我如何使用杰克逊JSON映射与Java 8 LocalDateTime?

jsonmappingexception:不能实例化类型[简单类型,java.time类]的值。LocalDateTime] from JSON字符串;没有单字符串构造函数/工厂方法(通过引用链:MyDTO["field1"]->SubDTO["date"])


当前回答

对于spring引导api:

@Configuration
public class JsonConfig {

    @Bean
    public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
        MappingJackson2HttpMessageConverter jsonConverter = new MappingJackson2HttpMessageConverter();
        ObjectMapper mapper = new ObjectMapper();

        mapper.registerModule(new ParameterNamesModule())
                .registerModule(new Jdk8Module())
                .registerModule(new JavaTimeModule());

        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);// will remove value properties
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        jsonConverter.setObjectMapper(mapper);
        return jsonConverter;
    }
}

导入以下依赖项:

implementation 'com.fasterxml.jackson.core:jackson-core:2.13.0'
implementation 'com.fasterxml.jackson.core:jackson-databind:2.13.0'
implementation 'com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.13.0'

其他回答

如果你正在使用Spring引导,并且在OffsetDateTime上有这个问题,那么需要使用上面@greperror回答的registerModules(5月28日16日13:04回答),但注意有一个区别。不需要添加提到的依赖项,因为我猜spring boot已经有它了。我有这个问题与春季启动,它为我工作,没有添加这个依赖。

        <dependency>
            <groupId>com.fasterxml.jackson.module</groupId>
            <artifactId>jackson-module-parameter-names</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jdk8</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jsr310</artifactId>
        </dependency>

添加这些依赖项并启用这些模块。这应该会有帮助

    private static final ObjectMapper mapper = new ObjectMapper().findAndRegisterModules();
@JsonDeserialize(using = LocalDateTimeDeserializer.class)
@JsonSerialize(using = LocalDateTimeSerializer.class)
private LocalDateTime createTime;

这对我来说很有效。

如果您因为GraphQL Java工具而遇到此问题,并试图从日期字符串编组Java Instant,则需要设置SchemaParser以使用具有特定配置的ObjectMapper:

在GraphQLSchemaBuilder类中,注入ObjectMapper并添加以下模块:

        ObjectMapper objectMapper = 
    new ObjectMapper().registerModule(new JavaTimeModule())
            .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);

并将其添加到选项中:

final SchemaParserOptions options = SchemaParserOptions.newOptions()
            .objectMapperProvider(fieldDefinition -> objectMapper)
            .typeDefinitionFactory(new YourTypeDefinitionFactory())
            .build();

参见https://github.com/graphql-java-kickstart/graphql-spring-boot/issues/32

如果你因为任何原因不能使用jackson-modules-java8,你可以(反)序列化即时字段,只要使用@JsonIgnore和@JsonGetter和@JsonSetter:

public class MyBean {

    private Instant time = Instant.now();

    @JsonIgnore
    public Instant getTime() {
        return this.time;
    }

    public void setTime(Instant time) {
        this.time = time;
    }

    @JsonGetter
    private long getEpochTime() {
        return this.time.toEpochMilli();
    }

    @JsonSetter
    private void setEpochTime(long time) {
        this.time = Instant.ofEpochMilli(time);
    }
}

例子:

@Test
public void testJsonTime() throws Exception {
    String json = new ObjectMapper().writeValueAsString(new MyBean());
    System.out.println(json);
    MyBean myBean = new ObjectMapper().readValue(json, MyBean.class);
    System.out.println(myBean.getTime());
}

收益率

{"epochTime":1506432517242}
2017-09-26T13:28:37.242Z