MappingFactory: respect datatype for constants

Constants in the mapping have sometimes their own datatype already specified, use it.

Author: DylanVanAssche

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Fixed
 - Better handle unsupported reference formulation (See [issue 247](https://github.com/RMLio/rmlmapper-java/issues/247))
 - Graph Maps with default graph must not be ignored (See [issue 252](https://github.com/RMLio/rmlmapper-java/issues/252))
+- Honor datatypes for constants (See [issue 251](https://github.com/RMLio/rmlmapper-java/issues/251))
 
 ## [7.3.2] - 2025-03-04
 

src/main/java/be/ugent/rml/MappingFactory.java

@@ -202,7 +202,8 @@ private void parseObjectMapsAndShortcutsWithCallback(Term termMap, BiConsumer<Ma
             SingleRecordFunctionExecutor fn = new ConstantExtractor(o.getValue());
 
             if (o instanceof Literal) {
-                gen = new LiteralGenerator(fn);
+                Term datatype = new NamedNode(((Literal) o).getDatatype().toString());
+                gen = new LiteralGenerator(fn, datatype);
             } else {
                 gen = new NamedNodeGenerator(fn, baseIRI, strictMode);
             }