In my REST application I am using fasterxml to serialize and deserialize POJOs to JSON. I run into problems with collections such as List in a case like this.
public class JsonRequest {
public int anumber;
public String astring;
public List<XyzClass> data;
}
The properties anumber and astring convert back and forth just fine without any annotations. For **data*, although the compiler can see that the List elements are (should be) XyzClass that information is not available to the jackson framework, so it doesn't know what class to use when deserializing the elements.
For some reason I can't make sense of the documentation as to which annotation to use to fix this. The #JsonDeserialize annotation doesn't help this. Can anyone point me in the right direction?
After some research I finally found out how to make this work.
public class JsonRequest {
public int anumber;
public String astring;
#JsonDeserialize(contentAs = XyzClass.class) // <-- Added
public List<XyzClass> data;
}
To answer the questions in comments above, the code for XyzClass is just a trivial POJO like:
public class XyzClass {
public String name;
public int age;
}
What was tripping me up is that I was looking for an annotation to the effect of #JsonDeserializeContentAs(class = XyzClass.class) which doesn't exist because I missed the fact that #JsonDeserilize had a contentAs option.
Hopefully this posting will save someone else the same trouble.
Related
I am returning a list of products of type ListProd in my Spring Boot controller, and such object has a nested property of type List<Product> ... something like this:
public class Product implements Serializable {
int codProdct;
String dsc;
public Product(){};
// plus getters and setters (omitted for simplicity)
}
public class ListProd implements Serializable {
int codList;
List<Product> products;
public ListProd(){};
// also here getters and setters
}
and in my angular project I have the next analogoust entities:
export class Product {
public codProduct:number;
public dsc:string;
constructor(){
codProduct=null; //just for completness
dsc='';
}
}
export class ListProd {
public codList:number;
public products:Product[];
constructor(){
this.codList=null; //just for completness
this.products=null;
}
}
I'm sending a ListProd object through my Spring controller and Angular gets such an object correctly and assigns the type also correctly:
return this.http.get<ListProd>(this.apiUrl + "/getListProds", httpOptions);
but ... it is only casting correctly the parent object, when I check the type of the 'products' object (which is recived correctly, only untyped) y get type: Object
I tried to make it a Products[] in my ListProd class in java, but i get the same result. I don't know much about the 'magic' Angular does to assign those types properly, am I missing something important here? Is there a chance to force the casting on the Angular side?
Thanks in advance.
Well, if ListProd is supposed to hold array of Product[] there is a typo here.
public products:Product[];
Not knowing full extent why you use class over an interface I would advise you also to go over this. Maybe there is a reason but for being able to strong type simple interface would be better. https://www.javatpoint.com/typescript-class-vs-interface
I have a model that looks like this (Play 2.1.1 java ebean)
#Entity
public class Link extends Model {
#Id
public Long id;
#Lob
public String points;
}
where points is a raw json string that contains x, y coordinates in an array.
I don't want to have to deserialize it to an array of Points, because it's only going to be used for the UI. and thus, I would like to save it to a text field in the database
I want the property points to get serialized as a json array when sent over the wire to the frontend and I want the frontend to be able to send an json array and make it into a string again.
In the controller:
// Serialize
List<Link> links = Link.findAll();
return ok(Json.toJson(links));
// Deserialize
Link link = Json.fromJson(request().body().asJson(), Link.class);
How should I do this?
Custom serializer, deserializer?
#JsonRawValue?
Any other annotation?
The answer was a lot simpler than you would suspect.
#Lob
public String points;
public JsonNode getPoints() {
return Json.parse(StringUtils.isBlank(points) ? "[]" : points);
}
#JsonSetter
public void setPoints(JsonNode json) {
points = json.toString();
}
Though I'm not that fond of getter's and setter's it works.
If anyone has a better solution that is more generic, feel free to post another answer :)
My question is, whether it is necessary to add #XmlElement before each element in your pojo to be picked up by jaxb, when making a JSON response. I am using jersey-json 1.17 . The reason I ask this is because, the example given on Jersey site does not use the annotation.
I get an out put as {}, but when I add #XmlElement before the attributes, I get the expected JSON output. Am I doing something wrong, because of which my JSON string is empty ?
My code :
The vertices list is populated in the constructor.
This produces the wrong output of {}
#XmlRootElement
public class SquareModel {
List<Float> vertices = new ArrayList<Float>();
....
}
Whereas this produces the a correct JSON string :
#XmlRootElement
public class SquareModel {
#XmlElement(name="vertices")
List<Float> vertices = new ArrayList<Float>();
....
}
My resource class which returns the JSON
#GET
#Produces(MediaType.APPLICATION_JSON)
public SquareModel getJsonString() {
return new SquareModel();
}
Thanks :)
No, by default a JAXB (JSR-22#) implementation will treat all public fields and properties (get/set combinations) as mapped (not requiring the #XmlElement annotation).
http://blog.bdoughan.com/2012/07/jaxb-no-annotations-required.html
If you wish to annotate a field I would recommend annotating your class with #XmlAccessorType(XmlAccessType.FIELD)
http://blog.bdoughan.com/2011/06/using-jaxbs-xmlaccessortype-to.html
According to this http://jersey.java.net/nonav/documentation/latest/json.html#json.jaxb.approach.section
You should have this annotation (I'm also using it in my code, even though it XML oriented, but it gives me cool JSON also)
Taking this approach will save you a lot of time, if you want to
easily produce/consume both JSON and XML data format. Because even
then you will still be able to use a unified Java model. Another
advantage is simplicity of working with such a model, as JAXB
leverages annotated POJOs and these could be handled as simple Java
beans.
A disadvantage of JAXB based approach could be if you need to work
with a very specific JSON format. Then it could be difficult to find a
proper way to get such a format produced and consumed. This is a
reason why a lot of configuration options are provided, so that you
can control how things get serialized out and deserialized back.
Following is a very simple example of how a JAXB bean could look like.
Example 5.3. Simple JAXB bean implementation
#XmlRootElement
public class MyJaxbBean {
public String name;
public int age;
public MyJaxbBean() {} // JAXB needs this
public MyJaxbBean(String name, int age) {
this.name = name;
this.age = age;
}
}
I have some json :
{
key: "CORE-19",
fields: { summary: "iblah" }
}
I want to pack it into a POJO that looks more like:
#JsonIgnoreProperties(ignoreUnknown=true)
public class JiraIssue
{
private String mKey;
private String mSummary;
public String getKey(){ return(mKey);}
public void setKey(String inKey){mKey = inKey;}
public String getSummary(){return(mSummary);}
public void setSummary(String summary){ mSummary = summary; }
}
So basically I don't want to create a 'Fields' object as it is a bit superfluous for my needs. However I really can't see any way in Jackson to tell it that the 'summary' property actually comes from the 'fields' property. Is this possible?
Serialization of this class is not a concern, it will only ever be used for Deserialization. I have no control over the JSON format as it is coming from an external source (and the above is just a snippet). Also I'm actually using Jackson with Jersey.
Thanks!
There is actually an open issue for this kind of structural change. There is no way as of now to do that easily with annotation only without modifying your class. What you could do instead is handle the "fields" property as a "false" property, by adding the following method:
public void setFields(Map<String, String> fields) {
setSummary(fields.get("summary"));
}
This way you "unwrap" the property yourself.
Try:
#JsonProperty("fields.summary")
private String mSummary;
I'm using JAXB/Jersey (1.3) to convert java to json in a REST API.
I read a lot about this problem, I tryed this solution, it work a half:
#XmlRootElement
public class ArrayWrapper
{
public List<String> list = new LinkedList<String>();
}
and my ContextResolver:
#Provider
public class JAXBContextResolver implements ContextResolver<JAXBContext> {
private JAXBContext context;
private Class[] types = {ArrayWrapper.class,Wrapper.class};
public JAXBContextResolver() throws Exception {
MappedBuilder builder = JSONConfiguration.mapped();
builder.arrays("list");
builder.rootUnwrapping(true);
this.context = new JSONJAXBContext(builder.build(), types);
}
ArrayWrapper aw=new ArrayWrapper();
aw.list.add("test");
I get {"list":["test"]} so it works but when I wrapp ArrayWrapper in an other class it don't work:
#XmlRootElement
public class Wrapper
{
public ArrayWrapper aw;
public Wrapper()
{
aw=new ArrayWrapper();
aw.list.add("test");
}
}
new Wrapper();
I get {"aw":{"list":"test"}}
Anyone know how to fix it?
I am not quite sure if you got it working so I am contributing my bit.
I also stumbled upon this issue recently. I found a post in stackoverflow that helped me, but even more helpful was this article (introducing Jackson might help).
I hope this helps you, too. For me it was a matter of 5 minutes to fix the issue.