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48.2. Building the Client Target

Overview
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After creating the initial Client instance, the next step is to build up the request URI. The WebTarget builder class enables you to configure all aspects of the URI, including the URI path and query parameters.

WebTarget builder class
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The javax.ws.rs.client.WebTarget builder class provides the part of the fluent API that enables you to build up the REST URI for the request.

Create the client target
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To create a WebTarget instance, invoke one of the target methods on a javax.ws.rs.client.Client instance. For example: 
// Java
import javax.ws.rs.client.WebTarget;
...
WebTarget base = client.target("http://example.org/bookstore/");
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Base path and path segments
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You can specify the complete path all in one go, using the target method; or you can specify a base path, and then add path segments piece by piece, using a combination of the target method and the path methods. The advantage of combining a base path with path segments is that you can easily re-use the base path WebTarget object for multiple invocations on slightly different targets. For example: 
// Java
import javax.ws.rs.client.WebTarget;
...
WebTarget base = client.target("http://example.org/bookstore/");
WebTarget headers     = base.path("bookheaders");
// Now make some invocations on the 'headers' target...
...
WebTarget collections = base.path("collections");
// Now make some invocations on the 'collections' target...
...
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URI template parameters
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The syntax of the target path also supports URI template parameters. That is, a path segment can be initialized with a template parameter, {param}, which subsequently gets resolved to a specify value. For example: 
// Java
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.Response;
...
WebTarget base = client.target("http://example.org/bookstore/");
WebTarget books = base.path("books").path("{id}");
...
Response resp = books.resolveTemplate("id", "123").request("application/xml").get();
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Where the resolveTemplate method replaces the path segment, {id}, with the value 123.

Define query parameters
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Query parameters can be appended to the URI path, where the beginning of the query parameters is marked by a single ? character. This mechanism enables you to set a series of name/value pairs, using the syntax: ?name1=value1&name2=value2&...
A WebTarget instance enables you to define query parameters using the queryParam method, as follows: 
// Java
WebTarget target = client.target("http://example.org/bookstore/")
                         .queryParam("userId","Agamemnon")
                         .queryParam("lang","gr");
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Define matrix parameters
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Matrix parameters are somewhat similar to query parameters, but are not as widely supported and use a different syntax. To define a matrix parameter on a WebTarget instance, invoke the matrixParam(String, Object) method.
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