I'm facing some difficulties while trying to convert JSON response which contains properties with under_score, to DTO with lowerCamelCase properties.
JSON for example:
{
"promoted_by": "",
"parent": "",
"caused_by": "jenkins",
"watch_list": "prod",
"u_automation": "deep",
"upon_reject": "cancel"
}
DTO for example:
#Data
public class TicketDTO {
private String promotedBy;
private String parent;
private String causedBy;
private String watchList;
private String uAutomation;
private String uponReject;
}
Mapper:
#Mapper(componentModel = "spring")
public interface ITicketMapper {
default TicketDTO toDTO(JsonObject ticket) {
Gson gson = new GsonBuilder()
.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE)
.create();
return gson.fromJson(incident, TicketDTO.class);
}
}
This example is not working of course, I would like to know if it's possible to do this conversion with Gson.
Appriciate your help.
You should use LOWER_CASE_WITH_UNDERSCORES
Using this naming policy with Gson will modify the Java Field name from its camel cased form to a lower case field name where each word is separated by an underscore (_).
Here's a few examples of the form "Java Field Name" ---> "JSON Field Name":
someFieldName ---> some_field_name
someFieldName ---> _some_field_name
aStringField ---> a_string_field
aURL ---> a_u_r_l
setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
The UPPER_CAMEL_CASE is used for different purpose
Using this naming policy with Gson will ensure that the first "letter" of the Java field name is capitalized when serialized to its JSON form.
{
"id":100,
"name":"Ram",
"flag" : FALSE,
"dept" :"Software"
}
Above is my JSON input format for one of my Spring 4.x REST API. Following is my DTO.
public class EmployeeDTO {
private long id;
private String name;
private Boolean flag;
private String dept;
//getXXX & setXXX
}
If I am passing any extra parameters like below, additional parameters are ignored by the application (by default, please correct if my assumption is wrong).
{
"id":100,
"name":"Ram",
"flag" : FALSE,
"dept" :"Software"
"extra1":"unwanted",
"extra2" :"This also unwanted"
}
But, I do not want any extra fields to be in the input format, rather I want to restrict only DTO variables to be included in the input JSON. Can anyone help me in this.
Thanks in advance.
Suppose I have the following JPA entities:
#Entity
public class Inner {
#Id private Long id;
private String name;
// getters/setters
}
#Entity
public class Outer {
#Id private Long id;
private String name;
#ManyToOne private Inner inner;
// getters/setters
}
Both Spring and java EE have REST implementations with default serializers which will marshall the entities to/from JSON without further coding. But when converting Outer to JSON, both Spring and EE nest a full copy of Inner within it:
// Outer
{
"id": "1234",
"name": "MyOuterName",
"inner": {
"id": "4321",
"name": "MyInnerName"
}
}
This is correct behavior but problematic for my web services, since the object graphs can get deep/complex and can contain circular references. Is there any way to configure the supplied marshaller to marshall the POJOs/entities in a "shallow" way instead without having to create a custom JSON serializer for each one? One custom serializer that works on all entities would be fine. I'd ideally like something like this:
// Outer
{
"id": "1234",
"name": "MyOuterName",
"innerId": "4321"
}
I'd also like it to "unmarshall" the JSON back into the equivalent java object. Bonus kudos if the solution works with both Spring and java EE. Thanks!
After many problems I give reason to Cássio Mazzochi Molin saying that "the use of entities persistence in your REST API can not be a good idea"
I would do that the business layer transform persistence entities to DTO.
You can do this very easily with libraries like mapstruct
If you still want to continue with this bad practice you can use jackson and customize your jackson mapper
To unscramble complex object graphs using jaxb #XmlID and #XmlIDREF is made for.
public class JSONTestCase {
#XmlRootElement
public static final class Entity {
private String id;
private String someInfo;
private DetailEntity detail;
#XmlIDREF
private DetailEntity detailAgain;
public Entity(String id, String someInfo, DetailEntity detail) {
this.id = id;
this.someInfo = someInfo;
this.detail = detail;
this.detailAgain = detail;
}
// default constructor, getters, setters
}
public static final class DetailEntity {
#XmlID
private String id;
private String someDetailInfo;
// constructors, getters, setters
}
#Test
public void testMarshalling() throws JAXBException {
Entity e = new Entity( "42", "info", new DetailEntity("47","detailInfo") );
JAXBContext context = org.eclipse.persistence.jaxb.JAXBContextFactory.createContext(new Class[]{Entity.class}, null);
Marshaller m = context.createMarshaller();
m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
m.setProperty(MarshallerProperties.MEDIA_TYPE, "application/json");
m.setProperty(MarshallerProperties.JSON_INCLUDE_ROOT, false);
m.marshal(e, System.out);
}
}
This will result in the following json-fragment
{
"detailAgain" : "47",
"detail" : {
"id" : "47",
"someDetailInfo" : "detailInfo"
},
"id" : "42",
"someInfo" : "info"
}
Unmarshalling of this json will ensure that detail and detailAgain are the same instances.
The two annotations are part of jaxb, so it will work in Spring as well as in java EE. Marshalling to json is not part of the standard, so i use moxy in the example.
Update
Explicitly using moxy is not neccessary in a JAX-RS Resource. The following snipped perfectly runs on a java-EE-7 container (glassfish 4.1.1) and results in the above json-fragment:
#Stateless
#Path("/entities")
public class EntityResource {
#GET
#Produces(MediaType.APPLICATION_JSON)
public Entity getEntity() {
return new Entity( "42", "info", new DetailEntity("47","detailInfo") );
}
}
I had the same problem and ended up using jackson annotations on my Entities to control the serialization:
What you need is #JsonIdentityReference(alwaysAsId=true) to instruct the bean serializer that this reference should be only an ID. You can see an example on my repo:
https://github.com/sashokbg/company-rest-service/blob/master/src/main/java/bg/alexander/model/Order.java
#OneToMany(mappedBy="order", fetch=FetchType.EAGER)
#JsonIdentityReference(alwaysAsId=true) // otherwise first ref as POJO, others as id
private Set<OrderDetail> orderDetails;
If you want a full control of how your entities are represented as JSON, you can use JsonView to define which field is serialized related to your view.
#JsonView(Views.Public.class)
public int id;
#JsonView(Views.Public.class)
public String itemName;
#JsonView(Views.Internal.class)
public String ownerName;
http://www.baeldung.com/jackson-json-view-annotation
Cheers !
for this problem There are two solutions.
1-using jackson json view
2- Createing two mapping classe for innner entity. one of them includes custom fields and another one includes all fields ...
i think jackson json view is better solution ...
Go through the FLEXJSON library to smartly include/exclude nested class hierarchy while serializing Java objects.
Examples for flexjson.JSONSerializer presented here
You can detach the JPA entity before serialization, if you use lazyloading it's avoid to load sub objects.
Another way, but is depend of the JSON serializer API, you can use "transient" or specifics annotation.
Why does JPA have a #Transient annotation?
A bad way is to use tool like dozer to copy JPA object in another class with only the properties need for json (but it works... little overhead of memory, CPU and time...)
#Entity
public class Outer {
#Id private Long id;
private String name;
#ManyToOne private Inner inner;
//load manually inner.id
private final Long innerId;
// getters/setters
}
Assume I have the following class:
public class ChildEntity {
...
#ManyToOne
private ParentEntity parent;
...
}
Now, I have a REST endpoint that retrieves a child entity object from the database, thus my JSON is the following:
{"id": "123", "name":"someName", "parent": { //parent fields here } ... }
I want to format my JSON responses in another way. I want parent display only the id from the database, instead of the whole object:
{"id": "123", "name":"someName", "parentId": "1" ... }
Basically returning entities directly from endpoints isn't a good idea. You make very tight coupling between DB model and responses. Instead, implement a POJO class that will be equivalent of the HTTP response you sent.
This POJO will have all ChildEntity fields and parentId only and will be constructed in HTTP layer.
Please, see the discussion in comments, basically such an object returned from web layer is not a DTO according to me.
I am annotating #JsonIgnore which ever field I do not want to be part of JSON response. Creating parallel POJO for each entity is costly affair.
#JsonIgnore
#NotNull
#Column(name="DELETED")
private boolean deleted = false;
I've got a strange mapping Issue with Jackson on Android.
I've got a "Content" Class which should be used by the Jackson Mapper.
It looks like this:
public class content {
private String header;
private String subheader;
private String bodytext;
#JsonProperty("singleimage")
private String image;
#JsonProperty("uid")
private String id;
#JsonProperty("link")
private String article;
#JsonProperty("CType")
private String cType;
// Eclipse auto generated getters & setters
...
}
The corresponding JSON Object looks like this:
{
"header": "xyz",
"subheader": "abc",
"bodytext": "abc",
"singleimage": "abc",
"images": "abc.jpg",
"teaser_elements": "",
"uid": "13",
"link": "xyz.htm",
"CType": "row_header"
}
Now when I use the Jackson Maper to create instances of Content from a provided JSON all fields of the content class get populated correctly - all except "cType".
I already tried to move the #JsonProperty("CType") annotation to the setCType Method but still no effect.
I don't get any Exceptions while mapping the class or anything else and as it seems to me that all mappings pretty much do the same (mapping to String) im kinda buffled why it doesn't work wit the "CType".
Any suggestions what the problem might be are highly appreciated.