使用Jackson从字符串反序列化LocalDateTime

Question

我正在尝试使用Jackson将String反序列化为LocalDateTime，但它不起作用。

我有一个带有LocalDateTime字段的数据类：

@Data
public class Registration {
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd hh:mm:ss")
    private LocalDateTime timestamp;
}

我添加了特殊的Jackson数据类型模块:

compile("com.fasterxml.jackson.datatype:jackson-datatype-jsr310")

序列化可以在以下情况下正常工作：

new ObjectMapper().registerModule(new JavaTimeModule()).writeValueAsString(registration);

结果字符串：

{"timestamp":"2018-09-03 10:09:35"}

但反序列化不适用于：

new ObjectMapper().registerModule(new JavaTimeModule()).readValue(json.traverse(), Registration.class)

作为错误，我得到：

Cannot deserialize value of type `java.time.LocalDateTime` from String "2018-09-03 10:09:35": 
    Failed to deserialize java.time.LocalDateTime: 
        (java.time.format.DateTimeParseException) Text '2018-09-03 10:09:35' could not be parsed: 
            Unable to obtain LocalDateTime from TemporalAccessor: 
                {MinuteOfHour=9, NanoOfSecond=0, SecondOfMinute=35, MicroOfSecond=0, MilliOfSecond=0, HourOfAmPm=10},
                ISO resolved to 2018-09-03 of type java.time.format.Parsed

我错过了什么？我对串行化有效而反序列化无效感到困惑。

MWE：（小格拉德尔Java项目）

Main.java:

import java.io.IOException;
import java.time.LocalDateTime;

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.core.TreeNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;

public class Main {

    public static void main(String[] args) throws IOException {
        Registration registration = new Registration();
        registration.setTimestamp(LocalDateTime.now());

         ObjectMapper objectMapper = new ObjectMapper().registerModule(new JavaTimeModule());

         String s = objectMapper.writeValueAsString(registration);
         TreeNode treeNode = objectMapper.readTree(s);

         //Fails here:
         Registration registration1 = objectMapper.readValue(treeNode.traverse(), Registration.class);

        System.out.println(registration1);
    }
}

class Registration {
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd hh:mm:ss")
    private LocalDateTime timestamp;

    public Registration() {
    }

    public LocalDateTime getTimestamp() {
        return this.timestamp;
    }

    public void setTimestamp(LocalDateTime localDateTime) {
        this.timestamp = localDateTime;
    }
}

build.gradle：

plugins {
    id 'java'
}

group 'dateMWE'
version '1.0-SNAPSHOT'

sourceCompatibility = 10

repositories {
    mavenCentral()
}

dependencies {
    compile("com.fasterxml.jackson.core:jackson-annotations:2.9.6")
    compile("com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.9.6")
}

Answer 1

您的ObjectMapper不受Spring管理，因为您正在使用new创建对象。在配置文件中将ObjectMapper配置为Bean。您需要使用LocalDateTimeDeserializer注册DateTimeFormat。然后在JavaTimeModule中设置您的Deserializer。

@Bean
 Public ObjectMapper objectMapper() {
   JavaTimeModule module = new JavaTimeModule();
   LocalDateTimeDeserializer localDateTimeDeserializer =  new 
   LocalDateTimeDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
   module.addDeserializer(LocalDateTime.class, localDateTimeDeserializer);
   ObjectMapper objectMapperObj = Jackson2ObjectMapperBuilder.json()
            .modules(module)
            .featuresToDisable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
            .build();
return objectMapperObj ;

在您的Spring配置中设置上述配置。

Answer 2

问题与JSON反序列化无关，而是与时间格式字符串有关：

pattern = "yyyy-MM-dd hh:mm:ss"

请注意，小时设置为hh：这是一个12小时格式，需要“AM”或“PM”值。

如果模式被改变为

pattern = "yyyy-MM-dd HH:mm:ss"

这个问题应该得到解决。