Part 0: first serialise/deserialise round-trip

src/main/java/com/ankurm/jackson3/part0setup/A01FirstRoundTrip.java

@@ -0,0 +1,49 @@
+package com.ankurm.jackson3.part0setup;
+
+import tools.jackson.databind.json.JsonMapper;
+
+/**
+ * Post: Jackson 101 — https://ankurm.com/jackson-java-tutorial/
+ * Section: "Your First Serialise/Deserialise Example"
+ *
+ * The simplest possible Jackson 3 round-trip: a POJO out to JSON and back.
+ */
+public class A01FirstRoundTrip {
+
+    /** A plain POJO with getters and setters — the classic Jackson shape. */
+    public static class ProductSummary {
+        private Long   productId;
+        private String productName;
+        private double listPrice;
+
+        public ProductSummary() { }                       // needed for deserialisation
+        public ProductSummary(Long id, String name, double price) {
+            this.productId = id; this.productName = name; this.listPrice = price;
+        }
+        public Long   getProductId()   { return productId; }
+        public String getProductName() { return productName; }
+        public double getListPrice()   { return listPrice; }
+        public void setProductId(Long v)     { this.productId = v; }
+        public void setProductName(String v) { this.productName = v; }
+        public void setListPrice(double v)   { this.listPrice = v; }
+    }
+
+    public static void main(String[] args) {
+        // Jackson 3: JsonMapper.builder().build() replaces `new ObjectMapper()`.
+        // The result is IMMUTABLE — you cannot reconfigure it afterwards.
+        JsonMapper mapper = JsonMapper.builder().build();
+
+        // Serialise: Java object -> JSON string
+        ProductSummary product = new ProductSummary(1L, "Mechanical Keyboard", 79.99);
+        String jsonOutput = mapper.writeValueAsString(product);
+        System.out.println(jsonOutput);
+
+        // Deserialise: JSON string -> Java object
+        ProductSummary restored = mapper.readValue(jsonOutput, ProductSummary.class);
+        System.out.println(restored.getProductName());
+
+        // Note: no `throws` clause anywhere in this method. In Jackson 3 the
+        // exception hierarchy is rooted at JacksonException extends RuntimeException,
+        // so serialisation failures are UNCHECKED. See beyond/Y01UncheckedExceptions.
+    }
+}