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
在Jackson JSR的新版本中,例如,registerModule(new JSR310Module())已弃用,现在建议使用JavaTimeModule
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JacksonFactory {
private static ObjectMapper objectMapper = null;
public static ObjectMapper getObjectMapper() {
if (objectMapper == null) {
objectMapper = new ObjectMapper();
objectMapper.registerModule(new JavaTimeModule());
}
return objectMapper;
}
}
其他回答
如果你正在使用Jersey,那么你需要像其他人建议的那样添加Maven依赖项(jackson- dattype -jsr310),并像这样注册你的对象映射器实例:
@Provider
public class JacksonObjectMapper implements ContextResolver<ObjectMapper> {
final ObjectMapper defaultObjectMapper;
public JacksonObjectMapper() {
defaultObjectMapper = createDefaultMapper();
}
@Override
public ObjectMapper getContext(Class<?> type) {
return defaultObjectMapper;
}
private static ObjectMapper createDefaultMapper() {
final ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
return mapper;
}
}
当在你的资源中注册Jackson时,你需要像这样添加这个映射器:
final ResourceConfig rc = new ResourceConfig().packages("<your package>");
rc
.register(JacksonObjectMapper.class)
.register(JacksonJaxbJsonProvider.class);
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());
}
}
如果有人在使用SpringBoot时遇到问题,这里是我在不添加新的依赖项的情况下修复问题的方法。
在Spring 2.1.3中,Jackson期望在此yyyy-MM-dd HH:mm:ss中出现日期字符串2019-05-21T07:37:11.000。在LocalDateTime中反序列化SSS格式。确保日期字符串用T分隔日期和时间,而不是用空格。秒(ss)和毫秒(SSS)可以省略。
@JsonProperty("last_charge_date")
public LocalDateTime lastChargeDate;
<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();
如果您正在使用fastxml的ObjectMapper类, 默认情况下,ObjectMapper不理解LocalDateTime类,所以,你需要在你的gradle/maven中添加另一个依赖项:
compile 'com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.7.3'
现在你需要将这个库提供的数据类型支持注册到你的objectmapper对象中,这可以通过以下方式完成:
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.findAndRegisterModules();
现在,在你的jsonString中,你可以很容易地把你的java。LocalDateTime字段如下所示:
{
"user_id": 1,
"score": 9,
"date_time": "2016-05-28T17:39:44.937"
}
通过这样做,你的Json文件到Java对象的转换将工作良好,你可以通过以下方式读取文件:
objectMapper.readValue(jsonString, new TypeReference<List<User>>() {
});