Spring Matrix Variables require at least one template variable to work? - spring

Question

I've been trying to get a simple REST API to list contents of a collection and I'm using matrix variables to control the pagination.
My controller has the following method to list contents of a collection:
#RequestMapping(
value = "articles",
method = RequestMethod.GET,
produces = MediaType.APPLICATION_JSON_VALUE)
public #ResponseBody ArticlePageRestApiResponse listArticles(
#MatrixVariable(required = true, defaultValue = 100, value = "resultsPerPage") int resultsPerPage,
#MatrixVariable(required = true, defaultValue = 0, value = "pageNumber") int pageNumber) {
// some logic to return the collection
}
If I then do a GET http://example.com/articles;resultsPerPage=22;pageNumber=33 it fails to find a request mapping. I have enabled matrix variables support by adding the following:
#Configuration
public class EnableUriMatrixVariableSupport extends WebMvcConfigurationSupport {
#Override
#Bean
public RequestMappingHandlerMapping requestMappingHandlerMapping() {
RequestMappingHandlerMapping hm = super.requestMappingHandlerMapping();
hm.setRemoveSemicolonContent(false);
return hm;
}
}
What I've found is that if the matrix variables are prefixed with at least one template variable then the matrix variables are correctly assigned. The following works but is ugly where I've had to make part of the URI path a template variable that is always going to be "articles" to trick the Request Mapping Handler into thinking there is at least one URI template variable :
#RequestMapping(
value = "{articles}",
method = RequestMethod.GET,
produces = MediaType.APPLICATION_JSON_VALUE)
public #ResponseBody ArticlePageRestApiResponse listArticles(
#PathVariable("articles") String ignore,
#MatrixVariable(required = true, defaultValue = 100, value = "resultsPerPage") int resultsPerPage,
#MatrixVariable(required = true, defaultValue = 0, value = "pageNumber") int pageNumber) {
// some logic to return the collection
}
Have I found a bug or am I mis-understanding matrix variables?

Answer 1

According to Spring documentation
If a URL is expected to contain matrix variables, the request mapping
pattern must represent them with a URI template. This ensures the
request can be matched correctly regardless of whether matrix
variables are present or not and in what order they are provided.
In your first example you use no templates (like {articles}) in URL mapping, so Spring is unable to detect matrix parameters.
I'd rather call it not a bug, but an implemnetation side effect. We have it just because #MatrixVariable support is build on the top of the old #PathVariable parsing mechanism.