Azure Adapter Cold Start Fix

spring is not loaded before the first request. Can we add static { initialize(); } inside the class AzureFunctionInstanceInjector
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 * Copyright 2021-2022 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
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 * See the License for the specific language governing permissions and
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package org.springframework.cloud.function.adapter.azure;

import java.util.Map;

import com.microsoft.azure.functions.spi.inject.FunctionInstanceInjector;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.boot.ResourceBanner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.WebApplicationType;
import org.springframework.cloud.function.utils.FunctionClassUtils;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.io.DefaultResourceLoader;
import org.springframework.util.ClassUtils;
import org.springframework.util.CollectionUtils;

/**
 * The instance factory used by the Spring framework to initialize Azure function instance. It is waived with the Azure
 * Java Worker through the META-INFO/services/com.microsoft.azure.functions.spi.inject.FunctionInstanceInjector service
 * hook. The Azure Java Worker delegates scans the classpath for service definition and delegates the function class
 * creation to this instance factory.
 * @author Christian Tzolov
 * @since 3.2.9
 */
public class AzureFunctionInstanceInjector implements FunctionInstanceInjector {

    private static Log logger = LogFactory.getLog(AzureFunctionInstanceInjector.class);

    private static ConfigurableApplicationContext APPLICATION_CONTEXT;

    static {
        initialize();
    }

    /**
     * This method is called by the Azure Java Worker on every function invocation. The Worker sends in the classes
     * annotated with @FunctionName annotations and allows the Spring framework to initialize the function instance as a
     * Spring Bean and return the instance. Then the Worker uses the created instance to invoke the function.
     * @param functionClass the class that contains customer Azure functions (e.g. @FunctionName annotated )
     * @param <T> customer Azure functions class type
     * @return the instance that will be invoked on by azure functions java worker
     * @throws Exception any exception that is thrown by the Spring framework during instance creation
     */
    @Override
    public <T> T getInstance(Class<T> functionClass) throws Exception {
        try {
            // Backward compatibility workaround. If the function class is of type FunctionInvoker then create plain
            // Java instance and delegate to FunctionInvoker adaptor approach.
            if (ClassUtils.isAssignable(FunctionInvoker.class, functionClass)) {
                return functionClass.getDeclaredConstructor().newInstance();
            }

            initialize();

            Map<String, T> azureFunctionBean = APPLICATION_CONTEXT.getBeansOfType(functionClass);
            if (CollectionUtils.isEmpty(azureFunctionBean)) {
                throw new IllegalStateException(
                        "Failed to retrieve Bean instance for: " + functionClass
                                + ". The class should be annotated with @Component to let the Spring framework initialize it!");
            }
            return azureFunctionBean.entrySet().iterator().next().getValue();
        }
        catch (Exception e) {
            if (APPLICATION_CONTEXT != null) {
                APPLICATION_CONTEXT.close();
            }
            throw new IllegalStateException("Failed to initialize", e);
        }
    }

    /**
     * Create a static Application Context instance shared between multiple function invocations.
     */
    private static void initialize() {
        synchronized (AzureFunctionInstanceInjector.class.getName()) {
            if (APPLICATION_CONTEXT == null) {
                Class<?> springConfigurationClass = FunctionClassUtils.getStartClass();
                logger.info("Initializing: " + springConfigurationClass);
                APPLICATION_CONTEXT = springApplication(springConfigurationClass).run();
            }
        }
    }

    private static SpringApplication springApplication(Class<?> configurationClass) {
        SpringApplication application = new org.springframework.cloud.function.context.FunctionalSpringApplication(
                configurationClass);
        application.setWebApplicationType(WebApplicationType.NONE);
        application.setBanner(new ResourceBanner(
                new DefaultResourceLoader().getResource("classpath:/spring-azure-function-banner.txt")));
        return application;
    }
}
spring-cloud / spring-cloud-function

Azure Adapter Cold Start Fix #1167
