refactor: extract InitializableLambdaContainerHandler interface to be…

… used by SpringDelegatingLambdaContainerHandler later on

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/AsyncInitializationWrapper.java

@@ -13,7 +13,7 @@
 package com.amazonaws.serverless.proxy;
 
 import com.amazonaws.serverless.exceptions.ContainerInitializationException;
-import com.amazonaws.serverless.proxy.internal.LambdaContainerHandler;
+import com.amazonaws.serverless.proxy.internal.InitializableLambdaContainerHandler;
 import com.amazonaws.services.lambda.runtime.Context;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import org.slf4j.Logger;
@@ -26,10 +26,10 @@
 
 /**
  * An async implementation of the <code>InitializationWrapper</code> interface. This initializer calls the
- * {@link LambdaContainerHandler#initialize()} in a separate thread. Then uses a latch to wait for the maximum Lambda
+ * {@link InitializableLambdaContainerHandler#initialize()} in a separate thread. Then uses a latch to wait for the maximum Lambda
  * initialization time of 10 seconds, if the <code>initialize</code> method takes longer than 10 seconds to return, the
- * {@link #start(LambdaContainerHandler)} returns control to the caller and lets the initialization thread continue in
- * the background. The {@link LambdaContainerHandler#proxy(Object, Context)} automatically waits for the latch of the
+ * {@link #start(InitializableLambdaContainerHandler)} returns control to the caller and lets the initialization thread continue in
+ * the background. The {@link com.amazonaws.serverless.proxy.internal.LambdaContainerHandler#proxy(Object, Context)} automatically waits for the latch of the
  * initializer to be released.
  *
  * The constructor of this class expects an epoch long. This is meant to be as close as possible to the time the Lambda
@@ -72,7 +72,7 @@ public AsyncInitializationWrapper() {
     }
 
     @Override
-    public void start(LambdaContainerHandler handler) throws ContainerInitializationException {
+    public void start(InitializableLambdaContainerHandler handler) throws ContainerInitializationException {
         if(ASYNC_INIT_DISABLED){
             log.info("Async init disabled due to \"{}\" initialization", INITIALIZATION_TYPE);
             super.start(handler);
@@ -107,18 +107,18 @@ public long getActualStartTimeMs() {
 
     @Override
     public CountDownLatch getInitializationLatch() {
-        if(ASYNC_INIT_DISABLED){
+        if (ASYNC_INIT_DISABLED){
             return super.getInitializationLatch();
         }
         return initializationLatch;
     }
 
     private static class AsyncInitializer implements Runnable {
-        private LambdaContainerHandler handler;
+        private final InitializableLambdaContainerHandler handler;
         private CountDownLatch initLatch;
         private Logger log = LoggerFactory.getLogger(AsyncInitializationWrapper.class);
 
-        AsyncInitializer(CountDownLatch latch, LambdaContainerHandler h) {
+        AsyncInitializer(CountDownLatch latch, InitializableLambdaContainerHandler h) {
             initLatch = latch;
             handler = h;
         }

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/InitializationWrapper.java

@@ -13,13 +13,13 @@
 package com.amazonaws.serverless.proxy;
 
 import com.amazonaws.serverless.exceptions.ContainerInitializationException;
-import com.amazonaws.serverless.proxy.internal.LambdaContainerHandler;
+import com.amazonaws.serverless.proxy.internal.InitializableLambdaContainerHandler;
 
 import java.util.concurrent.CountDownLatch;
 
 /**
- * This class is in charge of initializing a {@link LambdaContainerHandler}.
- * In most cases, this means calling the {@link LambdaContainerHandler#initialize()} method. Some implementations may
+ * This class is in charge of initializing a {@link InitializableLambdaContainerHandler}.
+ * In most cases, this means calling the {@link InitializableLambdaContainerHandler#initialize()} method. Some implementations may
  * require additional initialization steps, in this case implementations should provide their own
  * <code>InitializationWrapper</code>. This library includes an async implementation of this class
  * {@link AsyncInitializationWrapper} for frameworks that are likely to take longer than 10 seconds to start.
@@ -31,7 +31,7 @@ public class InitializationWrapper {
      * @param handler The container handler to be initializer
      * @throws ContainerInitializationException If anything goes wrong during container initialization.
      */
-    public void start(LambdaContainerHandler handler) throws ContainerInitializationException {
+    public void start(InitializableLambdaContainerHandler handler) throws ContainerInitializationException {
         handler.initialize();
     }
 

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/internal/InitializableLambdaContainerHandler.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2024 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except in compliance
+ * with the License. A copy of the License is located at
+ *
+ * http://aws.amazon.com/apache2.0/
+ *
+ * or in the "license" file accompanying this file. This file is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES
+ * OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
+ */
+package com.amazonaws.serverless.proxy.internal;
+
+import com.amazonaws.serverless.exceptions.ContainerInitializationException;
+
+/**
+ * Interface to define initialization/ cold-start related methods.
+ * See also the documentation for
+ * <a href="https://docs.aws.amazon.com/lambda/latest/operatorguide/execution-environments.html">
+ *     AWS Lambda Execution Environments</a>.
+ */
+public interface InitializableLambdaContainerHandler {
+
+    /**
+     * This method is called on the first (cold) invocation
+     *
+     * @throws ContainerInitializationException in case initialization fails
+     */
+    void initialize() throws ContainerInitializationException;
+}

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/internal/LambdaContainerHandler.java

@@ -45,7 +45,8 @@
  * @param <ContainerRequestType> The request type for the wrapped Java container
  * @param <ContainerResponseType> The response or response writer type for the wrapped Java container
  */
-public abstract class LambdaContainerHandler<RequestType, ResponseType, ContainerRequestType, ContainerResponseType> {
+public abstract class LambdaContainerHandler<RequestType, ResponseType, ContainerRequestType, ContainerResponseType>
+        implements InitializableLambdaContainerHandler {
 
     //-------------------------------------------------------------
     // Constants