Spring Boot JSON消息转换器

package com.lawu.eshop.merchant.api.config;


import java.io.IOException;


import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;


import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;


@Configuration
public class WebConfig {


// @Bean
// public MappingJackson2HttpMessageConverter customJackson2HttpMessageConverter() {
// MappingJackson2HttpMessageConverter jsonConverter = new MappingJackson2HttpMessageConverter();
// ObjectMapper objectMapper = new ObjectMapper();
// objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
// jsonConverter.setObjectMapper(objectMapper);
// return jsonConverter;
// }
//
// @Override
// public void configureMessageConverters(List> converters) {
// converters.add(customJackson2HttpMessageConverter());
// super.addDefaultHttpMessageConverters(converters);
// }

@Bean
    @Primary
    @ConditionalOnMissingBean(ObjectMapper.class)
    public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
        ObjectMapper objectMapper = builder.createXmlMapper(false).build();
        
        /*
         * 返回的JSON字符串中含有我们并不需要的字段，那么当对应的实体类中不含有该字段时，会抛出一个异常，告诉你有些字段没有在实体类中找到
         */
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        
        SerializerProvider serializerProvider = objectMapper.getSerializerProvider();
        
        // 允许单引号 
        //objectMapper.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES, true);  
        // 字段和值都加引号  
        //objectMapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);  
        // 数字也加引号  
        //objectMapper.configure(JsonGenerator.Feature.WRITE_NUMBERS_AS_STRINGS, true);  
        //objectMapper.configure(JsonGenerator.Feature.QUOTE_NON_NUMERIC_NUMBERS, true);  
        
        //Null值输出空字符串
        serializerProvider.setNullValueSerializer(new JsonSerializer