I think it's none of Spring HandlerMapping business.
when you click search button, the form http url posted depends on http base uri and your relative path(usually in action attribute)
"localhost:8080/spring-mvc-project-web-war/searchProjects" it's base uri is
localhost:8080/spring-mvc-project-web-war/
and "localhost:8080/spring-mvc-project-web-war/searchProjects/" base uri is
localhost:8080/spring-mvc-project-web-war/searchProjects/
In order to further understand,we can read Fielding's rfc document [Page 11]