feat(dataconverter): add compression, encryption, and S3 offload samples

Add a new  package with three production-ready
custom  implementations following the
take-and-go layout: gzip compression, AES-256-GCM encryption, and an
S3 / claim-check offload pattern (with a zero-config local-filesystem
default and a commented AWS SDK v2 stub). One worker hosts all three
on three task lists and prints per-sample stats banners on startup.

Signed-off-by: “Kevin” <kevlar_ksb@yahoo.com>

Author: Bueller87

README.md

@@ -29,6 +29,8 @@ These samples demonstrate various capabilities of Java Cadence client and server
 
 * **Custom Workflow Controls** ([`com.uber.cadence.samples.query`](src/main/java/com/uber/cadence/samples/query/)) — workflow queries that return **markdown** for Cadence Web (Markdoc buttons that **signal** workflows or **start** new workflows). **Requires Cadence Web v4.0.14+.** Copy-paste run instructions: [query samples README](src/main/java/com/uber/cadence/samples/query/README.md).
 
+* **DataConverter Samples** ([`com.uber.cadence.samples.dataconverter`](src/main/java/com/uber/cadence/samples/dataconverter/)) — three production-ready custom `DataConverter` patterns (gzip compression, AES-256-GCM encryption, and S3 / claim-check offload) that transparently transform every workflow input, output, and activity parameter. Copy-paste run instructions: [dataconverter samples README](src/main/java/com/uber/cadence/samples/dataconverter/README.md).
+
 ## Get the Samples
 
 Run the following commands:
@@ -139,6 +141,20 @@ Starters (pick one per run):
 
 In Cadence Web, open the workflow → **Query** tab → run query **`Signal`**, **`options`**, or **`dashboard`** (matching the starter you used).
 
+### DataConverter Samples
+
+Three samples (compression, encryption, S3 offload) demonstrating custom `DataConverter` implementations. One worker hosts all three on three task lists. See [src/main/java/com/uber/cadence/samples/dataconverter/README.md](src/main/java/com/uber/cadence/samples/dataconverter/README.md) for full details, encryption-key configuration, and S3 swap instructions.
+
+Worker (hosts all three samples; prints per-sample stats banners on startup):
+
+    ./gradlew -q execute -PmainClass=com.uber.cadence.samples.dataconverter.DataConverterWorker
+
+Starters (pick one per run; each starts a new workflow execution and exits):
+
+    ./gradlew -q execute -PmainClass=com.uber.cadence.samples.dataconverter.CompressionStarter
+    ./gradlew -q execute -PmainClass=com.uber.cadence.samples.dataconverter.EncryptionStarter
+    ./gradlew -q execute -PmainClass=com.uber.cadence.samples.dataconverter.S3OffloadStarter
+
 ### Trip Booking
 
 Cadence implementation of the [Camunda BPMN trip booking example](https://github.com/berndruecker/trip-booking-saga-java)

src/main/java/com/uber/cadence/samples/dataconverter/BlobStore.java

@@ -0,0 +1,36 @@
+/*
+ *  Copyright 2012-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ *  Modifications copyright (C) 2017 Uber Technologies, Inc.
+ *
+ *  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.uber.cadence.samples.dataconverter;
+
+import java.io.IOException;
+
+/**
+ * Abstraction over any external object store (local filesystem, S3, GCS, etc.).
+ *
+ * <p>{@link S3OffloadDataConverter} uses this interface to store large payloads outside Cadence
+ * history. The default implementation is {@link LocalFsBlobStore}, which writes to the system
+ * temporary directory and requires no external services.
+ */
+public interface BlobStore {
+
+  /** Stores {@code data} under {@code key}, overwriting any existing value. */
+  void put(String key, byte[] data) throws IOException;
+
+  /** Returns the bytes previously stored under {@code key}. */
+  byte[] get(String key) throws IOException;
+}