Spring MVC populate @RequestParam Map<String, String>

Question

I have the following method in my Spring MVC @Controller :

@RequestMapping(method = RequestMethod.GET)
public String testUrl(@RequestParam(value="test") Map<String, String> test) {   
    (...)
}

I call it like this :

http://myUrl?test[A]=ABC&test[B]=DEF

However the "test" RequestParam variable is always null

What do I have to do in order to populate "test" variable ?

Answer 1

As detailed here https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/bind/annotation/RequestParam.html

If the method parameter is Map or MultiValueMap and a parameter name is not specified, then the map parameter is populated with all request parameter names and values.

So you would change your definition like this.

@RequestMapping(method = RequestMethod.GET)
public String testUrl(@RequestParam Map<String, String> parameters) 
{   
  (...)
}

And in your parameters if you called the url http://myUrl?A=ABC&B=DEF

You would have in your method

parameters.get("A");
parameters.get("B");

Answer 2

Spring doesn't have default conversion strategy from multiple parameters with the same name to HashMap. It can, however, convert them easily to List, array or Set.

@RequestMapping(value = "/testset", method = RequestMethod.GET)
    public String testSet(@RequestParam(value = "test") Set<String> test) {

        return "success";
    }

I tested with postman like http://localhost:8080/mappings/testset?test=ABC&test=DEF

You will see set having data, [ABC, DEF]

Answer 3

You can create a new class that contains the map that should be populated by Spring and then use that class as a parameter of your @RequestMapping annotated method.

In your example create a new class

public static class Form {
   private Map<String, String> test;
   // getters and setters
}

Then you can use Form as a parameter in your method.

@RequestMapping(method = RequestMethod.GET)
public String testUrl(Form form) {
  // use values from form.getTest()
}