java - 如何在 lamda 流的反序列化过程中忽略 NULL 值？

Question

我有getter方法

@JsonInclude(Include.NON_NULL)
public Date getVerifiedFrom() {
    if(invoices == null || invoices.isEmpty()) {
       return null;
    }
    return invoices.stream().filter(i->i.getVerifiedDate() != null).map(Invoice::getVerifiedDate).min(Date::compareTo).get();
}

我尝试了几个链接，但没有帮助，

http://www.java2novice.com/java-json/jackson/ignore-json-null-elements/

How to deserialize Jackson Json NULL String to Date with JsonFormat

http://www.davismol.net/2016/01/08/jackson-how-to-exclude-null-value-properties-from-json-serialization/

How to tell Jackson to ignore a field during serialization if its value is null?

错误:

Resolved exception caused by Handler execution: org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: No value present; 
nested exception is com.fasterxml.jackson.databind.JsonMappingException: No value present (through reference chain: java.util.ArrayList[0]->com.enkindle.service.resource.TradeDebtResource["verifiedFrom"])

Answer 1

你得到的异常是由于流是空的，这导致 min 返回一个空的可选值，当你调用 get 时会抛出异常。您没有得到原始 NPE 的原因是 Jackson 可能只提取了消息。

您应该将 get() 替换为 orElse(null)。还有一个处理 Optional 的 Jackson 模块。