(java): Use futures to write concurrently

Author: alex9smith

TODO.md

@@ -2,7 +2,7 @@
 
 ## Lambdas
 
-- Use futures / async to write to DynamoDB concurrently in the Rust & Java lambdas
+- Use futures / async to write to DynamoDB concurrently in the Rust lambda
 
 ## Benchmark
 

lambda/java/JavaLambda/src/main/java/alex9smith/App.java

@@ -1,5 +1,9 @@
 package alex9smith;
 
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+
 import com.amazonaws.services.lambda.runtime.Context;
 import com.amazonaws.services.lambda.runtime.RequestHandler;
 import com.amazonaws.services.lambda.runtime.events.SQSEvent;
@@ -80,6 +84,7 @@ public App() {
 
   @Override
   public SQSEvent handleRequest(final SQSEvent input, final Context context) {
+    ArrayList<CompletableFuture<PutItemResponse>> futures = new ArrayList<>();
     for (SQSMessage message : input.getRecords()) {
       try {
         jsonSchema.validate(message.getBody(), InputFormat.JSON);
@@ -88,7 +93,7 @@ public SQSEvent handleRequest(final SQSEvent input, final Context context) {
             .tableName(tableName)
             .item(event.toAttributeMap())
             .build();
-        dynamoDbClient.putItem(request).join();
+        futures.add(dynamoDbClient.putItem(request));
 
       } catch (JsonProcessingException e) {
         e.printStackTrace();
@@ -97,6 +102,9 @@ public SQSEvent handleRequest(final SQSEvent input, final Context context) {
 
     }
 
+    List<PutItemResponse> results = futures.stream().map(CompletableFuture::join).toList();
+    System.out.println(results.size());
+
     return input;
   }
 }