最近正在做一個後臺管理系統的項目,前端是基於Metronic的Bootstrap開發框架,管理後臺大部分是將服務端查詢的數據顯示在表格中,由於某些字段可能爲空,顯示在表格中爲null,不太優雅,所以想顯示成空字符串或者“-”,服務端是spring boot2.0,過濾null值爲空字符串一般是在序列化的時候設置值。
controller層使用@ResponseBody返回json格式數據,而這個註解內部使用了ObjectMapper類做序列化,所以只要重寫objectmapper,設置他的幾個屬性就可以做到,如果你在網上搜索了一大堆博客,他們只提供瞭如下代碼:
@Configuration
public class JacksonConfig {
@Bean
@Primary
@ConditionalOnMissingBean(ObjectMapper.class)
public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
ObjectMapper objectMapper = builder.createXmlMapper(false).build();
objectMapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer<Object>() {
@Override
public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeString("");
}
});
return objectMapper;
}
}
你會發現配置在你的項目中不生效,因爲我也試過了,其實正確的寫法是:
@Configuration
public class JacksonConfig implements WebMvcConfigurer{
// 下面這個重寫方法至關重要
@Override
protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.add(new MappingJackson2HttpMessageConverter(objectMapper()));
super.configureMessageConverters(converters);
}
@Bean
@Primary
public ObjectMapper objectMapper() {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer<Object>() {
@Override
public void serialize(Object paramT, JsonGenerator paramJsonGenerator,
SerializerProvider paramSerializerProvider) throws IOException {
// 設置返回null轉爲 空字符串""
paramJsonGenerator.writeString("");
}
});
return objectMapper;
}
}
當你重寫了object mapper後,一定要把新的object mapper設置到converter中才能生效