MockMvc doesn't honor params in RequestMapping when no equal sign [SPR-15831]

[spring-projects-issues]

Jean-Baptiste Nizet opened SPR-15831 and commented

When two resource methods are defined as following:

    @GetMapping
    public String noParam() {
        return "noParam";
    }

    @GetMapping(params = "foo")
    public String paramFoo() {
        return "paramFoo";
    }

and a MockMvc test tries executing the second method using

mvc.perform(get("/api/bug?foo"))

then the first method is invoked instead. Adding an equal sign at the end fixes the issue, but the equl sign shouldn't be necessary. BTW, in production, sending a request to /api/bug?foo does invoke the second method as expected.

Here's a repro project: https://github.com/jnizet/param-bug-demo

Note that the original bug has been detected in a Spring Boot 2.0.0.M2 project, so the bug is still there in the latest version of Spring.

---

Affects: 4.3.10, 5.0 RC3

Referenced from: commits 4fc0ce1

[spring-projects-issues]

Rossen Stoyanchev commented

It looks like Servlet containers (at least current Tomcat and Jetty) do not differentiate between empty value ("foo=") and no value ("foo") and always return an empty value.

In the Spring Framework however we do and always have. In this case UriComponentsBuilder parses "foo" as a parameter with a null value, MockHttpServletRequestBuilder preserves that distinction, MockHttpServletRequest stores it as a String[] with one null value, and at request time ParamsRequestCondition calls WebUtils.hasSubmitParameter(request, name) which does request.getParameter(name) != null and that is null.

I am not sure whether the Servlet container behavior has changed over time or this simply hasn't surfaced until now. I could not find anything the Servlet spec and API that talks about empty parameter values.

We could make an improvement in ParamsRequestCondition to perform the name-only match via request.getParameterMap().contains(name). One could argue that WebUtils.hasSubmitParameter is fine as it is since a submit parameter is a more specific use case for a browser form button.