自定义 JsonSerializer

package com.sdhs.wash.admin.component.jackson;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

import java.io.IOException;
import java.util.Collection;
import java.util.Map;

/**
 * JackJson空值处理
 * 只对bean处理
 * <p>
 * 字符串 ""
 * 集合 []
 * map {}
 *
 * @author seer
 * @version 1.0
 * @date 2021/8/24 14:38
 */
public class NullValueSerializer extends JsonSerializer<Object> {

    @Override
    public void serialize(Object value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
        String fieldName = gen.getOutputContext().getCurrentName();
        Class<?> clazz = gen.getCurrentValue().getClass();
        if (Map.class.isAssignableFrom(clazz)) {
            // map的不处理
            gen.writeNull();
            return;
        }
        Class<?> fieldType;
        try {
            fieldType = gen.getCurrentValue().getClass().getDeclaredField(fieldName).getType();
        } catch (NoSuchFieldException e) {
            throw new IOException(e);
        }
        // 字符串 ""
        if (String.class.isAssignableFrom(fieldType)) {
            gen.writeString("");
            return;
        }
        // 集合 []
        if (Collection.class.isAssignableFrom(fieldType)) {
            gen.writeStartArray();
            gen.writeEndArray();
            return;
        }
        // 布尔 false
        // if (Boolean.class.isAssignableFrom(fieldType)) {
        //     gen.writeBoolean(false);
        //     return;
        // }
        // map {}
        if (Map.class.isAssignableFrom(fieldType)) {
            gen.writeStartObject();
            gen.writeEndObject();
            return;
        }

        // 其它还是null
        gen.writeNull();
    }
}

注册到 ObjectMapper

public class JsonMapper {

    private static ObjectMapper mapper;

    public static ObjectMapper getMapper() {
        if (null == mapper) {
            mapper = new ObjectMapper();
            // 反序列化，未知字段不失败
            mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
            // 序列化，空bean不失败，被 @JsonIgnore 注解的bean
            mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
            mapper.registerModule(new Jdk8Module());
            // 默认 LocalDateTime 格式
            JavaTimeModule timeModule = new JavaTimeModule();
            DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(DatePattern.yyyy_MM_dd_HH_mm_ss, Locale.CHINA);
            timeModule.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer(dateTimeFormatter));
            timeModule.addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer(dateTimeFormatter));
            mapper.registerModule(timeModule);
            // 默认 Date 格式
            mapper.setDateFormat(new SimpleDateFormat(DatePattern.yyyy_MM_dd_HH_mm_ss));
            // 注解 Introspector 不处理会导致注解失效
            mapper.setAnnotationIntrospector(new JsonFormatIntrospector());
            // 所有序列化的对象都将按改规则进行系列化
            mapper.setSerializationInclusion(JsonInclude.Include.ALWAYS);
            // null 序列化
            mapper.getSerializerProvider().setNullValueSerializer(new NullValueSerializer());
        }
        return mapper;
    }
}

使用

JsonMapper.getMapper().writeValueAsString(xxx);