Added a utility class for safely accessing nested Map structures

Author: viveknaskar

src/main/java/com/javaexperiments/NestedMapExtractor.java

@@ -0,0 +1,90 @@
+package com.javaexperiments;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * Utility class for safely accessing nested Map structures.
+ * Ideal for processing dynamic data such as JSON payloads.
+ */
+public class NestedMapExtractor {
+
+ /**
+ * Safely extract a nested map from a parent map.
+ *
+ * @param map the parent map
+ * @param key the key whose value should be a nested map
+ * @return the nested map if present and valid, otherwise an empty map
+ */
+ public static Map<String, Object> get(Map<?, ?> map, String key) {
+ if (map == null) return new HashMap<>();
+
+ return Optional.ofNullable(key)
+ .map(map::get)
+ .filter(Map.class::isInstance)
+ .map(value -> {
+ @SuppressWarnings("unchecked")
+ Map<String, Object> nested = (Map<String, Object>) value;
+ return nested;
+ })
+ .orElse(new HashMap<>());
+ }
+
+ /**
+ * Safely extract a value of a specific type from a map.
+ *
+ * @param map the map to extract from
+ * @param key the key to look up
+ * @param clazz the expected type class
+ * @param <T> the type of the value
+ * @return the value if present and of the correct type, otherwise null
+ */
+ public static <T> T get(Map<String, Object> map, String key, Class<T> clazz) {
+ if (map == null || key == null || clazz == null) return null;
+
+ Object value = map.get(key);
+ if (clazz.isInstance(value)) {
+ return clazz.cast(value);
+ }
+ return null;
+ }
+
+ /**
+ * Retrieves a String value from a nested "Something" map within the payload.
+ *
+ * @param payload the top-level payload map
+ * @param key the key inside the "Something" context
+ * @return the string value, or null if missing or not a string
+ */
+ public static String getFromContext(Map<String, Object> payload, String key) {
+ Map<String, Object> context = get(payload, "Something");
+ return get(context, key, String.class);
+ }
+
+ /**
+ * Demonstrates usage of the utility methods with various scenarios.
+ */
+ public static void main(String[] args) {
+ Map<String, Object> userDetails = new HashMap<>();
+ userDetails.put("username", "bruce.wayne");
+ userDetails.put("email", "brucewayne@google.com");
+ userDetails.put("accessLevel", 2);
+
+ Map<String, Object> payload = new HashMap<>();
+ payload.put("Something", userDetails);
+
+ // Example 1: Expected string
+ String username = getFromContext(payload, "username");
+ System.out.println("Username: " + username); // bruce.wayne
+
+ // Example 2: Type mismatch
+ String accessLevel = getFromContext(payload, "accessLevel");
+ System.out.println("AccessLevel (as String): " + accessLevel); // null
+
+ // Example 3: Missing key
+ String nonExistent = getFromContext(payload, "nonExistentKey");
+ System.out.println("Non-existent key: " + nonExistent); // null
+ }
+
+}