Springboot @JsonSerialize 相关使用（jsonUtil）

基础注解使用

1、实现JsonSerializer接口
例：

public class MySerializerUtils extends JsonSerializer<Integer> {
    @Override
    public void serialize(Integer status, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
        String statusStr = "";
         switch (status) {
             case 0:
                 statusStr = "新建状态";
                 break;
                 }
                 jsonGenerator.writeString(statusStr);
     }
 }

2、添加注解
注:@JsonSerialize注解,主要应用于数据转换,该注解作用在该属性的getter()方法上。

①用在属性上（自定义的例子）

@JsonSerialize(using = MySerializerUtils.class)
private int status;

②用在属性上（jackson自带的用法）

@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
    @JsonDeserialize(using = LocalDateTimeDeserializer.class)
    @JsonSerialize(using = LocalDateTimeSerializer.class)
private LocalDateTime sendTime;

③用在空对象上可以转化

@JsonSerialize
public class XxxxxBody {
	// 该对象暂无字段，直接new了返回
}

框架层面的使用
jsonUtil工具类
实现json转换时所有的null转为“”

1、实现JsonSerializer类

public class CustomizeNullJsonSerializer {
    public static class NullStringJsonSerializer extends JsonSerializer<Object> {
        @Override
        public void serialize(Object value, JsonGenerator jsonGenerator,
                              SerializerProvider serializerProvider) throws IOException {
            jsonGenerator.writeString("");
        }
    }
}

2、实现BeanSerializerModifier类

public class CustomizeBeanSerializerModifier extends BeanSerializerModifier {

    @Override
    public List<BeanPropertyWriter> changeProperties(SerializationConfig config,
                                                     BeanDescription beanDesc,
                                                     List<BeanPropertyWriter> beanProperties) {
        for (int i = 0; i < beanProperties.size(); i++) {
            BeanPropertyWriter writer = beanProperties.get(i);
            if (isStringType(writer)) {
                writer.assignNullSerializer(new CustomizeNullJsonSerializer.NullStringJsonSerializer());
            }
        }
        return beanProperties;
    }
    /**
     * 是否是String
     */
    private boolean isStringType(BeanPropertyWriter writer) {
        Class<?> clazz = writer.getType().getRawClass();
        return CharSequence.class.isAssignableFrom(clazz) || Character.class.isAssignableFrom(clazz);
    }
}

3、工具类调用

public class JsonUtil {
//序列化时String 为null时变成""
    private static ObjectMapper mapperContainEmpty = new ObjectMapper();
static {
        mapperContainEmpty.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
        mapperContainEmpty.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        mapperContainEmpty.setSerializerFactory(mapperContainEmpty.getSerializerFactory()
                .withSerializerModifier(new CustomizeBeanSerializerModifier()));
    }

 /**
     * 将对象转换为Json串,针对String 类型 null 转成""
     */
    public static String toJsonContainEmpty(Object o) {
        try {
            return mapperContainEmpty.writeValueAsString(o);
        } catch (IOException e) {
            logger.error("render object to json error: {}", e.getMessage(), e);
            throw new RuntimeException("render object to json error!", e);
        }
    }
}

附：jsonUtil完整代码

/**
 * json串和对象之间相互转换工具类
 */
public class JsonUtil {
    private static Logger logger = LoggerFactory.getLogger(JsonUtil.class);
    private static ObjectMapper mapper = new ObjectMapper();
    //序列化时String 为null时变成""
    private static ObjectMapper mapperContainEmpty = new ObjectMapper();

    static {
        mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        mapper.setSerializationInclusion(Include.NON_NULL);

        mapperContainEmpty.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
        mapperContainEmpty.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        mapperContainEmpty.setSerializerFactory(mapperContainEmpty.getSerializerFactory()
                .withSerializerModifier(new CustomizeBeanSerializerModifier()));
    }

    /**
     * 将对象转换为Json串
     */
    public static String toJson(Object o) {
        try {
            return mapper.writeValueAsString(o);
        } catch (IOException e) {
            logger.error("render object to json error: {}", e.getMessage(), e);
            throw new RuntimeException("render object to json error!", e);
        }
    }

    /**
     * 将对象转换为Json串,针对String 类型 null 转成""
     */
    public static String toJsonContainEmpty(Object o) {
        try {
            return mapperContainEmpty.writeValueAsString(o);
        } catch (IOException e) {
            logger.error("render object to json error: {}", e.getMessage(), e);
            throw new RuntimeException("render object to json error!", e);
        }
    }

    /**
     * 将Json串转换为对象
     */
    public static <T> T toObject(String json, Class<T> clazz) {
        try {
            return mapper.readValue(json, clazz);
        } catch (IOException e) {
            logger.error("render json to object error: {}", e.getMessage(), e);
            throw new RuntimeException("render json to object error!", e);
        }
    }

    /**
     * 将Json串转换为List
     */
    public static <T> List<T> toList(String json, Class<T> clazz) {
        try {
            JavaType javaType = mapper.getTypeFactory().constructParametricType(List.class, clazz);
            return mapper.readValue(json, javaType);
        } catch (IOException e) {
            logger.error("render json to List<T> error: {}", e.getMessage(), e);
            throw new RuntimeException("render json to List<T> error!", e);
        }
    }

    /**
     * 将Json串转换为Map
     */
    public static <K, V> Map<K, V> toMap(String json, Class<K> clazzKey, Class<V> clazzValue) {
        try {
            JavaType javaType = mapper.getTypeFactory().constructParametricType(Map.class, clazzKey, clazzValue);
            return mapper.readValue(json, javaType);
        } catch (IOException e) {
            logger.error("render json to Map<K, V> error: {}", e.getMessage(), e);
            throw new RuntimeException("render json to Map<K, V> error!", e);
        }
    }
}