java - JSON:尝试反序列化具有空值的对象时出现 JsonMappingException

Question

我尝试反序列化包含空属性并具有 JsonMappingException 的对象。

我的工作:

String actual = "{\"@class\" : \"PersonResponse\"," +
                "  \"id\" : \"PersonResponse\"," +
                "  \"result\" : \"Ok\"," +
                "  \"message\" : \"Send new person object to the client\"," +
                "  \"person\" : {" +
                "    \"id\" : 51," +
                "    \"firstName\" : null}}";
ObjectMapper mapper = new ObjectMapper();
mapper.readValue(new StringReader(json), PersonResponse.class); //EXCEPTION!

但是:如果丢弃 "firstName = null" 属性 - 一切正常!我的意思是传递下一个字符串:

String test = "{\"@class\" : \"PersonResponse\"," +
                "  \"id\" : \"PersonResponse\"," +
                "  \"result\" : \"Ok\"," +
                "  \"message\" : \"Send new person object to the client\"," +
                "  \"person\" : {" +
                "    \"id\" : 51}}";
ObjectMapper mapper = new ObjectMapper();
mapper.readValue(new StringReader(json), PersonResponse.class); //ALL WORKS FINE!

问题:如何避免此异常或保证 Jackson 在序列化期间忽略空值？

throw :

消息:

com.fasterxml.jackson.databind.MessageJsonException:
 com.fasterxml.jackson.databind.JsonMappingException:
  N/A (through reference chain: person.Create["person"]->Person["firstName"])

原因:

com.fasterxml.jackson.databind.MessageJsonException:
 com.fasterxml.jackson.databind.JsonMappingException:
  N/A (through reference chain: prson.Create["person"]->Person["firstName"])

原因: java.lang.NullPointerException

Answer 1

当不小心使用原始类型作为非原始字段的 getter 的返回类型时，有时会出现此问题:

public class Item
{
    private Float value;

    public float getValue()
    {
        return value;
    }

    public void setValue(Float value)
    {
        this.value = value;
    }   
}

注意 getValue() 方法的“float”而不是“Float”，这可能导致空指针异常，即使您已添加

objectMapper.setSerializationInclusion(Include.NON_NULL);