Favicon not showing with Spring 6.2.x Spring Boot 3.4.x

[danielkelemen]

Environment (Required on creation)

Environments with Spring Boot 3.4.* (7.22, 7.23).

Description (Required on creation; please attach any relevant screenshots, stacktraces, log files, etc. to the ticket)

Camunda Webapps don't show the favicon with Spring Boot 3.4.x and related Spring versions.
The issue doesn't happen with earlier versions.

Steps to reproduce (Required on creation)

Start Camunda with Spring Boot 3.4.x.
For instance create a new setup with https://start.camunda.com/ and set versions to Camunda 7.22.2 and Spring Boot 3.4.2.

Observed Behavior (Required on creation)

• Camunda favicon not displayed in browser tab.
• Url http://localhost:8080/camunda/favicon.ico doesn't work.
• Additionally there is a WARN displayed:

  2025-02-10T13:23:12.648+01:00  WARN 72446 --- [           main] 
  o.s.w.s.resource.ResourceHandlerUtils    : 
  Appended trailing slash to static resource location: classpath:/META-INF/resources/webjars/camunda/
  

Expected behavior (Required on creation)

• Camunda favicon displayed in browser tab.
• Url http://localhost:8080/camunda/favicon.ico works.
• No WARN log displayed.

Root Cause (Required on prioritization)

We define the favicon's resource location without trailing slash Source which until now was fine.
Recently, as the WARN log also suggests, Spring automatically adds a trailing slash to it.

Due to this trailing slash the resource resolution tries to load META-INF/resources/webjars/camunda/camunda/favicon.ico instead of META-INF/resources/webjars/camunda/favicon.ico. With twice /camunda in path:

If we add a trailing slash then the favicon doesn't work with earlier Spring versions either.

Spring resource resolving:

1. PathResourceResolver
2. ClassPathResource
3. StringUtils.applyRelativePath
   • It cuts of the part from the last trailing slash and adds the relativePath.
   • Before:
     • META-INF/resources/webjars/camunda
     • META-INF/resources/webjars + /camunda/favicon.ico ✅
     • Does it work with custom applicationPath?
   • Now:
     • META-INF/resources/webjars/camunda/
     • META-INF/resources/webjars/camunda + /camunda/favicon.ico ❌

Related issues:

• Experiencing similar: Spring Boot 3.4.0 static files cannot be retrieved successfully. spring-projects/spring-framework#33999
• The change with trailing slash: ResourceHttpRequestHandler throwing IllegalArgumentException if resource doesn't end with slash breaks some third-party libraries spring-projects/spring-framework#33815

Solution Ideas

• Add custom ResourceResolver for favicon: fix: add favicon resource resolver #4931
• Find a nicer built-in way of defining this properly.
• Double check the behaviour with custom applicationPath. I suspect that might also have issues.

Hints

Links

• https://jira.camunda.com/browse/SUPPORT-25702

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