当我使用来自 com.fasterxml.jackson.databind
包的 ObjectMapper
类时,遇到了一个 JSON 解析问题,错误信息如下:
com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of com.graybar.utilities.ups.beans.Address: no String-argument constructor/factory method to deserialize from String value ('')
这个问题发生的Web应用程序是一个使用AngularJS前端的Spring MVC应用程序,但我可以通过一个更小的、完全由Java编写的程序复制该问题。以下是我的bean:
Shipment.java
@JsonIgnoreProperties(ignoreUnknown = true)
public class Shipment {
@JsonProperty("Activity")
private ArrayList<Activity> activity;
public ArrayList<Activity> getActivity() {
return activity;
}
public void setActivity(ArrayList<Activity> activity) {
this.activity = activity;
}
}
Activity.java
@JsonIgnoreProperties(ignoreUnknown = true)
public class Activity {
@JsonProperty("ActivityLocation")
private ArrayList<ActivityLocation> activityLocation;
public ArrayList<ActivityLocation> getActivityLocation() {
return activityLocation;
}
public void setActivityLocation(ArrayList<ActivityLocation> activityLocation) {
this.activityLocation = activityLocation;
}
}
ActivityLocation.java
@JsonIgnoreProperties(ignoreUnknown = true)
public class ActivityLocation {
@JsonProperty("Address")
private Address address;
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
}
Address.java
@JsonIgnoreProperties(ignoreUnknown = true)
public class Address {
@JsonProperty("City")
private String city;
@JsonProperty("StateProvinceCode")
private String stateProvinceCode;
@JsonProperty("CountryCode")
private String countryCode;
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getCountryCode() {
return countryCode;
}
public void setCountryCode(String countryCode) {
this.countryCode = countryCode;
}
public String getStateProvinceCode() {
return stateProvinceCode;
}
public void setStateProvinceCode(String stateProvinceCode) {
this.stateProvinceCode = stateProvinceCode;
}
}
以下是我可以正确映射JSON的代码:
public static void main(String[] args) {
String jsonMessage = "" +
"{" +
" \"Activity\": [{ " +
" \"ActivityLocation\": { " +
" \"Address\": { " +
" \"City\": \"Hana\", " +
" \"StateProvinceCode\": \"Hi\", " +
" \"CountryCode\": \"US\" " +
" } " +
" } " +
" }, " +
" { " +
" \"ActivityLocation\": { " +
" \"Address\": { " +
" \"City\": \"Honolulu\", " +
" \"StateProvinceCode\": \"Hi\", " +
" \"CountryCode\": \"US\" " +
" } " +
" } " +
" }] " +
"} ";
try {
ObjectMapper mapper = new ObjectMapper();
mapper.enable(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY);
Shipment shipment = mapper.readValue(jsonMessage, Shipment.class);
System.out.println("shipment.toString = " + shipment.toString());
} catch (Exception e) {
e.printStackTrace();
}
}
当调整jsonMessage
变量中的数据时,我遇到了上述提到的错误:
"{" +
" \"Activity\": [{ " +
" \"ActivityLocation\": { " +
" \"Address\": { " +
" \"City\": \"Hana\", " +
" \"StateProvinceCode\": \"Hi\", " +
" \"CountryCode\": \"US\" " +
" } " +
" } " +
" }, " +
" { " +
" \"ActivityLocation\": { " +
" \"Address\": \"\" " +
" } " +
" } " +
" }] " +
"} ";
那么,当将json从这样的格式更改时会出现问题:
{
"ActivityLocation": {
"Address": {
"City": "Honolulu",
"StateProvinceCode": "Hi",
"CountryCode": "US"
}
}
}]
变成这样:
{
"ActivityLocation": {
"Address": ""
}
}
我收到的数据中,我的Address
对象的属性值都是空字符串。但很遗憾的是,这些数据是从第三方那里接收到的,我无法控制。
是否需要添加注释来处理这个问题?