fix: ignore absence of file-routes.json at startup in dev mode (#2423)

* fix: ignore absence of file-routes.json at startup in dev mode

Fixes #2408

* apply suggestions from code review

* Update packages/java/endpoint/src/main/java/com/vaadin/hilla/route/ClientRouteRegistry.java

Co-authored-by: Artur <artur@vaadin.com>

---------

Co-authored-by: Zhe Sun <31067185+ZheSun88@users.noreply.github.com>
Co-authored-by: Artur <artur@vaadin.com>

packages/java/endpoint/src/main/java/com/vaadin/hilla/route/ClientRouteRegistry.java

@@ -18,6 +18,7 @@
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.vaadin.flow.function.DeploymentConfiguration;
+import com.vaadin.flow.server.frontend.FrontendUtils;
 import com.vaadin.hilla.route.records.ClientViewConfig;
 
 import org.slf4j.Logger;
@@ -144,9 +145,9 @@ private String removeTrailingSlash(String path) {
     public synchronized void registerClientRoutes(
             DeploymentConfiguration deploymentConfiguration,
             LocalDateTime lastUpdated) {
-        var viewsJsonAsResource = getViewsJsonAsResource(
+        var fileRoutesJsonAsResource = getFileRoutesJsonAsResource(
                 deploymentConfiguration);
-        if (viewsJsonAsResource == null) {
+        if (fileRoutesJsonAsResource == null) {
             LOGGER.debug(
                     "No {} found under {} directory. Skipping client route registration.",
                     FILE_ROUTES_JSON_NAME,
@@ -155,7 +156,7 @@ public synchronized void registerClientRoutes(
                             : "'frontend/generated'");
             return;
         }
-        try (var source = viewsJsonAsResource.openStream()) {
+        try (var source = fileRoutesJsonAsResource.openStream()) {
             if (source != null) {
                 clearRoutes();
                 mapper.readValue(source,
@@ -165,8 +166,16 @@ public synchronized void registerClientRoutes(
                 this.lastUpdated = lastUpdated;
             }
         } catch (IOException e) {
-            LOGGER.warn("Failed load {} from {}", FILE_ROUTES_JSON_NAME,
-                    viewsJsonAsResource.getPath(), e);
+            if (deploymentConfiguration.isProductionMode()) {
+                // The file should be available in production mode:
+                LOGGER.error("Failed to load {} from {}", FILE_ROUTES_JSON_NAME,
+                        fileRoutesJsonAsResource.getPath(), e);
+            } else {
+                LOGGER.debug(
+                        "Failed to load {} from {}. Skipping client route registration. "
+                                + "There might be a problem with the contents of the file-routes.json file.",
+                        FILE_ROUTES_JSON_NAME, "'frontend/generated'");
+            }
         }
     }
 
@@ -190,18 +199,25 @@ public synchronized void loadLatestDevModeFileRoutesJsonIfNeeded(
         }
     }
 
-    private URL getViewsJsonAsResource(
+    private URL getFileRoutesJsonAsResource(
             DeploymentConfiguration deploymentConfiguration) {
         var isProductionMode = deploymentConfiguration.isProductionMode();
         if (isProductionMode) {
             return getClass().getResource(FILE_ROUTES_JSON_PROD_PATH);
         }
         try {
-            return deploymentConfiguration.getFrontendFolder().toPath()
-                    .resolve("generated").resolve(FILE_ROUTES_JSON_NAME).toUri()
-                    .toURL();
+            var fileRoutesJson = FrontendUtils
+                    .getFrontendGeneratedFolder(
+                            deploymentConfiguration.getFrontendFolder())
+                    .toPath().resolve(FILE_ROUTES_JSON_NAME).toFile();
+            if (!fileRoutesJson.exists()) {
+                return null;
+            } else {
+                return fileRoutesJson.toURI().toURL();
+            }
         } catch (MalformedURLException e) {
-            LOGGER.warn("Failed to find {} under frontend/generated",
+            LOGGER.error(
+                    "Unexpected error while getting {} as resource from 'frontend/generated'.",
                     FILE_ROUTES_JSON_NAME, e);
             throw new RuntimeException(e);
         }