Client and WebTarget

Now that we have a Client, there’s a bunch of stuff we can do with this object. Like ClientBuilder, the Client interface implements Configurable. This allows you to change configuration and register components for the Client on the fly as your application executes. The most important purpose of Client, though, is to create WebTarget instances:

package javax.ws.rs.client.Client;

public interface Client extends Configurable<Client> {

    public void close();

    public WebTarget target(String uri);
    public WebTarget target(URI uri);
    public WebTarget target(UriBuilder uriBuilder);
    public WebTarget target(Link link);

...
}

The WebTarget interface represents a specific URI you want to invoke on. Through the Client interface, you can create a WebTarget using one of the target() methods:

package javax.ws.rs.client.Client;

public interface WebTarget extends Configurable<WebTarget> {
    public URI getUri();
    public UriBuilder getUriBuilder();

    public WebTarget path(String path);
    public WebTarget resolveTemplate(String name, Object value);
    public WebTarget resolveTemplate(String name, Object value,
                                      boolean encodeSlashInPath);
    public WebTarget resolveTemplateFromEncoded(String name, Object value);
    public WebTarget resolveTemplates(Map<String, Object> templateValues);
    public WebTarget resolveTemplates(Map<String, Object> templateValues,
                                      boolean encodeSlashInPath);
    public WebTarget resolveTemplatesFromEncoded(
                                      Map<String, Object> templateValues);
    public WebTarget matrixParam(String name, Object... values);
    public WebTarget queryParam(String name, Object... values);

    ...
}

WebTarget has additional methods to extend the URI you originally constructed it with. You can add path segments or query parameters by invoking path() and queryParam(). If the WebTarget represents a URI template, the resolveTemplate() methods can fill in those variables:

WebTarget target = client.target("http://commerce.com/customers/{id}")
                         .resolveTemplate("id", "123")
                         .queryParam("verbose", true);

In this example, we initialized a WebTarget with a URI template string. The resolveTemplate() method fills in the id expression, and we add another query parameter. If you take a look at the UriBuilder class, you’ll see that WebTarget pretty much mirrors it. Instead of building URIs, though, WebTarget is building instances of WebTargets that you can use to invoke HTTP requests.