SpringBoot对空值处理，null转空串""，List、Array转[]，Int转0

jackson方式

先定义转换器 JacksonHttpMessageConverter

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import org.apache.commons.lang3.StringUtils;
import java.io.IOException;

class JacksonHttpMessageConverter {

    /**
     * 处理数组类型的null值
     */
    public static class NullArrayJsonSerializer extends JsonSerializer<Object> {

        @Override
        public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
            if (value == null) {
                jgen.writeStartArray();
                jgen.writeEndArray();
            }
        }
    }


    /**
     * 处理字符串等类型的null值
     */
    public static class NullStringJsonSerializer extends JsonSerializer<Object> {

        @Override
        public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
            jsonGenerator.writeString(StringUtils.EMPTY);
        }
    }

    /**
     * 处理字符串等类型的null值
     */
    public static class NullNumberJsonSerializer extends JsonSerializer<Object> {

        @Override
        public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
            jsonGenerator.writeNumber(0);
        }
    }

    /**
     * 处理字符串等类型的null值
     */
    public static class NullBooleanJsonSerializer extends JsonSerializer<Object> {

        @Override
        public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
            jsonGenerator.writeBoolean(false);
        }
    }

}

定义序列化修饰器 SerializerModifier

import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.SerializationConfig;
import com.fasterxml.jackson.databind.ser.BeanPropertyWriter;
import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
import java.util.Collection;
import java.util.List;

public class CustomSerializerModifier extends BeanSerializerModifier {


    @Override
    public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {
        //循环所有的beanPropertyWriter
        for (Object beanProperty : beanProperties) {
            BeanPropertyWriter writer = (BeanPropertyWriter) beanProperty;
            //判断字段的类型，如果是array，list，set则注册nullSerializer
            if (isArrayType(writer)) {
                //给writer注册一个自己的nullSerializer
                writer.assignNullSerializer(new JacksonHttpMessageConverter.NullArrayJsonSerializer());
            } else if (isNumberType(writer)) {
                writer.assignNullSerializer(new JacksonHttpMessageConverter.NullNumberJsonSerializer());
            } else if (isBooleanType(writer)) {
                writer.assignNullSerializer(new JacksonHttpMessageConverter.NullBooleanJsonSerializer());
            } else if (isStringType(writer)) {
                writer.assignNullSerializer(new JacksonHttpMessageConverter.NullStringJsonSerializer());
            }
        }
        return beanProperties;
    }

    /**
     * 是否是数组
     */
    private boolean isArrayType(BeanPropertyWriter writer) {
        Class<?> clazz = writer.getType().getRawClass();
        return clazz.isArray() || Collection.class.isAssignableFrom(clazz);
    }

    /**
     * 是否是string
     */
    private boolean isStringType(BeanPropertyWriter writer) {
        Class<?> clazz = writer.getType().getRawClass();
        return CharSequence.class.isAssignableFrom(clazz) || Character.class.isAssignableFrom(clazz);
    }


    /**
     * 是否是int
     */
    private boolean isNumberType(BeanPropertyWriter writer) {
        Class<?> clazz = writer.getType().getRawClass();
        return Number.class.isAssignableFrom(clazz);
    }

    /**
     * 是否是boolean
     */
    private boolean isBooleanType(BeanPropertyWriter writer) {
        Class<?> clazz = writer.getType().getRawClass();
        return clazz.equals(Boolean.class);
    }

}

定义配置类JacksonConfig

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import java.text.SimpleDateFormat;


@Configuration
public class JacksonConfig {

    @Bean
    public ObjectMapper objectMapper() {
        // 创建一个ObjectMapper实例
        ObjectMapper objectMapper = new ObjectMapper();

        // 设置日期格式
        objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
        // 忽略未知字段
      objectMapper.configure(com.fasterxml.jackson.databind.DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

        // 设置输出时包含属性的风格，这里选择忽略空值
        objectMapper.setSerializationInclusion(JsonInclude.Include.ALWAYS);
                  objectMapper.setSerializerFactory(objectMapper.getSerializerFactory().withSerializerModifier(new CustomSerializerModifier()));

        // 设置输出格式化
        objectMapper.enable(SerializationFeature.INDENT_OUTPUT);
        // 启用或禁用某些序列化特性
        // 输出格式化
        objectMapper.enable(SerializationFeature.INDENT_OUTPUT);
        // 不使用时间戳方式
        objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

        return objectMapper;
    }
}

fastjson方式

定义配置类 CustomFastJsonConfig

import com.alibaba.fastjson.PropertyNamingStrategy;
import com.alibaba.fastjson.serializer.SerializeConfig;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.alibaba.fastjson.support.config.FastJsonConfig;
import com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;

import java.nio.charset.StandardCharsets;
import java.util.Arrays;

@Configuration
public class CustomFastJsonConfig {
    /**
     * QuoteFieldNames     输出key时是否使用双引号,默认为true
     * UseSingleQuotes     使用单引号而不是双引号,默认为false
     * WriteMapNullValue     是否输出值为null的字段,默认为false
     * WriteEnumUsingToString     Enum输出name()或者original,默认为false
     * UseISO8601DateFormat     Date使用ISO8601格式输出，默认为false
     * WriteNullListAsEmpty     List字段如果为null,输出为[],而非null
     * WriteNullStringAsEmpty     字符类型字段如果为null,输出为”“,而非null
     * WriteNullNumberAsZero     数值字段如果为null,输出为0,而非null
     * WriteNullBooleanAsFalse     Boolean字段如果为null,输出为false,而非null
     * SkipTransientField     如果是true，类中的Get方法对应的Field是transient，序列化时将会被忽略。默认为true
     * SortField     按字段名称排序后输出。默认为false
     * WriteTabAsSpecial     把\t做转义输出，默认为false     不推荐
     * PrettyFormat     结果是否格式化,默认为false
     * WriteClassName     序列化时写入类型信息，默认为false。反序列化是需用到
     * DisableCircularReferenceDetect     消除对同一对象循环引用的问题，默认为false
     * WriteSlashAsSpecial     对斜杠’/’进行转义
     * BrowserCompatible     将中文都会序列化为XXXX格式，字节数会多一些，但是能兼容IE 6，默认为false
     * WriteDateUseDateFormat     全局修改日期格式,默认为false。JSON.DEFFAULT_DATE_FORMAT = “yyyy-MM-dd”;JSON.toJSONString(obj, SerializerFeature.WriteDateUseDateFormat);
     * DisableCheckSpecialChar     一个对象的字符串属性中如果有特殊字符如双引号，将会在转成json时带有反斜杠转移符。如果不需要转义，可以使用这个属性。默认为false
     * NotWriteRootClassName     含义
     * BeanToArray     将对象转为array输出
     * WriteNonStringKeyAsString     Map<Integer,Stirng> 输出 key 默认为 Integer添加此属性，Integer 添加了 “”，变成字符型
     * NotWriteDefaultValue     将基础类型的默认值屏蔽
     * BrowserSecure     含义
     * IgnoreNonFieldGetter     含义
     * WriteEnumUsingName     用枚举name()输出
     *
     * 仅在@ResponseBody，@RequestBody生效
     */
    @Bean
    public FastJsonHttpMessageConverter fastJsonHttpMessageConverter(){
        FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
        FastJsonConfig fastJsonConfig = new FastJsonConfig();
        fastJsonConfig.setCharset(StandardCharsets.UTF_8);
        fastJsonConfig.setSerializerFeatures(
                //List字段如果为null,输出为[],而非null
                SerializerFeature.WriteNullListAsEmpty,
                //是否输出值为null的字段,默认为false
                SerializerFeature.WriteMapNullValue,
                //字符串null返回空字符串
                SerializerFeature.WriteNullStringAsEmpty,
                //空布尔值返回false
                SerializerFeature.WriteNullBooleanAsFalse
                //结果是否格式化,默认为false
                //SerializerFeature.PrettyFormat
        );
        //驼峰转下划线
        SerializeConfig serializeConfig = new SerializeConfig();
        serializeConfig.setPropertyNamingStrategy(PropertyNamingStrategy.SnakeCase);
        fastJsonConfig.setSerializeConfig(serializeConfig);
        //格式化日期 Date类型会被自动转换成下述规则
        fastJsonConfig.setDateFormat("yyyy-MM-dd HH:mm:ss");
        converter.setFastJsonConfig(fastJsonConfig);
        converter.setDefaultCharset(StandardCharsets.UTF_8);
        //支持格式
        converter.setSupportedMediaTypes(Arrays.asList(MediaType.APPLICATION_JSON));
        return converter;
    }
}