Populate dropdown based on another dropdown selection Spring MVC AJAX

Question

I have 2 dropdowns: one for categories and one for subcategories. Based on what category I select on the first dropdown I want that the second dropdown to be dynamically populated with the subcategories of the selected category. This is what I have so far:

Controller to populate the first dropdown:

@RequestMapping(value = "/post_project", method = RequestMethod.GET)
    public String postProjectPage(Model model) {
        Project project = new Project();
        List<Category> categoriesList = categoryService.getAllCategories();
        model.addAttribute("projectForm", project);
        model.addAttribute("categoriesList", categoriesList);
        return "post_project";
    }

JSP:

<form:form id="post_project" action="/post_project" method="post" modelAttribute="projectForm"> 
    <form:select class="form-control" id="selectCategory" path="category">
         <option value="">-Select-</option>
         <form:options items="${categoriesList}" itemValue="id" itemLabel="category_name"/>
    </form:select>

For the subcategories I have the following controller:

@RequestMapping(value = "/post_project", method = RequestMethod.POST)
    public @ResponseBody  List<Subcategory> getAllSubcategories(@RequestParam(value="categoryId") int categoryId) {
        return categoryService.getAllSubcategories(categoryId);
    }

JSP:

  <form:select class="form-control" id="selectSubcat" path="subcategory">
       <option value="-1" label="-Select-"/>
    </form:select>

For populating the second dropdown I used AJAX, but I am very new with this and I don't know if it is right.

("#selectCategory").change(function(){
        var categoryId = $(this).val();
        $.ajax({
            type: 'POST',
            url: "/post_project",
            data: {"categoryId" : categoryId},
            success: function(data){
                var slctSubcat=$('#selectSubcat'), option="";
                slctSubcat.empty();

                for(var i=0; i<data.length; i++){
                    option = option + "<option value='"+data[i].id + "'>"+data[i].subcateogory_name + "</option>";
                }
                slctSubcat.append(option);
            },
            error:function(){
                alert("error");
            }

        });
    });

Of course it does not work. When I select a cateogry nothing shows up in the second dropdown. I don't know what to do anymore and I've tried everything. Can someone please tell me what I am doing wrong?

Answer 1

Make you request as a GET:

("#selectCategory").change(function(){
    var categoryId = $(this).val();
    $.ajax({
        type: 'GET',
        url: "/categories/" + categoryId,
        success: function(data){
            var slctSubcat=$('#selectSubcat'), option="";
            slctSubcat.empty();

            for(var i=0; i<data.length; i++){
                option = option + "<option value='"+data[i].id + "'>"+data[i].subcateogory_name + "</option>";
            }
            slctSubcat.append(option);
        },
        error:function(){
            alert("error");
        }

    });
});

Server Side controller method:

@RequestParam is used to get the query parameters. So, it would be like ..../post_project?categoryId=1

Instead of @RequestParam use @PathVariable as below:

So to get the subcategories, you have @RequestMapping like .../categories/1

@RequestMapping(value = "/categories/{categoryId}", method = RequestMethod.GET)
public @ResponseBody  List<Subcategory> getAllSubcategories(@PathVariable("categoryId") int categoryId) {
    return categoryService.getAllSubcategories(categoryId);
}