springboot返回前端对象null转为空字符串

  1  
  2 import com.fasterxml.jackson.core.JsonGenerator;
  3 import com.fasterxml.jackson.core.JsonProcessingException;
  4 import com.fasterxml.jackson.databind.BeanDescription;
  5 import com.fasterxml.jackson.databind.JsonSerializer;
  6 import com.fasterxml.jackson.databind.SerializationConfig;
  7 import com.fasterxml.jackson.databind.SerializerProvider;
  8 import com.fasterxml.jackson.databind.ser.BeanPropertyWriter;
  9 import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
 10 import org.apache.commons.lang3.StringUtils;
 11 import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 12  
 13 import java.io.IOException;
 14 import java.util.Collection;
 15 import java.util.List;
 16  
 17  
 18 /**
 19  * 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
 20  */
 21 class JacksonHttpMessageConverter extends MappingJackson2HttpMessageConverter {
 22  
 23     /**
 24      * 处理数组类型的null值
 25      */
 26     public class NullArrayJsonSerializer extends JsonSerializer<Object> {
 27  
 28         @Override
 29         public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
 30             if (value == null) {
 31                 jgen.writeStartArray();
 32                 jgen.writeEndArray();
 33             }
 34         }
 35     }
 36  
 37  
 38     /**
 39      * 处理字符串类型的null值
 40      */
 41     public class NullStringJsonSerializer extends JsonSerializer<Object> {
 42  
 43         @Override
 44         public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
 45             jsonGenerator.writeString(StringUtils.EMPTY);
 46         }
 47     }
 48  
 49     /**
 50      * 处理数字类型的null值
 51      */
 52     public class NullNumberJsonSerializer extends JsonSerializer<Object> {
 53  
 54         @Override
 55         public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
 56             jsonGenerator.writeNumber(0);
 57         }
 58     }
 59  
 60     /**
 61      * 处理布尔类型的null值
 62      */
 63     public class NullBooleanJsonSerializer extends JsonSerializer<Object> {
 64  
 65         @Override
 66         public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
 67             jsonGenerator.writeBoolean(false);
 68         }
 69     }
 70  
 71  
 72     public class MyBeanSerializerModifier extends BeanSerializerModifier {
 73  
 74  
 75         @Override
 76         public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {
 77             //循环所有的beanPropertyWriter
 78             for (Object beanProperty : beanProperties) {
 79                 BeanPropertyWriter writer = (BeanPropertyWriter) beanProperty;
 80                 //判断字段的类型，如果是array，list，set则注册nullSerializer
 81                 if (isArrayType(writer)) {
 82                     //给writer注册一个自己的nullSerializer
 83                     writer.assignNullSerializer(new NullArrayJsonSerializer());
 84                 } else if (isNumberType(writer)) {
 85                     writer.assignNullSerializer(new NullNumberJsonSerializer());
 86                 } else if (isBooleanType(writer)) {
 87                     writer.assignNullSerializer(new NullBooleanJsonSerializer());
 88                 } else if (isStringType(writer)) {
 89                     writer.assignNullSerializer(new NullStringJsonSerializer());
 90                 }
 91             }
 92             return beanProperties;
 93         }
 94  
 95         /**
 96          * 是否是数组
 97          */
 98         private boolean isArrayType(BeanPropertyWriter writer) {
 99             Class<?> clazz = writer.getType().getRawClass();
100             return clazz.isArray() || Collection.class.isAssignableFrom(clazz);
101         }
102  
103         /**
104          * 是否是string
105          */
106         private boolean isStringType(BeanPropertyWriter writer) {
107             Class<?> clazz = writer.getType().getRawClass();
108             return CharSequence.class.isAssignableFrom(clazz) || Character.class.isAssignableFrom(clazz);
109         }
110  
111  
112         /**
113          * 是否是int
114          */
115         private boolean isNumberType(BeanPropertyWriter writer) {
116             Class<?> clazz = writer.getType().getRawClass();
117             return Number.class.isAssignableFrom(clazz);
118         }
119  
120         /**
121          * 是否是boolean
122          */
123         private boolean isBooleanType(BeanPropertyWriter writer) {
124             Class<?> clazz = writer.getType().getRawClass();
125             return clazz.equals(Boolean.class);
126         }
127  
128     }
129  
130     JacksonHttpMessageConverter() {
131         getObjectMapper().setSerializerFactory(getObjectMapper().getSerializerFactory().withSerializerModifier(new MyBeanSerializerModifier()));
132     }
133  
134 }

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