Part 6: tree navigation, path() vs get(), treeToValue

src/main/java/com/ankurm/jackson3/part6streaming/G03TreeModelNavigation.java

@@ -0,0 +1,50 @@
+package com.ankurm.jackson3.part6streaming;
+
+import tools.jackson.databind.JsonNode;
+import tools.jackson.databind.json.JsonMapper;
+
+/**
+ * Post: Streaming API and JsonNode — https://ankurm.com/jackson-streaming-api-jsonnode/
+ * Sections: "The Tree Model" and "Mixing Tree Model with Data Binding"
+ *
+ * Jackson 3 difference: JsonNode.asText() is now asString(). asInt() survives.
+ */
+public class G03TreeModelNavigation {
+
+    public record CustomerRecord(String name, String tier) { }
+
+    private static final String JSON = "{"
+            + "\"orderId\":1001,"
+            + "\"customer\":{\"name\":\"Alice\",\"tier\":\"gold\"},"
+            + "\"items\":[{\"sku\":\"KB-01\",\"qty\":2},{\"sku\":\"MS-42\",\"qty\":1}]"
+            + "}";
+
+    public static void main(String[] args) {
+        JsonMapper mapper = JsonMapper.builder().build();
+
+        JsonNode rootNode = mapper.readTree(JSON);
+
+        // path() never returns null — a missing node is a MissingNode.
+        String customerName = rootNode.path("customer").path("name").asString();
+        System.out.println("Customer: " + customerName);
+
+        for (JsonNode itemNode : rootNode.path("items")) {
+            System.out.println(itemNode.path("sku").asString() + " x" + itemNode.path("qty").asInt());
+        }
+
+        System.out.println("Has discount: " + rootNode.has("discountCode"));
+
+        // path() vs get() on an absent field — the difference that causes NPEs.
+        System.out.println("path(missing) : " + rootNode.path("nope")
+                + "  (class " + rootNode.path("nope").getClass().getSimpleName() + ")");
+        System.out.println("get(missing)  : " + rootNode.get("nope"));
+
+        // Deep navigation stays null-safe all the way down.
+        System.out.println("deep path     : '"
+                + rootNode.path("a").path("b").path("c").asString("<default>") + "'");
+
+        // Switch from tree to data binding at any node.
+        CustomerRecord customer = mapper.treeToValue(rootNode.path("customer"), CustomerRecord.class);
+        System.out.println("treeToValue   : " + customer);
+    }
+}