1 pom.xml 中添加依赖 

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.41</version>
        </dependency>

2 配制 FastJson --->创建FastJsonConfiguration

@Configuration
public class FastJsonConfiguration extends WebMvcConfigurerAdapter {

    /**
     * 自定义消息转换器
     *
     * @param converters
     */
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        super.configureMessageConverters(converters);
        //1.构建了一个HttpMessageConverter  FastJson   消息转换器
        FastJsonHttpMessageConverter fastConverter = new FastJsonHttpMessageConverter();
        //2.定义一个配置，设置编码方式，和格式化的形式
        FastJsonConfig fastJsonConfig = new FastJsonConfig();
        //3.设置成了PrettyFormat格式
        fastJsonConfig.setSerializerFeatures(
                SerializerFeature.WriteMapNullValue,//是否输出值为null的字段,默认为false
                SerializerFeature.WriteNullBooleanAsFalse,//Boolean字段如果为null,输出为false,而非null
                SerializerFeature.WriteNullListAsEmpty,//List字段如果为null,输出为[],而非nul
                SerializerFeature.DisableCircularReferenceDetect,//消除对同一对象循环引用的问题，默认为false
                SerializerFeature.WriteNullStringAsEmpty//字符类型字段如果为null,输出为"",而非null
        );
        //4.处理中文乱码问题
        List<MediaType> fastMediaTypes = new ArrayList<>();
        fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
        fastConverter.setSupportedMediaTypes(fastMediaTypes);

        //5.将fastJsonConfig加到消息转换器中
        fastConverter.setFastJsonConfig(fastJsonConfig);
        converters.add(fastConverter);
    }
}