MalformedURLException when loading style sheets #24028
Description
Description of the bug
After updating our application from Vaadin 25.0.x to 25.1.0 we see the ERROR log entries when Vaadin loads style sheets.
The reason seems to be the change #23751.
VaadinServletService.getStaticResource(String) -> VaadinServletService.getStaticResource(ServletContent, String) -> ServletContext.getResource(String) but ServletContext.getResource(String) must be called with a path starting with / (see https://jakarta.ee/specifications/platform/11/apidocs/jakarta/servlet/servletcontext#getResource(java.lang.String))
2026-03-26 19:11:07,808 WARN [com.vaadin.flow.server.VaadinServletService] (default task-2) Error finding resource for 'lumo/lumo.css': java.net.MalformedURLException: UT010021: Path lumo/lumo.css must start with a /
at io.undertow.servlet@2.0.0.Alpha2//io.undertow.servlet.spec.ServletContextImpl.getResource(ServletContextImpl.java:298)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.VaadinServletService.getStaticResource(VaadinServletService.java:338)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.VaadinServletService.getStaticResource(VaadinServletService.java:259)
at deployment.xxxxxxxxx.war//com.vaadin.flow.internal.ResourceContentHash.openResource(ResourceContentHash.java:101)
at deployment.xxxxxxxxx.war//com.vaadin.flow.internal.ResourceContentHash.computeHash(ResourceContentHash.java:78)
at deployment.xxxxxxxxx.war//com.vaadin.flow.internal.ResourceContentHash.lambda$getContentHash$0(ResourceContentHash.java:73)
at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1724)
at deployment.xxxxxxxxx.war//com.vaadin.flow.internal.ResourceContentHash.getContentHash(ResourceContentHash.java:72)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.AppShellRegistry.lambda$addStyleSheets$9(AppShellRegistry.java:442)
at java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:987)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.AppShellRegistry.addStyleSheets(AppShellRegistry.java:439)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.AppShellRegistry.createSettings(AppShellRegistry.java:277)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.AppShellRegistry.modifyIndexHtml(AppShellRegistry.java:332)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.communication.IndexHtmlRequestHandler.synchronizedHandleRequest(IndexHtmlRequestHandler.java:163)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:72)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.VaadinService.handleRequest(VaadinService.java:1834)
at deployment.xxxxxxxxx.war//com.vaadin.flow.server.VaadinServlet.service(VaadinServlet.java:402)
at deployment.xxxxxxxxx.war//com.vaadin.cdi.CdiVaadinServlet.service(CdiVaadinServlet.java:66)
at jakarta.servlet.api@6.1.0//jakarta.servlet.http.HttpServlet.service(HttpServlet.java:723)
...
Expected behavior
In Vaadin 25.0.x there was no exception.
Minimal reproducible example
Using @StyleSheet(Lumo.STYLESHEET) on a custom AppShellConfigurator.
Versions
- Vaadin / Flow version: 25.1.0
- Java version: 25.0.2
- OS version: AL 2023
- Browser version (if applicable): all
- Application Server (if applicable): Wildfly 39.0.1
- IDE (if applicable): IntelliJ