Gain insights into Java 17, cloud and microservices, reactive programming, and top JVM languages. Explore hands-on projects using Scala, Groovy, and Gradle to boost your software development career.

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This course is meant for Java programmers or aspiring programmers who want to know about the latest Java and JVM technology. Throughout this course, you will get several opportunities to get hands-on experience with various Java concepts. 

This course will help you understand the latest in Java up to version 17; cloud and microservices; build, testing, and web frameworks; reactive programming in Java; and the best JVM languages so you can advance your career in software development. 

Moreover, you will also get to work with Scala, Groovy, and Gradle. The course explains Java concepts in detail and also draws comparisons with its older versions, as well as JVM languages.

The All-in-One Guide to Java Programming

## JAX-RS 1.0
JAX-RS 1.0 (the Java API for RESTful Web Services) was defined in JSR-311¹⁶⁴.
It has many implementations, including the following:
* **[CXF](http://cxf.apache.org/)**: A merger between XFire and Celtix (an Open Source ESB, sponsored by IONA, and
originally hosted at ObjectWeb).
* **[Jersey](https://community.oracle.com/hub/)** : The JAX-RS Reference Implementation from Oracle.
* **[RESTEasy](https://resteasy.github.io/)** : JBoss’s JAX-RS project.

JAX-RS defines a set of request method designators for the common HTTP methods: `@GET`, `@POST`, `@PUT`, `@DELETE`, and `@HEAD`.

When a resource class is instantiated, the values of fields and bean properties annotated with one of the following annotations are set according to the semantics of the annotation:
* `@MatrixParam`: Extracts the value of a URI matrix parameter.
* `@QueryParam`: Extracts the value of a URI query parameter.
* `@PathParam`: Extracts the value of a URI template parameter.
* `@CookieParam`: Extracts the value of a cookie.
* `@HeaderParam`: Extracts the value of a header.
* `@Context`: Injects an instance of a supported resource.

### Gotcha's
* If a subclass or implementation method has any JAX-RS annotations, then all of the annotations on the superclass or interface method are ignored.
* If you’re using Spring AOP on your web-service classes, this interferes with the ability of your JAX-RS library to get your annotations. Either all of your methods should be added to the interface or CGLIB proxies have to be explicitly enabled. Consult Spring AOP documentation for more details.


## JAX-RS 2.0
JAX-RS 2.0 adds a lot of new features to the REST API and comes with Java EE 7. It adds a client API, asynchronous processing for client and server, filters and interceptors, and some HATEOS (Hypermedia as the Engine of Application State) features.

### Client API
JAX-RS 2.0 adds a client API to the standard. You can use the ClientFactory to  `Client` and then a `WebTarget`. For example:

```
// Default instance of client
Client client = ClientFactory.newClient();
// Create WebTarget instance base
WebTarget base = client.target("http://example.org/");
// Create new WebTarget instance hello and configure it
WebTarget hello = base.path("hello").path("{whom}");
hello.register(MyProvider.class);
```
Then, to execute on the Web Target, do the following:
```
Response res = hello.pathParam("whom", "world").request("...").get();
This would result in a GET request on the URL http://example.org/hello/world
```

### Asynchronous Processing
Asynchronous Processing and
Asynchronous REST API calls were added as a first-class feature to JAX-RS. This allows the REST
client to issue multiple requests in parallel and the server to handle such requests.
* Server API support
  * Offload I/O container threads
  * Suspendable client connection
  * Leverage Servlet 3.x async support (if available)
* Client API Support: `request().async().get( callback )`.

### Filters & interceptors
On the server-side, we have two different types of filters:
* `ContainerRequestFilter` runs before your JAX-RS resource method is invoked.
* `ContainerResponseFilter` runs after our resource method.

On the client side, we also have two types of filters: **ClientRequestFilter** and **ClientResponseFilter**. ClientRequestFilters run before our HTTP request is sent to the server. ClientResponseFilters run after a response is received, but before the response body is unmarshalled. Filters are useful for cross-cutting features, such as:
* Logging
* Security
* Compression

While filters modify request or response headers, interceptors deal with message bodies. Interceptors
are executed in the same call stack as their corresponding reader or writer. There are two interceptor
interfaces:

• `ReaderInterceptor`
• `WriterInterceptor`

For example, Interceptors can be used to add digital signatures or “gzip” message bodies. Sometimes we want a filter or interceptor to only run for a specific resource method. We can do this with a `@NameBinding` annotation. Annotate a custom annotation with `@NameBinding`, and then apply that custom annotation to your filter and resource method.

```
@NameBinding
public @interface MyFilterBinding {}

@MyFilterBinding
public class MyFilter implements ContainerRequestFilter {
   /* code... */
}
```
Then, in your RESTful Service:
```
@Path
public class RestfulService {

     @GET
     @MyFilterBinding
     public String get() { /* code... */ }
```
### HATEOS
JAX-RS 2.0 adheres more closely with REST principles and includes features of HATEOS.

It includes the following:
* ID’s and links
* (RFC-5988 Web Linking) Link types: Structural and Transitional
* Use `@Produces` to define what is returned:

```
@GET
@Produces("text/plain", "text/html")
public Widget getWidget();
```

# JAX-RS 1.0
JAX-RS 1.0 (the Java API for RESTful Web Services) was defined in JSR-311¹⁶⁴.
It has many implementations, including the following:
* **[CXF](http://cxf.apache.org/)**: A merger between XFire and Celtix (an Open Source ESB, sponsored by IONA, and
originally hosted at ObjectWeb).
* **[Jersey](https://community.oracle.com/hub/)** : The JAX-RS Reference Implementation from Oracle.
* **[RESTEasy](https://resteasy.github.io/)** : JBoss’s JAX-RS project.

JAX-RS defines a set of request method designators for the common HTTP methods: `@GET`, `@POST`, `@PUT`, `@DELETE`, and `@HEAD`.

When a resource class is instantiated, the values of fields and bean properties annotated with one of the following annotations are set according to the semantics of the annotation:
* `@MatrixParam`: Extracts the value of a URI matrix parameter.
* `@QueryParam`: Extracts the value of a URI query parameter.
* `@PathParam`: Extracts the value of a URI template parameter.
* `@CookieParam`: Extracts the value of a cookie.
* `@HeaderParam`: Extracts the value of a header.
* `@Context`: Injects an instance of a supported resource.

## Gotcha's
* If a subclass or implementation method has any JAX-RS annotations, then all of the annotations on the superclass or interface method are ignored.
* If you’re using Spring AOP on your web-service classes, this interferes with the ability of your JAX-RS library to get your annotations. Either all of your methods should be added to the interface or CGLIB proxies have to be explicitly enabled. Consult Spring AOP documentation for more details.


# JAX-RS 2.0
JAX-RS 2.0 adds a lot of new features to the REST API and comes with Java EE 7. It adds a client API, asynchronous processing for client and server, filters and interceptors, and some HATEOS (Hypermedia as the Engine of Application State) features.

## Client API
JAX-RS 2.0 adds a client API to the standard. You can use the ClientFactory to  `Client` and then a `WebTarget`. For example:

```
// Default instance of client
Client client = ClientFactory.newClient();
// Create WebTarget instance base
WebTarget base = client.target("http://example.org/");
// Create new WebTarget instance hello and configure it
WebTarget hello = base.path("hello").path("{whom}");
hello.register(MyProvider.class);
```
Then, to execute on the Web Target, do the following:
```
Response res = hello.pathParam("whom", "world").request("...").get();
This would result in a GET request on the URL http://example.org/hello/world
```

## Asynchronous Processing
Asynchronous Processing and
Asynchronous REST API calls were added as a first-class feature to JAX-RS. This allows the REST
client to issue multiple requests in parallel and the server to handle such requests.
* Server API support
  * Offload I/O container threads
  * Suspendable client connection
  * Leverage Servlet 3.x async support (if available)
* Client API Support: `request().async().get( callback )`.

## Filters & interceptors
On the server-side, we have two different types of filters:
* `ContainerRequestFilter` runs before your JAX-RS resource method is invoked.
* `ContainerResponseFilter` runs after our resource method.

On the client side, we also have two types of filters: **ClientRequestFilter** and **ClientResponseFilter**. ClientRequestFilters run before our HTTP request is sent to the server. ClientResponseFilters run after a response is received, but before the response body is unmarshalled. Filters are useful for cross-cutting features, such as:
* Logging
* Security
* Compression

While filters modify request or response headers, interceptors deal with message bodies. Interceptors
are executed in the same call stack as their corresponding reader or writer. There are two interceptor
interfaces:

• `ReaderInterceptor`
• `WriterInterceptor`

For example, Interceptors can be used to add digital signatures or “gzip” message bodies. Sometimes we want a filter or interceptor to only run for a specific resource method. We can do this with a `@NameBinding` annotation. Annotate a custom annotation with `@NameBinding`, and then apply that custom annotation to your filter and resource method.

```
@NameBinding
public @interface MyFilterBinding {}

@MyFilterBinding
public class MyFilter implements ContainerRequestFilter {
   /* code... */
}
```
Then, in your RESTful Service:
```
@Path
public class RestfulService {

     @GET
     @MyFilterBinding
     public String get() { /* code... */ }
```
## HATEOS
JAX-RS 2.0 adheres more closely with REST principles and includes features of HATEOS.

It includes the following:
* ID’s and links
* (RFC-5988 Web Linking) Link types: Structural and Transitional
* Use `@Produces` to define what is returned:

```
@GET
@Produces("text/plain", "text/html")
public Widget getWidget();
```

Learn about Java APIs for RESTful web services.

JAX-RS

Introduction

Java Syntax and Conventions

Java 7

Idiomatic Java 8: Lambdas, Streams, and Dates

New Date and Time API

Java 8 Miscellaneous

Advantages of Java 9

Java 10 - 17

Java Ecosystem

Maven and JUnit

Utilizing Essential Libraries

Modern Java Concurrency

RxJava

Other JVM Languages

Groovy

Gradle

Spock

Scala

RESTful

Microservices and Clouds

Grails

Spark

Spring Boot

Play Framework

Ratpack

Final Thoughts

Appendix

JAX-RS

JAX-RS 1.0