我正在開發一個 PATCH API。如果字段作為JSON null值發送，我需要將它們保存為null. 但是我無法區分它們是已發送null還是從未發送。{ "max_amount": null}Double maxAmount;我有Double、Integer等Date字段。當它們真正被發送時Double.NAN，我可以將它們反序列化為，以了解它們是否被發送為。但是當字段為 時，反序列化器不起作用。當然，可以選擇發送“-1”或無法定義的值，但我不喜歡這種方法。我必須同意所有類型的客戶。在這種情況下最好的方法是什么？Integer.MIN_VALUEnullnullnullnull
1 回答
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TA貢獻1866條經驗 獲得超5個贊
在這種情況下，您應該定義POJO類，并將屬性設置為預定義undefined like數據。例如，對于Integer財產，如果從商業角度來看不允許使用負數，則可能是-1。然后，當JSON反序列化為設置POJO為覆蓋默認值的屬性時null，您就會知道它已發送。應該有3個選項：
常規值 in
JSON- 正確反序列化為值 inPOJOnull值 inJSON- 反序列化為nullinPOJO不可用對
key-value- 中的默認值POJO不會被覆蓋。
以下示例Jackson在版本中使用2.9.9：
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import java.time.LocalDateTime;
public class JsonApp {
public static void main(String[] args) throws Exception {
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
String[] jsons = {
"{\"number\":1,\"date\":\"2019-01-01T22:23:11\",\"max_amount\":4.9}",
"{\"number\":null,\"date\":null,\"max_amount\":null}",
"{}",
"{\"number\":1}",
"{\"date\":\"2019-01-01T22:23:11\"}",
"{\"max_amount\":4.9}",
"{\"number\":1,\"date\":null,\"max_amount\":null}"
};
for (String json : jsons) {
System.out.println(json + " => " + mapper.readValue(json, Pojo.class));
}
}
}
class Pojo {
private static final LocalDateTime NULL_DATE = LocalDateTime.of(1900, 1, 1, 12, 13);
@JsonProperty("max_amount")
private Double maxAmount = Double.MIN_VALUE;
private Integer number = Integer.MIN_VALUE;
@JsonFormat(shape = JsonFormat.Shape.STRING)
private LocalDateTime date = NULL_DATE;
public Double getMaxAmount() {
return maxAmount;
}
public void setMaxAmount(Double maxAmount) {
this.maxAmount = maxAmount;
}
public Integer getNumber() {
return number;
}
public void setNumber(Integer number) {
this.number = number;
}
public LocalDateTime getDate() {
return date;
}
public void setDate(LocalDateTime date) {
this.date = date;
}
@Override
public String toString() {
return "{" +
"number=" + number +
", date=" + date +
", maxAmount=" + maxAmount +
'}';
}
}
上面的代碼打?。?/p>
{"number":1,"date":"2019-01-01T22:23:11","max_amount":4.9} => {number=1, date=2019-01-01T22:23:11, maxAmount=4.9}
{"number":null,"date":null,"max_amount":null} => {number=null, date=null, maxAmount=null}
{} => {number=-2147483648, date=1900-01-01T12:13, maxAmount=4.9E-324}
{"number":1} => {number=1, date=1900-01-01T12:13, maxAmount=4.9E-324}
{"date":"2019-01-01T22:23:11"} => {number=-2147483648, date=2019-01-01T22:23:11, maxAmount=4.9E-324}
{"max_amount":4.9} => {number=-2147483648, date=1900-01-01T12:13, maxAmount=4.9}
{"number":1,"date":null,"max_amount":null} => {number=1, date=null, maxAmount=null}
當然，您應該選擇默認值，這樣可以最大限度地減少客戶端意外發送undefined您的API.
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