SpringBoot中返回数据序列化NULL值处理

 1、使用默认的jackson处理

1、定义json处理方式

public class NullCustomConverter {

    /**
     * json处理器
     */
    public static class MyBeanSerializerModifier extends BeanSerializerModifier {
        private NullArrayJsonSerializer array = new NullArrayJsonSerializer();
        private NullStringJsonSerializer string = new NullStringJsonSerializer();
        private NullNumberJsonSerializer number = new NullNumberJsonSerializer();
        private NullObjectJsonSerializer object = new NullObjectJsonSerializer();

        @Override
        public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {
            /*需要进行添加序列化的类型我们可以在这里进行添加和判断*/
            for (int i = 0; i < beanProperties.size(); i++) {
                BeanPropertyWriter writer = beanProperties.get(i);
                /*判断字段的类型，如果是数组或集合则注册nullSerializer*/
                if (isArrayType(writer)) {
                    /*数组*/
                    writer.assignNullSerializer(this.array);
                } else if (isStringType(writer)) {
                    /*字符串*/
                    writer.assignNullSerializer(this.string);
                } else if (isNumberType(writer)) {
                    /*整形*/
                    writer.assignNullSerializer(this.number);
                } else {
                    writer.assignNullSerializer(this.object);
                }
            }
            return beanProperties;
        }
    }

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

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

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

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

    /**
     * 处理数组集合类型的null值
     */
    private static class NullArrayJsonSerializer extends JsonSerializer<Object> {
        @Override
        public void serialize(Object value, JsonGenerator jsonGenerator,
                              SerializerProvider serializerProvider) throws IOException {
            jsonGenerator.writeStartArray();
            jsonGenerator.writeEndArray();
        }
    }

    /**
     * 处理字符串类型的null值
     */
    private static class NullStringJsonSerializer extends JsonSerializer<Object> {
        @Override
        public void serialize(Object value, JsonGenerator jsonGenerator,
                              SerializerProvider serializerProvider) throws IOException {
            jsonGenerator.writeString("");
        }
    }

    /**
     * 处理数值类型的null值
     */
    private static class NullNumberJsonSerializer extends JsonSerializer<Object> {
        @Override
        public void serialize(Object value, JsonGenerator jsonGenerator,
                              SerializerProvider serializerProvider) throws IOException {
            jsonGenerator.writeNumber(0);
        }
    }

    /**
     * 处理boolean类型的null值
     */
    private static class NullBooleanJsonSerializer extends JsonSerializer<Object> {
        @Override
        public void serialize(Object value, JsonGenerator jsonGenerator,
                              SerializerProvider serializerProvider) throws IOException {
            jsonGenerator.writeBoolean(false);
        }
    }

    /**
     * 处理实体对象类型的null值
     */
    private static class NullObjectJsonSerializer extends JsonSerializer<Object> {
        @Override
        public void serialize(Object value, JsonGenerator jsonGenerator,
                              SerializerProvider serializerProvider) throws IOException {
            jsonGenerator.writeStartObject();
            jsonGenerator.writeEndObject();
        }
    }
}

2、配置让我们springboot进行加载

@Configuration
public class JsonConfig {

    @Value("${spring.jackson.date-format}")
    private String dataFormat;

    @Value("${spring.jackson.time-zone}")
    private String timeZone;

    @Bean
    public MappingJackson2HttpMessageConverter mappingJacksonHttpMessageConverter() {
        final MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
        ObjectMapper mapper = converter.getObjectMapper();
        /*添加null值设置*/
        mapper.setSerializerFactory(mapper.getSerializerFactory().withSerializerModifier(new NullCustomConverter.MyBeanSerializerModifier()));
        /*日期处理，自定义后一些配置文件里面的信息没有生效，我们手动操作*/
        mapper.setDateFormat(new SimpleDateFormat(dataFormat));
        /*时区处理*/
        mapper.setTimeZone(TimeZone.getTimeZone(timeZone));
        return converter;
    }

}

在测试过程中发现了，我们在配置文件里面配置的属性没有进行加载，所以我们这里手动去操作：

/*日期处理，自定义后一些配置文件里面的信息没有生效，我们手动操作*/
mapper.setDateFormat(new SimpleDateFormat(dataFormat));
/*时区处理*/
mapper.setTimeZone(TimeZone.getTimeZone(timeZone));

2、使用fastjson 

实现我们的WebMvcConfigurer

@Configuration
public class WebContextConfiguration implements WebMvcConfigurer {
   @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        /*添加fastjson*/
        converters.add(fastJsonHttpMessageConverters(converters));
        
    }

    /**
     * 定义fastjson替代jackson，有些地方单独使用了fastjson所以无法使用fastjson做全局配置
     *
     * @return
     */
    private HttpMessageConverter fastJsonHttpMessageConverters(List<HttpMessageConverter<?>> converters) {
        /*排除掉Jackson*/
        for (int i = converters.size() - 1; i >= 0; i--) {
            if (converters.get(i) instanceof MappingJackson2HttpMessageConverter) {
                converters.remove(i);
            }
        }
        FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
        /*自定义fastjson配置*/
        FastJsonConfig config = new FastJsonConfig();
        config.setSerializerFeatures(
                /*是否输出值为null的字段,默认为false,我们将它打开*/
                SerializerFeature.WriteMapNullValue,
                /*将Collection类型字段的字段空值输出为[]*/
                SerializerFeature.WriteNullListAsEmpty,
                /*将字符串类型字段的空值输出为空字符串*/
                SerializerFeature.WriteNullStringAsEmpty,
                /*将数值类型字段的空值输出为0*/
                SerializerFeature.WriteNullNumberAsZero,
                /*自定义日期格式*/
                SerializerFeature.WriteDateUseDateFormat,
                /*禁用循环引用*/
                SerializerFeature.DisableCircularReferenceDetect
        );
        fastJsonHttpMessageConverter.setFastJsonConfig(config);
        /*但是MappingJackson2HttpMessageConverter里面支持的MediaTypes为application/json*/
        List<MediaType> fastMediaTypes = new ArrayList<>();
        fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
        fastJsonHttpMessageConverter.setSupportedMediaTypes(fastMediaTypes);
        return fastJsonHttpMessageConverter;
    }
}