使用@ResponseBody注释时,将空值作为空字符串

Question

有没有办法使用@ResponseBody注释将空值映射到空字符串？

Answer 1

您将不得不编写一个自定义的Jackson Serializer - 这是一个很好的例子 - http://wiki.fasterxml.com/JacksonHowToCustomSerializers(有一个如何将空值转换为可以使用的空字符串的具体示例)

以下是所有步骤(杰克逊<2.0):

编写自定义null序列化程序:

import java.io.IOException;

import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.SerializerProvider;

public class NullSerializer extends JsonSerializer<Object> {

    @Override
    public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
        jgen.writeString("");
    }
}

使用Jackson Objectmapper注册:

import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.ser.StdSerializerProvider;


public class CustomObjectMapper extends ObjectMapper{
    public CustomObjectMapper(){
        StdSerializerProvider sp = new StdSerializerProvider();
        sp.setNullValueSerializer(new NullSerializer());
        this.setSerializerProvider(sp);
    }

}

使用Spring MVC注册此objectmapper:

<mvc:annotation-driven> 
   <mvc:message-converters register-defaults="true">
       <bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
           <property name="objectMapper">
               <bean class="CustomObjectMapper"/>
           </property>
       </bean>
   </mvc:message-converters>
</mvc:annotation-driven>