to split a web application in different wars as modules?

I have a web application with different features such as map view, dashboard, report etc. But now, we are planning to split the application in different modules such as map module, dashboard module, etc. to make plug-gable as per the requirement. As all the modules will have their respective htmls, js, controllers, dao layers, how can be these divided as independent modules? Will it be a war or a jar files?
Need a suggestion or example which can help me move forward.
Thanks.

If you have different modules, with independent features. Its possible.
I recommend you, to first, find what features are common to all web-modules, so this common-module, should be installed (as a jar for example) in the library folder of your server.
Then, all the modules could be installed in the webapps of your server (in tomcat is called as webapps).
Important:
You must be careful not to duplicate libraries in each web-module, beacause this would generate conflicts. All your common jars (libraries or your own modules should be installed in the libs folder).
If you are using maven I recommend you to have a parent maven project with all your dependencies included, and then all the modules which needs these dependencies can import it as provided.

Microservices might be your best approach given the requirement you are sharing here. Each module i.e reporting, dashboard etc will be a separate microservice. If you use spring boot, you will end up creating multiple jar files and each jar file can be booted on the VM as a separate process and each one comes with its own container (tomcat). Makes things simple.

If all sub modules of your project are tightly coupled it is very difficult to split it. I suggest you to develop new different projects using reference of your old project. There is no technique to split existing project to different war files.

if you use Maven, you can create a parent with all common dependencies, and in its pom.xml you should define all your modules in <modules> </modules> tag. Be careful about the version of the artifacts, it should be the same version when you reference it in child pom.xml, in the parent tag.
About microservices, they are independent services and on every server is just running a single service. So, if you have multiple modules or if you more than one service on each server, it will be in conflict with MS concept.

Sharing a Spring MVC project

I need to do a Java web project. I'm going to be using Eclipse.
I thought of using Spring MVC. As far as I can tell - it's gonna require me to add some "extra" stuff to a "clean" Java web project. I don't mind that - the thing is - one of the project requirements is - that I'll be able to send the project to someone else - that doesn't have any extra installation and/or configuration - and he will be able to compile the project.
Is that possible with Spring MVC? Does the Spring MVC framework is just a "JAR" like addition to the project - therefore - the project can be shared without a problem?
Thanks.

Short answer: yes, you are right.
To use Spring in your Java web project, you generally need to add two things:
the appropriate Spring configuration file(s) (XML)
the appropriate Spring JAR files (traditionally placed in /WEB-INF/lib, the same as other JARs). By the way, it is NOT a single JAR file, but several JAR files.
That is all there is to it.

Spring has nothing to do with "sharing the project".
To "share" the project with someone else, you put it on the SCM of your choice and your collaborators will be able to get the code and work on it.
Building the project is a different aspect. To correctly compile the project you have to make sure that all the classes and/or jars are visible in the classpath (and runtime if you want to execute the code). Spring is made of a bunch of jars that, depending on which classes of the framework you use, must be in the classpath (eg. putting them in the /WEB-INF/lib directory). You may version them as well, or just version the configuration (I'm thinking about Maven for example, that will take care of resolving the dependencies).
Another piece of the puzzle is making all of this work in your IDE. This is a matter of taste. I prefer not to version ide-specific files (in the case of Eclipse, .settings and .project files/folders). You can do that, making sure you do not use absolute path anywhere, and technically you will be able to import the project without problems from another machine.

Yes.
If the other person has nothing extra installed and configured, namely no build tool, you need to put every needed Spring and other Jar into a folder, typically called "lib" and tell him to add them into his compile process. If he just uses the JDK he will get an enormous command line. It is much better to use a build tool like Maven or Ant+Ivy for building and dependency resolution. But that would be an "extra installation" per your question.
If he has Eclipse installed like you have and you use Eclipse internal for building:
Put the JARs in a lib folder
Configure the build path
Make a local test build
Export the project as zip (File menu > Export)
" The other person needs to import the project into his workspace
The exported project should not have any absolute paths as long as you didn't set some deliberately in the build path.
This works but is not exactly best practice. Installing a build tool like Maven is absolutely worth the time and should be preferred under any circumstances. It will save you a lot of time and nerves.

Creating a Java application that downloads its own dependencies

I'm interested in how to distribute a Java application that has a lot of dependencies (specified in a pom.xml in Maven).
Obviously it would be possible to just package everything in one big .jar file. However that seems wasteful, since an update of the application would require sending a new copy of all the dependencies as well.
So I'm looking for a way of distributing the app that does the following:
Only includes the core application in the main .jar file
Downloads dependencies as needed when the .jar file is run
Keeps copies of the dependencies locally, so that if an application update is distributed the dependencies don't need to be downloaded again
What's the best way of achieving this?

Can you just use Maven, with something like described at Maven Run Project ?
This is how I have some of my own applications setup within my own network. I've never needed to worry about messing with the classpaths or downloading / providing dependencies for programs setup like this for a long time. This approach also meets all of your criteria.

you can distribute your file using the web start technology (aka distribute a jnlp file). i believe this will handle most of this functionality for you, including updatability.

Deploying Java Files

What are the best practices (and enabling tools) to deploy Java standalone applications along with any required jar dependencies, config files, and launch scripts?
Are there any Maven plugins that easies publishing binary releases, so that users don't need to use maven for example?

Are there any Maven plugins that easies publishing binary releases, so that users don't need to use maven for example?
Use the Maven Assembly Plugin to create a binary distribution as zip/tar.gz/tar.bz2 of your project. This plugin is extremely flexible - at the price of some complexity - and you can do almost anything you want. Then deploy (in the maven sense) the produced artifact, upload it somewhere, etc.

As for dependency, I just use maven dependency copy plugin and copy all dependencies into a ./lib folder, and supply a launch script that uses the class path wildcard (that way you can change your dependencies as much as you want and don't have to change the launch script). As for configuration files, I put it in a ./config folder and again include it in my app's classpath in the launch script (The former admittedly only works for > java 1.6).
So in the end almost all my app has the following structure:
mystuff.jar launch.sh
./lib
./config
Then I'll just zip up the whole thing and give it to my users. The whole process is probably easy to automate using maven, but I confess that I do it by hand :p
If you prefer and the licenses permit, you could also just bundle all dependencies into a single jar (with expanded dependencies inside) using the assembly plugin. This tends to make the jar bulky and giving the users an updated app. more difficult. Also I had issues with it several time because of class files getting overwritten or something so I personally stick to the ./lib folder.

There's launch4j, which, if you can get it to work, will bundle up a Java app into an executable for your platform.

If your deployment target supports RPM files, I strongly suggest you investigate the rpm-maven-plugin. It allows you to easily map your project artifacts , including dependencies, to a RPM package.
I've been using it with great success to medium-scale application deployment.

You can use Oracle's ant or maven scripts:
http://docs.oracle.com/javafx/2/deployment/jfxpub-deployment.htm
The above will not only compile your code and create jar files, but it will also create binary executable (windows exe file or Mac app file). It can also create native installers. In addition it lets you include JVM with your distribution so the end use doesn't need to install Java.

Take a look at the Appassembler Maven Plugin. You may also want to combine it with the Assembly Maven Plugin.
Use the appassembler plugin to generate a set of "programs" by specifying executable names and main classes. You can also have it prepend and create an etc directory in which you can add configuration files.
If generating the directory with the start-up scripts and directory of binary files isn't enough, you can use the assembly plugin to copy over additional files (say your configuration files) into the appropriate directory and/or package your application into an archive.

How do I package multiple WAR files in one Maven project?

I am writing an application that integrates Geoserver with a custom component, intended to be hosted on a single servlet engine. Both are Maven based projects, and I would like to stay in Maven land to package it all into a nice distributable. The general idea I have is to add another module to my application that packages the application itself, Geoserver and all dependencies into one nice archive.
I am aware of the maven-assembly-plugin and its capability of storing all dependencies in a target folder, but I am not sure what would be the best way to create a package that it easy to deploy. Googling for any examples has not been successful.
Extra bonus points if the module can be started via mvn jetty:run.

Have you considered packaging them into an EAR project. It will bundle a set of WARs (and jars), and allows you to specify or generate a deployment descriptor.