@JsonSerialize

1. 针对属性

@JsonSerialize 注解可指定自定义序列化器来序列化实体，可以配置在实体类、Getter 方法或属性字段上：

@Getter
@Setter
public static class User {
    private String name;
    @JsonSerialize(using = CustomDateSerializer.class)
    private Date birthday;
}

我们显式对 User 实体的 birthday 属性进行自定义的序列化逻辑：

public class CustomDateSerializer extends StdSerializer<Date> {
    private static final SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    public CustomDateSerializer() {
        this(null);
    }
    protected CustomDateSerializer(Class<Date> t) {
        super(t);
    }
    @Override
    public void serialize(Date value, JsonGenerator gen, SerializerProvider provider) throws IOException {
        gen.writeString(format.format(value));
    }
}

对其进行序列化：

public static void main(String[] args) throws JsonProcessingException {
    User user = new User();
    user.setName("张三");
    user.setBirthday(new Date());
    System.out.println(MAPPER.writeValueAsString(user));
}
// 输出结果：{"name":"张三","birthday":"2021-09-10 11:13:33"}

2. 针对对象

如果想要对整个类进行自定义的序列化：

@Getter
@Setter
@JsonSerialize(using = CustomUserSerializer.class)
public static class User {
    private String name;
    private Date birthday;
}

自定义序列化器的逻辑为：

public class CustomUserSerializer extends StdSerializer<JsonSerializeTest.User> {
    private static final SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    public CustomUserSerializer() {
        this(null);
    }
    protected CustomUserSerializer(Class<JsonSerializeTest.User> t) {
        super(t);
    }
    @Override
    public void serialize(JsonSerializeTest.User value, JsonGenerator gen, SerializerProvider provider) throws IOException {
        gen.writeStartObject();
        gen.writeStringField("name", value.getName() + "^^");
        gen.writeStringField("birthday", format.format(value.getBirthday()) + "^^");
        gen.writeEndObject();
    }
}
// 输出结果：{"name":"张三^^","birthday":"2021-09-10 13:02:26^^"}

@JsonDeserialize

1. 针对属性

�@JsonDeserialize 注解用于自定义反序列化的逻辑：

@Getter
@Setter
public static class User {
    private String name;
    @JsonDeserialize(using = CustomDateDeserializer.class)
    private Date birthday;
}

自定义反序列化器：

public class CustomDateDeserializer extends StdDeserializer<Date> {
    private static final SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    public CustomDateDeserializer() {
        this(null);
    }
    protected CustomDateDeserializer(Class<?> vc) {
        super(vc);
    }
    @Override
    public Date deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        String date = p.getText();
        try {
            return format.parse(date);
        } catch (ParseException e) {
            throw new RuntimeException(e);
        }
    }
}

对其进行反序列化：

public static void main(String[] args) throws JsonProcessingException {
    User userD = MAPPER.readValue("{\"name\":\"张三\",\"birthday\":\"2021-09-10 11:13:33\"}", User.class);
    System.out.println(userD.getBirthday());
}
// 输出结果：Fri Sep 10 11:13:33 CST 2021
// 如果不加自定义的反序列化器，Jackson 默认是无法识别这种日期格式的

2. 针对对象

如果想要对整个类进行自定义的反序列化：

@Getter
@Setter
@JsonDeserialize(using = CustomUserDeserializer.class)
public static class User {
    private String name;
    private Date birthday;
}

自定义反序列化器的逻辑为：

public class CustomUserDeserializer extends StdDeserializer<JsonDeserializeTest.User> {
    private static final SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    public CustomUserDeserializer() {
        this(null);
    }
    protected CustomUserDeserializer(Class<?> vc) {
        super(vc);
    }
    @Override
    public JsonDeserializeTest.User deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        JsonDeserializeTest.User user = new JsonDeserializeTest.User();
        ObjectCodec codec = p.getCodec();
        JsonNode jsonNode = codec.readTree(p);
        try {
            String name = jsonNode.get("name").asText();
            user.setName(name);
            String birthday = jsonNode.get("birthday").asText();
            user.setBirthday(format.parse(birthday));
            return user;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

通过 Module 注册

通过注解声明的方式比较局限，此外，我们也可以通过 Jackson 提供的 Module 机制把自定义的序列化、反序列化器注册到 ObjectMapper 上：

CustomUserDeserializer userDeserializer = new CustomUserDeserializer();
// 创建一个模块,将自定义序列化、反序列化器注册到模块
SimpleModule module = new SimpleModule();
module.addDeserializer(JsonDeserializeTest.User.class, userDeserializer);
// 注册模块到ObjectMapper
MAPPER.registerModule(module);