Map<String,String> Integer cannot be cast to class String

Question

There's a way to handle this validation ?

class java.lang.Integer cannot be cast to class java.lang.String

Code:

private List<Map<String,String>> getEmpRegistry(
        List<Map<String,String>> tblObjRowsList,
        Integer rowNumber
){
    List<Map<String,String>> empRegistry = new ArrayList<>();
    for (Map<String,String> empR : tblObjRowsList){
        if (empR.get("id").equals(rowNumber)){
            empRegistry.add(empR);
        }
    }
    return empRegistry;
}

Looks wrong, because I can't compare String and Integer.

But for some reason tblObjRowsList is extracted from stored procedure in MySQL via Spring Data:

@Query(value="CALL SP_ObjsRowDetails2(:Id,:templateId,:strMode)",nativeQuery = true)
List<Map<String,String>> getRowDetail  (@PathParam("Id") Integer id,
                                        @PathParam("templateId") Integer templateId,
                                        @PathParam("strMode") Integer strMode);

Extract the data like this:

I tried:

Integer.parseInt(empR.get("id")).equals(rowNumber)

Integer.parseInt(empR.get("id").toString()).equals(rowNumber)

empR.get("id").toString().equals(String.valueOf(rowNumber))

And the most interesting thing is:

Doesn't make sense, if the source variable is Map<String,String>

GPI · Accepted Answer · 2021-06-29 17:05:03Z

That declaration of List<Map<String,String>> getRowDetail(...) is probably a "lie". That's the problem with runtime, dynamic code generation...

Spring data generates the implementation for you, and there is no proof that it will generate a Map<String, String> in reality, it all depends on what the SQL type will actually be in your procedure

Spring can and will produce a Map but you can not know what types lie therein, the actual types will be chosen once the metadata for the SQL result set comes back.

The compiler is happy, because generics are erased after compilation anyway, so as long as it's a Map, it's fine.

In the end you only realise Spring did not do "the right thing" (or actually, what you expected, because in its view it did the right thing) until runtime.

There is no easy way out. Either you fully acknowledge the unknowable nature of the contents of the map, and declare a Map<Object, Object> as the return type. And your code will have to cast to operate on the data.

Or you make sure you adapt the Java to the SQL or vice-versa with less generic types (eg <String, Integer>) - and find a way to make sure nobody changes the SQL without applying the change to the Java side, or vice-versa.

Michał Marcinkowski · Accepted Answer · 2021-06-29 16:55:35Z

2

I believe that instead of Map<String, String> use Map<String, Object> and then according to the type inside of the value just cast it to to integer, string, or whatever.

answered Jun 29, 2021 at 16:55

Michał Marcinkowski

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