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How to remove a field from POJO

public class user {
private String planId;
private String eid;
#JsonProperty(access = JsonProperty.Access.WRITE_ONLY)
private Collection<String> userIds;
}
I have a pojo like above
and the code which is use for creating the json request object is this :
public UserCollection getUserCollection(final user args) {
Map<String, String> headersMap = new HashMap<>();
ObjectMapper jacksonMapper = new ObjectMapper();
jacksonMapper.disable(MapperFeature.USE_ANNOTATIONS); // this line is creating the userIds field to reflect
//By any code we can remove the userId field from the args object
String responseBody = null;
String responseStatus = null;
String jsonRequestBody = jacksonMapper.writeValueAsString(args);
}
I just want to remove userIds from the args by not removing any of the above code.
Thanks in advance.

I don't know how you should solve this without removing the annotation processing code, you should maybe add a custom serializer. You can read further about the topic at here.
public class HelloWorld {
public static void main(String[] args) throws JsonProcessingException {
User myItem = new User("planId", "eId", List.of("1", "2"));
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addSerializer(User.class, new UserSerializer());
mapper.registerModule(module);
String serialized = mapper.writeValueAsString(myItem);
}
#Data
#AllArgsConstructor
public static class User {
private String planId;
private String eId;
private Collection<String> userIds;
}
public static class UserSerializer extends StdSerializer<User> {
public UserSerializer() {
this(null);
}
public UserSerializer(Class<User> t) {
super(t);
}
#Override
public void serialize(User value, JsonGenerator gen, SerializerProvider provider) throws IOException{
gen.writeStartObject();
gen.writeStringField("planId", value.planId);
gen.writeStringField("eId", value.eId);
gen.writeEndObject();
}
}
}
If you had to use it without annotations, and cannot add a custom serializer you should map the User class into a more specific class without the field in question and then serialize that one.

Java Jackson: why do I get JsonMappingException although I used #JsonDeserialize

I need some help with Jackson library in Java. I have the following class:
#JsonIgnoreProperties(ignoreUnknown = true)
public class MarketHistoryData {
private String countryCode;
#JsonDeserialize(keyUsing = BpTimeDeserializer.class)
private Map<BpTime, Double> hourToExpectedEngagePaidListings;
#JsonDeserialize(keyUsing = BpTimeDeserializer.class)
private Map<BpTime, Double> hourMinuteToExpectedEngagePaidListings;
public MarketHistoryData() {}
...
// getters and setters
}
I understood that Jackson has difficulties with deserializing a map which its keys are an object. Therefore, I added the annotations:
#JsonDeserialize(keyUsing = BpTimeDeserializer.class)
The class BpTimeDeserializer is:
public class BpTimeDeserializer extends KeyDeserializer {
private ObjectMapper mapper = new ObjectMapper();
#Override
public BpTime deserializeKey(String key, DeserializationContext ctxt) throws IOException {
return mapper.readValue(key, BpTime.class);
}
}
Still, I get an error during the deserialization process:
*****.UncheckedExecutionException:
com.fasterxml.jackson.databind.JsonMappingException: Unrecognized
token 'com': was expecting (JSON String, Number, Array, Object or
token 'null', 'true' or 'false') at [Source:
(String)"****BpTime#5922062e[hour=1,minute=0]";
line: 1, column: 1] (through reference chain:
***PacerCycleOutput["campaignIdToFactorComputationData"]->java.util.LinkedHashMap["1011620661"]->****FactorComputationData["selectedMarketHistoryDataForCampaign"]->***MarketHistoryData["hourToExpectedEngagePaidListings"])
Do you know what I can do to overcome this error?

I finally found a way how to resolve this error.
#JsonIgnoreProperties(ignoreUnknown = true)
public class MarketHistoryData {
private String countryCode;
#JsonDeserialize(keyUsing = BpTimeDeserializer.class)
#JsonSerialize(keyUsing = BpTimeSerializer.class)
private Map<BpTime, Double> hourToExpectedEngagePaidListings;
#JsonDeserialize(keyUsing = BpTimeDeserializer.class)
#JsonSerialize(keyUsing = BpTimeSerializer.class)
private Map<BpTime, Double> hourMinuteToExpectedEngagePaidListings;
...
}
public class BpTimeDeserializer extends KeyDeserializer {
private ObjectMapper mapper = new ObjectMapper();
#Override
public BpTime deserializeKey(String key, DeserializationContext ctxt) throws IOException {
String[] keySplit = key.split(" ");
BpTime bpTime = new BpTime();
if (!keySplit[0].equals("-1")) {
bpTime.setHour(Integer.parseInt(keySplit[0]));
}
if (!keySplit[1].equals("-1")) {
bpTime.setMinute(Integer.parseInt(keySplit[1]));
}
return bpTime;
}
}
public class BpTimeSerializer extends StdSerializer<BpTime> {
public BpTimeSerializer() {
this(null);
}
public BpTimeSerializer(Class<BpTime> t) {
super(t);
}
#Override
public void serialize(BpTime value, JsonGenerator generator, SerializerProvider arg2) throws IOException {
generator.writeFieldName(String.format("%s %s", ofNullable(value.getHour()).orElse(-1),
ofNullable(value.getMinute()).orElse(-1)));
}
}

Trying to deserialize json array into java String using Jackson in Spring-boot

I'm new to Spring-boot and am trying to deserialize json array into java String using Jackson in a Spring-boot Application. Something like
{"history": ["historyA", "historyB"]} (JSON Request Body) -> String history;
However, the following error message got logged.
Cannot deserialize instance of `java.lang.String` out of START_ARRAY token
My Controller is similar to
#RestController
public class PatientController {
#PostMapping
public void create(#RequestBody #Valid Patient patient) {
mapper.create(patient);
}
}
My POJO is similar to:
#Data
#NoArgsConstructor
public class Patient {
#JsonDeserialize(contentUsing = PatientHistoryDeserializer.class, contentAs = List.class)
private String history;
My Json Deserializer is similar to:
public class PatientHistoryDeserializer extends JsonDeserializer<String> {
#Override
public String deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
List<String> histories = new LinkedList<>();
if (p.getCurrentToken() == JsonToken.START_ARRAY) {
while (p.getCurrentToken() != JsonToken.END_ARRAY) {
String history = p.getValueAsString();
if(history.contains("#"))
throw new ClientError(HttpServletResponse.SC_BAD_REQUEST, "invalid...");
histories.add(history);
}
}
return String.join("#", histories);
}
}
Is my goal achievable ? Or any suggestions on how to convert as I wanted ?

This can be done like this
public class PatientHistoryDeserializer extends JsonDeserializer<String> {
#Override
public String deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
if (jsonParser.currentToken() == JsonToken.START_ARRAY) {
List<String> histories = new ArrayList<>();
jsonParser.nextToken();
while (jsonParser.hasCurrentToken() && jsonParser.currentToken() != JsonToken.END_ARRAY) {
histories.add(jsonParser.getValueAsString());
jsonParser.nextToken();
}
return String.join("#", histories);
}
return null;
}
}
And usage would like
#JsonDeserialize(using = PatientHistoryDeserializer.class)
String histories;
The purpose of contentUsing and contentAs are a bit different than the use case here. let's take the following example.
class Histories {
Map<String, String> content;
}
and JSON is something like this
{"content": { "key" : ["A","B"]}}
and you want to deserialize this into a map having (key = "A#B")
there are two ways to do it, write custom deserializer or use contentUsing attribute to specify how your values should be deserialized
#JsonDeserialize(contentUsing = PatientHistoryDeserializer.class)
Map<String, String> content;
Similarly, you can use other annotation attributes like keyUsing for keys for maps.

#JsonDeserialize doesn't work when I put it above the method

I'm trying to custom deserialize incoming json to the field, but #JsonDeserialize is not working wheh I put it above the setter of the field I want to deserialize.
public class MyEntity {
#JsonProperty("identifier")
private String identifier;
#JsonDeserialize(using = IdentifierDeserializer.class)
public void setIdentifier(String identifier)
{
this.identifier = identifier;
}
}
....
public class IdentifierDeserializer
extends JsonDeserializer<String>
{
#Override
public String deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException
{
ObjectCodec oc = jp.getCodec();
JsonNode node = oc.readTree(jp);
final JsonNode entity = node.get("entity");
return entity.get("id").asText();
}
}
Im doing this via _restTemplate httpMessageConverter flow, just standar API calls, and no, it does not throw any exceptions, it just not invoked, because I this this with debug and my breakpoints left untouched.
HttpEntity<T> httpEntity = new HttpEntity<>(entity, httpHeaders());
MappingJackson2HttpMessageConverter jsonConverter = new MappingJackson2HttpMessageConverter();
jsonConverter.setSupportedMediaTypes(Lists.newArrayList(MediaType.APPLICATION_JSON_UTF8));
_restTemplate.getMessageConverters().add(jsonConverter);
return _restTemplate.exchange(url, method, httpEntity, MyEntity.class).getBody();
But #JsonDeserialize does work when I put it above the class. So what's the problem guys? Thanks.

Custom JSON Deserialization with Jackson

I'm using the Flickr API. When calling the flickr.test.login method, the default JSON result is:
{
"user": {
"id": "21207597#N07",
"username": {
"_content": "jamalfanaian"
}
},
"stat": "ok"
}
I'd like to parse this response into a Java object:
public class FlickrAccount {
private String id;
private String username;
// ... getter & setter ...
}
The JSON properties should be mapped like this:
"user" -> "id" ==> FlickrAccount.id
"user" -> "username" -> "_content" ==> FlickrAccount.username
Unfortunately, I'm not able to find a nice, elegant way to do this using Annotations. My approach so far is, to read the JSON String into a Map<String, Object> and get the values from there.
Map<String, Object> value = new ObjectMapper().readValue(response.getStream(),
new TypeReference<HashMap<String, Object>>() {
});
#SuppressWarnings( "unchecked" )
Map<String, Object> user = (Map<String, Object>) value.get("user");
String id = (String) user.get("id");
#SuppressWarnings( "unchecked" )
String username = (String) ((Map<String, Object>) user.get("username")).get("_content");
FlickrAccount account = new FlickrAccount();
account.setId(id);
account.setUsername(username);
But I think, this is the most non-elegant way, ever. Is there any simple way, either using Annotations or a custom Deserializer?
This would be very obvious for me, but of course it doesn't work:
public class FlickrAccount {
#JsonProperty( "user.id" ) private String id;
#JsonProperty( "user.username._content" ) private String username;
// ... getter and setter ...
}

You can write custom deserializer for this class. It could look like this:
class FlickrAccountJsonDeserializer extends JsonDeserializer<FlickrAccount> {
#Override
public FlickrAccount deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
Root root = jp.readValueAs(Root.class);
FlickrAccount account = new FlickrAccount();
if (root != null && root.user != null) {
account.setId(root.user.id);
if (root.user.username != null) {
account.setUsername(root.user.username.content);
}
}
return account;
}
private static class Root {
public User user;
public String stat;
}
private static class User {
public String id;
public UserName username;
}
private static class UserName {
#JsonProperty("_content")
public String content;
}
}
After that, you have to define a deserializer for your class. You can do this as follows:
#JsonDeserialize(using = FlickrAccountJsonDeserializer.class)
class FlickrAccount {
...
}

Since I don't want to implement a custom class (Username) just to map the username, I went with a little bit more elegant, but still quite ugly approach:
ObjectMapper mapper = new ObjectMapper();
JsonNode node = mapper.readTree(in);
JsonNode user = node.get("user");
FlickrAccount account = new FlickrAccount();
account.setId(user.get("id").asText());
account.setUsername(user.get("username").get("_content").asText());
It's still not as elegant as I hoped, but at least I got rid of all the ugly casting.
Another advantage of this solution is, that my domain class (FlickrAccount) is not polluted with any Jackson annotations.
Based on #Michał Ziober's answer, I decided to use the - in my opinion - most straight forward solution. Using a #JsonDeserialize annotation with a custom deserializer:
#JsonDeserialize( using = FlickrAccountDeserializer.class )
public class FlickrAccount {
...
}
But the deserializer does not use any internal classes, just the JsonNode as above:
class FlickrAccountDeserializer extends JsonDeserializer<FlickrAccount> {
#Override
public FlickrAccount deserialize(JsonParser jp, DeserializationContext ctxt) throws
IOException, JsonProcessingException {
FlickrAccount account = new FlickrAccount();
JsonNode node = jp.readValueAsTree();
JsonNode user = node.get("user");
account.setId(user.get("id").asText());
account.setUsername(user.get("username").get("_content").asText());
return account;
}
}

You can also use SimpleModule.
SimpleModule module = new SimpleModule();
module.setDeserializerModifier(new BeanDeserializerModifier() {
#Override public JsonDeserializer<?> modifyDeserializer(
DeserializationConfig config, BeanDescription beanDesc, JsonDeserializer<?> deserializer) {
if (beanDesc.getBeanClass() == YourClass.class) {
return new YourClassDeserializer(deserializer);
}
return deserializer;
}});
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.registerModule(module);
objectMapper.readValue(json, classType);

I made it this way:
public class FlickrAccount {
private String id;
#JsonDeserialize(converter = ContentConverter.class)
private String username;
private static class ContentConverter extends StdConverter<Map<String, String>, String> {
#Override
public String convert(Map<String, String> content) {
return content.get("_content"));
}
}
}

You have to make Username a class within FlickrAccount and give it a _content field