springboot返回前端对象null转为空字符串

 
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializationConfig;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.BeanPropertyWriter;
import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
import org.apache.commons.lang3.StringUtils;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 
import java.io.IOException;
import java.util.Collection;
import java.util.List;
 
 
/**
 * 使用官方自带的json格式类库，fastjson因为content type问题时不时控制台报错、无法直接返回二进制等问题
 */
class JacksonHttpMessageConverter extends MappingJackson2HttpMessageConverter {
 
    /**
     * 处理数组类型的null值
     */
    public class NullArrayJsonSerializer extends JsonSerializer<Object> {
 
        @Override
        public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
            if (value == null) {
                jgen.writeStartArray();
                jgen.writeEndArray();
            }
        }
    }
 
 
    /**
     * 处理字符串类型的null值
     */
    public class NullStringJsonSerializer extends JsonSerializer<Object> {
 
        @Override
        public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
            jsonGenerator.writeString(StringUtils.EMPTY);
        }
    }
 
    /**
     * 处理数字类型的null值
     */
    public class NullNumberJsonSerializer extends JsonSerializer<Object> {
 
        @Override
        public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
            jsonGenerator.writeNumber(0);
        }
    }
 
    /**
     * 处理布尔类型的null值
     */
    public class NullBooleanJsonSerializer extends JsonSerializer<Object> {
 
        @Override
        public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
            jsonGenerator.writeBoolean(false);
        }
    }
 
 
    public class MyBeanSerializerModifier extends BeanSerializerModifier {
 
 
        @Override
        public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {
            //循环所有的beanPropertyWriter
            for (Object beanProperty : beanProperties) {
                BeanPropertyWriter writer = (BeanPropertyWriter) beanProperty;
                //判断字段的类型，如果是array，list，set则注册nullSerializer
                if (isArrayType(writer)) {
                    //给writer注册一个自己的nullSerializer
                    writer.assignNullSerializer(new NullArrayJsonSerializer());
                } else if (isNumberType(writer)) {
                    writer.assignNullSerializer(new NullNumberJsonSerializer());
                } else if (isBooleanType(writer)) {
                    writer.assignNullSerializer(new NullBooleanJsonSerializer());
                } else if (isStringType(writer)) {
                    writer.assignNullSerializer(new NullStringJsonSerializer());
                }
            }
            return beanProperties;
        }
 
        /**
         * 是否是数组
         */
        private boolean isArrayType(BeanPropertyWriter writer) {
            Class<?> clazz = writer.getType().getRawClass();
            return clazz.isArray() || Collection.class.isAssignableFrom(clazz);
        }
 
        /**
         * 是否是string
         */
        private boolean isStringType(BeanPropertyWriter writer) {
            Class<?> clazz = writer.getType().getRawClass();
            return CharSequence.class.isAssignableFrom(clazz) || Character.class.isAssignableFrom(clazz);
        }
 
 
        /**
         * 是否是int
         */
        private boolean isNumberType(BeanPropertyWriter writer) {
            Class<?> clazz = writer.getType().getRawClass();
            return Number.class.isAssignableFrom(clazz);
        }
 
        /**
         * 是否是boolean
         */
        private boolean isBooleanType(BeanPropertyWriter writer) {
            Class<?> clazz = writer.getType().getRawClass();
            return clazz.equals(Boolean.class);
        }
 
    }
 
    JacksonHttpMessageConverter() {
        getObjectMapper().setSerializerFactory(getObjectMapper().getSerializerFactory().withSerializerModifier(new MyBeanSerializerModifier()));
    }
 
}

一定要在下面配置消息转换器，不然没效果

@Configuration
public class WebMvcConfig extends WebMvcConfigurationSupport {
    @Override
    protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        super.configureMessageConverters(converters);
        converters.add(new JacksonHttpMessageConverter());
    }
 
}

如果想要更丰富的可以在：MyBeanSerializerModifier中自定义。

原文: https://blog.csdn.net/qq_38132283/article/details/89339817?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-15.baidujs&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-15.baidujs