Initializing JAX-RS Sub-resources
Thursday, April 04, 2013 |This morning, I was reading through the Proposed Final Draft for JAX-RS 2.0 specification, when I found a little nugget that could have saved me some work, specificially in initializing subresources.
This is kind of sad to admit (though, surely — hopefully — I’m not alone in this :), but I have been initializing subresource manually. For example:
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public <T> T getSubResource(Class<T> clazz) {
try {
T resource = clazz.newInstance();
BaseResource br = (BaseResource)resource;
br.uriInfo = uriInfo;
br.securityContext = securityContext;
br.requestHeaders = requestHeaders;
return resource;
} catch (Exception ex) {
throw new WebApplicationException(ex, Status.INTERNAL_SERVER_ERROR);
}
}
While this works, the problems should be pretty obvious: it’s extremely inflexible. Fortunately, the JAX-RS Expert Group, who has clearly thought about this more than I, has a better solution: ResourceContext. Take this example, pulled from the spec:
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@Path("widgets")
public class WidgetsResource {
@Context
private ResourceContext rc;
@Path("{id}")
public WidgetResource findWidget(@PathParam("id") String id) {
return rc.initResource(new WidgetResource(id));
}
}
public class WidgetResource {
@Context
private HttpHeaders headers;
public WidgetResource(String id) {...}
@GET
public Widget getDetails() {...}
}
Notice the method WidgetsResource.findWidget(). The parent resource, WidgetsResource, has an instance of ResourceContext injected, which is then used to initialize the subresource instantiated in findWidget(). The benefit of this approach over the approach above is that everthing is injected, regardless of what I’m expecting to find.
I’ve been working with JAX-RS for over 3 years now, and I’m just now learning this. Shows that there’s always something to learn, and that reading specs pays off. :)
My name is Jason Lee. I am a software developer living in the middle of Oklahoma. I’ve been a professional developer since 1997,
using a variety of languages, including Java, Javascript, PHP, Python, Delphi, and even a bit of C#. I currently work for Red Hat
on the WildFly/EAP team, where, among other things, I maintain integrations for some MicroProfile specs, OpenTelemetry, Micrometer,
Jakarta Faces, and Bean Validation. (Full resume 