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<mvc:annotation-driven>
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    <mvc:message-converters register-defaults="true">
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        <bean class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
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            <property name="features">
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                <array>
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                    <!-- 下面配置，默认是false-->
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                    <value>WriteMapNullValue</value>
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                    <value>WriteNullNumberAsZero</value>
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                    <value>WriteNullListAsEmpty</value>
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                    <value>WriteNullStringAsEmpty</value>
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                    <value>WriteNullBooleanAsFalse</value>
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                    <value>WriteDateUseDateFormat</value>
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                </array>
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            </property>
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        </bean>
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    </mvc:message-converters>
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</mvc:annotation-driven>

配置如上配置,字面意思是通过json返回类型自动将值设置成不为null的值.

springboot配置如下:

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@Configuration
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public class FastJsonMessage {
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    @Bean
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    public HttpMessageConverters fastJsonHttpMessageConverters() {
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        //1、定义一个convert转换消息的对象
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        FastJsonHttpMessageConverter fastConverter = new FastJsonHttpMessageConverter();
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        //2、添加fastjson的配置信息
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        FastJsonConfig fastJsonConfig = new FastJsonConfig();
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       /* fastJsonConfig.setSerializerFeatures(
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                SerializerFeature.WriteEnumUsingToString,
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                SerializerFeature.WriteNullStringAsEmpty,
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                SerializerFeature.WriteMapNullValue,
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                SerializerFeature.WriteDateUseDateFormat);*/
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        fastJsonConfig.setSerializeFilters((ValueFilter) (o, s, source) -> {
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            if (source == null) {
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                return "";            //此处是关键,如果返回对象的变量为null,则自动变成""
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            }
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            if (source instanceof Date) {
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                return ((Date) source).getTime();
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            }
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            return source;
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        });
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        //2-1 处理中文乱码问题
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        List<MediaType> fastMediaTypes = new ArrayList<>();
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        fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
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        fastConverter.setSupportedMediaTypes(fastMediaTypes);
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        //3、在convert中添加配置信息
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        fastConverter.setFastJsonConfig(fastJsonConfig);
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        //4、将convert添加到converters中
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        HttpMessageConverter<?> converter = fastConverter;
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        return new HttpMessageConverters(converter);
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    }
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}

QuoteFieldNames———-输出key时是否使用双引号,默认为true 
WriteMapNullValue——–是否输出值为null的字段,默认为false 
WriteNullNumberAsZero—-数值字段如果为null,输出为0,而非null 
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 
WriteNullBooleanAsFalse–Boolean字段如果为null,输出为false,而非null