// ===== Jackson 写法 =====
@JsonPropertyOrder({"order_id", "user_id", "product_name", "amount", "create_time"})
@JsonIgnoreProperties(ignoreUnknown = true)
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Order {

    @JsonProperty("order_id")               // Jackson: 改字段名
    private Long orderId;

    @JsonProperty("user_id")
    private Long userId;

    @JsonProperty("product_name")
    private String productName;

    @JsonFormat(shape = JsonFormat.Shape.STRING)   // Jackson: 金额用字符串
    private BigDecimal amount;

    @JsonIgnore                                 // Jackson: 忽略字段
    private String internalNote;

    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss") // Jackson: 日期格式
    private LocalDateTime createTime;
}

// ===== Fastjson2 写法 =====
@JSONType(orders = {"order_id", "user_id", "product_name", "amount", "create_time"})
public class Order {

    @JSONField(name = "order_id")              // Fastjson2: 改字段名
    private Long orderId;

    @JSONField(name = "user_id")
    private Long userId;

    @JSONField(name = "product_name")
    private String productName;

    @JSONField(serializeFeatures = JSONWriter.Feature.WriteBigDecimalAsPlain)
    private BigDecimal amount;                  // Fastjson2: 金额不用科学计数法

    @JSONField(serialize = false)               // Fastjson2: 忽略字段
    private String internalNote;

    @JSONField(format = "yyyy-MM-dd HH:mm:ss") // Fastjson2: 日期格式
    private LocalDateTime createTime;
}

// Jackson——面向对象，所有操作通过 ObjectMapper 实例
ObjectMapper mapper = new ObjectMapper();  // 创建实例（可配置）
String json = mapper.writeValueAsString(obj);
Order order = mapper.readValue(json, Order.class);

// Fastjson2——静态方法，操作通过 JSON 工具类
String json = JSON.toJSONString(obj);      // 静态——不需要实例
Order order = JSON.parseObject(json, Order.class);

// ===== 场景一：普通序列化 =====
// Jackson
String json = mapper.writeValueAsString(order);
// Fastjson2
String json = JSON.toJSONString(order);

// ===== 场景二：美化输出 =====
// Jackson
String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(order);
// Fastjson2
String json = JSON.toJSONString(order, JSONWriter.Feature.PrettyFormat);

// ===== 场景三：null 字段不输出 =====
// Jackson
String json = mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL)
                   .writeValueAsString(order);
// Fastjson2
String json = JSON.toJSONString(order, JSONWriter.Feature.SkipNullValues);

// ===== 场景四：泛型反序列化 =====
// Jackson
List<Order> orders = mapper.readValue(json,
    new TypeReference<List<Order>>() {});
// Fastjson2
List<Order> orders = JSON.parseObject(json,
    new TypeReference<List<Order>>() {});

// ===== 场景五：Tree Model（不定义类，层级取值）=====
// Jackson
JsonNode root = mapper.readTree(json);
String productName = root.get("data").get("productName").asText();
// Fastjson2
JSONObject root = JSON.parseObject(json);
String productName = root.getJSONObject("data").getString("productName");

// Jackson——一切通过 ObjectMapper 实例
ObjectMapper mapper = new ObjectMapper();
mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
mapper.registerModule(new JavaTimeModule());
String json = mapper.writeValueAsString(order);

// Fastjson2——全局一次性配置
JSON.config(
    JSONWriter.Feature.SkipNullValues,
    JSONWriter.Feature.WriteDateTimeUseDateFormat,
    JSONWriter.Feature.WriteBigDecimalAsPlain);
String json = JSON.toJSONString(order);
// 注意：Fastjson2 的 JSON.config() 影响所有后续调用——全局生效