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"])
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
<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();
其他回答
不幸的是,这里提出的解决方案在我的环境中不起作用。 但说实话,使用java8时间对象作为dto毕竟不是一个很好的主意。
我建议创建自定义dto,不要依赖于不稳定的库,它可能在下次jdk发布后崩溃。这种方法也符合反腐败层和适配器模式的良好实践。
下面是DTO的示例:
public class ReportDTO implements Serializable {
private YearMonthDTO yearMonth;
public YearMonthDTO getYearMonth() {
return yearMonth;
}
public void setYearMonth(final YearMonthDTO yearMonth) {
this.yearMonth = yearMonth;
}
public void fromYearMonth(final YearMonth yearMonth) {
this.yearMonth = new YearMonthDTO(yearMonth.getYear(),
yearMonth.getMonthValue());
}
}
public static class YearMonthDTO {
private int year;
private int monthValue;
public YearMonthDTO() {
}
public YearMonthDTO(int year, int monthValue) {
this.year = year;
this.monthValue = monthValue;
}
public int getYear() {
return year;
}
public void setYear(int year) {
this.year = year;
}
public int getMonthValue() {
return monthValue;
}
public void setMonthValue(int monthValue) {
this.monthValue = monthValue;
}
}
当然,这取决于你的情况,以及你要用这个解决方案做的工作量。与任何模式一样,此解决方案并不适用于所有情况。
无论如何,目前最好的答案似乎不再适用了。我没有尝试其他解决方案,但我决定在这个简单的案例中不依赖任何库。
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
更新:由于历史原因,留下这个答案,但我不建议这样做。请参阅上面接受的答案。
告诉Jackson使用自定义的[反]序列化类进行映射:
@JsonSerialize(using = LocalDateTimeSerializer.class)
@JsonDeserialize(using = LocalDateTimeDeserializer.class)
private LocalDateTime ignoreUntil;
提供自定义类:
public class LocalDateTimeSerializer extends JsonSerializer<LocalDateTime> {
@Override
public void serialize(LocalDateTime arg0, JsonGenerator arg1, SerializerProvider arg2) throws IOException {
arg1.writeString(arg0.toString());
}
}
public class LocalDateTimeDeserializer extends JsonDeserializer<LocalDateTime> {
@Override
public LocalDateTime deserialize(JsonParser arg0, DeserializationContext arg1) throws IOException {
return LocalDateTime.parse(arg0.getText());
}
}
随机事实:如果我在类上面嵌套并且不使它们静态,错误消息是奇怪的: httpmediatypenotsupportedexception:内容类型'application/json;charset=UTF-8'不支持
对于那些正在寻找ES-8和Spring Boot:3.0版本的解决方案的人
创建一个扩展ElasticsearchConfiguration的配置文件,并覆盖clientConfiguration和elasticsearchClient的创建。
在创建elasticsearchClient期间,注入您自己的配置为使用Java 8时间模块的objectMapper,它将覆盖默认的objectMapper。
@Override
public ClientConfiguration clientConfiguration() {
return ClientConfiguration.builder()
.connectedTo(<Hostname> +":"+ <Port>)
.usingSsl()
.withBasicAuth(<Username>, <Password>)
.build();
}
@Override
public ElasticsearchClient elasticsearchClient(RestClient restClient) {
Assert.notNull(restClient, "restClient must not be null");
//Create Java8 time module
JavaTimeModule module = new JavaTimeModule();
module.addSerializer(new LocalDateTimeSerializer(DateTimeFormatter.ofPattern(DateFormat.date_time_no_millis.getPattern())));
//Register the module with objectMapper
ObjectMapper objectMapper=new ObjectMapper()
.registerModule(module);
//To convert datetime to ISO-8601
objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
//Creating our own jsonpMapper
JsonpMapper jsonpMapper=new JacksonJsonpMapper(objectMapper);
// Create the transport with a Jackson mapper
ElasticsearchTransport transport = new RestClientTransport(
restClient, jsonpMapper);
// And create the API client
return new ElasticsearchClient(transport);
}
Maven的依赖:
<dependency>
<groupId>com.fasterxml.jackson.datatype</groupId>
<artifactId>jackson-datatype-jsr310</artifactId>
<version>2.14.0</version>
</dependency>
这只是一个例子,如何使用它在一个单元测试,我黑调试这个问题。 关键成分是
mapper。registerModule(从新JavaTimeModule (); <artifactId>jack -datatyp -jsr310</artifactId>的maven dependency
代码:
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import org.testng.Assert;
import org.testng.annotations.Test;
import java.io.IOException;
import java.io.Serializable;
import java.time.Instant;
class Mumu implements Serializable {
private Instant from;
private String text;
Mumu(Instant from, String text) {
this.from = from;
this.text = text;
}
public Mumu() {
}
public Instant getFrom() {
return from;
}
public String getText() {
return text;
}
@Override
public String toString() {
return "Mumu{" +
"from=" + from +
", text='" + text + '\'' +
'}';
}
}
public class Scratch {
@Test
public void JacksonInstant() throws IOException {
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
Mumu before = new Mumu(Instant.now(), "before");
String jsonInString = mapper.writeValueAsString(before);
System.out.println("-- BEFORE --");
System.out.println(before);
System.out.println(jsonInString);
Mumu after = mapper.readValue(jsonInString, Mumu.class);
System.out.println("-- AFTER --");
System.out.println(after);
Assert.assertEquals(after.toString(), before.toString());
}
}