如何通过注释有条件地使用自定义 JsonSerializer

Question

我已经编写了一个自定义的 JsonSerializer 来将 BigDecimal 转换为 String。我想使用 @JsonSerialize 注释来调用这个序列化程序，但有条件地，即如果一个特定的布尔值是 true，那么这个 BigDecimal 到 String 的转换应该不做。

我有一个 POJO，它有一个 BigDecimal price 字段。这个 POJO 是为了响应两个 rest 调用而发送的：

• 期望价格字段为数值 //所以@JsonSerialize 应该 不运行
• 期望价格字段为字符串值 //so @JsonSerialize 应该运行

谁能建议我如何实现它？

下面是我写的自定义序列化器的sn-p代码：

public class BigDecimalToStringSerializer extends JsonSerializer<BigDecimal> {

    @Override
    public void serialize(BigDecimal value, JsonGenerator gen, SerializerProvider serializers) throws IOException,
        JsonProcessingException {
        gen.writeString(value.toString());
    }

}

具有价格字段的 POJO 文件：

JsonInclude(Include.NON_NULL)
public class Price{
    private BigDecimal price;
    public Price() {
    }
    @JsonSerialize(using = BigDecimalToStringSerializer.class)
    public BigDecimal getPrice() {
        return price;
    }   
    public void setPrice(BigDecimal pric) {
        this.price  = price;
    }
}

提前致谢！！

Answer 1

您可以为此实现PropertyFilter。首先，您需要在我们的实体上定义过滤器，使用@JsonFilter 注解：

@JsonFilter("stringValueFilter")
public class Price {
  private BigDecimal price;
  public Price() {
  }

  public BigDecimal getPrice() {
     return price;
  }   
  public void setPrice(BigDecimal pric) {
     this.price  = price;
  }
}

这是你的PropertyFilter

public interface PropertyFilter {
    void serializeAsField(Object pojo, JsonGenerator jgen, SerializerProvider prov, PropertyWriter writer);

    void serializeAsElement(Object elementValue, JsonGenerator jgen, SerializerProvider prov, PropertyWriter writer) throws Exception;

    void depositSchemaProperty(PropertyWriter writer, JsonObjectFormatVisitor objectVisitor, SerializerProvider provider) throws JsonMappingException;

    @Deprecated 
    void depositSchemaProperty(PropertyWriter writer, ObjectNode propertiesNode, SerializerProvider provider) throws JsonMappingException;
}

第一种方法需要针对您的情况进行特殊实现：

public class StringValueFilter implements PropertyFilter {
    void serializeAsField(Object pojo, JsonGenerator jgen, SerializerProvider prov, PropertyWriter writer) {
        if (pojo instanceof Price && isValueFieldNumber((Price) pojo)) {
            return; // skip this field
        }
        writer.serializeAsField(pojo, jgen, prov);
    }

    private isValueFieldNumber(Price price) {
        return: //check your logic and return
     }

    void serializeAsElement(Object elementValue, JsonGenerator jgen, SerializerProvider prov, PropertyWriter writer) throws Exception {
        writer.serializeAsField(elementValue, jgen, prov);
    }

    void depositSchemaProperty(PropertyWriter writer, JsonObjectFormatVisitor objectVisitor, SerializerProvider provider) throws JsonMappingException {
        writer.depositSchemaProperty(objectVisitor);
    }

    @Deprecated 
    void depositSchemaProperty(PropertyWriter writer, ObjectNode propertiesNode, SerializerProvider provider) throws JsonMappingException {
        writer.depositSchemaProperty(propertiesNode, provider);
    }
}

此过滤器包含根据其值决定price 字段是否将被序列化的实际逻辑。

接下来，您需要将此过滤器挂钩到ObjectMapper：

final ObjectMapper mapper = new ObjectMapper();
final FilterProvider filterProvider = new SimpleFilterProvider()
        .addFilter("stringValueFilter", new StringValueFilter());
mapper.setFilters(filterProvider);

Answer 2

1.Place @JsonFilter 你的价格等级：

@JsonFilter("myFilter")
@JsonInclude(Include.NON_NULL)
public class Price {
    private BigDecimal price;
    public Price() {}
    @JsonSerialize(using = BigDecimalToStringSerializer.class)
    public BigDecimal getPrice() {
        return price;
    }
    public void setPrice(BigDecimal pric) {
        this.price = price;
    }
}

2.定义CustomFilter逻辑

检查字段是否为“价格”：
如果没有，则正常序列化并返回 如果是这样，请检查您的布尔字段以查看您是否可以序列化

    public class CustomFilter extends SimpleBeanPropertyFilter {
    @Override
    public void serializeAsField
        (Object pojo, JsonGenerator jgen, SerializerProvider provider, PropertyWriter writer)
    throws Exception {
        if (include(writer)) {
            if (!writer.getName().equals("price")) {
                writer.serializeAsField(pojo, jgen, provider);
                return;
            }
            Boolean toSerializeOrNot = ((MyDtoWithFilter) pojo).getYourCoditionalField();
            if (toSerializeOrNot) {
                writer.serializeAsField(pojo, jgen, provider);
            }
        } else if (!jgen.canOmitFields()) { 
            writer.serializeAsOmittedField(pojo, jgen, provider);
        }
    }
    @Override
    protected boolean include(BeanPropertyWriter writer) {
        return true;
    }
    @Override
    protected boolean include(PropertyWriter writer) {
        return true;
    }
}

更多信息

https://www.baeldung.com/jackson-serialize-field-custom-criteria

Answer 3

自定义序列化程序类中唯一需要更改：

public class BigDecimalToStringSerializer extends JsonSerializer<BigDecimal> {

    @Override
    public void serialize(BigDecimal value, JsonGenerator gen, SerializerProvider serializers) throws IOException,
        JsonProcessingException {
    if (pojo instanceof Price && ((Price) pojo).shouldConvertInString()) {
        gen.writeString(value.toString());
    } else {
        gen.writeNumber(value);
    }
    }

}