When im tryin got do a Post request through my JAX-RS API it always sends a null value. I dont know if the Jackson annotations are incorrect or if i need to use an ObjectMapper.
These are my classes:
public class ClassA{
private String name;
private ClassB classB;
public ClassA(){}
public ClassA(String name, ClassB classB){
this.name = name;
this.classB = classB;
}
#JsonGetter
public String getName(){ return name; }
#JsonGetter
public ClassB getClassB(){ return classB; }
and this is the classB
public class ClassB{
#JsonProperty("type")
private String type;
#JsonProperty("number")
private int number;
public ClassB(){}
#JsonPropertyOrder({"type, number"})
public ClassB(String type, int number){
this.type= type;
this.number= number;
}
#JsonGetter
public String getType(){ return type; }
#JsonGetter
public int getNumber(){ return number; }
My JSON file:
{
"type": "typeExample;
"classB": {
"type": "classBTypeExample";
"int": 10;
}
}
I want Jackson to read the file and then add an Object type ClassA to a list (the problem is that is not even reading it)
This is the API code:
#Path("/path")
public class Requests {
private Set<ClassA> classesA = Collections.newSetFromMap(Collections.synchronizedMap(new LinkedHashMap<>()));
#GET
public Set<ClassA> list() {
return classesA;
}
#POST
public Set<ClassA> add(ClassA classA){
classesA.add(classA);
return classesA;
}
}
I already added the quarkus.jackson.fail-on-unknown-properties=true to the application.properies file
It was a simple thing that i didnt notice. I forgot to set the values on the constructer. So i just had to add the #ConstructorProperties({}) to the classes constructors and it worked out.
With a simple class/interface like this
public interface IThing
{
string Name { get; set; }
}
public class Thing : IThing
{
public int Id { get; set; }
public string Name { get; set; }
}
How can I get the JSON string with only the "Name" property (only the properties of the underlying interface) ?
Actually, when i make that :
var serialized = JsonConvert.SerializeObject((IThing)theObjToSerialize, Formatting.Indented);
Console.WriteLine(serialized);
I get the full object as JSON (Id + Name);
The method I use,
public class InterfaceContractResolver : DefaultContractResolver
{
private readonly Type _InterfaceType;
public InterfaceContractResolver (Type InterfaceType)
{
_InterfaceType = InterfaceType;
}
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
//IList<JsonProperty> properties = base.CreateProperties(type, memberSerialization);
IList<JsonProperty> properties = base.CreateProperties(_InterfaceType, memberSerialization);
return properties;
}
}
// To serialize do this:
var settings = new JsonSerializerSettings() {
ContractResolver = new InterfaceContractResolver (typeof(IThing))
};
string json = JsonConvert.SerializeObject(theObjToSerialize, settings);
Improved version with nested interfaces + support for xsd.exe objects
Yet another variation here. The code came from http://www.tomdupont.net/2015/09/how-to-only-serialize-interface.html with the following improvements over other answers here
Handles hierarchy, so if you have an Interface2[] within an Interface1 then it will get serialized.
I was trying to serialize a WCF proxy object and the resultant JSON came up as {}. Turned out all properties were set to Ignore=true so I had to add a loop to set them all to not being ignored.
public class InterfaceContractResolver : DefaultContractResolver
{
private readonly Type[] _interfaceTypes;
private readonly ConcurrentDictionary<Type, Type> _typeToSerializeMap;
public InterfaceContractResolver(params Type[] interfaceTypes)
{
_interfaceTypes = interfaceTypes;
_typeToSerializeMap = new ConcurrentDictionary<Type, Type>();
}
protected override IList<JsonProperty> CreateProperties(
Type type,
MemberSerialization memberSerialization)
{
var typeToSerialize = _typeToSerializeMap.GetOrAdd(
type,
t => _interfaceTypes.FirstOrDefault(
it => it.IsAssignableFrom(t)) ?? t);
var props = base.CreateProperties(typeToSerialize, memberSerialization);
// mark all props as not ignored
foreach (var prop in props)
{
prop.Ignored = false;
}
return props;
}
}
Inspired by #user3161686, here's a small modification to InterfaceContractResolver:
public class InterfaceContractResolver<TInterface> : DefaultContractResolver where TInterface : class
{
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
IList<JsonProperty> properties = base.CreateProperties(typeof(TInterface), memberSerialization);
return properties;
}
}
You can use conditional serialization. Take a look at this link. Basicly, you need to implement the IContractResolver interface, overload the ShouldSerialize method and pass your resolver to the constructor of the Json Serializer.
An alternative to [JsonIgnore] are the [DataContract] and [DataMember] attributes. If you class is tagged with [DataContract] the serializer will only process properties tagged with the [DataMember] attribute (JsonIgnore is an "opt-out" model while DataContract is "op-in").
[DataContract]
public class Thing : IThing
{
[DataMember]
public int Id { get; set; }
public string Name { get; set; }
}
The limitation of both approaches is that they must be implemented in the class, you cannot add them to the interface definition.
You can add the [JsonIgnore] annotation to ignore an attribute.
I'd like to share what we ended up doing when confronted with this task. Given the OP's interface and class...
public interface IThing
{
string Name { get; set; }
}
public class Thing : IThing
{
public int Id { get; set; }
public string Name { get; set; }
}
...we created a class that is the direct implementation of the interface...
public class DirectThing : IThing
{
public string Name { get; set; }
}
Then simply serialized our Thing instance, deserialized it as a DirectThing, then Serialized it as a DirectThing:
var thing = new Thing();
JsonConvert.SerializeObject(
JsonConvert.DeserializeObject<DirectThing>(JsonConvert.SerializeObject(thing)));
This approach can work with a long interface inheritance chain...you just need to make a direct class (DirectThing in this example) at the level of interest. No need to worry about reflection or attributes.
From a maintenance perspective, the DirectThing class is easy to maintain if you add members to IThing because the compiler will give errors if you haven't also put them in DirectThing. However, if you remove a member X from IThing and put it in Thing instead, then you'll have to remember to remove it from DirectThing or else X would be in the end result.
From a performance perspective there are three (de)serialization operations happening here instead of one, so depending on your situation you might like to evaluate the performance difference of reflector/attribute-based solutions versus this solution. In my case I was just doing this on a small scale, so I wasn't concerned about potential losses of some micro/milliseconds.
Hope that helps someone!
in addition to the answer given by #monrow you can use the default [DataContract] and [DataMember]
have a look at this
http://james.newtonking.com/archive/2009/10/23/efficient-json-with-json-net-reducing-serialized-json-size.aspx
Finally I got when it will not work...
If you want to have inside another complex object it will not be properly serialized.
So I have made version which will extract only data stored in specific assembly and for types which have the same base interface.
So it is made as .Net Core JsonContractResolver.
In addition to data extraction it solves:
a) camelCase conversion before sending data to client
b) uses top most interface from allowed scope (by assembly)
c) fixes order of fields: field from most base class will be listed first and nested object will meet this rule as well.
public class OutputJsonResolver : DefaultContractResolver
{
#region Static Members
private static readonly object syncTargets = new object();
private static readonly Dictionary<Type, IList<JsonProperty>> Targets = new Dictionary<Type, IList<JsonProperty>>();
private static readonly Assembly CommonAssembly = typeof(ICommon).Assembly;
#endregion
#region Override Members
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
if (type.Assembly != OutputJsonResolver.CommonAssembly)
return base.CreateProperties(type, memberSerialization);
IList<JsonProperty> properties;
if (OutputJsonResolver.Targets.TryGetValue(type, out properties) == false)
{
lock (OutputJsonResolver.syncTargets)
{
if (OutputJsonResolver.Targets.ContainsKey(type) == false)
{
properties = this.CreateCustomProperties(type, memberSerialization);
OutputJsonResolver.Targets[type] = properties;
}
}
}
return properties;
}
protected override string ResolvePropertyName(string propertyName)
{
return propertyName.ToCase(Casing.Camel);
}
#endregion
#region Assistants
private IList<JsonProperty> CreateCustomProperties(Type type, MemberSerialization memberSerialization)
{
// Hierarchy
IReadOnlyList<Type> types = this.GetTypes(type);
// Head
Type head = types.OrderByDescending(item => item.GetInterfaces().Length).FirstOrDefault();
// Sources
IList<JsonProperty> sources = base.CreateProperties(head, memberSerialization);
// Targets
IList<JsonProperty> targets = new List<JsonProperty>(sources.Count);
// Repository
IReadOnlyDistribution<Type, JsonProperty> repository = sources.ToDistribution(item => item.DeclaringType);
foreach (Type current in types.Reverse())
{
IReadOnlyPage<JsonProperty> page;
if (repository.TryGetValue(current, out page) == true)
targets.AddRange(page);
}
return targets;
}
private IReadOnlyList<Type> GetTypes(Type type)
{
List<Type> types = new List<Type>();
if (type.IsInterface == true)
types.Add(type);
types.AddRange(type.GetInterfaces());
return types;
}
#endregion
}
Rest Controller:
#RequestMapping(value = "/admin/rest/new-subscriptions")
public List<NewSubscriptionDTO> getNewSubscriptions() {
NewSubscriptionDTO dto = new NewSubscriptionDTO();
dto.setId("54");
dto.setName("John Doe");
return Arrays.asList(dto);
}
NewSubscriptionDTO:
package dermatica.web.admin.rx;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.joda.time.DateTime;
import java.io.Serializable;
public class NewSubscriptionDTO implements Serializable {
private String id;
private String name;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
I get the following exception:
no properties discovered to create BeanSerializer (to avoid exception,
disable SerializationFeature.FAIL_ON_EMPTY_BEANS)
If I annotate the fields with #JsonProperty it work fine.
Is there a way for the serialization to work automatically without needing this annotation?
#JsonProperty auto-generates a getter/setter that Jackson uses to read/write to the fields during serialization/deserialization. Here are some alternative approaches:
Provide your own public getters/setters for all fields
Make the fields public, generally frowned upon, but if you're creating a simple DTO, that may be acceptable.
Setting ObjectMapper Visibility for FIELD to ANY (see here)
Disable the FAIL_ON_EMPTY_BEANS exception (see here)
Given that your DTO class has getters and setters, this should work without #JsonProperty. I wasn't able to reproduce the exact error message you showed, but here are some suggestions that may help:
[Controller] Explicitly specify the method type as GET, either using method = GET or #GetMapping - not necessary, but it's good to be explicit
[Controller] Make sure you annotate the controller class with #RestController, indicating the response is serialized to JSON and wrapped in an HttpResponse object.
[DTO] You don't need to extend Serializable (see here).
The final controller would look like this:
#RestController
public class MyController {
#GetMapping(value = "/admin/rest/new-subscriptions")
public List<MyDTO> getDTO() {
MyDTO dto = new MyDTO();
dto.setId("54");
dto.setName("John Doe");
return Collections.singletonList(dto);
}
}
Response:
[{"id":"54","name":"John Doe"}]
I am trying to restrict which properties from a JSON object are deserialised using Jackson JSONViews. The aim is to use this to prevent consumers of my API from submitting data that they shouldn't.
The problem is, I have either misunderstood JSONViews or I am doing something wrong. See below.
I started trying to do this in Spring but have noticed that even the simple test below doesn't work.
Account Class
public class Account {
#Id
private String id;
private String name;
private List<String> items;
private List<User> users;
#JsonView(AccountViews.Private.class)
public void setId(String id) {
this.id = id;
}
#JsonView(AccountViews.Public.class)
public void setName(String name) {
this.name = name;
}
#JsonView(AccountViews.Public.class)
public void setItems(List<String> items) {
this.items = items;
}
#JsonView(AccountViews.Private.class)
public void setUsers(List<User> users) {
this.users = users;
}
}
Views
public class AccountViews {
public interface Public {}
public interface Private extends Public {}
}
Test
#Test
public void testDeserialization(){
ObjectMapper mapper = new ObjectMapper();
mapper.disable(MapperFeature.DEFAULT_VIEW_INCLUSION);
Account account = mapper.readerWithView(AccountViews.Public.class).forType(Account.class).readValue("{ \"name\": \"account1\", \"items\": [\"item1\"], \"users\": [ { \"firstname\": \"user1_firstname\", \"lastname\": \"user1_lastname\" }] }");
assertEquals(account.getName(), "account1");
assertNull(account.getUsers());
}
Unforunately, the 2nd assertion fails because Users has a user object inside.
Basically, even though "users" is a property of Account, I don't want the value to be deserialized because I have used the JSONView (AccountViews.Public.class). However, whatever I try it always seems to be deserialized and is present on the account object.
Any help much appreciated.
Error
`java.lang.AssertionError: expected null, but was:<[User#609db43b]>
at org.junit.Assert.fail(Assert.java:88)
at org.junit.Assert.failNotNull(Assert.java:755)
at org.junit.Assert.assertNull(Assert.java:737)
at org.junit.Assert.assertNull(Assert.java:747)
at`
Jackson throwing an exception in deserialization with protected access modifier.
I am trying to deserialize one object then accessing protected properties of parent class is throwing exception.
Class com.fasterxml.jackson.databind.deser.impl.FieldProperty can not
access a member "protected"
Make sure that Jackson can see protected fields. E.g.
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import static com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility.PROTECTED_AND_PUBLIC;
#JsonAutoDetect(fieldVisibility = PROTECTED_AND_PUBLIC)
class Person {
protected String name;
}
Or define getters and setters as needed. E.g. :
class Person {
protected String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}