springboot自定义ObjectMapper序列化、配置序列化对LocalDateTime的支持

背景

1. 问题1：项目中使用默认自带的jackson进行前后端交互，实现数据对象的序列化和反序列化，默认的ObjectMapper采用小驼峰的格式，但是调用其他业务的http接口时，ObjectMapper需要使用蛇形的格式，因此就需要自定义ObjectMapper，然后封装RestTemplate。
2. 问题2：前后端交互时，JSR310日期序列化时，格式错误；

注意点

1. 自定义的ObjectMapper不能被IOC管理，因为Springboot默认的ObjectMapper生成条件是：只有当该实例不存在的时候才会创建！
2. 自定义时，需要支持JSR310的日期，否则序列化LocalDateTime、LocalDate、LocalTime时，就会返回错误的格式。
3. 使用springboot自带的jackson，是不支持JSR310的日期，可以通过下面方式解决
   • 全局配置
   • 在实体类上增加 @JsonFormat(pattern = "yyyy-MM-dd")
   • 在controller方法参数中增加 @DateTimeFormat(pattern = "yyyy-MM-dd")

自定义ObjectMapper

@Slf4j
public class JsonFormatUtils {
    private static final DateTimeFormatter DATE_TIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    private static final DateTimeFormatter DATE_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd");
    private static final DateTimeFormatter TIME_FORMATTER = DateTimeFormatter.ofPattern("HH:mm:ss");
    public static final ObjectMapper objectMapper = new ObjectMapper();

    static {
        //取消时间的转化格式，默认是时间戳,同时需要设置要表现的时间格式
        objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        objectMapper.configure(SerializationFeature.WRITE_DURATIONS_AS_TIMESTAMPS, false);
        objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
        JavaTimeModule javaTimeModule = new JavaTimeModule();   // 默认序列化没有实现，反序列化有实现
        javaTimeModule.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer(DATE_TIME_FORMATTER));
        javaTimeModule.addSerializer(LocalDate.class, new LocalDateSerializer(DATE_FORMATTER));
        javaTimeModule.addSerializer(LocalTime.class, new LocalTimeSerializer(TIME_FORMATTER));
        objectMapper.registerModule(javaTimeModule);
        // 设置时区
        objectMapper.setTimeZone(TimeZone.getDefault());
        // 设置格式化输出
//        objectMapper.enable(SerializationFeature.INDENT_OUTPUT);
        // 设置蛇形格式
        objectMapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);
    }

    public static String writeValueAsString(Object obj) {
        String result = null;
        try {
            result = objectMapper.writeValueAsString(obj);
        } catch (JsonProcessingException e) {
            log.error("objectMapper writeValueAsString exception, e:", e);
        }
        return result;
    }

    public static <T> T readValue(String str, Class<T> tClass) {
        T t = null;
        try {
            t = objectMapper.readValue(str, tClass);
        } catch (JsonProcessingException e) {
            log.error("objectMapper readValue exception, e:", e);
        }
        return t;
    }
}

封装RestTemplate

@Configuration
public class RestTemplateConfig {
    @Bean("otherRestTemplate")
    public RestTemplate algoRestTemplate() {
        // 使用apache的httpComponents，封装restTemplate
        ClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory(httpClient());
        RestTemplate restTemplate = new RestTemplate(factory);
        // 使用自定义的ObjectMapper
        ObjectMapper objectMapper = JsonFormatUtils.objectMapper;
        MappingJackson2HttpMessageConverter messageConverter = new MappingJackson2HttpMessageConverter();
        messageConverter.setPrettyPrint(false);
        messageConverter.setObjectMapper(objectMapper);

        List<HttpMessageConverter<?>> messageConverters = restTemplate.getMessageConverters();
        messageConverters.removeIf(item -> item.getClass().getName().equals(MappingJackson2HttpMessageConverter.class.getName()));
        messageConverters.add(messageConverter);
        return restTemplate;
    }

    private HttpClient httpClient() {
        PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
        connectionManager.setMaxTotal(50);
        connectionManager.setDefaultMaxPerRoute(10);
        connectionManager.setValidateAfterInactivity(2000);
        RequestConfig requestConfig = RequestConfig.custom()
                .setSocketTimeout(10000)
                .setConnectTimeout(5000)
                .setConnectionRequestTimeout(1000)
                .build();
        return HttpClientBuilder.create().setDefaultRequestConfig(requestConfig).setConnectionManager(connectionManager).build();
    }
}

全局配置

底层默认是通过Jackson2ObjectMapperBuilderCustomizer创建的ObjectMapper

@Configuration
public class LocalDateTimeSerializerConfig {

    private static final DateTimeFormatter DATE_TIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    private static final DateTimeFormatter DATE_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd");
    private static final DateTimeFormatter TIME_FORMATTER = DateTimeFormatter.ofPattern("HH:mm:ss");


    @Bean
    public Jackson2ObjectMapperBuilderCustomizer jackson2ObjectMapperBuilderCustomizer() {
        Map<Class<?>, JsonSerializer<?>> serializers = new HashMap<>();
        serializers.put(LocalDateTime.class, new LocalDateTimeSerializer(DATE_TIME_FORMATTER));
        serializers.put(LocalDate.class, new LocalDateSerializer(DATE_FORMATTER));
        serializers.put(LocalTime.class, new LocalTimeSerializer(TIME_FORMATTER));

        Map<Class<?>, JsonDeserializer<?>> deserializers = new HashMap<>();
        deserializers.put(LocalDateTime.class, new LocalDateTimeDeserializer(DATE_TIME_FORMATTER));
        deserializers.put(LocalDate.class, new LocalDateDeserializer(DATE_FORMATTER));
        deserializers.put(LocalTime.class, new LocalTimeDeserializer(TIME_FORMATTER));
        return builder -> builder.serializersByType(serializers).deserializersByType(deserializers);
    }
}