08. Filters & Interceptors. CDI . Conclusions

As Java Brains says we should distinguish several components that can be used both from client and server in order intercept the request or response and modify them.

1 Interceptors, Filters and MessageBody

• Interceptors manipulate entities (body) in input and output streams while filters only manipulate the request or response params like headers, URIs etc
• There are 2 kinds of interceptors ReaderInterceptor and WriterInterceptor. To create an interceptor, you should implement one of the 2 interfaces. One of the possible use is to GZip the body for slow communications.There are 2 kinds too of filters Container RequestFilters and ContainerResponseFilters one for the request and the other for the response. the basic usages are Logging, security..
• Filters and interceptors can work both on the client and server side.
• On the client side, we have these filters: ClientRequestFilter and ClientResponseFilter.
• We also have MessageBodyReader and MessageBodyWriter for the body manipulation.

Here is a schema of a Request and a Response and the order these elements interact

2. CDI Injection

JAX-RS Resources can be converted to Singleton and Stateless beans. This can be achieved by means of annotations. Here are some examples:

2.1 Stateless bean

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@Stateless @Path("stateless-bean") public class StatlesResource() {}

2.2 Singleton bean

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@Singleton @Path("singleton-bean") public class SingletonResource() {}

2.3 Request scoped bean

This is the default, so it is not necessary o annotate i 

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@RequestScoped @Path("/employee/{id}") public class RequestScopedResource() {}

3. Conclusions

We have seen:

• Create a JAX-RS application that extends Application and may have an annotation @ApplicationPath("somePath")
• Created Resources with annotations like @Path(), @GET or @Produces
• Resource lifecycle, Singleton etc.
• Custom PartamConverters that implement ParamConverterProviders and provide a class conversion. The annotation used is @Provider and should implement ParamConverterProvider interface.
• MessageBodyReaders and MessageBodyWriters to convert data types that should implement the correspònding interface and use the @Provider annotation.
• Create our own Custom Media Types with the annotation @Produces in the MessageBodyWriter
• Created a JAX-RS client with ClientBuilder and make a request and response.
• Used WebTarget class to manipulate URLs and parameters as templates and assign parameters to produce client request.
• Created POST request and have seen how the Response class has some methods to see cookies, headers and so on.
• Can prepare request with the buildGet() method in the client (instead of get())
• We can also use the GenericType<> wrapper to get the elements of a response in the client
• Used Filters for Base Security implementation using header parameters Authentication Basic user:password 
• We have seen about interceptors, Request and Response flows
• CDI (@Singleton, @Stateless, and default @RequestScoped)