I am beginner in Jackson. I am trying this -:
public class A {
boolean property1;
String property2;
// public getters and setters for both
}
public abstract class MixIn {
#JsonIgnore
boolean property1;
}
ObjectMapper mapper = new ObjectMapper();
mapper.addMixInAnnotations(A.class, MixIn.class);
Now,
String result = mapper.writeValueAsString(new A())
gives me result like this - {"property2" : "value"} which is correct but if try to convert the result in the object again -:
mapper.readValue(result, A.class);
I am getting property1 back object A this -:
A {property1 : false, property2 : value}
Why is objectMapper not ignoring the property again. Note - I tried directly putting #JsonIgnore on property1 and it worked fine but I have to use MixIn for this. I had tried putting JsonIgnore on getter and setters in MixIn too but that didn't work too.
Ok. I got it now. #JsonIgnore means that the property won't be written in the serialized string but if any string would be deserialized the same property would have defaults which in case of a boolean is always false which I realised when I tried with adding more properties so mix-in is actually working. It's just that I thought that in some magical way it would remove the property from the object itself. (I know it's silly.)
Related
I have a class with the following fields and their respective getters, plus an additional method getTotalBalance for which I don't have any field but a custom implementation.
public class demo{
private String balance;
private String blockedBalace;
private String futureBalance;
private String availableBalance;
//getters for previous fields
public String getTotalBalance(){
//something..
}
When I serialize an object of this class I get the following JSON output.
{
"balance": "12.30",
"blockedBalance":"23.45",
"futureBalance" :"56.22",
"availableBalance" :"12.30",
"totalBalance" : "34.11"
}
Even if I didn't declare a field for totalBalance, I've got this serialized in the end. How is it possible?
Jackson by default uses the getters for serializing and setters for deserializing.
You can use #JsonIgnore over your getter method to ignore it, OR you can configure your object mapper to use the fields only for serialization/des:
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.NONE);
objectMapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
Jackson doesn't (by default) care about fields. It will simply serialize everything provided by getters and deserialize everything with a matching setter. What those getters/setters do is of no consequence.
Mind you though, that every little thing about Jackson can be deeply customized and configured, so I'm only talking about the default setup.
i am trying to map certain json fields to a class instance variable.
My sample Person class looks like:
public class Person {
private String name;
private Address address;
//many more fields
//getters and setters
}
The sample Address class is:
public class Address {
private String street;
private String city;
//many more fields
// getters and setters
}
The json object to be deserialized to my Person class doesn't contain "address" field. It looks like:
{
"name":"Alexander",
"street":"abc 12",
"city":"London"
}
Is there a way to deserialize the json to the Person pojo where the Address fields are also mapped properly?
I have used a custom Address deserializer as mentioned in so many posts here. However, it's not being called as the Json object doesn't contain "address" field.
I had resolved this problem by mapping each field manually using JsonNode, however in my real project, it's not a nice solution.
Is there any work around for such problem using jackson?
Plus if this question has been asked before then apologies on my behalf as as i have intensively searched for the solution and might have not seen it yet. .
#JsonUnwrapped annotation was introduced for this problem. Model:
class Person {
private String name;
#JsonUnwrapped
private Address address;
// getters, setters, toString
}
class Address {
private String street;
private String city;
// getters, setters, toString
}
Usage:
ObjectMapper mapper = new ObjectMapper();
String json = "{\"name\":\"Alexander\",\"street\":\"abc 12\",\"city\":\"London\"}";
System.out.println(mapper.readValue(json, Person.class));
Prints:
Person{name='Alexander', address=Address{street='abc 12', city='London'}}
For more info read:
Jackson Annotation Examples
Annotation Type JsonUnwrapped
Jackson JSON - Using #JsonUnwrapped to serialize/deserialize properties as flattening data structure
I don't think you really have a deserialization problem here but rather a general Java problem: how to make sure the address field always contains a value. All you need to do is either assign address to a default value in the Person constructor, or generate and assign a default value for address in the Person.getAddress method.
I understood your problem so that it is about flat Json that has all Address fields at the same level as Person. Even if it is not exactly so this might help you. JsonDeserializer will do fine but you need to apply it to Person because it is the level where all the fields are.
So like this:
public class CustomDeserializer extends JsonDeserializer<Person> {
// need to use separate ObjectMapper to prevent recursion
// this om will not be registered with this custom deserializer
private final ObjectMapper om;
{
om = new ObjectMapper();
// this is needed because flat json contains unknown fields
// for both types.
om.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
}
#Override
public Person deserialize(JsonParser parser, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
// make a string of json tree so not any particular object
String json = om.readTree(parser).toString();
// deserialize it as person (ignoring unknown fields)
Person person = om.readValue(json, Person.class);
// set address deserializing it from teh same string, same manner
person.setAddress(om.readValue(json, Address.class));
return person;
}
}
Of course this is not the only way and might not have the best performance but it is only about how you do the deserialization in your custom deserializer. If your Person & Address objects are havin like 10 fields each using this should not be a problem.
Update
I think that in your case - based on your example data - Michał Ziober's
answer might be the best but if you need any more complex handling than plain unwrapping for your data you just need to deserialize Person class somehow like I presented.
Is it possible to have the #JsonProperty required dynamically set or set at call?
The reason behind this...
I'm generating json files which describes a schema and defines
What are the required fields for a new item
What are the required fields for an update to an item.
So, a creation requires only foo
and an update requires foo and bar
Can I make things so I can pass in something to say bar is now required?
or would I need to duplicate this code in order to have different settings for JsonProperty?
#JsonInclude(Include.NON_NULL)
public class Bean {
#JsonProperty(value="foo", required=false)
private FooProperty fooProperty;
#JsonProperty(value="bar", required=false)
private BarProperty barProperty;
//
public FooProperty getFooProperty() { return fooProperty; }
public void setFooProperty(FooProperty argFooProperty) {
this.fooProperty = argFooProperty
}
public BarProperty getBarProperty() { return barProperty; }
public void setFooProperty(BarProperty argBarProperty) {
this.barProperty = argBarProperty
}
}
You could solve this issue in couple of ways. First one would be as Franjavi suggested you could use a mixin.
Have a mixin class which will mark your foo as one of the ignored properties. In your main class mark both the fiends required and you can inject this mixin whenever this is an option field.
#JsonIgnoreProperties("foo")
public abstract class mixinClass {
}
You configure your mixin into your mapper as follows.
ObjectMapper mapper = new ObjectMapper();
mapper.addMixInAnnotations(Bean.class, mixinClass.class);
This is not always a working option whenever you are getting this response from a third party API where you might be serializing/deserializing using the default jackson mapper which are provided by them like Resttemplate.
In this case, instead of having the foo property, you can just included whatever the properties that are present in all the responses and handle the rest of the properties using #JsonAnyGetter and #JsonAnySetter. You can capture this in a map with key being your object name which is in this case foo. You need to have the following part in your parent node or whichever node that will encapsulates these optional properties.
#JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();
#JsonAnyGetter
public Map<String, Object> getAdditionalProperties() {
return this.additionalProperties;
}
#JsonAnySetter
public void setAdditionalProperty(String name, Object value) {
this.additionalProperties.put(name, value);
}
Let me know if you need any further clarification!!
You can play wiht Mixins and the mapper:
public interface BarRequiredMixIn {
#JsonProperty(value="bar", required=true)
private BarProperty barProperty;
}
ObjectMapper mapper = new ObjectMapper();
// When you want that it is required
mapper.addMixInAnnotations(Bean.class, BarRequiredMixIn.class);
But I strongly recommend to avoid to use this kind of conditional restrictions with Jackson, since it is not designed for it, and it looks kind of confusing.
Based on the example you have given, setting the following in your POJO would be sufficient & Jackson would be able to figure out whether to deserialize it/not . All #JsonProperty are required by default, so with the code below, you would be able to achieve optional bar value in your Create/Update scenarios based on payload in the request
#JsonProperty(value="bar", required=false)
private Bar bar;
I'd like to go further on what this question was about, I've been roaming SO for a solid hour now without finding anything.
Basically, what I'm trying to do is having a property properly instanciated through Jackson internal reflection algorithm during deserialization but having this same property not serialized when it comes to serialization.
I know about #JsonIgnore and #JsonIgnoreProperties but apparently I can't seem to use them right : either my property is correctly deserialized when I feed Jackson a proper map of properties but it also appears in the serialized results, either (when using #JsonIgnore) it is not serialized (which is wanted) but also not deserialized (not wanted).
Example :
public class Foo {
/* This is the property I want to be instanciated by Jackson upon deserialization
* but not serialized upon serialization
*/
private final Object bar = null;
public Object getBar() {
return bar;
}
}
To make things worse, as you can see, the property is final (this is why I'm keen on using Jackson reflection ability upon Foo instanciation through deserialization). I've read on potential solution about annotating the setter and the getter differently but I'd like to keep this property final if possible. If not possible, I'd settle for a non-final property.
I would appreciate answers not suggesting custom serializer/deserializer, my code base is currently free of such and if the solution could be of minimal impact, that would be perfect. Again, I'm no Jackson expert so if what I'm asking is not possible I'll obviously accept alternative answers.
I've also read this thread on github but none of the suggested ways of implementation have actually been implemented at the moment.
Thanks
EDIT : to make things clearer
public class Foo {
private final String bar = null;
public String getBar() {
return bar;
}
#Override
public String toString() {
return bar;
}
}
public void testMethod() throws IOException {
String json = "{\"bar\":\"Value\"}";
ObjectMapper mapper = new ObjectMapper();
Foo foo = mapper.readValue(json, Foo.class);
System.out.println(foo); // should have a bar property set to "Value"
System.out.println(mapper.writeValueAsString(foo)); // should return an empty JSON object
}
I am not sure whether it is elegant solution but you can use MixIn feature. You have to create new interface which could look like below:
interface FooMixIn {
#JsonIgnore
String getBar();
}
Assume that your POJO looks like this:
class Foo {
private final String bar = null;
public String getBar() {
return bar;
}
#Override
public String toString() {
return bar;
}
}
Now you have to tell Jackson that you want to ignore this property:
String json = "{\"bar\":\"Value\"}";
System.out.println(json);
ObjectMapper deserializeMapper = new ObjectMapper();
deserializeMapper.addMixInAnnotations(Foo.class, FooMixIn.class);
System.out.println(deserializeMapper.readValue(json, Foo.class));
Above example prints:
{"bar":"Value"}
null
Without deserializeMapper.addMixInAnnotations(Foo.class, FooMixIn.class); line above program prints:
{"bar":"Value"}
Value
EDIT 1
If you want to achieve result like you showed you have to create two ObjectMappers and customize them. See below example:
String json = "{\"bar\":\"Value\"}";
ObjectMapper deserializerMapper = new ObjectMapper();
Foo foo = deserializerMapper.readValue(json, Foo.class);
System.out.println("Foo object: " + foo);
ObjectMapper serializerMapper = new ObjectMapper();
serializerMapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
serializerMapper.addMixInAnnotations(Foo.class, FooMixIn.class);
System.out.println("JSON: " + serializerMapper.writeValueAsString(foo));
For serialization you have to use one instance and for deserialization you have to use another instance.
Starting with Jackson 2.6, a property can be marked as read- or write-only. It's simpler than hacking the annotations on both accessors (for non-final fields) and keeps all the information in one place. It's important to note that a final field is considered writable by default by Jackson.
However, it's not enough for a final field to allow deserialization, because you can't have a setter on that field: it needs to be set via the constructor, either directly or using a builder or another type that can be deserialized by Jackson. When using the constructor with the properties as parameters, you need to specify which parameter corresponds to which property, using #JsonProperty:
public class Foo {
#JsonProperty(access = JsonProperty.Access.WRITE_ONLY)
private final String bar;
public Foo(#JsonProperty("bar") String bar) {
this.bar = bar;
}
public String getBar() {
return prop;
}
}
I'm calling a rest service that returns a json object. I'm trying to deserialize the responses to my Java Beans using Jackson and data-binding.
The example Json is something like this:
{
detail1: { property1:value1, property2:value2},
detail2: { property1:value1, property2:value2},
otherObject: {prop3:value1, prop4:[val1, val2, val3]}
}
Essentially, detail1 and detail2 are of the same structure, and thus can be represented by a single class type, whereas OtherObject is of another type.
Currently, I've set up my classes as follows (this is the structure I would prefer):
class ServiceResponse {
private Map<String, Detail> detailMap;
private OtherObject otherObject;
// getters and setters
}
class Detail {
private String property1;
private String property2;
// getters and setters
}
class OtherObject {
private String prop3;
private List<String> prop4;
// getters and setters
}
Then, just do:
String response = <call service and get json response>
ObjectMapper mapper = new ObjectMapper();
mapper.readValue(response, ServiceResponse.class)
The problem is I'm getting lost reading through the documentation about how to configure the mappings and annotations correctly to get the structure that I want. I'd like detail1, detail2 to create Detail classes, and otherObject to create an OtherObject class.
However, I also want the detail classes to be stored in a map, so that they can be easily distinguished and retrieved, and also the fact that the service in in the future will return detail3, detail4, etc. (i.e., the Map in ServiceResponse would look like
"{detail1:Detail object, detail2:Detail object, ...}).
How should these classes be annotated? Or, perhaps there's a better way to structure my classes to fit this JSON model? Appreciate any help.
Simply use #JsonAnySetter on a 2-args method in ServiceResponse, like so:
#JsonAnySetter
public void anySet(String key, Detail value) {
detailMap.put(key, value);
}
Mind you that you can only have one "property" with #JsonAnySetter as it's a fallback for unknown properties. Note that the javadocs of JsonAnySetter is incorrect, as it states that it should be applied to 1-arg methods; you can always open a minor bug in Jackson ;)