fix: Update link tag on stylesheet modification #22504

mshabarov · 2025-10-13T09:50:21Z

Reverts previously added file watcher for stylesheet files as the static resource folder is already watched by hotswap mechanism.
Updates link tag once a modification is detected so stylesheet is hot reloaded.

Related-to: #22465

…urces folder (#22392)" This reverts commit bd9b2cf

github-actions · 2025-10-13T10:07:10Z

Test Results

1 271 files +1 1 271 suites +1 1h 19m 1s ⏱️ + 1m 0s
8 796 tests - 1 8 729 ✅ - 1 67 💤 ±0 0 ❌ ±0
9 248 runs - 2 9 171 ✅ - 2 77 💤 ±0 0 ❌ ±0

Results for commit 1b53372. ± Comparison against base commit 1777b02.

This pull request removes 4 and adds 3 tests. Note that renamed tests count towards both.

com.vaadin.base.devserver.PublicResourcesCssLiveUpdaterTest ‑ cssChangeTriggersUpdate
com.vaadin.base.devserver.PublicResourcesCssLiveUpdaterTest ‑ devModeHandler_watchesAllStaticResourcePathsForCss
com.vaadin.base.devserver.PublicResourcesCssLiveUpdaterTest ‑ devModeHandler_watchesNestedCssFilesUnderStaticRoot
com.vaadin.base.devserver.PublicResourcesCssLiveUpdaterTest ‑ nonCssChangeIsIgnored

com.vaadin.flow.hotswap.HotswapperResourcesTest ‑ cssResourceChange_noLiveReloadAvailable_noCrash
com.vaadin.flow.hotswap.HotswapperResourcesTest ‑ cssResourceChange_triggersLiveReloadUpdateWithRelativePath
com.vaadin.flow.server.AppShellRegistryStyleSheetDataFilePathTest ‑ modifyIndex_addsDataFilePathAttributes_normalized

♻️ This comment has been updated with latest results.

…' into hot-reload-for-css-modifications

mshabarov · 2025-10-13T15:04:09Z

flow-server/src/main/java/com/vaadin/flow/hotswap/Hotswapper.java

+                            String path = resourcePath
+                                    .replace(staticResourcesPath, "");


To be able to compare with the existing link tag, we should cut off the path part that points to resource dir inside build dir.

mshabarov · 2025-10-13T15:07:36Z

Tried to test with Gradle project, but ended up receiving

HOTSWAP AGENT: 14:06:49.506 INFO (org.hotswap.agent.plugin.spring.reload.SpringBeanReload) - try to add changed property 'file:/.../base-starter-spring-gradle/build/resources/main/application.properties' into org.springframework.beans.factory.support.DefaultListableBeanFactory@1df32c09

while changing src/main/resources/META-INF/resources/styles.css.

…' into hot-reload-for-css-modifications

flow-server/src/main/java/com/vaadin/flow/server/AppShellRegistry.java

caalador · 2025-10-14T07:37:17Z

flow-server/src/main/java/com/vaadin/flow/server/AbstractConfiguration.java

+        }
+        String buildFolderName = getBuildFolder();
+        File buildFolder = new File(projectFolder, buildFolderName);
+        if (Constants.TARGET.equals(buildFolderName)) {


This might not match maven as you can define your own build folder.
Perhaps the better check would be to see if build_folder/classes exist or build_folder/resources

done, thanks!

…difications # Conflicts: # vaadin-dev-server/src/test/java/com/vaadin/base/devserver/PublicResourcesCssLiveUpdaterTest.java

…' into hot-reload-for-css-modifications

mshabarov · 2025-10-14T12:41:58Z

I couldn't really test this with Gradle-based project, because HotswapAgent always passes {projectDir}/src/main/resources/application.properties to resourceChanged method as a URI, even for my styles.css file.

Might be a bug in HotswapAgent, but I have no idea why this so specific to Gradle.

mcollovati · 2025-10-14T12:56:52Z

I guess the problem with Gradle is how it integrates with IntelliJ.
I think, by default, IDEA delegates the build to Gradle, so most likely it is Gradle that copies application.properties to the build classes folder.
If you change the following setting from "Gradle (default)" to "IntelliJ IDEA" then the application.properties file is not copied anymore, unless you explicitly modify it.

mshabarov · 2025-10-14T13:13:43Z

I changed it to "IntelliJ IDEA" and now it doesn't stop on the breakpoint in VaadinPlugin or Hotswapper at all, and doesn't hot reload the CSS 🤔

mcollovati · 2025-10-14T13:20:23Z

When I switch to "IntelliJ IDEA", I can see the following logs when I save the CSS file

2025-10-14T15:18:50.518+02:00 TRACE 137735 --- [     Thread-270] com.vaadin.flow.hotswap.Hotswapper       : Created resources: [file:///xxxxx/base-starter-spring-gradle/out/production/resources/META-INF/resources/styles.css], modified resources: [], deletedResources: [file:///home/xxxxx/base-starter-spring-gradle/out/production/resources/META-INF/resources/styles.css].
2025-10-14T15:18:54.725+02:00 TRACE 137735 --- [     Thread-276] com.vaadin.flow.hotswap.Hotswapper       : Created resources: [file:///xxxxx/base-starter-spring-gradle/out/production/resources/META-INF/resources/styles.css], modified resources: [], deletedResources: [file:///xxxxx/base-starter-spring-gradle/out/production/resources/META-INF/resources/styles.css].

mcollovati · 2025-10-14T13:21:37Z

Maybe some other IDEA setting, e.g. compile on save (don't know if such a thing exists :) )?

mshabarov · 2025-10-14T15:19:22Z

Maybe some other IDEA setting

Yes, might be it, because even for V24.9 I have the same observation.

flow-server/src/main/java/com/vaadin/flow/server/PropertyDeploymentConfiguration.java

flow-server/src/test/java/com/vaadin/flow/hotswap/HotswapperResourcesTest.java

mcollovati

Tested with Gradle and now it seems to work fine.
It happened once that the first modification of the stylesheet was not propagated, but this is probably something related to my IDE or Gradle.
Added some comment for potential improvements

flow-server/src/main/java/com/vaadin/flow/server/AppShellRegistry.java

flow-server/src/main/java/com/vaadin/flow/hotswap/Hotswapper.java

flow-server/src/test/java/com/vaadin/flow/hotswap/HotswapperResourcesTest.java

vaadin-dev-server/src/main/frontend/vaadin-dev-tools.ts

mcollovati · 2025-10-15T05:41:26Z

flow-server/src/main/java/com/vaadin/flow/hotswap/Hotswapper.java

                    createdResources, modifiedResources, deletedResources);
        }

+        if (anyMatches(".*\\.css", createdResources, modifiedResources,


Just a note for a future improvement: we could refactor a bit of the code to add a onResourceEvent(ResourceEvent event) on VaadinHotswapper interface and move the logic in this method into two separate classes (for styles and translations).

…' into hot-reload-for-css-modifications

mshabarov · 2025-10-15T06:26:56Z

Re-tested with maven project - works as expected.

sonarqubecloud · 2025-10-15T06:30:39Z

Quality Gate passed

Issues
2350 New issues
2 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

mshabarov and others added 3 commits October 13, 2025 12:44

Revert "feat: Watch the CSS files in the project's public static reso…

f384a69

…urces folder (#22392)" This reverts commit bd9b2cf

fix: Update link tag on stylesheet modification

30572e8

Merge branch 'main' into hot-reload-for-css-modifications

f830a88

vaadin-bot added the +0.0.1 label Oct 13, 2025

mshabarov and others added 4 commits October 13, 2025 17:33

take into account gradle path to build dir

e4025a7

add unit tests

5f82132

Merge remote-tracking branch 'origin/hot-reload-for-css-modifications…

3c12c5d

…' into hot-reload-for-css-modifications

Merge branch 'main' into hot-reload-for-css-modifications

65ecfd5

vaadin-bot added +0.1.0 and removed +0.0.1 labels Oct 13, 2025

mshabarov commented Oct 13, 2025

View reviewed changes

mshabarov added 2 commits October 13, 2025 18:17

add method to PropertyDeploymentConfiguration

e694f6e

Merge remote-tracking branch 'origin/hot-reload-for-css-modifications…

7740e3c

…' into hot-reload-for-css-modifications

mshabarov marked this pull request as ready for review October 13, 2025 15:17

caalador reviewed Oct 14, 2025

View reviewed changes

mshabarov and others added 4 commits October 14, 2025 11:35

fix maven/gradle detection, imports

869217f

Merge branch 'main' into hot-reload-for-css-modifications

d9f9a4a

Merge remote-tracking branch 'origin/main' into hot-reload-for-css-mo…

a1405cf

…difications # Conflicts: # vaadin-dev-server/src/test/java/com/vaadin/base/devserver/PublicResourcesCssLiveUpdaterTest.java

Merge remote-tracking branch 'origin/hot-reload-for-css-modifications…

e24dac3

…' into hot-reload-for-css-modifications

mshabarov requested review from caalador and mcollovati October 14, 2025 11:05

use all entries and swap the resource folder detection

fc55ffc

caalador reviewed Oct 15, 2025

View reviewed changes

flow-server/src/main/java/com/vaadin/flow/server/PropertyDeploymentConfiguration.java Show resolved Hide resolved

flow-server/src/test/java/com/vaadin/flow/hotswap/HotswapperResourcesTest.java Outdated Show resolved Hide resolved

mshabarov and others added 2 commits October 15, 2025 08:18

use util method

008a09c

Merge branch 'main' into hot-reload-for-css-modifications

db1204e

mcollovati reviewed Oct 15, 2025

View reviewed changes

mshabarov added 2 commits October 15, 2025 09:20

improve cache killer token, use replaceAll, refactorings

140e7b6

Merge remote-tracking branch 'origin/hot-reload-for-css-modifications…

1b53372

…' into hot-reload-for-css-modifications

mshabarov requested a review from mcollovati October 15, 2025 06:26

mcollovati approved these changes Oct 15, 2025

View reviewed changes

mshabarov merged commit b091938 into main Oct 15, 2025
29 checks passed

mshabarov deleted the hot-reload-for-css-modifications branch October 15, 2025 07:24

		String path = resourcePath
		.replace(staticResourcesPath, "");

fix: Update link tag on stylesheet modification #22504

fix: Update link tag on stylesheet modification #22504

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