while (parser.nextToken() != null) {

    if (parser.currentToken() == JsonToken.FIELD_NAME
        && "pages".equals(parser.currentName())) {

        parser.nextToken(); // START_ARRAY

        while (parser.nextToken() != JsonToken.END_ARRAY) {

            Integer currentPage = null;

            while (parser.nextToken() != JsonToken.END_OBJECT) {

                if (parser.currentToken() == JsonToken.FIELD_NAME
                    && "page_number".equals(parser.currentName())) {

                    parser.nextToken();
                    currentPage = parser.getIntValue();
                }

                if (parser.currentToken() == JsonToken.FIELD_NAME
                    && "elements".equals(parser.currentName())) {

                    parser.nextToken(); // START_ARRAY

                    while (parser.nextToken() != JsonToken.END_ARRAY) {

                        Integer id = null;
                        String type = null;
                        String text = null;

                        while (parser.nextToken() != JsonToken.END_OBJECT) {

                            if (parser.currentToken() == JsonToken.FIELD_NAME) {

                                String field = parser.currentName();
                                parser.nextToken();

                                if ("id".equals(field))
                                    id = parser.getIntValue();

                                if ("type".equals(field))
                                    type = parser.getValueAsString();

                                if ("text".equals(field))
                                    text = parser.getValueAsString();
                            }
                        }

                        if (text != null && currentPage != null && id != null) {
                            writer.write(currentPage + "$$" + id + "$$" + type + "$$" + text);
                            writer.newLine();
                        }
                    }
                }
            }
        }
    }
}

ObjectMapper mapper = new ObjectMapper();
JsonNode root = mapper.readTree(jsonFile);

for (JsonNode page : root.get("pages")) {
    int pageNumber = page.get("page_number").asInt();

    for (JsonNode el : page.get("elements")) {
        int id = el.get("id").asInt();
        String type = el.get("type").asText();
        String text = el.get("text").asText();

        writer.write(pageNumber + "$$" + id + "$$" + type + "$$" + text);
        writer.newLine();
    }
}

private static void convertSingleJson(Path jsonFile,
                                      Path txtDir,
                                      ObjectMapper mapper) throws IOException {

    // 출력 파일 경로 생성
    String fileName = jsonFile.getFileName().toString()
            .replace(".json", ".csv");

    Path outputFile = txtDir.resolve(fileName);

    try (BufferedWriter writer = Files.newBufferedWriter(
            outputFile,
            StandardOpenOption.CREATE,
            StandardOpenOption.TRUNCATE_EXISTING)) {

        // 헤더
        writer.write("page_number$$element_id$$type$$text");
        writer.newLine();

        // JSON 읽기
        JsonNode root = mapper.readTree(jsonFile);

        JsonNode pages = root.get("pages");
        if (pages == null || !pages.isArray()) {
            return; // pages 없으면 종료
        }

        for (JsonNode page : pages) {

            Integer pageNumber = page.has("page_number")
                    ? page.get("page_number").asInt()
                    : null;

            if (pageNumber == null) continue;

            JsonNode elements = page.get("elements");
            if (elements == null || !elements.isArray()) continue;

            for (JsonNode element : elements) {

                Integer id = element.has("id")
                        ? element.get("id").asInt()
                        : null;

                String type = element.has("type")
                        ? element.get("type").asText()
                        : "-";

                String text = element.has("text")
                        ? element.get("text").asText()
                        : null;

                if (id == null || text == null || text.isBlank()) continue;

                // 줄바꿈/개행 정리
                text = text.replace("\r", " ")
                           .replace("\n", " ")
                           .trim();

                writer.write(pageNumber + "$$"
                        + id + "$$"
                        + type + "$$"
                        + text);

                writer.newLine();
            }
        }
    }
}