Part 6: 1M-record generator with measured heap delta

src/main/java/com/ankurm/jackson3/part6streaming/G02StreamingGenerator.java

@@ -0,0 +1,55 @@
+package com.ankurm.jackson3.part6streaming;
+
+import tools.jackson.core.JsonEncoding;
+import tools.jackson.core.JsonGenerator;
+import tools.jackson.core.ObjectWriteContext;
+import tools.jackson.core.json.JsonFactory;
+
+import java.io.File;
+
+/**
+ * Post: Streaming API and JsonNode — https://ankurm.com/jackson-streaming-api-jsonnode/
+ * Section: "Writing JSON with JsonGenerator"
+ *
+ * Jackson 3 differences: writeNumberField/writeStringField are now
+ * writeNumberProperty/writeStringProperty, and the factory needs an
+ * ObjectWriteContext. The post's 1,000,000-record loop is kept — it is the whole
+ * point of streaming — and the peak heap is measured so "constant memory" is a
+ * number rather than a claim.
+ */
+public class G02StreamingGenerator {
+
+    private static final int RECORD_COUNT = 1_000_000;
+
+    public static void main(String[] args) throws Exception {
+        File output = File.createTempFile("output", ".json");
+        output.deleteOnExit();
+
+        JsonFactory jsonFactory = new JsonFactory();
+        Runtime runtime = Runtime.getRuntime();
+        long before = runtime.totalMemory() - runtime.freeMemory();
+        long start  = System.nanoTime();
+
+        try (JsonGenerator generator = jsonFactory.createGenerator(
+                ObjectWriteContext.empty(), output, JsonEncoding.UTF8)) {
+
+            generator.writeStartArray();
+            for (int recordIndex = 0; recordIndex < RECORD_COUNT; recordIndex++) {
+                generator.writeStartObject();
+                generator.writeNumberProperty("id",     recordIndex);
+                generator.writeStringProperty("status", "active");
+                generator.writeEndObject();
+            }
+            generator.writeEndArray();
+        }
+
+        long elapsedMs = (System.nanoTime() - start) / 1_000_000;
+        long after     = runtime.totalMemory() - runtime.freeMemory();
+
+        System.out.println("records written : " + RECORD_COUNT);
+        System.out.println("file size       : " + (output.length() / 1024 / 1024) + " MB");
+        System.out.println("elapsed         : " + elapsedMs + " ms");
+        System.out.println("heap delta      : " + ((after - before) / 1024 / 1024) + " MB"
+                + "   <- the document is never held in memory");
+    }
+}