InvalidDefinitionException：找不到内部类的序列化程序答案

【问题标题】：InvalidDefinitionException: No serializer found for inner classInvalidDefinitionException：找不到内部类的序列化程序
【发布时间】：2019-08-04 13:24:18
【问题描述】：

我有这门课，我想以JSON 格式返回RestAPI 调用

return ResponseEntity.ok().cacheControl(CacheControl.maxAge(5, TimeUnit.MINUTES))
                    .body(hotelChart2);

类：

public class HotelChart2 {



    public HotelChart2() {
        super();
    }

    public class Statistics {

         double min;
         double max;
         double average;

         public Statistics() {
            super();
         }

        public Statistics(double min, double max, double average) {
            super();
            this.min = min;
            this.max = max;
            this.average = average;
        }

    }

    Map<LocalDateTime, DoubleSummaryStatistics> las24HPerHour;

    Map<LocalDate, Statistics> last30DPerDay;

    Map<LocalDate, Statistics> last3MPerDay;

    Map<LocalDate, Statistics> last6MPerDay;

    Map<LocalDate, Statistics> last1YPerDay;



    public Map<LocalDateTime, DoubleSummaryStatistics> getLas24HPerHour() {
        return las24HPerHour;
    }

    public void setLas24HPerHour(Map<LocalDateTime, DoubleSummaryStatistics> las24hPerHour) {
        las24HPerHour = las24hPerHour;
    }

    public Map<LocalDate, Statistics> getLast30DPerDay() {
        return last30DPerDay;
    }

    public void setLast30DPerDay(Map<LocalDate, Statistics> last30dPerDay) {
        last30DPerDay = last30dPerDay;
    }

    public Map<LocalDate, Statistics> getLast3MPerDay() {
        return last3MPerDay;
    }

    public void setLast3MPerDay(Map<LocalDate, Statistics> last3mPerDay) {
        last3MPerDay = last3mPerDay;
    }

    public Map<LocalDate, Statistics> getLast6MPerDay() {
        return last6MPerDay;
    }

    public void setLast6MPerDay(Map<LocalDate, Statistics> last6mPerDay) {
        last6MPerDay = last6mPerDay;
    }




    public Map<LocalDate, Statistics> getLast1YPerDay() {
        return last1YPerDay;
    }

    public void setLast1YPerDay(Map<LocalDate, Statistics> last1yPerDay) {
        last1YPerDay = last1yPerDay;
    }


}

但我收到了这个错误：

Type definition error: [simple type, class com.tdk.api.json.HotelChart2$Statistics]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class com.tdk.api.json.HotelChart2$Statistics and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: com.tdk.api.json.HotelChart2["last3MPerDay"]->java.util.HashMap["2019-01-27"])
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:293)
    at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:103)
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:290)

【问题讨论】：

标签： java json rest spring-boot jackson

【解决方案1】：

这两种解决方案中的任何一种都有效！

公开所有成员（默认情况下，Jackson 在公共成员字段上工作）

 public double min; //note: members are made public
 public double max;
 public double average;
 public Map<LocalDateTime, DoubleSummaryStatistics> las24HPerHour;
 // ..... modify all map as public

如果要修改 Jackson 默认属性，请修改 ObjectMapper

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setVisibility(mapper.getVisibilityChecker()
             .withFieldVisibility(JsonAutoDetect.Visibility.ANY));

【讨论】：

【解决方案2】：

您需要将getters 添加到您的内部Statistics 类（首选）或在ObjectMapper 级别启用fields 可见性：

ObjectMapper mapper = new ObjectMapper();
mapper.setVisibility(mapper.getVisibilityChecker()
     .withFieldVisibility(JsonAutoDetect.Visibility.ANY));

【讨论】：