Dynamic styling

General
1

Hello All ! (hope you are at best),

I would like to define styles dynamically but it does not work.
These styles are to be applied on nodes of a TreeGrid with :

addColumn(createTemplate()).setClassNameGenerator(new ValueProvider<UITreeNode<DATA>, String>() {
            // Style name generator.
            @Override
            public String apply(UITreeNode<DATA> node) {
                return node.getStyle();
            }
        });

As a test case, I define a string (later it will be built by enumerating styles like words from a dictionary; all combinations for bold, italic, underline, color, … ; each combination has a functional meaning) :

private static final String STYLE =
            "import '@vaadin/vaadin-grid/vaadin-grid.js';\n"
                    + "import { html } from '@polymer/polymer/lib/utils/html-tag.js';\n"
                    + "const $_documentContainer = html`\n"
                    + "<dom-module id=\"uitree-style\" theme-for=\"vaadin-grid\">"
                    + " <template>"
                    + "  <style>"
                    + "   [part~=\"cell\"]
.style1 {"
                    + "    background: blue;"
                    + "   }"
                    + "   [part~=\"cell\"]
.style2 {"
                    + "    background: yellow;"
                    + "   }"
                    + "  </style>"
                    + " </template>"
                    + "</dom-module>`;\n"
                    + "document.head.appendChild($_documentContainer.content);";

Then in the constructor :

VaadinSession session = UI.getCurrent().getSession();
        StreamResourceRegistry registry=session.getResourceRegistry();
        StreamRegistration resource =
                registry.registerResource(new StreamResource("uitree-style.js", new InputStreamFactory() {
                    @Override
                    public InputStream createInputStream() {
                        byte[] bytes = STYLE.getBytes(StandardCharsets.UTF_8);
                        return new ByteArrayInputStream(bytes);
                    }
                }));

        String url = resource.getResourceUri().toString();
        System.out.println("url=" + url);

        Page page = UI.getCurrent().getPage();
        page.addJsModule("file://" + url); // No effect.

I use spring-boot-starter-parent 2.1.6.RELEASE and Vaadin 14.1.16 .
All is fine when exactly the same String STYLE is put in a file “frontend\styles\custom-tree.js” and the annotation @JsModule(“./styles/custom-tree.js”) is used (of course, i could put the definitions of our 64 styles there).
What is the right syntax for the url in method addJsModule ?

Thanks and best regards,

Nicolas Culem