java - 带有空白字符串的Jackson com.fasterxml.jackson.databind.exc.MismatchedInputException

Question

具有以下json片段:

"Location": {
    "Address": ""
},

还有我的Pojo

public class Address implements Serializable
{

    @JsonProperty("City")
    private String city;
    @JsonProperty("StateProvinceCode")
    private String stateProvinceCode;
    @JsonProperty("PostalCode")
    private String postalCode;
    @JsonProperty("CountryCode")
    private String countryCode;
    private final static long serialVersionUID = -4475717488164417476L;

    /**
     * No args constructor for use in serialization
     * 
     */
    public Address() {
    }

    /**
     * 
     * @param city
     * @param countryCode
     * @param postalCode
     * @param stateProvinceCode
     */
    public Address(String city, String stateProvinceCode, String postalCode, String countryCode) {
        super();
        this.city = city;
        this.stateProvinceCode = stateProvinceCode;
        this.postalCode = postalCode;
        this.countryCode = countryCode;
    }

getters and settes ...

我有
com.fasterxml.jackson.databind.exc.MismatchedInputException:无法构造 com.xxx.Address实例(尽管至少存在一个Creator):在[来源:UNKNOWN中，没有从字符串值('')\ n反序列化的String参数构造函数/工厂方法;行:-1，列:-1]

这似乎很明显，空字符串不能反序列化为Address。这里的问题是响应有时是空字符串，而其他则是完整的地址对象。

我如何配置Jackson objectMapper告诉忽略是否存在空字符串？

该响应来自外部来源，因此我无法修改该响应。

这是我的对象映射器配置

@Bean
  public ObjectMapper objectMapper() {
    ObjectMapper mapper = new ObjectMapper();
    mapper.registerModule(new Jdk8Module());
    mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    mapper.configure(DeserializationFeature.FAIL_ON_IGNORED_PROPERTIES, false);
    mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
    return mapper;
  }

附加说明:Pojo类是使用jsonschema2pojo gradle插件生成的，并且基于json模式

Answer 1

根据@Dmitry Zagorulkin的建议，将DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT转换为true。有关更多详细信息，请检查docs。

这是我尝试复制该问题并通过添加注释突出显示的行来解决的代码。

public class JacksonExample2 {

    private static String json1 = "{\r\n" + 
         "  \"Location\": {\r\n" + 
         "    \"Address\": \"\"\r\n" + 
         "  }\r\n" + 
         "}";


    public static void main(String[] args) throws JSONException, IOException {
        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(new Jdk8Module());
        mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        mapper.configure(DeserializationFeature.FAIL_ON_IGNORED_PROPERTIES, false);
        // Add this line
        mapper.configure(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);
        ParentData parentData = mapper.readValue(json1, ParentData.class);
        Address address = new Address("New York", null, null, null);
        LocationData locationData = new LocationData(address);
        System.out.println(parentData);
    }

}

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@ToString
class ParentData {
    @JsonProperty("Location")
    private LocationData locationData;
}

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@ToString
class LocationData {
    @JsonProperty("Address")
    private Address address;
}

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@ToString
class Address implements Serializable {

    @JsonProperty("City")
    private String city;
    @JsonProperty("StateProvinceCode")
    private String stateProvinceCode;
    @JsonProperty("PostalCode")
    private String postalCode;
    @JsonProperty("CountryCode")
    private String countryCode;
    private final static long serialVersionUID = -4475717488164417476L;
}