Java 8 date time types serialized as object with Spring Boot

Question

I have an entity with fields of Java 8 date time types. The issue is that these fields are serialized as object. I added the jackson-datatype-jsr310 dependency, so Spring Boot 1.5.7 would auto configure the JavaTimeModule that handles Java 8 date time types. It seems that the module is not registered (I put a breakpoint in JavaTimeModule constructor). I know I don't need a custom ObjectMapper. I spent hours reading about that issue and the solution is always to add the jackson-datatype-jsr310 dependency but it does not work in my case.

The entity:

@Entity
public class DateTimeEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private LocalDate localDate;

    private LocalDateTime localDateTime;

    private Instant instant;

    private OffsetDateTime offsetDateTime;

    private ZonedDateTime zonedDateTime;

}

The RestController method:

@GetMapping("/datetimes/{id}")
public ResponseEntity<DateTimeEntity> getById(@PathVariable Long id) {
    DateTimeEntity dateTimeEntity = dateTimeRepository.findOne(id);
    return new ResponseEntity<DateTimeEntity>(dateTimeEntity, HttpStatus.OK);

}

The JSON object returned:

    {
    "id": 1,
    "localDate": null,
    "localDateTime": null,
    "instant": {
        "epochSecond": 1508772600,
        "nano": 0
    },
    "offsetDateTime": {
        "offset": {
            "totalSeconds": 0,
            "id": "Z",
            "rules": {
                "fixedOffset": true,
                "transitionRules": [],
                "transitions": []
            }
        },
        "dayOfMonth": 23,
        "dayOfWeek": "MONDAY",
        "dayOfYear": 296,
        "month": "OCTOBER",
        "monthValue": 10,
        "year": 2017,
        "hour": 15,
        "minute": 30,
        "nano": 0,
        "second": 0
    },
    "zonedDateTime": {
        "offset": {
            "totalSeconds": 0,
            "id": "Z",
            "rules": {
                "fixedOffset": true,
                "transitionRules": [],
                "transitions": []
            }
        },
        "zone": {
            "totalSeconds": 0,
            "id": "Z",
            "rules": {
                "fixedOffset": true,
                "transitionRules": [],
                "transitions": []
            }
        },
        "dayOfMonth": 23,
        "dayOfWeek": "MONDAY",
        "dayOfYear": 296,
        "month": "OCTOBER",
        "monthValue": 10,
        "year": 2017,
        "hour": 15,
        "minute": 30,
        "nano": 0,
        "second": 0,
        "chronology": {
            "id": "ISO",
            "calendarType": "iso8601"
        }
    }
}

The POM file:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>framework-demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.7.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
        <mockito.version>2.11.0</mockito.version>
        <org.mapstruct.version>1.2.0.Final</org.mapstruct.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct-jdk8</artifactId>
            <version>${org.mapstruct.version}</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jsr310</artifactId>
        </dependency>

        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jsr310</artifactId>
            <version>${jackson.version}</version>
            <scope>test</scope>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                    <annotationProcessorPaths>
                        <path>
                            <groupId>org.mapstruct</groupId>
                            <artifactId>mapstruct-processor</artifactId>
                            <version>${org.mapstruct.version}</version>
                        </path>
                    </annotationProcessorPaths>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.asciidoctor</groupId>
                <artifactId>asciidoctor-maven-plugin</artifactId>
                <version>1.5.5</version>
                <executions>
                    <execution>
                        <id>output-html</id>
                        <phase>generate-resources</phase>
                        <goals>
                            <goal>process-asciidoc</goal>
                        </goals>
                        <configuration>
                            <backend>html</backend>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

Answer 1

I started having this issue in the upgrade of spring boot from 2.3.7 to 2.5.1.

If you have an ObjectMapper @Bean defined, then you'll want to register the time module with it.

@Bean
public ObjectMapper defaultMapper() {
    ObjectMapper objectMapper = new ObjectMapper(); 
    objectMapper.registerModule(new JavaTimeModule()); 
    return objectMapper;
}

A lot of the time, coders will just create a "new ObjectMapper()" when using jackson serialization so keep an eye out for using the vanilla mapper, rather than autowiring a pre-configured default that has the time module registered.

As mentioned, you'll need the jackson-datatype-jsr310, but this is included in spring boot as a managed version.

If you don't define an object mapper bean manually, then spring boot should automatically provide one with the time module registered.

Answer 2

According to How to customize ObjectMapper :

Any beans of type com.fasterxml.jackson.databind.Module will be automatically registered with the auto-configured Jackson2ObjectMapperBuilder and applied to any ObjectMapper instances that it creates. This provides a global mechanism for contributing custom modules when you add new features to your application.

Just adding the dependancy is not enough, you have to declare a @Bean of you module like follow:

@Bean
public Module dateTimeModule(){
    return new JavaTimeModule();
}

Plus jackson-datatype-jsr310 module is deprecated you should use JavaTimeModule instead.