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How to create a java client for a Spring service?

I have a service definition using Spring annotations. Example (source):
#RequestMapping(value = "/ex/foos/{id}", method = GET)
#ResponseBody
public String getFoosBySimplePathWithPathVariable(
#PathVariable("id") long id) {
return "Get a specific Foo with id=" + id;
}
The question is whether spring (or another library) can auto-create a remote implementation (client) of the same API without the need to manually type paths, method type, param names, etc. (like needed when using RestTemplate)?
Example of an such a client usage:
FooClient fooClient = new FooClient("http://localhost:8080");
String foo = fooClient.getFoosBySimplePathWithPathVariable(3l);
How can I get to such a client "generated" implementation"?

You are probably looking for Feign Client. It does everything you need: calling one service via HTTP is similar to calling method of Java interface. But to make it work you need Spring Cloud, standard Spring framework doesn't have this feature yet.

You can generate it using Swagger Editor. You shoud just define the path of the resources and then it'll generate for you the client for almost any language of your choice

XACML application on SOAP Web Services

I'm new to web-services and i would like to know the answer to some questions.
First, i know that REST APIS can be consumed just by having the URL of the rest endpoint, on the other side (SOAP), you can't consume any distant SOAP WS unless you develop a client. Is it correct? And if it is, is it the only difference between the 2 big families ?
Second, i would like to apply XACML on some SOAP Web Services for security purpose of course. I made a figure that resumes the entire process of XACML.
I developed some basic SOAP web services with simple 2 methods, and i don't know from where should i start the XACML code and configuration. I'm asking you guys for some good and helpful links to apply the XACML security filter.

You can find an example of CXF interceptor doing XACML-based (XACML 3.0) authorization on Colm O hEigeartaigh's blog (Colm is one of the main CXF developers). The actual source code of the CXF Interceptor: XACML3AuthorizingInterceptor. It is using OpenAZ as XACML implementation, but you can adapt it to use another XACML implementation, such as Axiomatics mentioned here by David Brossard, or AuthzForce (supporting embedded or remote RESTful PDP modes), or other implementations mentioned at the end of the XACML TC's page.
The first important part of the CXF Interceptor is at the beginning of the handleMessage(Message message) method:
SecurityContext sc = message.get(SecurityContext.class);
The SecurityContext gives you information about the authenticated user such as the user roles, which you can use as XACML subject attributes in the XACML request.
The code further creates the XACML Request using the DefaultXACML3RequestBuilder class, that extracts other information from the CXF Message using CXFMessageParser - that you can find in the cxf-rt-security-saml library - such as the SOAP service name, operation name (as defined in the WSDL), and the endpoint URI:
CXFMessageParser messageParser = new CXFMessageParser(message);
...
String actionToUse = messageParser.getAction(action);
...
QName serviceName = messageParser.getWSDLService();
QName operationName = messageParser.getWSDLOperation();
...

REST API invocation in Java

Suppose I need to write a Java client, which calls a REST API (with HTTP GET). I know it returns the data in JSON by default and I do not need to supply any headers.
Now I can use either Apache HttpClient to invoke the API or read the URL directly (get a stream from the URL with url.openStream and read the data). The second approach seems to me much simpler. Which one would you suggest and why ?

All the REST clients provide a wrapper over basic java URL based APIs. These clients are easy to use and provide all the necessary functionality. Your code will be much cleaner in case you use Apache HttpClient. And Apache's API are quite reliable.

I would use special libraries for that, like Jersey client or Apache CXF client.
https://jersey.java.net/documentation/latest/client.html
http://cxf.apache.org/docs/jax-rs.html
These ones are part of Java EE standard, a well defined specification which is widely used.
For JSON, consider https://github.com/FasterXML/jackson. Depending on what client you use, you will find information about how to make it work.

If you are not a big fan of JavaEE, and you look for neat and elegant API, and you are interested in working with a language on top of Java, Groovy HTTPBuilder is such a library that works like a charm!
twitter = new RESTClient( 'https://twitter.com/statuses/' )
resp = twitter.post( path : 'update.xml',
body : [ status:msg, source:'httpbuilder' ],
requestContentType : URLENC )
assert resp.status == 200
assert resp.data.user.screen_name == userName

You can use spring-data-rest and Spring's RestTemplate. No need to write a webapp as you can bootstrap Spring easily into a standalone java application putting AnnotationConfigApplicationContext in the Main(). It's quite simple.
For example, suppose you have a Restful URL, http://localhost:8080/croot/books/ that returns a list of books (deserialized into objects of type Book).
Using Spring's RestTemplate you can do the following:
public Resource<List<Resource<Book>>> findAll() {
return restTemplate
.exchange(
"http://localhost:8080/croot/books/",
HttpMethod.GET,
null,
new ParameterizedTypeReference<Resource<List<Resource<Book>>>>() {
}).getBody();
}
You can also process this using spring-data-hateoas allowing you to further decouple the client from the server and helps process what to do next, say in pagination.
This is a very simplified/contrived example but the REST support in Spring 3 combined with the spring-data framework is quite elegant.
Using Spring you also get the advantage of Jackson for JSON processing as the RestTemplate will have one of the flavors of Jackson's message converters (provided through MappingJackson2HttpMessageConverter for example) in it's list of default converters used for processing.

Java WebService

What is the Java equivalent to Script service (like web service but with JSON instead of XML) in the .net world?
I am looking for a way of creating and invoiking web services using java. I prefer to find a way that will allow me define a method that will act as web service. I don't like the solutions of "dedicated jsp or servlet" for the specific request.
Is there any wat of doing so?

There are a lot of frameworks that help you to do this. I personally prefer Spring.
But you can just search for "Java based RESTful web services frameworks". Here is a list of such framework from Wikipedia: http://en.wikipedia.org/wiki/List_of_web_service_frameworks
Enjoy.

You can use libraries like Jersey or RESTeasy for the implementation of web services. For the consumers, you can use the built in classes of the same libraries or, if you prefer, can use Apache HttpClient
I personally prefer using Jersey + HttpClient combination :)

I would prefer RESTful services which fits for your need of "I prefer to find a way that will allow me define a method that will act as web service." Just with REST annotations You can set a method as a Service.
Code Snippet simple REST
#Path("/rest")
public Class MyFirstService
{
//Method without Path parameters
#GET
#Path("/name")
#Produces("application/json")
public String getMyName()
{
return "My Name:";
}
//Method with Path parameters
#GET
#Path("/name/{id}")
#Produces("application/json")
public String getMyName(#Pathparam("id")String Id)
{
if(Id.equals("1")
return "My Name:";
else
return "None";
}
}
RESTful Services give four major Services as -
GET
PUT
POST
DELETE

I would recommend JEE6, especially if your focus is going to be on REST based services. Glassfish 3 and JBoss 7 are neck and neck now with their implementation, either would be a good choice (though JBoss is my personal preference). With the JAX-RS and JAS-WS specifications you simply annotate your classes and they become web service capable:
Make your bean a SOAP based web service:
#WebService
public class AccountImpl {
// You can explicitly mark the methods you want to make available in your WSDL
#WebMethod
public BigDecimal getBalance() {}
}
Make your bean a REST based web service:
#Path("/rs/account")
public class AccountImpl {
#GET
#Path("/balance")
#Produces("application/json")
public BigDecimal getBalance() {}
}
The code snippet is just an example. You can find more resources online for learning JAX-RS and JAX-WS. Here are a few links:
RESTEasy
Jersey
JAX-WS Tutorial
Note: I included information about JAX-WS for reference only. You indicated you wanted to build JSON services, which implies REST

Suggestions on RESTful Java Web Services Framework...

I googled some information about web services, it seems like a enterprise level application. I found that RESTful design is very cool idea on this. I find that Apache CXF looks cool, it support RESTful design and Java. It is a good choice for beginner to start writing an application using Apache CXF? or any other framework is suggested?

I'd go for Jersey, the RI of JAX-RS (JSR 311), the Java API for RESTful Web Services (i.e. a standard).

I recommend to use JAX-RS because IMHO it is the most neutral framework in terms of telling you how REST should be done. I have not used CXF, only Jersey. It is a very solid implementation and comes with a good client side connector, too (client side not part of JAX-RS yet).
Being neutral with regard to 'how to do REST' is important because there is not yet an acknowledged 'best' way to approach certain aspects (e.g. design of hypermedia).
Congrats to going the REST way - you won't regret it.
Jan

The much simpler implementation for a beginner would be spring 3.0 REST support. Spring MVC 3.0 has REST support and is very much simpler compared to Apache CXF.

Restlet in another RESTful web framework for Java : http://www.restlet.org/

I get started REST with RESTEasy and get it up in 30 minutes. You can use it as stand-alone lib in your favorite servlet container without all this JBoss stuff.

You should try PlayFramework. Just take a loot at a sample route file and you will know how easy it is to use play to implement RESTFul web app:
# ====== Order service =========================
GET /orders Orders.list
GET /orders/{<[0-9]+>id} Orders.show
PUT /orders/{<[0-9]+>id} Order.saveUpdate
POST /orders Orders.saveNew
# ==============================================
And corresponding controller methods:
public class Orders extends Controller {
public static void list() {
List<Order> orders = Order.all();
render(orders);
}
public static void show(long id) {
Order order = Order.findById(id);
notFoundIfNull(order);
render(order);
}
public static void saveUpdate(long id, Order update) {
Order order = Order.findById(id);
notFoundIfNull(order);
order.update(update);
show(id);
}
public static void saveNew(Order order) {
order.save();
show(order.getId());
}
}
There are some utilities enable you to interact with other Web Services:
String url = "https://ajax.googleapis.com/ajax/services/search/web";
Map<String, Object> params = new HashMap<String, Object>();
params.put("v", "1.0");
params.put("q", searchStr);
params.put("key", Play.configuration.get("app.google.key"));
params.put("userip", myIpAddr);
HttpResponse resp = WS.url(url).params(params).get();
return resp.getString();