How to check the map type?

Question

I am setting the data in model as:

@RequestMapping("/forms/builder/")
public void renderMethod1(Model model) {            
    SoyMapData x=new SoyMapData("class","menu horizontal right");
    model.addAttribute("pageTitles", x);        
}

Which is mapped to below function via Spring:

@Override
protected void renderMergedTemplateModel(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) {
    String renderedResponse = null;
    renderedResponse = compiledSoyTemplates.render(templateName, model, messageBundle);
}

Here I need to check if model is of type SoyMapData, if yes then set the type of model to SoyMapDataelse map. How can I do this?

I have tried below approach its not working.

Answer 1

You can do that with the instanceof operator:

SoyMapData soyModel;
if (model instanceof SoyMapData) {
    // It is, get a reference using that type
    soyModel = (SoyMapData)model;
}

...but if you need to do that, it suggests a problem with the encapsulation in the API design. Your render method shouldn't need to know what kind of Map it's receiving, that breaks encapsulation.

There are many ways to solve that. One is by deriving a new interface from Map that allows render to do its job, and then using that interface rather than Map in the method signature. But that's only one way.

---

Update: Re your updated code, if I understand you correctly, you want to call compiledSoyTemplates.render with either a SoyDataModel argument or a Map argument depending on whether model is a SoyDataModel. (E.g., it's an overloaded method and you want the compiler to know which one to use.) If so, then you just use the information I gave you above like this:

@Override
protected void renderMergedTemplateModel(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) {
        String renderedResponse = null;
        if (model instanceof SoyDataModel) {
            renderedResponse = compiledSoyTemplates.render(
                templateName,
                (SoyDataModel)model,
                messageBundle
            );
        }
        else {
            renderedResponse = compiledSoyTemplates.render(
                templateName,
                model,
                messageBundle
            );
        }
}

Answer 2

You cannot change the type of a variable/parameter in Java. You can check the type of the object, and if it matches your criteria, create another variable of the new type as follows

if (model instanceof SoyMapData) {
   SoyMapData soyModel = (SoyMapData)model;
   ...
}

Answer 3

Edit:: SoyMapData is placed inside model in renderMethod1. If the parameter model in renderMergedTemplateModel references the same object (then Model needs to implement the interface Map) you need to get the object at the key pageTitles.

If the above assumptions hold,

if (model.get("pageTitles") instanceof SoyMapData) {
  SoyMapData sModel = (SoyMapData)model.get("pageTitles");
}

should work.

instanceof is used to check the runtime type of an instance:

if (model instanceof SoyMapData) {
  SoyMapData sData = (SoyMapData)model;
  ...
} else {
  ...
}