48.3. Building the Client Invocation
Overview
After building the target URI, using the
WebTarget builder class, the next step is to configure the other aspects of the request—such as HTTP headers, cookies, and so on—using the Invocation.Builder class. The final step in building the invocation is to invoke the appropriate HTTP verb (GET, POST, PUT, or DELETE) and provide a message body, if required.
Invocation.Builder class
The
javax.ws.rs.client.Invocation.Builder builder class provides the part of the fluent API that enables you to build up the contents of the HTTP message and to invoke a HTTP method.
Create the invocation builder
To create an
Invocation.Builder instance, invoke one of the request methods on a javax.ws.rs.client.WebTarget instance. For example:
// Java
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.client.Invocation.Builder;
...
WebTarget books = client.target("http://example.org/bookstore/books/123");
Invocation.Builder invbuilder = books.request();Define HTTP headers
You can add a HTTP header to the request message using the
header method, as follows:
Invocation.Builder invheader = invbuilder.header("From", "fionn@example.org");Define cookies
You can add a cookie to the request message using the
cookie method, as follows:
Invocation.Builder invcookie = invbuilder.cookie("myrestclient", "123xyz");Define properties
You can set a property in the context of this request using the property method, as follows:
Invocation.Builder invproperty = invbuilder.property("Name", "Value");Define accepted media types, languages, or encodings
You can define accepted media types, languages, or encodings, as follows:
Invocation.Builder invmedia = invbuilder.accept("application/xml")
.acceptLanguage("en-US")
.acceptEncoding("gzip");Invoke HTTP method
The process of building a REST invocation is terminated by invoking a HTTP method, which performs the HTTP invocation. The following methods (inherited from the
javax.ws.rs.client.SyncInvoker base class) can be invoked:
get post delete put head trace options
If the specific HTTP verb you want to invoke is not on this list, you can use the generic
method method to invoke any HTTP method.
Typed responses
All of the HTTP invocation methods are provided with an untyped variant and a typed variant (which takes an extra argument). If you invoke a request using the default
get() method (taking no arguments), a javax.ws.rs.core.Response object is returned from the invocation. For example:
Response res = client.target("http://example.org/bookstore/books/123")
.request("application/xml").get();
It is also possible, however, to ask for the response to be returned as a specific type, using the
get(Class<T>) method. For example, to invoke a request and ask for the response to be returned as a BookInfo object:
BookInfo res = client.target("http://example.org/bookstore/books/123")
.request("application/xml").get(BookInfo.class);
In order for this to work, however, you must register a suitable entity provider with the
Client instance, which is capable of mapping the response format, application/xml, to the requested type. For more details about entity providers, see Section 48.4, “Parsing Requests and Responses”.
Specifying the outgoing message in post or put
For HTTP methods that include a message body in the request (such as POST or PUT), you must specify the message body as the first argument of the method. The message body must be specified as a
javax.ws.rs.client.Entity object, where the Entity encapsulates the message contents and its associated media type. For example, to invoke a POST method, where the message contents are provided as a String type:
import javax.ws.rs.client.Entity;
...
Response res = client.target("http://example.org/bookstore/registerbook")
.request("application/xml")
.put(Entity.entity("Red Hat Install Guide", "text/plain"));
If necessary, the
Entity.entity() constructor method will automatically map the supplied message instance to the specified media type, using the registered entity providers. It is always possible to specify the message body as a simple String type.
Delayed invocation
Instead of invoking the HTTP request right away (for example, by invoking the
get() method), you have the option of creating an javax.ws.rs.client.Invocation object, which can be invoked at a later time. The Invocation object encapsulates all of the details of the pending invocation, including the HTTP method.
The following methods can be used to build an
Invocation object:
buildGet buildPost buildDelete buildPut build
For example, to create a GET
Invocation object and invoke it at a later time, you can use code like the following:
import javax.ws.rs.client.Invocation;
import javax.ws.rs.core.Response;
...
Invocation getBookInfo = client.target("http://example.org/bookstore/books/123")
.request("application/xml").buildGet();
...
// Later on, in some other part of the application:
Response = getBookInfo.invoke();Asynchronous invocation
The JAX-RS 2.0 client API supports asynchronous invocations on the client side. To make an asynchronous invocation, simply invoke the
async() method in the chain of methods following request(). For example:
Future<Response> res = client.target("http://example.org/bookstore/books/123")
.request("application/xml")
.async()
.get();
When you make an asynchronous invocation, the returned value is a
java.util.concurrent.Future object. For more details about asynchronous invocations, see Section 48.6, “Asynchronous Processing on the Client”.
