本文为解决：前端json传String格式时间参数，后端无法解析。

有的人说单独写一个localDateTime配置类，看了一下可以不用。
直接写WebMvcConfig里面就行

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;
import com.fasterxml.jackson.datatype.jsr310.deser.LocalDateDeserializer;
import com.fasterxml.jackson.datatype.jsr310.deser.LocalDateTimeDeserializer;
import com.fasterxml.jackson.datatype.jsr310.deser.LocalTimeDeserializer;
import com.fasterxml.jackson.datatype.jsr310.ser.LocalDateSerializer;
import com.fasterxml.jackson.datatype.jsr310.ser.LocalDateTimeSerializer;
import com.fasterxml.jackson.datatype.jsr310.ser.LocalTimeSerializer;
import lombok.AllArgsConstructor;
import org.springframework.context.annotation.Configuration;
import org.springframework.format.FormatterRegistry;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import java.math.BigInteger;
import java.nio.charset.Charset;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;

@EnableWebMvc
@Configuration
@AllArgsConstructor
public class WebMvcConfig implements WebMvcConfigurer {

    protected static final String DEFAULT_DATE_TIME_FORMAT = "yyyy-MM-dd HH:mm:ss";
    protected static final String DEFAULT_DATE_FORMAT = "yyyy-MM-dd";
    protected static final String DEFAULT_TIME_FORMAT = "HH:mm:ss";
    /**
     * 处理 Long 类型在 Jackson 中丢失精度
     * 如果使用 FastJson 可以修改这里对实现
     * @param converters 消息转换器
     */
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        MappingJackson2HttpMessageConverter jackson2HttpMessageConverter =
                new MappingJackson2HttpMessageConverter();

        ObjectMapper objectMapper = new ObjectMapper();
        SimpleModule simpleModule = new SimpleModule();
        simpleModule.addSerializer(BigInteger.class, ToStringSerializer.instance)
                .addSerializer(Long.class, ToStringSerializer.instance)
                .addSerializer(Long.TYPE, ToStringSerializer.instance)
                //加上就能将前端json中String类型时间解析为LocalDateTime类型
                .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)))
                .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)));;
        objectMapper.registerModule(simpleModule);
        jackson2HttpMessageConverter.setObjectMapper(objectMapper);
        converters.add(jackson2HttpMessageConverter);
        converters.add(new StringHttpMessageConverter(Charset.forName("UTF-8")));
    }

}