Jackson JSON Can not construct instance of "About" : deserialize issue - json

Question

I've make HttpsURLConnection to receive some information about my server.
The result of response is :
{"about":{"title":"NiFi","version":"1.1.0","uri":"https://localhost:443/api/","contentViewerUrl":"/nifi-content-viewer/","timezone":"CET"}}
How is possible to extract all attributes and key/value ?
About.class file
public class About {
private List<AboutObject> about;
public About()
{
// this.about = about;
}
public List<AboutObject> getAbout() {
return this.about;
}
public void setAbout(List<AboutObject> about) {
this.about = about;
}
}
AboutObject.class
public class AboutObject {
private String title;
private String uri;
private String contentViewerUrl;
private String timezone;
public String getTitle()
{
return this.title;
}
public void setTitle(String title)
{
this.title = title;
}
public String getUri()
{
return this.uri;
}
public void setUri(String uri)
{
this.uri = uri;
}
public String getContentViewerUrl()
{
return this.contentViewerUrl;
}
public void setContentViewerUrl(String contentViewerUrl)
{
this.contentViewerUrl = contentViewerUrl;
}
public String getTimeZone()
{
return this.timezone;
}
public void setTimeZone(String timezone)
{
this.timezone = timezone;
}
}
Main.class
HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();
// optional default is GET
con.setRequestMethod("GET");
//add request header
con.setRequestProperty("User-Agent", USER_AGENT);
int responseCode = con.getResponseCode();
System.out.println("\nSending 'GET' request to URL : " + url);
System.out.println("Response Code : " + responseCode);
BufferedReader in = new BufferedReader(
new InputStreamReader(con.getInputStream()));
String inputLine;
StringBuffer response = new StringBuffer();
while ((inputLine = in.readLine()) != null) {
response.append(inputLine);
}
in.close();
//print result
System.out.println(response.toString());
System.out.println("Contenu de in = " + in.toString());
ObjectMapper mapper = new ObjectMapper();
//Staff objStaff = new Staff();
System.out.println("Object to JSON in file");
mapper.writeValue(new File("output/file.json"), response);
System.out.println("Convert JSON string from file to Object");
//String about = mapper.readValue(new File("output/file.json"), String.class);
About about = mapper.readValue(new File("output/file.json"), About.class);
Error
Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of About: no String-argument constructor/factory method to deserialize from String value ('{"about":{"title":"NiFi","version":"1.1.0","uri":"https://localhost:443/api/","contentViewerUrl":"/nifi-content-viewer/","timezone":"CET"}}') at [Source: output/file.json; line: 1, column: 1]
Thanks for you help

Answer 1

The test json you show doesn't have the array wrapper used in your About object. You're also missing the version field in your AboutObject and the timezone field uses the wrong case.
Your example worked when I updated your objects:
public class About {
private AboutObject about;
public AboutObject getAbout() {
return about;
}
public void setAbout(AboutObject about) {
this.about = about;
}
}
public class AboutObject {
private String title;
private String uri;
private String contentViewerUrl;
private String timezone;
private String version;
public String getTitle() {
return this.title;
}
public void setTitle(String title) {
this.title = title;
}
public String getUri() {
return this.uri;
}
public void setUri(String uri) {
this.uri = uri;
}
public String getContentViewerUrl() {
return this.contentViewerUrl;
}
public void setContentViewerUrl(String contentViewerUrl) {
this.contentViewerUrl = contentViewerUrl;
}
public String getTimezone() {
return timezone;
}
public void setTimezone(String timezone) {
this.timezone = timezone;
}
public String getVersion() {
return version;
}
public void setVersion(String version) {
this.version = version;
}
}
Test:
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
String obj = "{\"about\":{\"title\":\"NiFi\",\"version\":\"1.1.0\",\"uri\":\"https://localhost:443/api/\",\"contentViewerUrl\":\"/nifi-content-viewer/\",\"timezone\":\"CET\"}}";
About about = mapper.readValue(obj, About.class);
}