Request param value with curly braces throws IllegalArgumentException

[dreambrother]

Example:

@ResponseBody
@RequestMapping(value = "", method = RequestMethod.GET)
public Resources<FileResource> listFilesHal(
        @RequestParam(value = "q") String query) {
    Link self = linkTo(methodOn(FileRestController.class).listFilesHal(query)).withSelfRel();
    return new Resources<>(listFilesImpl(query), self);
}

If q contains curly braces (and it does because it's JSON) then linkTo throws
GET http://localhost:8080/files?q={"foo": "bar"}

java.lang.IllegalArgumentException: Map has no value for '"foo"'
    at org.springframework.web.util.UriComponents$MapTemplateVariables.getValue(UriComponents.java:276)
    at org.springframework.web.util.UriComponents.expandUriComponent(UriComponents.java:221)
    at org.springframework.web.util.HierarchicalUriComponents.expandInternal(HierarchicalUriComponents.java:326)
    at org.springframework.web.util.HierarchicalUriComponents.expandInternal(HierarchicalUriComponents.java:46)
    at org.springframework.web.util.UriComponents.expand(UriComponents.java:152)
    at org.springframework.web.util.UriComponentsBuilder.buildAndExpand(UriComponentsBuilder.java:302)
    at org.springframework.hateoas.mvc.ControllerLinkBuilderFactory.linkTo(ControllerLinkBuilderFactory.java:145)
    at org.springframework.hateoas.mvc.ControllerLinkBuilder.linkTo(ControllerLinkBuilder.java:135)

[vivin]

According to RFC 1738, curly braces are illegal in URLs, so what you have is actually not a valid URL. if your query parameter has a JSON value, you should URL encode it. " and space are illegal as well, whereas : is reserved. In this case, you would end up with GET http://localhost:8080/files?q=%7B%22foo%22%3A%20%22bar%22%7D.

[dreambrother]

@vivin, seems spring-hateoas should do this automatically

[vivin]

Oh, my mistake. I thought that was a request coming in. This is a URL that Spring HATEOAS generates?

[dreambrother]

Parameter came as URL encoded value, then spring-mvc automatically decodes it and if I pass it to the linkTo method, it throws strange exception.

[vivin]

Yeah, I'd imagine that it should urlencode it on its own.

[SingleShot]

There appears no way around this. If one encodes the query parameter, it ends up double-encoded.

An example of how we are encountering this error:

linkTo(methodOn(SomeController.class).someMethod("id:{<123>, <456>}"))

Note this is not JSON - our domain has text with curly braces in it.

It appears Spring HATEOAS is trying to do template variable expansion on a value passed into the linkTo/methodOn controller signature.

[SingleShot]

We are just gonna do a workaround for this, which is to call methodOn with a null value:

linkTo(methodOn(SomeController.class).someMethod(null))

Then we call a method that knows about that particular parameters (in our case, it is called "query") and adds it into the URL manually:

Link addQueryToLink(String query, Link link) {

  final UriComponentsBuilder builder = UriComponentsBuilder.fromUriString(link.getHref());

  if (query == null || query.isEmpty()) {
    builder.replaceQueryParam("query");
  } else {
    builder.replaceQueryParam("query", query);
  }

  return new Link(builder.build().encode().toUriString(), link.getRel());
}

Obviously this can be improved upon, made more generic, etc. but ideally we should not have to do it.

[wendelicious]

So, i hit this once per quarter or so, and it seems to always be a user error: I'll annotate the request method arguments as @PathParam. smh Should be @PathVariable. @PathVariable for the win.

fwiw