JSON: JsonMappingException，同时尝试用空值反序列化对象

Question

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

我所做的：

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：如果要扔掉"firstName = null"属性--一切都很好！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：在序列化过程中如何避免此异常或保证Jackson忽略空值？

抛出：

消息：

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

事业：

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

如果不想序列化null值，可以使用以下设置(序列化期间)：

objectMapper.setSerializationInclusion(Include.NON_NULL);

希望这能解决你的问题。

但是反序列化过程中获得的NullPointerException在我看来是可疑的(理想情况下，杰克逊应该能够处理序列化输出中的null值)。你能把对应于PersonResponse类的代码寄出去吗？

Answer 2

有时，当不小心将基元类型用作非原始字段的getter的返回类型时，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;
    }   
}

请注意getValue()-method的"float“而不是”-method“，这可能导致一个空指针异常，即使您已经添加了

objectMapper.setSerializationInclusion(Include.NON_NULL);

Answer 3

我也面临着同样的问题。

我只是在模型类中包含了一个默认构造函数，以及带有参数的其他构造函数。

啊，真灵。

package objmodel;

import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;

public class CarModel {

private String company;
private String model;
private String color;
private String power;


public CarModel() {
}

public CarModel(String company, String model, String color, String power) {
    this.company = company;
    this.model = model;
    this.color = color;
    this.power = power;

}

@JsonDeserialize
public String getCompany() {
    return company;
}

public void setCompany(String company) {
    this.company = company;
}

@JsonDeserialize
public String getModel() {
    return model;
}

public void setModel(String model) {
    this.model = model;
}

@JsonDeserialize
public String getColor() {
    return color;
}

public void setColor(String color) {
    this.color = color;
}

@JsonDeserialize
public String getPower() {
    return power;
}

public void setPower(String power) {
    this.power = power;
}
}