Part 6: streaming parser filter with the Jackson 3 token/accessor names

src/main/java/com/ankurm/jackson3/part6streaming/G01StreamingParserFilter.java

@@ -0,0 +1,73 @@
+package com.ankurm.jackson3.part6streaming;
+
+import tools.jackson.core.JsonParser;
+import tools.jackson.core.JsonToken;
+import tools.jackson.core.json.JsonFactory;
+
+import java.io.File;
+import java.nio.file.Files;
+
+/**
+ * Post: Streaming API and JsonNode — https://ankurm.com/jackson-streaming-api-jsonnode/
+ * Section: "Reading a Large JSON Array with JsonParser"
+ *
+ * Jackson 3 differences from the post's code:
+ *   1. JsonFactory is in tools.jackson.core.json — NOT tools.jackson.core.
+ *   2. parser.getCurrentName() is now parser.currentName().
+ *   3. parser.getText() is now parser.getString().
+ *   4. JsonToken.FIELD_NAME is now JsonToken.PROPERTY_NAME.
+ *   5. No `throws IOException` — Jackson 3 exceptions are unchecked.
+ */
+public class G01StreamingParserFilter {
+
+    private static final String SAMPLE = """
+            [
+              {"level":"INFO","message":"Application started"},
+              {"level":"ERROR","message":"Database connection failed"},
+              {"level":"INFO","message":"Retrying connection"}
+            ]
+            """;
+
+    public static void main(String[] args) throws Exception {
+        File logFile = File.createTempFile("large-logs", ".json");
+        Files.writeString(logFile.toPath(), SAMPLE);
+        logFile.deleteOnExit();
+
+        JsonFactory jsonFactory = new JsonFactory();
+        int errorCount = 0;
+
+        try (JsonParser parser = jsonFactory.createParser(tools.jackson.core.ObjectReadContext.empty(), logFile)) {
+
+            // Confirm the root is an array
+            if (parser.nextToken() != JsonToken.START_ARRAY) {
+                throw new IllegalStateException("Expected a JSON array at the root");
+            }
+
+            // Walk each element in the array
+            while (parser.nextToken() != JsonToken.END_ARRAY) {
+
+                String logLevel   = null;
+                String logMessage = null;
+
+                // Walk each property inside the current object
+                while (parser.nextToken() != JsonToken.END_OBJECT) {
+                    String fieldName = parser.currentName();
+                    parser.nextToken();                       // move to the value
+
+                    if ("level".equals(fieldName)) {
+                        logLevel = parser.getString();
+                    } else if ("message".equals(fieldName)) {
+                        logMessage = parser.getString();
+                    }
+                    // All other fields are skipped automatically
+                }
+
+                if ("ERROR".equals(logLevel)) {
+                    System.out.println("ERROR: " + logMessage);
+                    errorCount++;
+                }
+            }
+        }
+        System.out.println("Total errors found: " + errorCount);
+    }
+}