How to run Spring Cloud Azure Functions with Java 17?

Spring Boot 3 only has support to Java 17, 21 and 24.

I see that there is a Spring Cloud Functions Azure Adapter, which should help doing that, however it is missing a step-by-step guide.

So here's my step-by-step attempt:

1. Used spring initializr to set a project with spring boot 3.4.5 and Java 17, dependencies: lombok
2. I executed mvn wrapper:wrapper in order to download mvn wrapper
3. I added the following dependency to my pom.xml

      <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-function-adapter-azure</artifactId>
        <version>4.2.2</version>
      </dependency>
   

4. I added the following plugin to my pom.xml

      
      <plugin>
          <groupId>com.microsoft.azure</groupId>
          <artifactId>azure-functions-maven-plugin</artifactId>
          <version>1.38.0</version>
          <configuration>
           <appName>scf-samples</appName>
           <resourceGroup>java-functions-group</resourceGroup>
           <region>westus</region>
           <appServicePlanName>java-functions-app-service-plan</appServicePlanName>
           <pricingTier>EP1</pricingTier>
           <hostJson>${project.basedir}/src/main/resources/host.json</hostJson>
      
           <runtime>
            <os>linux</os>
            <javaVersion>17</javaVersion>
           </runtime>
      
           <funcPort>7072</funcPort>
      
           <appSettings>
            <property>
             <name>FUNCTIONS_EXTENSION_VERSION</name>
             <value>~4</value>
            </property>
           </appSettings>
          </configuration>
          <executions>
           <execution>
            <id>package-functions</id>
            <goals>
             <goal>package</goal>
            </goals>
           </execution>
          </executions>
         </plugin>
        </plugins>
      </build>
   

5. I added the following host.json file under main/resources directory

      {
        "version": "2.0",
        "extensionBundle": {
          "id": "Microsoft.Azure.Functions.ExtensionBundle",
          "version": "[4.*, 5.0.0)"
        }
      }
   

6. Added bean definition in the main class

      import java.util.function.Function;
      import org.springframework.boot.SpringApplication;
      import org.springframework.boot.autoconfigure.SpringBootApplication;
      import org.springframework.context.annotation.Bean;
      
      @SpringBootApplication
      public class ServerlessApplication {
      
        public static void main(String[] args) {
         SpringApplication.run(ServerlessApplication.class, args);
        }
      
        @Bean
        public UpperCaseFunction uppercase() {
         return String::toUpperCase;
        }
      
        @Bean
        public Function<String, String> reverse() {
         return payload -> new StringBuilder(payload).reverse().toString();
        }
      
      }
   

7. Created a new Spring Component

      import com.microsoft.azure.functions.ExecutionContext;
      import com.microsoft.azure.functions.HttpMethod;
      import com.microsoft.azure.functions.HttpRequestMessage;
      import com.microsoft.azure.functions.annotation.AuthorizationLevel;
      import com.microsoft.azure.functions.annotation.FunctionName;
      import com.microsoft.azure.functions.annotation.HttpTrigger;
      import java.util.Optional;
      import java.util.function.Function;
      import org.springframework.beans.factory.annotation.Autowired;
      import org.springframework.cloud.function.context.FunctionCatalog;
      import org.springframework.stereotype.Component;
      
      @Component
      public class AzureJavaExampleFunctionWithSpring {
          /**
           * Plain Spring bean (not Spring Cloud Functions!)
           */
          @Autowired
          private Function<String, String> uppercase;
      
          /**
           * The FunctionCatalog leverages the Spring Cloud Function framework.
           */
          @Autowired
          private FunctionCatalog functionCatalog;
      
          @FunctionName("bean")
          public String plainBeans(
              @HttpTrigger(name = "req", methods = { HttpMethod.GET,
                  HttpMethod.POST }, authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Optional<String>> request,
              ExecutionContext context) {
      
            // Use plain Spring Beans.
            return uppercase.apply(request.getBody().orElse("Hello World"));
          }
      
          @FunctionName("scf")
          public String springCloudFunction(
              @HttpTrigger(name = "req", methods = { HttpMethod.GET,
                  HttpMethod.POST }, authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Optional<String>> request,
              ExecutionContext context) {
      
            // Use SCF composition.
            Function composed = this.functionCatalog.lookup("reverse|uppercase");
      
            return (String) composed.apply(request.getBody().orElse("Hello World"));
          }
      }
      
   

8. Compiled using maven wrapper

      ./mvnw clean install
      ./mvnw clean package
   

9. Run function locally

      ./mvnw azure-functions:run
   

   I expected this to work as there were no build errors, but here's what I got: [2025-05-09T16:34:20.687Z] Worker process started and initialized. [2025-05-09T16:34:20.736Z] Worker failed to load function: 'scf' with functionId: 'bd71dc2c-1d4e-4d09-8ce0-3806fefe07a4'. [2025-05-09T16:34:20.737Z] Result: Failure [2025-05-09T16:34:20.736Z] Worker failed to load function: 'bean' with functionId: 'cdd49f11-c457-4d7d-a5bd-e503461b6b7e'. Then it says the reason is ClassNotFoundException for AzureJavaExampleFunctionWithSpring.