# Package javax.ws.rs.client

The JAX-RS client API

See: Description

- Interface Summary
  Interface | Description
  --- | ---
  AsyncInvoker | Uniform interface for asynchronous invocation of HTTP methods.
  Client | Client is the main entry point to the fluent API used to build and execute client requests in order to consume responses returned.
  ClientRequestContext | Client request filter context.
  ClientRequestFilter | An extension interface implemented by client request filters.
  ClientResponseContext | Client response filter context.
  ClientResponseFilter | An extension interface implemented by client response filters.
  Invocation | A client request invocation.
  Invocation.Builder | A client request invocation builder.
  InvocationCallback<RESPONSE> | Callback that can be implemented to receive the asynchronous processing events from the invocation processing.
  SyncInvoker | Uniform interface for synchronous invocation of HTTP methods.
  WebTarget | A resource target identified by the resource URI.

- Class Summary
  Class | Description
  --- | ---
  ClientBuilder | Main entry point to the client API used to bootstrap `Client` instances.
  Entity<T> | Encapsulates message entity including the associated variant information.

- Exception Summary
  Exception | Description
  --- | ---
  ResponseProcessingException | JAX-RS client-side runtime processing exception thrown to indicate that response processing has failed (e.g.

## Package javax.ws.rs.client Description

# The JAX-RS client API

The JAX-RS client API is a Java based API used to access Web resources. It is not restricted to resources implemented using JAX-RS. It provides a higher-level abstraction compared to a `plain HTTP communication API` as well as integration with the JAX-RS extension providers, in order to enable concise and efficient implementation of reusable client-side solutions that leverage existing and well established client-side implementations of HTTP-based communication.

The JAX-RS Client API encapsulates the Uniform Interface Constraint – a key constraint of the REST architectural style – and associated data elements as client-side Java artifacts and supports a pluggable architecture by defining multiple extension points.

## Client API Bootstrapping and Configuration

The main entry point to the API is a `ClientBuilder` that is used to bootstrap `Client` instances - `configurable`, heavy-weight objects that manage the underlying communication infrastructure and serve as the root objects for accessing any Web resource. The following example illustrates the bootstrapping and configuration of a `Client` instance:

       Client client = ClientBuilder.newClient();

       client.property("MyProperty", "MyValue")
             .register(MyProvider.class)
             .enable(MyFeature.class);

## Accessing Web Resources

A Web resource can be accessed using a fluent API in which method invocations are chained to configure and ultimately submit an HTTP request. The following example gets a `text/plain` representation of the resource identified by `"http://example.org/hello"`:

       Client client = ClientBuilder.newClient();
       Response res = client.target("http://example.org/hello").request("text/plain").get();

Conceptually, the steps required to submit a request are the following:

1. obtain an `Client` instance
2. create a `WebTarget` pointing at a Web resource
3. `build` a request
4. submit a request to directly retrieve a response or get a prepared `Invocation` for later submission

As illustrated above, individual Web resources are in the JAX-RS Client API represented as resource targets. Each `WebTarget` instance is bound to a concrete URI, e.g. `"http://example.org/messages/123"`, or a URI template, e.g. `"http://example.org/messages/{id}"`. That way a single target can either point at a particular resource or represent a larger group of resources (that e.g. share a common configuration) from which concrete resources can be later derived:

       // Parent target for all messages
       WebTarget messages = client.target("http://example.org/messages/{id}");

       WebTarget msg123 = messages.resolveTemplate("id", 123); // New target for http://example.org/messages/123
       WebTarget msg456 = messages.resolveTemplate("id", 456); // New target for http://example.org/messages/456

## Generic Invocations

An `Invocation` is a request that has been prepared and is ready for execution. Invocations provide a generic interface that enables a separation of concerns between the creator and the submitter. In particular, the submitter does not need to know how the invocation was prepared, but only whether it should be executed synchronously or asynchronously.

       Invocation inv1 = client.target("http://example.org/atm/balance")
           .queryParam("card", "111122223333").queryParam("pin", "9876")
           .request("text/plain").buildGet();
       Invocation inv2 = client.target("http://example.org/atm/withdrawal")
           .queryParam("card", "111122223333").queryParam("pin", "9876")
           .request().buildPost(text("50.0")));

       Collection invs = Arrays.asList(inv1, inv2);
       // Executed by the submitter
       Collection ress = Collections.transform(invs, new F() {
          public Response apply(Invocation inv) {return inv.invoke(); }
       });

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