public class CustomLanguageServerImpl extends LanguageServerImpl {

...

        @Override
	protected ServerCapabilities createServerCapabilities(InitializeParams params) {

                ServerCapabilities capabilities = super.createServerCapabilities(params);

                // Create server capabilities for semantic tokens.
		SemanticTokensWithRegistrationOptions options = new SemanticTokensWithRegistrationOptions();

		List<String> tokenTypes = new ArrayList<String>();
		tokenTypes.add(SemanticTokenTypes.Namespace);
                ...

		List<String> tokenModifiers = new ArrayList<String>();
		tokenModifiers.add(SemanticTokenModifiers.Declaration);
                ...
		
                options.setLegend(new SemanticTokensLegend(tokenTypes, tokenModifiers));
		options.setRange(false);
		options.setFull(true);

		capabilities.setSemanticTokensProvider(options);

		return capabilities;
        }

        @Override
	public CompletableFuture<SemanticTokens> semanticTokensFull(SemanticTokensParams params) {
          ...
	}

	@Override
	public CompletableFuture<SemanticTokens> semanticTokensRange(SemanticTokensRangeParams params) {
            ...
	}

	@Override
	public CompletableFuture<Either<SemanticTokens, SemanticTokensDelta>> semanticTokensFullDelta(
		...
	}
}