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Java Decorate Functions

I am new to Java so apologies if this is a simple thing. I have built decorators in Python for authorizing RESTFul endpoints in Flask and have just built my first Java Webserver but am unable to figure out how to create a similar decorator in Java.
I want to do some pre-checks before running the method (i.e. is the user allowed to access this route). Ideally this would be a decorator like #authorize that, if authorized, will execute the method, but if unauthorized then it would through a 403 error instead.
#Path("/")
public final class HelloWorld {
#GET
#Path("/hello")
#authorize // How would I implement this?
public String sayHelloWorld() {
return "Hello World!";
}
}
EDIT: I am using Grizzly as the web Framework and I will be using an external Policy Management System (Apache Ranger) for managing authorization.

First of all: defining such custom annotations is exactly how you can approach such things in Java. The JAX-RS specification provides all the things you need for such kind of method binding.
The thing that is slightly more complicated: how to nicely do that for the framework that you are using.
With JAX-RS and Jersey for example, creating your own annotations is well documented. And Jersey might be a good starting point, as that is simply a straight forward way to get JAX-RS working.
So, first you start by learning how to use Jersey in general, for example from vogella. Next: you can start to add your custom annotations, see here for an example.
There is even an existing question about using custom annotations for access validation.

Create REST Services using Java in Eclipse

I have been looking for a few days at tutorials on this subject but either they aren't exactly what i'm looking for or I cant get them to work. I cant imagine that more people aren't confused on the subject so I will ask here.
What I would like to create is a REST service in Eclipse that I can run on my web server and "connect to" using ajax from a separate dynamic web project. All i'm looking for here at the moment is a simple hello world example of a service returning ajax working alongside a separate web project that consumes the JSON it returns.
Im hoping to get a usable user guide (or at least links to one) that will help me out and future people looking for this same thing.
I have gotten as far as this simple class (i have included Jersey Jars but I dont understand what to do from here):
public class UserRestService {
private static final Logger log = Logger.getLogger(UserRestService.class.getName());
private CreateUserService createUser;
#POST
#Path("/CreateUser/{name}/{age}")
#Consumes("text/html")
public User createUser(#PathParam("name") String name, #PathParam("age") Integer age) {
return createUser.createUser(name, age);
}
}
How do i get this class to be an accessible api service on my tomcat server? How do I setup another web project to consume it (I understand how to make an ajax call this is more a question of how do i setup the projects)? Where do servlets come in ?

Rather than copying jars, it would be better to use maven or gradle for package management. A simple pom.xml (maven) with the dependencies can help you abstract determining the compile and runtime dependencies.

Okay so the Java standard is jaxrs (https://jax-rs-spec.java.net/). You can use Jersey which is the rest implementation of jaxrs (https://jersey.java.net/).
A sample of implementing a service using eclipse, jersey and tomcat can be found here: http://www.vogella.com/articles/REST/article.html
If you are feeling like an adventure you can look at vertx.io (http://vertx.io) and my beta release of jaxrs 2.0 framework for vertx called 'vest' (https://github.com/kevinbayes/vest)
Addition:
Jersey provides examples on github of how to implement services at https://github.com/jersey/jersey/tree/master/examples

apache thrift integration with spring framework

I am looking to use thrift for my web service calls. From what I've read so far from thrift documentation is that I'll have to write a thrift file containing my POJOs and services that I want to expose. This file then needs to be compiled using a thrift compiler to generate the Java classes. And then client and servers have to be written using these.
Is there a simpler way to achieve this (any annotation based or Spring framework integrations available)?

I wrote an article about Spring Boot and Thrift integration with detailed explanation how to combine them together : ) You can find my article here:
Java.DZone: Building Microservices with Spring Boot and Apache Thrift.
In general, you should create Servlet bean like this:
#Bean
public TProtocolFactory tProtocolFactory() {
return new TBinaryProtocol.Factory();
}
#Bean
public Servlet calculator(TProtocolFactory protocolFactory, CalculatorServiceHandler handler) {
return new TServlet(new TCalculatorService.Processor<CalculatorServiceHandler>(handler), protocolFactory);
}
where TCalculatorService is your Thrift service

Nope, there's no custom binding between spring and thrift. Once you've created your .thrift files, you will generate Java classes that will form the thrift communication layer.
For example, I've created a Java server that calls SQL over hibernate (this is one layer) and returns data over thrift (another layer). Unfortunately, there has to be some Java code that will process moving abstract data from one layer into another.

You can use this project for integration between SpringBoot and Apache Thrift https://github.com/aatarasoff/spring-thrift-starter.
As it is described in README you simply connect starter and create your handler like if you are using #RestController:
#ThriftHandler("/api")
public class TGreetingServiceHandler implements TGreetingService.Iface {
#Override
public String greet(TName name) throws TException {
// your logic
}
}

The following project seems to work on it
https://github.com/joshlong/spring-advanced-marhshallers-and-service-exporters/

Generate Wsdl/Client Stubs For Web Service

I have been doing some reading up on web services programming with Java, Eclipse, etc. and I found one particular example where the person created the web service and client by doing the following:
define the web service java class (interface + impl)
deploy the web service using Endpoint.publish
grab the wsdl from the url of the web service (eg, localhost://greeting?wsdl)
use wsimport to generate stubs
create a client class using generated stubs
Is there another way to generate the wsdl without having to publish the web service and download it? Perhaps a maven plugin to auto-generate wsdl and client stubs?
Update: Rather than creating a new question I am just going to piggyback on this one.
I have created my web service by defining an interface:
#WebService
public interface HelloWorldWs {
#WebMethod
public String sayHello(String name);
}
and an impl class:
#WebService(endpointInterface = "com.me.helloworldws.HelloWorldWs")
public class HelloWorldWsImpl implements HelloWorldWs {
#Override
#WebMethod
public String sayHello(String name) {
return "Hello World Ws, " + name;
}
}
When I run wsgen I get the following error:
The #javax.jws.WebMethod annotation cannot be used in with #javax.jws.WebService.endpointInterface element.
Eclipse seems to be okay with it.
Any idea why?
Note, I originally did not have the annotation but when I tried to call my webservice I got the following error:
com.me.helloworldws.HelloWorldWsImpl is not an interface

The JSR 224 says in 3.1 section:
An SEI is a Java interface that meets all of the following criteria:
Any of its methods MAY carry a javax.jws.WebMethod annotation (see 7.11.2).
javax.jws.WebMethod if used, MUST NOT have the exclude element set to true.
If the implementation class include the javax.jws.WebMethod, then you cant put #WebMethod(exclude=true) and that in not possible, according to specification.
Depends of custom version of Eclipse, shows a warning for this. e.g. Rational Application Developer for Websphere shows:
JSR-181, 3.1: WebMethod cannot be used with the endpointInterface
property of WebService

While programming/building a project (with some advanced IDE) normally you should be able to find it between auto-generated stuff - the IDE should generate it. Just check carefully.

How to publish wsdl for java

I have following java class and have published a wsdl for it, my question is that is there anyway to have different webservice classes and publish a single wsdl? I mean another seperate class to this one with number of methods or I have to have a webservice class as the main class of the application to keep all the webmethod methods and generate the wsdl from that?
package com.Services;
import javax.jws.WebService;
import javax.jws.WebMethod;
#WebService(name = "Hellos", targetNamespace = "http://localhost:8081/Mywebservice2/services/Hellos")
public class Hellos {
#WebMethod
public Customer[] mycustomers() {
.....
}
#WebMethod
public String Receiver(String name){
....
}
}

Exactly, that should be the way you should design your application. you should have one consolidated java file and that should be exposed. Clients should be given multiple end-points.

WSDL correspond to your service and literally each public method corresponds to a service. You can write many classes and methods but they will not be part of your wsdl if methods are private.
If you using any IDE plugin then it asks you during service creation what all public methods you want to be exposed to outer world. So in one java project you can have as many classes or methods you want. Finally when converting your project into web service you can decide which all methods can work as end point/service and then these will be part of your WSDL.

The tool wsgen since JDK 1.6 for generate de WSDL file takes only one Service Endpoint Interface or SEI.
wsgen [options] <SEI>
You can read that:
The wsgen tool generates JAX-WS portable artifacts used in JAX-WS web services. The tool reads a web service endpoint implementation class (SEI) and generates all the required artifacts for web service deployment, and invocation
And:
Note that you do not have to generate WSDL at the development time as JAXWS runtime will automatically generate a WSDL for you when you deploy your service.
In another hand, WSDL 1.1 supports having multiple services in a single WSDL file, but these services shares types. In that case, it's prefer put all in one service.