Log errors instead of throwing errors for duplicate keys in ImmutableMap

.changes/next-release/bugfix-AWSSDKforJavav2-01696b7.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "AWS SDK for Java v2",
+    "contributor": "",
+    "description": "Log error instead of throwing error for duplicate keys in ImmutableMap"
+}

utils/src/main/java/software/amazon/awssdk/utils/ImmutableMap.java

@@ -58,8 +58,8 @@
 @SdkProtectedApi
 public final class ImmutableMap<K, V> implements Map<K, V> {
 
+    private static final Logger log = Logger.loggerFor(ImmutableMap.class);
     private static final String UNMODIFIABLE_MESSAGE = "This is an immutable map.";
-    private static final String DUPLICATED_KEY_MESSAGE = "Duplicate keys are provided.";
 
     private final Map<K, V> map;
 
@@ -199,7 +199,9 @@ public static <K, V> ImmutableMap<K, V> of(K k0, V v0, K k1, V v1,
     private static <K, V> void putAndWarnDuplicateKeys(Map<K, V> map, K key,
                                                        V value) {
         if (map.containsKey(key)) {
-            throw new IllegalArgumentException(DUPLICATED_KEY_MESSAGE);
+            log.error(() -> String.format("Duplicate keys are provided for [%s]. The first value [%s] will be kept, and the "
+                                          + "second value [%s] will be ignored.", key, map.get(key), value));
+            return;
         }
         map.put(key, value);
     }
@@ -295,9 +297,8 @@ public Builder() {
         }
 
         /**
-         * Add a key-value pair into the built map. The method will throw
-         * IllegalArgumentException immediately when duplicate keys are
-         * provided.
+         * Add a key-value pair into the built map. If duplicate keys are provided, the first value will be kept and the second
+         * value will be ignored, and the SDK will log an error.
          *
          * @return Returns a reference to this object so that method calls can
          *         be chained together.

utils/src/test/java/software/amazon/awssdk/utils/ImmutableMapTest.java

@@ -71,18 +71,13 @@ public void testOfBuilder() {
     }
 
     @Test
-    public void testErrorOnDuplicateKeys() {
-        try {
-            Map<Integer, String> builtMap = new ImmutableMap.Builder<Integer, String>()
-                    .put(1, "one")
-                    .put(1, "two")
-                    .build();
-            fail("IllegalArgumentException expected.");
-        } catch (IllegalArgumentException iae) {
-            // Ignored or expected.
-        } catch (Exception e) {
-            fail("IllegalArgumentException expected.");
-        }
+    public void putDuplicateKeys_keepsFirstOneAndDoesNotThrowError() {
+        Map<Integer, String> builtMap = new ImmutableMap.Builder<Integer, String>()
+            .put(1, "one")
+            .put(1, "two")
+            .build();
+
+        assertEquals("one", builtMap.get(1));
     }
 
     @Test