Java function host failed to discover main classes for spring cloud function

[Flanker32]

Function host can't find the main class of spring cloud functions and report error. Both in azure services and local.

Investigative information

Function core tools 2.7.1948

Repro steps

1. Prepare a spring cloud function project, could do it by git clone https://github.com/Azure-Samples/hello-spring-function-azure.git.
2. Build the spring cloud function project by mvn clean package
3. Invoke the function locally by mvn azure-functions:run.
   • This issue could also repo in service side, just remove the MAIN_CLASS settings in azure function configuration

Expected behavior

The main class of the function should be automatically found. The MAIN_CLASS property should not need to be specified and users could access the function by curl http://localhost:7071/api/hello -d "{\"name\":\"Azure\"}"

Actual behavior

No response from curl, function host reports

 java.lang.IllegalStateException: Failed to discover main class. An attempt was made to discover main class as 'MAIN_CLASS' environment variable, system property as well as entry in META-INF/MANIFEST.MF (in that order).

Known workarounds

Set the MAIN_CLASS in app settings, for local run, add a local.settings.json file with MAIN_CLASS specified

Related information

Referred microsoft/azure-maven-plugins#912