场景

在项目中为前端返回对象时，需要转换为json数据格式，如果json对象中有时间类型的格式，需要转换为前端需要的String类型。 如：Date类型:Fri Dec 06 09:31:23 CST 2024 ===> 2024-12-06 09:31:23，其中后者为字符串，且格式可以自定义。

当时间类型为LocalDate

当时间类型为Date

定义Converter

定义一个继承AbstractHttpMessageConverter的转换器。

  • 初始化真正的消息转换接口实现类
  • 重写supports，来支持返回的对象的类型
  • 重写readInternal，writeInternal，定义宏观上的转换过程，一般不需要改动。

代码：

public class MyJacksonObjectMapper extends AbstractHttpMessageConverter {

    private final ObjectMapper objectMapper;

    public MyJacksonObjectMapper() {
        super(new MediaType("application", "json"));
        this.objectMapper = new JacksonObjectMapper();
    }

    @Override
    protected boolean supports(Class clazz) {
        return true;
    }

    @Override
    protected Object readInternal(Class clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
        return objectMapper.readValue(inputMessage.getBody(), clazz);
    }

    @Override
    protected void writeInternal(Object o, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
        objectMapper.writeValue(outputMessage.getBody(), o);
    }
}

定义映射器继承ObjectMapper

/**
 * 对象映射器:基于jackson将Java对象转为json，或者将json转为Java对象
 * 将JSON解析为Java对象的过程称为 [从JSON反序列化Java对象]
 * 从Java对象生成JSON的过程称为 [序列化Java对象到JSON]
 */
public class JacksonObjectMapper extends ObjectMapper {

    public static final String DEFAULT_DATE_FORMAT = "yyyy-MM-dd";
    public static final String DEFAULT_DATE_TIME_FORMAT = "yyyy-MM-dd HH:mm:ss";
    public static final String DEFAULT_TIME_FORMAT = "HH:mm:ss";

    public JacksonObjectMapper() {
        super();
        //收到未知属性时不报异常
        this.configure(FAIL_ON_UNKNOWN_PROPERTIES, false);

        //反序列化时，属性不存在的兼容处理
        this.getDeserializationConfig().withoutFeatures(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

        DateFormat dateFormat = new SimpleDateFormat(DEFAULT_DATE_TIME_FORMAT);

        SimpleModule simpleModule = new SimpleModule()
                .addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)))
                .addDeserializer(LocalDate.class, new LocalDateDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT)))
                .addDeserializer(LocalTime.class, new LocalTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)))
                // 定义Date类型的反序列化器
                .addDeserializer(Date.class, new CustomDateDeserializer(DEFAULT_DATE_TIME_FORMAT))
                // 定义Date类型的序列化器
                .addSerializer(Date.class, new DateSerializer(false, dateFormat))
                .addSerializer(BigInteger.class, ToStringSerializer.instance)
                .addSerializer(Long.class, ToStringSerializer.instance)
                .addSerializer(LocalDateTime.class, new LocalDateTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)))
                .addSerializer(LocalDate.class, new LocalDateSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT)))
                .addSerializer(LocalTime.class, new LocalTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)));

        //注册功能模块 例如，可以添加自定义序列化器和反序列化器
        this.registerModule(simpleModule);
    }
}

定义Date类型的反序列化器继承JsonDeserializer<Date>

核心是deserialize方法，在里面获取json中的字符串数据，实现具体的反序列化逻辑

public class CustomDateDeserializer extends JsonDeserializer<Date> {

    private final String dateFormat;

    public CustomDateDeserializer(String dateFormat) {
        this.dateFormat = dateFormat;
    }

    @Override
    public Date deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        String dateStr = p.getText();
        try {
            return new SimpleDateFormat(dateFormat).parse(dateStr);
        } catch (ParseException e) {
            log.info("Failed to parse date:{} with format:{} ", dateStr, dateFormat);
            throw new RuntimeException("Failed to parse date: " + dateStr + " with format: " + dateFormat, e);
        }
    }
}