Several Xtext based DSLs will use import statements that import JvmTypes, be them real Java types, or just inferred types produced with your IJvmModelInferrer. The check for a valid import might be simple, but here it is to just make it even easier for you. I just had the need to realize this to resolve Spray issue#113. Basically you need to get the IJvmTypeProvider, to which you gain access through the IJvmTypeProvider.Factory.

public class SprayJavaValidator extends AbstractSprayJavaValidator implements IssueCodes {
    @Inject
    private IJvmTypeProvider.Factory typeProviderFactory;
    @Check
    public void checkImports(final Import imp) {
        // don't check wildcard imports
        if (imp.getImportedNamespace().endsWith(".*"))
            return;
        IJvmTypeProvider typeProvider = typeProviderFactory.findOrCreateTypeProvider(imp.eResource().getResourceSet());
        JvmType jvmType = typeProvider.findTypeByName(imp.getImportedNamespace());
        if (jvmType == null) {
            error("The import " + imp.getImportedNamespace() + " cannot be resolved", SprayPackage.Literals.IMPORT__IMPORTED_NAMESPACE, IMPORT_NOTEXISTS, new String[0]);
        }
    }
    ...
}

That’s all.