Using the MvcUriComponentsBuilder to get a URL to a controller method adds empty parameter when the value is not provided [SPR-14890]

Cèsar Ordiñana opened SPR-14890 and commented

I'm developing a Spring boot with Spring MVC web app using Thymeleaf views. I'm using the Building URIs to Controllers and methods from views feature through the Thymeleaf #mvc.url utility.

I have the following sample controller:

@Controller
@RequestMapping(value = "/categories/{category}/products",
    name = "CategoriesItemProductsThymeleafController",
    produces = MediaType.TEXT_HTML_VALUE)
public class CategoriesItemProductsThymeleafController {
  public CategoryService categoryService;

  @Autowired
  public CategoriesItemProductsThymeleafController(CategoryService categoryService) {
    this.categoryService = categoryService;
  }

  @PostMapping(name = "addToProducts")
  @ResponseBody
  public ResponseEntity<?> addToProducts(@ModelAttribute Category category,
      @RequestParam("products") List<Long> products) {
    categoryService.addToProducts(category, products);
    return ResponseEntity.ok().build();
  }
}

In the Thymeleaf view I get the link to that controller method with something like:

<div id="create-url" data-data-create-url="${(#mvc.url('CategoriesItemProductsThymeleafController#addToProducts')).buildAndExpand('CATEGORY_ID')}"></div>

It uses internally the MvcUriComponentsBuilder.fromMappingName(String) method which returns a MethodArgumentBuilder. It expects a list of product ids as a request parameter, but I can't use the MethodArgumentBuilder.arg() method because the values I want to send are to be selected in javascript.

The problem with this method is that the Url return is the following one:

/categories/CATEGORY_ID/products?products

I use that Url as a parameter to call jQuery.ajax() using my own products values. If I use a GET method, the url ends up being:

/categories/CATEGORY_ID/products?products&products=1&products=2

Then the controller method receives the following list of values: [null, 1, 2]. As a workaround I can remove those null values from the list, but I think the Url is not constructed as it should.

After some debugging I've found the code which add those empty parameters is the HierarchicalUriComponents.getQuery() method. It has the following code:

for (Object value : values) {
    if (queryBuilder.length() != 0) {
        queryBuilder.append('&');
    }
    queryBuilder.append(name);

    if (value != null) {
        queryBuilder.append('=');
        queryBuilder.append(value.toString());
    }
  }

The problem could be solved by changing the code to add the parameter only if value!=null.

Affects: 4.3.3

Issue Links:

• #18113 UriComponentsBuilder interprets empty request parameters as null

1 votes, 3 watchers

Start with MvcUriComponentsBuilder.fromMappingName(String) and the mentioned HierarchicalUriComponents.getQuery() implementation. Reproduce the controller and URL-building example from the issue, then verify that an omitted request parameter does not produce a bare “?products” entry while explicitly added values still appear correctly.