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Spring mvc - Server side programming

I have a spring mvc application which i use as only a server. I have deployed some html and javascript files on my hosting account and sending post requests to my server only. Retrieve data from database and send back the data to the html or javascript pages. I don't use any servlets,jsp or jsf. Everywhere i look it says that i should use them however. Am i doing something wrong? It feels like bad practice but i don't know the right way to do it i guess. Any help would be appreciated.

As I already mentioned in my comments, you can look into creating a webservice. Since you are using Spring already, try this guide on Building a RESTful Web Service.
After creating the service, you can call it up like this, where you pass in input parameters to your rest endpoints,
http://localhost:8080/greeting?name=User
Now your service will respond back to your GET request and you'll be output a JSON/xml string which you can process later at the client side. The sample json response looks like this,
{"id":1,"content":"Hello, User!"}
Here's another example blog article on Spring Restful Web Service Example with JSON, Jackson and Client Program

Well, I think you should first expand your question a bit since one needs to assume a lot to give you an answer.
IMO, JSF is not great and there are other better options for UI and JSPs are dead. But I'm biased since I used last time JSF 1.X and then went with Spring MVC and Angular or Spring and Apache Wicket more recently.
I used for instance Spring MVC to implement an HTTP RPC API with JSON payloads to which an Angular frontend connected and it worked just fine. I also had the feeling that everyone is doing that nowadays:).
I also guess you are using at least one servlet to configure Spring DispatcherServlet. Right?

ReST webservice client - generate from WSDL or not?

I've some confusions about ReST clients and need a bit of help.
For ReST, does the service provider give WSDL document or not? If not, how does the client will know what kind of JSON data to expect? When I invoke the rest client, I will recieve the JSON/XML response in a string format which I'll need to convert it into a Java object(or Javascript, if using on client side) to do any meaningful tasks with the response. So it seems like I, as a client developer, need to know the WSDL or the Schema definition so that I can build a java object similar to the JSON response I'm expecting. But if you go by this answer, generating a client class based on the service definition flies directly in the face of ReST fullness. If that is the case, how do I go about creating my client code?

WADL/Web Application Description Language is not a standard but is gaining popularity for REST APIs contract definition.
The Web Application Description Language (WADL) is a machine-readable
XML description of HTTP-based web applications (typically REST web
services).1 WADL models the resources provided by a service and the
relationships between them.1 WADL is intended to simplify the reuse
of web services that are based on the existing HTTP architecture of
the Web.1[2] It is platform and language independent and aims to
promote reuse of applications beyond the basic use in a web
browser.

For documentation:
https://github.com/wordnik/swagger-core/tree/master/modules/swagger-jaxrs
For client code:
https://github.com/wordnik/swagger-ui
You integrate the library and annotate your resources and online documentation is generated on the fly.
You also need a client for which you can integrate the ui.
The dynamically generated REST client looks something like this:
http://petstore.swagger.wordnik.com/

What type of java project can serve web services?

Do I have been writing a java application, application is a console application.
Now, I want my application to listen to request at a port coming from web application and process those request and affect DB data.
I am not sure how to do it in a simple java project. Can I use some java webservices, and how?

Socket programming in Java is quite nice - a Socket is an abstraction that listens for data coming in on a single port from a single web address or server and can also send out.
http://zerioh.tripod.com/ressources/sockets.html
Note that listening for data blocks program flow.

Most likely you're looking at learning Java Servlet programming. There are a lot of good resources to learn from.
However, from my experience something like Netty could serve you really well from both learning and actual application development perspectives. The site contains very reasonable example driven documentation, which takes user from non-blocking TCP/IP programming to HTTP support.

Yes , web service API (JAX-WS 2.0) is added to the Java SE 6. You can use these API to create a simple web service for the Java SE application.
See the section "Using JAX-WS 2.0 to Create a Simple Web Service" for the example .It shows how to create a standard web service end-point using JAX-WS 2.0 for the Java SE application.
Beside , this 5 minutes tutorial is very good at introducing JAX-WS .It includes the demo for implementing the web-service end-point and client and provide the eclipse project source code to download too. Please note that it misses the step to use wsgen to generate the service classes for the WebService end-point ,but it is not so difficult to figure out how to use wsgen

Passing an xml document (as a parameter?) to a web service

I am developing a web service in java and Metro that requires a lot of information to be passed. For example, something like xml describing all the attributes of a customer.
I am wondering if there is some standard way in which to pass the data in a document. Currently I have been passing the data as a string parameter named 'customerXML'.
Any suggestions appreciated. FYI I have defined another restful ws using RestEasy which works great using input/output streams, but am looking for a way to leverage soap-based web services to expose similar functionality.

JAX WS is perfect for this requirement, It works on SOAP

My hypothesis is that there isn't a standard way to pass xml documents to a soap-based web service without coding the entire SOAP message yourself. Hence I do not think there is an easy way to do so and one reason why RESTful web services are gaining acceptance. The best way to do it using SOAP based web services is to pass the document as a string parameter and validate/parse within your server code.

What technology I should use to develop small Java webservice?

Basically I need webservice where client can request with id one boolean value from our webservice. What technology would be most suitable for this small API? Of course it is possible that there will be more functions to interface, but now we need only one function. It also needs to have authentication, so that only auhtorized clients can access service. And every client have different auth credientials.
What would be good technology for this purpose?

I am using resteasy to build my webservices and it is pretty easy to use ... just need to use annotations on my methods to deliver the webservices.
Here is a comparison of different JAX-RS frameworks. Take a look at it

First of all: authentication and authorization. Don't do it yourself, pick an app server or servlet container and configure it to do the job.
For the web service....
The simplest thing to do it just implement a servlet that responds to a POST (not a GET if request modifies internal state) and returns the result in the body. This way you don't need any frames works, no learning to do (if you already know servlets). The downside is it won't scale as you add more features, and your not using enough buzz words.
If you want a SOAP based webservice, then look at JAX-WS. Now that it's backed into java 6 it's pretty easy.
At the simplest level JAX-WS lets you put a few annotations on your class, like #WebService, and it auto generates a wsdl and exposes an instance of your class via the web service.
There is plenty of documenation out around how to do it:
http://java.sun.com/webservices/docs/2.0/tutorial/doc/
http://www.java-tips.org/java-ee-tips/java-api-for-xml-web-services/developing-web-services-using-j.html
http://cwiki.apache.org/GMOxDOC20/simple-web-service-with-jax-ws.html

JAX-WS + any servlet container (Tomcat is usual choice)
#WebService(targetNamespace = "http://affinity.foo.com", name="RewardsStatus")
#SOAPBinding(style=SOAPBinding.Style.RPC, use=SOAPBinding.Use.LITERAL)
public interface RewardsStatusIF {
#WebMethod(operationName="GetLastNotificationDate", action="urn:GetLastNotificationDate")
#WebResult(name="return")
public Date getLastNotificationDate() throws AffinityException;
...
Actually, you don't even need a servlet container. JAX-WS has a way to run the service under a standalone Java application. It has some limitations (I have failed to make a stateful service work), but it's
very simple to create.

Given that you tagged your question as "Java", I suggest Jetty. It is a very good small servlet engine. It has support for sessions, so adding authentication should not be a problem.

If you are using Java 6, there is already a HTTP Server builtin, it supports Http authentication. That's all you need. Check out,
com.sun.net.httpserver

You could use some restful framework like jersey.

An alternative to SOAP-based web services with JAX-WS would be JAX-RS (for RESTful web services).

We have a lot of scenarios on our project where we want small amounts of data available via simple HTTP URLs while the app is running and in my experience, Restlet (http://www.restlet.org/) seems to be one of the easiest things available for setting up simple "web-service"-like interfaces (RESTful interfaces) within Java apps.