有道无术，术尚可求，有术无道，止于术。

本系列Jackson 版本 2.17.0

本系列Spring Boot 版本 3.2.4

源码地址：https://gitee.com/pearl-organization/study-jaskson-demo

1. 场景描述

例如，用户对象中的性别字段，一般在数据库都是使用数值表示，枚举类如下：

public enum GenderEnum {MAN(1, "男"),WOMAN(2, "女");GenderEnum(int code, String desc) {this.code = code;this.desc = desc;}private int code;private String desc;public static String getDesc(int code) {for (GenderEnum c : GenderEnum.values()) {if (c.getCode() == code) {return c.getDesc();}}return null;}public int getCode() {return code;}public String getDesc() {return desc;}public void setCode(int code) {this.code = code;}public void setDesc(String desc) {this.desc = desc;}
}

用户对象如下：

@Data
@ToString
public class PersonVO implements Serializable {Long id;String username;@JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")Date birthday;Integer gender;

返回前端示例如下：

 {"id": "1699657986705854464","username": "jack","birthday": "2024-04-23 14:21:54","gender": 1}

这时，需要将数值类型翻译为对应的描述，例如性别1应该翻译为男。和上篇的数据脱敏一样，后端可以在数据库查询或者反序列化返回Http响应时进行处理。

2. 案例演示

演示需求：将性别编码值翻译后，返回给前端。

示例：

 {"id": "1699657986705854464","username": "jack","birthday": "2024-04-23 14:21:54","gender": 1,"genderText":"男"}

2.1 修改枚举

定义一个公共的枚举接口，定义一个根据编码值获取对应描述的方法：

public interface CommonEnum {/*** 根据编码值获取描述*/String getDescription(int code);
}

GenderEnum 实现公共枚举接口，并实现其方法，这里枚举类相当于一本字典，根据编码值可以翻译为描述字符串，实际开发时，也可以使用数据库或者缓存，建立专门的字典表进行维护：

public enum GenderEnum implements CommonEnum {MAN(1, "男"),WOMAN(2, "女");GenderEnum(int code, String desc) {this.code = code;this.desc = desc;}private int code;private String desc;@Overridepublic String getDescription(int code) {for (GenderEnum c : GenderEnum.values()) {if (c.getCode() == code) {return c.getDesc();}}return "";}public int getCode() {return code;}public String getDesc() {return desc;}public void setCode(int code) {this.code = code;}public void setDesc(String desc) {this.desc = desc;}
}

2.2 定义注解

定义一个字典注解，这里使用枚举类作为字典：

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.ANNOTATION_TYPE})
@JacksonAnnotationsInside
public @interface Dict {/*** 指定后缀* 翻译后的属性名称：添加了注解的属性名+指定后缀*/String suffix() default "Text";/*** 字典使用枚举（实际开发可以使用数据库或者缓存）*/Class<? extends CommonEnum> using();
}

2.3 自定义序列化器

自定义序列化器执行翻译写出操作：

public class DictJsonSerializer extends StdSerializer<Object> {private CommonEnum commonEnum;protected DictJsonSerializer() {super(Object.class);}protected DictJsonSerializer( CommonEnum commonEnum) {super(Object.class);this.commonEnum = commonEnum;}/*** 序列化*/@Overridepublic void serialize(Object code, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {// 获取枚举对应的翻译值并写出String description =commonEnum.getDescription(Integer.parseInt(code.toString()));jsonGenerator.writeString(description);}
}

2.4 自定义装饰器

自定义Bean对象序列化装饰器，解析添加了@Dict注解的属性，据此新建一个虚拟属性：

public class DictBeanSerializerModifier extends BeanSerializerModifier {public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {// 1. 创建新的属性集合List<BeanPropertyWriter> newBeanProperties = CollUtil.newArrayList(beanProperties);// 2. 循环所有属性for (BeanPropertyWriter propertyWriter : beanProperties) {// 3. 获取注解 @DictDict annotation = propertyWriter.getAnnotation(Dict.class);if (annotation == null) {annotation = propertyWriter.getContextAnnotation(Dict.class);}if (annotation != null) {// 4. 新建一个虚拟属性（名称为：添加了注解的属性名+指定后缀）NameTransformer transformer = NameTransformer.simpleTransformer("", annotation.suffix());BeanPropertyWriter newProperty = propertyWriter.rename(transformer);CommonEnum commonEnum = null;Class<? extends CommonEnum> using = annotation.using();// 5. 获取枚举示例（无法反射，所以直接 IF 判断）if (GenderEnum.class.isAssignableFrom(using)) {commonEnum = GenderEnum.MAN;}// 6. 设置虚拟属性的序列化器newProperty.assignSerializer(new DictJsonSerializer(commonEnum));newBeanProperties.add(newProperty);}}return newBeanProperties;}
}

2.5 配置

添加Spring配置类，注册自定义的ObjectMapper，并设置BeanSerializerModifier：

@Configuration
public class ObjectMapperConfig {@Bean@PrimaryObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {ObjectMapper objectMapper = builder.createXmlMapper(false).build();SerializerFactory serializerFactory = objectMapper.getSerializerFactory().withSerializerModifier(new DictBeanSerializerModifier());objectMapper.setSerializerFactory(serializerFactory);return objectMapper;}
}

2.6 测试

用户类添加翻译注解：

@Data
@ToString
public class PersonVO implements Serializable {Long id;String username;@JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")Date birthday;@Dict(using = GenderEnum.class)Integer gender;

访问测试接口：

    @RequestMapping("/test")public PersonVO test() {PersonVO vo = new PersonVO();vo.setId(1699657986705854464L);vo.setUsername("jack");vo.setBirthday(new Date());vo.setGender(2);return vo;}

返回结果：