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Communication between rest services hosted on different tomcat servers

I have a scenario where i am hosting different java Rest Services on different Tomcat instances (different machines). These projects running on the tomcats do not have any UI. For simplicity's sake, lets assume that the user will directly enter some URL in the browser (or curl) to avail these services. Now I need this service to be able to talk to (call functions) the services available in the other tomcat instance.
For eg. If TomcatInstance1 gets the call, and all this does is act as a 'router' to the different services, i want it to be able to place the Rest call for the other 'service' available on, say, TomcatInstance2. Is this possible?. If so, how to achieve that? (Tried searching for similar questions on SO, couldnt find any). Are there any online reference for the same?
PS: Hosting the services in the same Tomcat Instance is against the requirement that I'm having.

That is completely possible. You can use (for example) Jersey-client (http://jersey.java.net/) to make the queries to the other RESTful web services in the other Tomcat instances. Only need to define the correct URIs of the end points and query them according the the API exposed and call it (like you were a client from a browser, or curl).
See here a nice example of using Jersey-client to do that: http://www.mkyong.com/webservices/jax-rs/restful-java-client-with-jersey-client/

I would suggest Spring Restful api ( http://static.springsource.org/spring/docs/3.0.0.M3/reference/html/ch18s02.html , http://www.mkyong.com/spring-mvc/spring-3-rest-hello-world-example/ ).
As #emgsilva mentioned the only thing you need to do is to point correct uris between each other.
The beauty of spring restful api is it is simple to use and you don't deal with any serialization - deserialization.

How to call Java soap services thorough ajax in JqueryMobile framework

I have started working on web application using jquery touch. My web services is written in soap and I want to call from my application. Can you suggest me how should I move ahead.
Is it possible to call from ajax?

While many people thinks that managing the complexity of SOAP in a JavaScript environment would be counter-productive, it could nevertheless be done, in particular if you are familiar with SOAP web-services and want to avoid the need to learn another middle-layer framework; a library that I would suggest is Apache-CXF support for JavaScript.
The CXF JavaScript client library is indeed a code generator which (with some limitations), in its easiest form, wsdl2js, gets a wsdl file and generates JavaScript
contructors - for an service
methods - for any service operation, and
objects - for any web service complex element/type
which can be directly called in your scripting. Other available tools generate the javascript code starting with the Java code server-side implementation (java2js), or on-the-fly (dynamic javascript).
Pros:
leverage a component of a widely used library for web-services implementation (CXF)
avoid another layer in the middle
easy to use (run the tools against the wsdl, load the generated sources)
Downsides:
client knows nothings about WS urls and ports; you need the URL at which the ws ranswers and thats'it
as a code generator, the JavaScript client generator is parallel to JAXB or JAX-WS. It defines a mapping from an abstract model of a web service to JavaScript objects. Unlike JAXB and JAX-WS, there is no committee that has standardized a 'JavaScript binding.' The CXF binding may not be to everyone's tastes.
Soap 1.1 only
No Authentication support

Using soap from the browser is technically possible, but a very bad idea. You'll spend all your time fighting to get the soap protocol to work correctly and you'll miss all the benefits of soap.
A much better approach would be to build a back end for your new web application using the framework of your choice, eg. J2EE, .Net or any other. All those platforms have nice soap libraries that will do the work for you. Then you will either generate the html pages on server (old school web site) or use a static page and expose the data as a JSON rest API (modern single page app).
In summary: soap is good for communicating between servers, terrible for communication with the browser.

How to connect WSDL file in my application using SOAP service?

I am doing a project using Java and BPEL. I successfully created webservices in Java and integrated them using BPEL. All i generated a single output WSDL file. Now, I have to use this output WSDL file in my application using SOAP communication. How can i do that? Is there any help out side for such scenarios? Walkthroughs are really appreciated..

Depending on the architecture of your application (Standard Java, Spring-based, ...) there might or not be a documented procedure to consume a SOAP-based webservice.
On the other hand, you're always free to pick a webservice development framework to handle that. For instance, you could pick either CXF or AXIS2 (I believe these are the two most popular frameworks for Java WebServices). Each of these frameworks provides a tool called "wsdl2java" that helps you generate client-side/server-side/both Java classes. Then, you can easily add those classes and the requireds libraries to your application.
Having used CXF in the past, It even does provide several way to consume a webservice
Generating the client-side classes
Using CXF dynamic client factory : basically, you'll retrieve an endpoint proxy from a factory object.
Hope that'll help

I start with SoapUI (or downloadable from sourceforge), that will let you consume the WSDL and fire off requests against your server. Typically I'm hitting someone else's webservice, and trying to figure out what the data looks like before I start wiring my code together, but in your case its just a verification that the services would be/are working.
Then, as #KHY said, you can automatically convert the wsdl into java with a wsdl2java and start coding (look under the Related list on the right panel of this SO screen)

If it is a Java application, then the easiest way to consume a service is using JAX-WS. It's really easy to create a Web service client from WSDL.
See this link
Once you deploy the BPEL project on server, then refer the WSDL with http://server:port/application/YourBPELProjectService?WSDL in the consuming application. You will need to write different client code based on the BPEL type - Synchronous, Asynchronous etc.

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.

Testing Web Services Consumer

Here are some tools that I have found to test web services consumers:
http://www.soapui.org/
https://wsunit.dev.java.net/
Are there any others? I would prefer testing frameworks that are written in Java or Python.

I have used soapui by a maven plugin. It can create junit-linke reports to be run and analysed like unit tests. This can be easily integrated in continious build, also with the free distribution of soapui.

I've used Web Service Studio.
Web Service Studio is a tool to invoke web methods interactively. The
user can provide a WSDL endpoint. On clicking button Get the tool
fetches the WSDL, generates .NET proxy from the WSDL and displays the
list of methods available. The user can choose any method and provide
the required input parameters. On clicking Invoke the SOAP request is
sent to the server and the response is parsed to display the return
value.
This tool is meant for web service implementers to test their web
services without having to write the client code. This could also be
used to access other web services whose WSDL endpoint is known.
Also the Web Services Explorer in Eclipse which comes as part of the Web Tools Platform.
Through UDDI and WSIL, other applications can discover WSDL documents
and bind with them to execute transactions or perform other business
processes. The Web Services Explorer allows you to explore, import,
and test WSDL documents.

The Grinder is right up your ally with both Java and Python, that handles most web services, (SOAP/REST/CORBA/RMI/JMS/EJB) etc.
http://grinder.sourceforge.net/

You really need to be more specific: What is it that you want to test in your WS-consumer? That it calls the right WS? This looks a bit pointless - WS are a perfect place for mocking whatever may be called - without anything being called.
In order to test the consumer you'd otherwise be writing a Webservice that mocks the original, right? I'd suppose that the communication protocol that goes through the wire is not the clients domain - e.g. it's generated. So the only thing a WS-consumer's client sees is the interface. And there's nothing to test in an interface.
It might be that I completely misunderstood your question - please clarify if I did. I'll revise the answer then.