I have a a map that looks like this:
public class VerbResult {
#JsonProperty("similarVerbs")
private Map<Verb, List<Verb>> similarVerbs;
}
My verb class looks like this:
public class Verb extends Word {
#JsonCreator
public Verb(#JsonProperty("start") int start, #JsonProperty("length") int length,
#JsonProperty("type") String type, #JsonProperty("value") VerbInfo value) {
super(length, length, type, value);
}
//...
}
I want to serialize and deserialize instances of my VerbResult class, but when I do I get this error: Can not find a (Map) Key deserializer for type [simple type, class my.package.Verb]
I read online that you need to tell Jackson how to deserialize map keys, but I didn't find any information explaining how to go about doing this. The verb class needs to be serialized and deserialzed outside of the map as well, so any solution should preserve this functionality.
Thank you for your help.
After a day of searching, I came across a simpler way of doing it based on this question. The solution was to add the #JsonDeserialize(keyUsing = YourCustomDeserializer.class) annotation to the map. Then implement your custom deserializer by extending KeyDeserializer and override the deserializeKey method. The method will be called with the string key and you can use the string to build the real object, or even fetch an existing one from the database.
So first in the map declaration:
#JsonDeserialize(keyUsing = MyCustomDeserializer.class)
private Map<Verb, List<Verb>> similarVerbs;
Then create the deserializer that will be called with the string key.
public class MyCustomDeserializer extends KeyDeserializer {
#Override
public MyMapKey deserializeKey(String key, DeserializationContext ctxt) throws IOException, JsonProcessingException {
//Use the string key here to return a real map key object
return mapKey;
}
}
Works with Jersey and Jackson 2.x
As mentioned above the trick is that you need a key deserializer (this caught me out as well). In my case a non-String map key was configured on my class but it wasn't in the JSON I was parsing so an extremely simple solution worked for me (simply returning null in the key deserializer).
public class ExampleClassKeyDeserializer extends KeyDeserializer
{
#Override
public Object deserializeKey( final String key,
final DeserializationContext ctxt )
throws IOException, JsonProcessingException
{
return null;
}
}
public class ExampleJacksonModule extends SimpleModule
{
public ExampleJacksonModule()
{
addKeyDeserializer(
ExampleClass.class,
new ExampleClassKeyDeserializer() );
}
}
final ObjectMapper mapper = new ObjectMapper();
mapper.registerModule( new ExampleJacksonModule() );
Building on the answer given here that suggests to implement a Module with a deserializer. The JodaTime Module is an easy to understand full example of a module containing serializers and deserializers.
Please note that the Module feature was introduced in Jackson version 1.7 so you might need to upgrade.
So step by step:
create a module containing a (de)serializer for your class based on the Joda example
register that module with mapper.registerModule(module);
and you'll be all set
Assuming we have a Map property, like the following:
class MyDTO{
#JsonSerialize(keyUsing = MyObjectKeySerializer.class)
#JsonDeserialize(keyUsing = MyObjectKeyDeserilazer.class)
private Map<MyObjectKey , List<?>> map;
}
We serilize the MyObjectKey as a json string, while call objectMapper.writeAsString；
And deserilize from the json string,to MyObjectKey
public class MyObjectKeySerializer extends StdSerializer<MyObjectKey> {
public Serializer() {
super(MyObjectKey.class);
}
#Override
public void serialize(MyObjectKey value, JsonGenerator gen, SerializerProvider provider) throws IOException {
gen.writeFieldName(JsonUtil.toJSONString(value));
}
}
public class MyObjectKeyDeserializer extends KeyDeserializer {
#Override
public Object deserializeKey(String key, DeserializationContext ctxt) throws IOException {
return JsonUtil.toObject(key, MyObjectKey.class);
}
}
After scouring the web, I think I have a decent solution for how to handle POJO-style keys (although, as always, you are best served not using a full object as a map key).
Serializer (registered as a Jackson module, inside of Spring Boot):
#Bean
fun addKeySerializer(): Module =
SimpleModule().addKeySerializer(YourClass::class.java, YourClassSerializer())
class YourClassSerializer() : JsonSerializer<YourClass>() {
override fun serialize(value: DataElement, gen: JsonGenerator, serializers: SerializerProvider) {
gen.writeFieldName(jacksonObjectMapper().writeValueAsString(value))
}
}
(note that, in a standard Java environment, you will have to instantiate your own objectMapper instance here)
Deserializer:
#Bean
fun addKeyDeserializer(): Module =
SimpleModule().addKeyDeserializer(YourClass::class.java, YourClassDeserializer())
class YourClassDeserializer() : KeyDeserializer() {
override fun deserializeKey(key: String, ctxt: DeserializationContext): YourClass? {
return ctxt.parser.readValueAs(YourClass::class.java)
}
}
Related
I want the ability to serialize a field in an object based on the JsonView. It doesn't have to be JsonView, it's just what I have been exploring. Basically using #JsonView annotation on RestController class, it would serialize my POJO.
However I have a User and Admin view where there is an object:
Map secrets;
That for an Admin view I want both key:value to show up and serialize, but for a User I would only want a List keys or if its simpler, keep Map but only show the key and all of the values switch to '****' 4 asteriks or something.
I thought about having two getters but the JsonView annotation doesn't work like that where two getters can have different views and Jackson knows which one to call.
I'm not sure JsonView is the best thing here. Perhaps a JsonGetter method that serializes based on view or some custom serializer, but I think there might be a more straightforward way to do it with Jackson and few annotations
What I am looking to do is:
Person.java
Map<String,String> secrets;
This would serialize to (for Admin):
{
"person":{
"secrets":{
"password":"123456",
"creditCard":"1234 5678 9101"
}
}
}
This would serialize to (for User):
{
"person":{
"secrets":{
"password":"****",
"creditCard":"****"
}
}
}
However what I would envision what I could do is something like
#JsonView(View.User.class)
Map<String,String> getSecrets(){
this.secrets.forEach(value -> "****") //code would be different but basically setting all values to ****
return secrets;
}
#JsonView(View.Admin.class)
Map<String,String> getSecrets(){
//Returning secrets as they should be
return secrets;
}
You can try defining a custom serializer for the object mapper , so that whenever the object mapper is used for serialization you can check and convert the password and credit card field to the value you choose.For example
public class ItemSerializer extends StdSerializer<Item> {
public ItemSerializer() {
this(null);
}
public ItemSerializer(Class<Item> t) {
super(t);
}
#Override
public void serialize(
Item value, JsonGenerator jgen, SerializerProvider provider)
throws IOException, JsonProcessingException {
jgen.writeStartObject();
jgen.writeNumberField("id", value.id);
jgen.writeStringField("itemName", value.itemName);
jgen.writeNumberField("owner", value.owner.id);
jgen.writeEndObject();
}
}
You can provide an object mapper that utilizes this custom serializer then,
Item myItem = new Item(1, "theItem", new User(2, "theUser"));
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addSerializer(Item.class, new ItemSerializer());
mapper.registerModule(module);
String serialized = mapper.writeValueAsString(myItem);
In your case you can register the objectmapper bean with the custom serializer in the spring context and make jackson use your object mapper bean.
Or using #JsonSerialize annotation like :
public class Event {
public String name;
#JsonSerialize(using = CustomDateSerializer.class)
public Date eventDate;
}
Public class CustomDateSerializer extends StdSerializer<Date> {
private static SimpleDateFormat formatter
= new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
public CustomDateSerializer() {
this(null);
}
public CustomDateSerializer(Class<Date> t) {
super(t);
}
#Override
public void serialize(
Date value, JsonGenerator gen, SerializerProvider arg2)
throws IOException, JsonProcessingException {
gen.writeString(formatter.format(value));
}
}
Refer:
https://www.baeldung.com/jackson-json-view-annotation
https://www.baeldung.com/jackson-custom-serialization
I'm looking to have multiple jackson deserializers for the same object(s) all based on a custom annotation.
Ideally I'd have a single POJO like:
public class UserInfo {
#Redacted
String ssn;
String name;
}
Under "normal" conditions I want this object to be serialized the default way:
{"ssn":"123-45-6789", "name":"Bob Smith"}
but for logging purposes (for example) I want to redact the SSN so it doesn't get saved in our logs:
{"ssn":"xxx-xx-xxxx", "name":"Bob Smith"}
I've also looked into using #JsonSerialize and come up with:
public class UserInfo {
#JsonSerialize(using = RedactedSerializer.class, as=String.class)
String firstName;
String lastName;
}
The problem with this is that it ALWAYS uses this rule. Can multiple #JsonSerializers be added and only the specified one be used within the runtime code?
I've also seen "views" but ideally I'd like to atleast show that the field was present on the request - even if I dont know the value.
The 100% safe way would be to use different DTO in different requests. But yeah, if you cant do that, use #JsonView and custom serializer, something like:
class Views {
public static class ShowSSN {}
}
private static class MyBean{
#JsonSerialize(using = MyBeanSerializer.class)
#JsonView(Views.ShowSSN.class)
String ssn;
//getter setter constructor
}
private class MyBeanSerializer extends JsonSerializer<String> {
#Override
public void serialize(String value, JsonGenerator gen,
SerializerProvider serializers) throws IOException {
Class<?> jsonView = serializers.getActiveView();
if (jsonView == Views.ShowSSN.class)
gen.writeString(value); // your custom serialization code here
else
gen.writeString("xxx-xx-xxxx");
}
}
And use it like:
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
MyBean bean = new MyBean("123-45-6789");
System.out.println(mapper.writerWithView(Views.ShowSSN.class)
.writeValueAsString(bean));
// results in {"ssn":"123-45-6789"}
System.out.println(mapper.writeValueAsString(bean));
// results in {"ssn":"xxx-xx-xxxx"}
}
Also for example in spring it would be really easy to use
#Controller
public class MyController {
#GetMapping("/withView") // results in {"ssn":"123-45-6789"}
#JsonView(Views.ShowSSN.class)
public #ResponseBody MyBean withJsonView() {
return new MyBean("123-45-6789");
}
#GetMapping("/withoutView") // results in {"ssn":"xxx-xx-xxxx"}
public #ResponseBody MyBean withoutJsonView() {
return new MyBean("123-45-6789");
}
}
I think you could achieve that dynamically by coding not annotations,
inside your methods, you can set the proper Serializer and switch between them
(The code depends on your Jackson version)
ObjectMapper mapper = new ObjectMapper();
SimpleModule testModule = new SimpleModule("MyModule", new Version(1, 0, 0, null));
testModule.addSerializer(new RedactedSerializer()); // assuming serializer declares correct class to bind to
mapper.registerModule(testModule);
https://github.com/FasterXML/jackson-docs/wiki/JacksonHowToCustomSerializers
Is there a way by which Jackson allows custom serialization for a specific type only in a particular class?
Here is my scenario:
I have ClassA.java which is something like:
public Class ClassA {
byte[] token;
String name;
public getToken() {
return token;
}
public setToken(byte[] newToken) {
token = newToken;
}
public getName() {
return name;
}
public setName(String newName) {
name = newName;
}
}
I do not have access to this class as it is in an external jar. However, I want to serialize the token byte array here in a particular manner. I have created a Custom serializer that does that and tries adding it to the mapper in all the ways mentioned in Jackson docs.
public class ByteArrayJacksonSerializer extends JsonSerializer<byte[]> {
public void serialize(byte[] value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
String token = doMyThing(value);
jgen.writeString(token);
}
}
And in mapper, something like this:
public class MyObjectMapper extends ObjectMapper {
CustomSerializerFactory sf = new CustomSerializerFactory();
sf.addGenericMapping(byte[].class, new ByteArrayJacksonSerializer());
this.setSerializerFactory(sf);
and some more code here...
}
However I can do it only for byte[] in general, and not for ONLY byte[] in ClassA. Is there a way to let Jackson know that this custom serializer must be used ONLY for fields of byte[] type in ClassA, and to do serialization it's own way for all other classes?
You should use MixIn feature. In your example you have to create new interface:
interface ClassAMixIn {
#JsonSerialize(using = ByteArrayJacksonSerializer.class)
byte[] getToken();
}
which specifies custom serializer for given property. Now we have to configure ObjectMapper
ObjectMapper mapper = new ObjectMapper();
mapper.addMixInAnnotations(ClassA.class, ClassAMixIn.class);
Your custom serializer will be used only for serializing byte array property in ClassA.
FOUND SOLUTION TO THE PROBLEM For the people who will be stuck like me!:
in order to handle third party java or scala Objects for jackson deserialization, you can either use Mixins( but you need to reconfigure the jackson mapper or user Modules)
OR
you can simply create a class called MyClassDeserializer that extends JsonDeserializer
and use the #JsonDeserialize(using = MyClassDeserializer.class) annotation.
exemple :
it's really simple and works like a charm! :)
public class User implements Identity{
#JsonProperty("_id")
private String id;
#JsonDeserialize(using = OptionDeserializer.class)
public Option<String> email;
}
public class OptionDeserializer extends JsonDeserializer<Option> {
#Override
public Option deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException, JsonProcessingException {
//code can be improved
ObjectCodec oc = jsonParser.getCodec();
JsonNode node = oc.readTree(jsonParser);
return Option.apply(node.get("email").getText());
}
}
hello guys i'm having some bad time trying to deserialize this with jackson using Jongo
public class User implements Identity{
#JsonProperty("_id")
private String id;
public Option<String> email;
}
Option is an abstract type, I'm really new to this, is there a way to actually tell jackson how to translate it?
this User object is correctly saved to mongo, but cannot be read :/ i've spent so many hours trying to understand you guys are my last resort!
thanks (keeps looking)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can
not construct instance of scala.Option, problem: abstract types either
need to be mapped to concrete types, have custom deserializer, or be
instantiated with additional type information
at [Source: de.undercouch.bson4jackson.io.LittleEndianInputStream#6f255853; pos:
237] (through reference chain: models.User["email"])
posting popo joe's answer as an answer:
FOUND SOLUTION TO THE PROBLEM For the people who will be stuck like me!: in order to handle third party java or scala Objects for jackson deserialization, you can either use Mixins( but you need to reconfigure the jackson mapper or user Modules) OR you can simply create a class called MyClassDeserializer that extends JsonDeserializer and use the #JsonDeserialize(using = MyClassDeserializer.class) annotation.
example :
it's really simple and works like a charm! :)
public class User implements Identity{
#JsonProperty("_id")
private String id;
#JsonDeserialize(using = OptionDeserializer.class)
public Option<String> email;
}
public class OptionDeserializer extends JsonDeserializer<Option> {
#Override
public Option deserialize(JsonParser jsonParser,
DeserializationContext deserializationContext) throws IOException,
JsonProcessingException {`
//code can be improved`
ObjectCodec oc = jsonParser.getCodec();
JsonNode node = oc.readTree(jsonParser);
return Option.apply(node.get("email").getText());
}
}
I'm using Jackson for JSON serialization, and I would like to override the null serializer -- specifically, so that null values are serialized as empty strings in JSON rather than the string "null".
All of the documentation and examples I've found on how to set null serializers refers to Jackson 1.x -- for example, the code at the bottom of http://wiki.fasterxml.com/JacksonHowToCustomSerializers no longer compiles with Jackson 2.0 because StdSerializerProvider no longer exists in the library. That web page describes Jackson 2.0's module interface, but the module interface has no obvious way to override the null serializer.
Can anyone provide a pointer on how to override the null serializer in Jackson 2.0?
Override the JsonSerializer serialize method as below.
public class NullSerializer extends JsonSerializer<Object> {
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
// any JSON value you want...
jgen.writeString("");
}
}
then you can set NullSerializer as default for custom object mapper:
public class CustomJacksonObjectMapper extends ObjectMapper {
public CustomJacksonObjectMapper() {
super();
DefaultSerializerProvider.Impl sp = new DefaultSerializerProvider.Impl();
sp.setNullValueSerializer(new NullSerializer());
this.setSerializerProvider(sp);
}
}
or specify it for some property using #JsonSerialize annotation, e.g:
public class MyClass {
#JsonSerialize(nullsUsing = NullSerializer.class)
private String property;
}
I was not able to get the accepted answer to work for me. Perhaps because my ObjectMapper is a Spring Bean in my environment.
I reverted by to using a SimpleModule.
Same serializer:
public class NullSerializer extends JsonSerializer<Object> {
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
// any JSON value you want...
jgen.writeString("");
}
}
The annotation is located in a Mixin as I don't have access to modifying MyClass:
public abstract class MyClassMixin {
#JsonSerialize(nullsUsing = NullSerializer.class)
public String property;
}
To attach the serializer to my mapper, I use a module in my Spring component:
#AutoWired
ObjectMapper objectMapper;
#PostConstruct
public void onPostConstruct() {
SimpleModule module = new SimpleModule();
module.setMixInAnnotation(MyClass.class, MyClassMixin.class);
objectMapper.registerModule(module);
}