How to build Query Parameter using Spring Traverson

2
votes

I have a Spring Data Rest webservice with QueryDSL Web Support enabled so I can query any of the fields directly like below;

http://localhost:9000/api/prod1007?cinfo1=0126486035

And I was using Traverson to access this service but traverson is not generating the query parameter as above; below is my code (I have tried both withTemplateParameters() and withParameters() in Hop level)

Code:

Map<String,Object> parameters = new HashMap<String,Object>();
parameters.put("cinfo1", "0127498374");

PagedResources<Tbpinstance> items = traverson
.follow(Hop.rel("prod1007"))
.withTemplateParameters(parameters)
.toObject(resourceParameterizedTypeReference);

Any Help is much appreciated. Thanks!

2
spring-data-restspring-hateoas
Did you ever figure this out? I have the same issue - John Deverall
@JohnDeverall, how about you, did you figure it out? I've now posted an answer, see if that helps. - ZeroOne
@ZeroOne, yeah I got it figured out, we've got a nice solution I think now. Hit me up, I'm happy to share code. We're using what I've posted below on the server and then have some (hopefully nice stuff) that I plan to open source later in the client side (we have a client implementation written in java). - John Deverall

2 Answers

2
votes

Traverson needs to know where to put those parameters. They could be path parameters, or they could be query parameters. Furthermore, Traverson navigates the service from the root, so the parameters might need to be inserted somewhere in the middle, and not in the final step only.

For these reasons the server needs to clearly tell how to use the parameters. Traverson needs a HATEOAS-"directory" for the service. When Traverson HTTP GETs the http://localhost:9000/api document, it needs to contain a link similar to this:

"_links" : {
    "product" : {
      "href" : "http://localhost:9000/api/prod1007{?cinfo1}",
      "templated" : true
    },
}

Now it knows that the cinfo1 parameter is a query parameter and will be able to put it into its place.

2
votes

@ZeroOne, you are entirely correct, that is what the response from the server should look like. Currently spring-hateoas does not support responses that look like that (I expect it will in the future as I have seen comments by Oliver Gierke indicating that spring-hateoas is going through a major upgrade).

As at the time of writing, to generate responses from the server as you describe, we have used spring-hateoas-ext mentioned in https://github.com/spring-projects/spring-hateoas/issues/169. You can find code at https://github.com/dschulten/hydra-java#affordancebuilder-for-rich-hyperlinks-from-v-0-2-0.

This is a 'drop in replacement' for spring-hateoas' ControllerLinkBuilder.

Here is the maven dependency we use (but check for the latest version).

<!-- Drop in replacement from spring-hateoas ControllerLinkBuilder --> <dependency> <groupId>de.escalon.hypermedia</groupId> <artifactId>spring-hateoas-ext</artifactId> <version>0.3.0-beta6</version> </dependency>

Here's the import we use in our ResourceAssemblers.

import static de.escalon.hypermedia.spring.AffordanceBuilder.*;