Part 6 extra: the decision table measured on real data

src/main/java/com/ankurm/jackson3/part6streaming/G04ThreeApproachesMeasured.java

@@ -0,0 +1,101 @@
+package com.ankurm.jackson3.part6streaming;
+
+import tools.jackson.core.JsonParser;
+import tools.jackson.core.JsonToken;
+import tools.jackson.core.json.JsonFactory;
+import tools.jackson.core.type.TypeReference;
+import tools.jackson.databind.JsonNode;
+import tools.jackson.databind.json.JsonMapper;
+
+import java.io.File;
+import java.nio.file.Files;
+import java.util.List;
+
+/**
+ * BEYOND THE POST — the decision table, measured.
+ *
+ * The post ends with a table claiming data binding "loads full object", tree model
+ * "loads full tree", and streaming uses "constant" memory. This generates a real
+ * file and measures all three so the table has numbers behind it.
+ *
+ * These are indicative single-shot measurements on one JVM, not JMH benchmarks —
+ * the ordering is the point, not the absolute figures.
+ */
+public class G04ThreeApproachesMeasured {
+
+    public record LogEntry(long id, String level, String message) { }
+
+    private static final int ENTRIES = 200_000;
+
+    public static void main(String[] args) throws Exception {
+        File file = generate();
+        System.out.println("input file : " + (file.length() / 1024 / 1024) + " MB, "
+                + ENTRIES + " entries");
+        System.out.println();
+
+        JsonMapper mapper = JsonMapper.builder().build();
+
+        measure("data binding (readValue)", () -> {
+            List<LogEntry> all = mapper.readValue(file, new TypeReference<List<LogEntry>>() { });
+            return all.stream().filter(e -> e.level().equals("ERROR")).count();
+        });
+
+        measure("tree model (readTree)", () -> {
+            JsonNode root = mapper.readTree(file);
+            long n = 0;
+            for (JsonNode node : root) if ("ERROR".equals(node.path("level").asString())) n++;
+            return n;
+        });
+
+        measure("streaming (JsonParser)", () -> {
+            long n = 0;
+            JsonFactory factory = new JsonFactory();
+            try (JsonParser p = factory.createParser(tools.jackson.core.ObjectReadContext.empty(), file)) {
+                p.nextToken();
+                while (p.nextToken() != JsonToken.END_ARRAY) {
+                    String level = null;
+                    while (p.nextToken() != JsonToken.END_OBJECT) {
+                        String f = p.currentName();
+                        p.nextToken();
+                        if ("level".equals(f)) level = p.getString();
+                    }
+                    if ("ERROR".equals(level)) n++;
+                }
+            }
+            return n;
+        });
+
+        file.delete();
+    }
+
+    private interface Counter { long count() throws Exception; }
+
+    private static void measure(String label, Counter counter) throws Exception {
+        Runtime rt = Runtime.getRuntime();
+        System.gc();
+        Thread.sleep(120);
+        long heapBefore = rt.totalMemory() - rt.freeMemory();
+        long start = System.nanoTime();
+        long errors = counter.count();
+        long ms = (System.nanoTime() - start) / 1_000_000;
+        long heapAfter = rt.totalMemory() - rt.freeMemory();
+        System.out.printf("%-28s errors=%-6d  %5d ms   heap delta %5d MB%n",
+                label, errors, ms, (heapAfter - heapBefore) / 1024 / 1024);
+    }
+
+    private static File generate() throws Exception {
+        File f = File.createTempFile("logs", ".json");
+        f.deleteOnExit();
+        StringBuilder sb = new StringBuilder("[");
+        for (int i = 0; i < ENTRIES; i++) {
+            if (i > 0) sb.append(',');
+            sb.append("{\"id\":").append(i)
+              .append(",\"level\":\"").append(i % 50 == 0 ? "ERROR" : "INFO")
+              .append("\",\"message\":\"event number ").append(i)
+              .append(" with some padding to make the payload realistic\"}");
+        }
+        sb.append(']');
+        Files.writeString(f.toPath(), sb);
+        return f;
+    }
+}