jackson-databind-java-optional

A shim library to support mapping Java 8 Optional through Jackson. Forked from @realjenuis jackson-databind-java8 project.

This library is compiled with Java 8 and will thus only be useful in a Java 8 (or higher) runtime environment.

Alternatives

If you are starting a new project that requires support for Java 8 combined with Jackson Databind, you should probably have a look at FasterXML's JDK 8 module.

Usage

The library is distributed through Sonatype's OSS repo

Maven dependency

        <dependency>
            <groupId>org.zapodot</groupId>
            <artifactId>jackson-databind-java-optional</artifactId>
            <version>2.6.1</version>
        </dependency>

SBT

    libraryDependencies += "org.zapodot" % "jackson-databind-java-optional" % "2.6.1"

Registering module

The module is auto-discoverable using the Jackson ObjectMappers's findAndRegisterModules method

final ObjectMapper mapper = new ObjectMapper().findAndRegisterModules();

If you are not to crazy about using auto discovery, you can always register the module manually

final ObjectMapper objectMapper = new ObjectMapper()
                                          .registerModule(
                                                new JavaOptionalModule());

Serialization

Empty Optionals will be serialized as JSON nulls. Example:

    public class Bean {

        public static final String PRESENT_VALUE = "present";
        @JsonProperty
        private Optional<String> empty = Optional.empty();

        @JsonProperty
        private Optional<String> notSet;

        @JsonProperty
        private Optional<String> present = Optional.of(PRESENT_VALUE);

        public static void serialize() {
            final ObjectMapper mapper = new ObjectMapper().findAndRegisterModules();
            final String json = mapper.writeValueAsString(new Bean());
            System.out.println(json); // will print '{"empty":null,"notSet":null,"present":"present"}'
        }


    }

Deserialization

Nulls will be deserialized as Optional.empty() Example:

    public class JavaOptionalDeserializeTest {

        public static class Bean {

            public static final String PRESENT_VALUE = "present";

            @JsonProperty
            private Optional<String> empty = Optional.empty();

            @JsonProperty
            private Optional<String> notSet;

            @JsonProperty
            private Optional<String> present = Optional.of(PRESENT_VALUE);

        }

        @Test
        public void testDeserialize() throws Exception {
            final Bean bean = new ObjectMapper().findAndRegisterModules()
                                                .readValue("{\"empty\":null,\"notSet\":null}", Bean.class);
            assertNotNull(bean.empty);
            assertEquals(Optional.empty(), bean.empty);
            assertNotNull(bean.notSet);
            assertEquals(Optional.empty(), bean.notSet);
            assertEquals(Optional.of(Bean.PRESENT_VALUE), bean.present);

        }
    }