I've read countless articles about parsing Java objects to JSONs and still have issues...
I know that there are a bunch of frameworks out there and this is where things messed up I guess.
I'm trying to parse a map into a json:
Map<CategoryBean, Double> questionsPercentagePerCategory;
here's how CategoryBean looks like:
#XmlRootElement
public class CategoryBean implements Serializable{
private static final long serialVersionUID = -7306680546426636719L;
private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
questionsPercentagePerCategory is a variable inside a wrapper json called: PrePracticeBean
and this is how it looks:
#XmlRootElement
public class PrePracticeBean implements Serializable {
private int maxQuestionsAllowedForUser;
private int maxQuestionsAllowedForUserAfterCreditOver;
private int questionsInExam;
#XmlJavaTypeAdapter(XmlGenericMapAdapter.class)
private Map<CategoryBean, Double> questionsPercentagePerCategory;
private static final long serialVersionUID = -655358519739911024L;
public int getMaxQuestionsAllowedForUser() {
return maxQuestionsAllowedForUser;
}
public void setMaxQuestionsAllowedForUser(int maxQuestionsAllowedForUser) {
this.maxQuestionsAllowedForUser = maxQuestionsAllowedForUser;
}
public int getMaxQuestionsAllowedForUserAfterCreditOver() {
return maxQuestionsAllowedForUserAfterCreditOver;
}
public void setMaxQuestionsAllowedForUserAfterCreditOver(int maxQuestionsAllowedForUserAfterCreditOver) {
this.maxQuestionsAllowedForUserAfterCreditOver = maxQuestionsAllowedForUserAfterCreditOver;
}
public int getQuestionsInExam() {
return questionsInExam;
}
public void setQuestionsInExam(int questionsInExam) {
this.questionsInExam = questionsInExam;
}
public Map<CategoryBean, Double> getQuestionsPercentagePerCategory() {
return questionsPercentagePerCategory;
}
public void setQuestionsPercentagePerCategory(Map<CategoryBean, Double> questionsPercentagePerCategory) {
this.questionsPercentagePerCategory = questionsPercentagePerCategory;
}
}
as you can see I've marked both beans with #XmlRootElement annotation to get Jeresey's OOB bean to JSON parsing functionality as specified here
Furthermore, here's how the XMLGenericMapAdapter looks like:
public class XmlGenericMapAdapter<K, V> extends XmlAdapter<MapType<K, V>, Map<K, V>> {
#Override
public Map<K, V> unmarshal(MapType<K, V> orgMap) throws Exception {
HashMap<K, V> map = new HashMap<K, V>();
for (MapEntryType<K, V> mapEntryType : orgMap.getEntries()) {
map.put(mapEntryType.getKey(), mapEntryType.getValue());
}
return map;
}
#Override
public MapType<K, V> marshal(Map<K, V> v) throws Exception {
MapType<K, V> mapType = new MapType<K, V>();
for (Map.Entry<K, V> entry : v.entrySet()) {
MapEntryType<K, V> mapEntryType = new MapEntryType<K, V>();
mapEntryType.setKey(entry.getKey());
mapEntryType.setValue(entry.getValue());
mapType.getEntries().add(mapEntryType);
}
return mapType;
}
}
Well, the end result is what makes me crazy... it's intermittent... when running the code in debug mode, this works flawlessly showing a nested json for the map and each key:value pair is another nested json. However, when invoked in run mode, I get an ugly "memory address" instead of the CategoryBean key...
My only guess is that this is related to class loading matters and that I might be having some other JAR that's having a class which is loaded first in debug mode but not in run mode...
anyways, any suggestions as to how this should be done, would be appreciated.
thanks,
GBa.
Well, solved...
some JAXB/Jersey stuff which I'm not into understanding up to the last bit... but I bet that there's some JAXB guru out there who could give the right explanation why this is the case...
Anyways, bottom line is that the CategoryBean class should not have the annotation #XmlRootElement but instead should have #XmlAccessorType(XmlAccessType.FIELD)
I got the inspiration for that from Serializer for (Hash)Maps for Jersey use?
thanks,
GBa.
Related
In my Application i have something like this.
public class Question{}
public class MCQ extends Question{}
public class TrueAndFalse Question{}
public class Match Question{}
and in my RestController i have a service that adds question.
#RequestMapping(value = "/game/question/add", method = RequestMethod.POST)
public Question addQuuestion(#RequestParam("gameId") long id, #RequestBody Question question)
But i get an error when i try to call this service as i send json file with different structures one for MCQ, TrueAndFalse and Match.
so is it possible to deserialize the received json to Question abstract class.
And thanks in advance.
You can create a custom deserializer which will create Question instances based on json payload properties.
For example if the Question class looks like this:
public class Question {
private final String name;
#JsonCreator
Question(#JsonProperty("name") String name) {
this.name = name;
}
public String getName() {
return name;
}
}
And sub-class TrueAndFalse:
public class TrueAndFalse extends Question {
private final String description;
#JsonCreator
TrueAndFalse(#JsonProperty("name") String name,
#JsonProperty("description") String description) {
super(name);
this.description = description;
}
public String getDescription() {
return description;
}
}
Then you can create a deserializer, which will create an instance of TrueAndFale sub-class by checking if it has description property:
public class QuestionDeserializer extends JsonDeserializer<Question> {
#Override
public Question deserialize(JsonParser p, DeserializationContext ctx) throws IOException {
ObjectCodec codec = p.getCodec();
JsonNode tree = codec.readTree(p);
if (tree.has("description")) {
return codec.treeToValue(tree, TrueAndFalse.class);
}
// Other types...
throw new UnsupportedOperationException("Cannot deserialize to a known type");
}
}
And afterwards, make sure to register it on the object mapper:
#Configuration
public class ObjectMapperConfiguration {
#Bean
public ObjectMapper objectMapper() {
SimpleModule module = new SimpleModule();
module.addDeserializer(Question.class, new QuestionDeserializer());
return new ObjectMapper().registerModules(module);
}
}
I'm using JsonNode for getting data from any kind of jason format and storing it to mongoDb
But while fetching data from mongoDB it is throwing error as below.
Failed to instantiate com.fasterxml.jackson.databind.node.ObjectNode using constructor NO_CONSTRUCTOR with arguments
Below is my domain class
public class Profiler {
#Id
private String id;
#Field("email")
private String email;
#Field("profiler")
private Map<String,JsonNode> profiler;
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public Map<String, JsonNode> getProfiler() {
return profiler;
}
public void setProfiler(Map<String, JsonNode> profiler) {
this.profiler = profiler;
}
public Profiler(String email,Map<String,JsonNode> profiler){
this.email=email;
this.profiler = profiler;
}
#JsonCreator
public Profiler(#JsonProperty("_id")String id,#JsonProperty("email")String email,#JsonProperty("profiler")Map<String,JsonNode> profiler){
this.id=id;
this.email=email;
this.profiler = profiler;
}
public Profiler(String id){
this.id=id;
}
public Profiler(Map<String,JsonNode> profiler){
this.profiler = profiler;
}
public Profiler(){
}
}
public interface ProfilerRepository extends MongoRepository<Profiler, String>{
public Profiler findOneByEmail(String email);
}
And my controller call is as below and I'm getting the error on this line.
Profiler profile=profileService.findOneByEmail(email);
I have made this changes and work as expected.
Map<String, Object> profile;
This problem occurs because com.fasterxml.jackson.databind.node.ObjectNode class doesn't have default constructor (no argument constructor) and Jackson expects the default constructor.
Related Post refer azerafati's answer
The problem can be resolved if you define the profiler field as static in domain class.
private static Map<String, JsonNode> profiler;
Please note that static fields have its own limitations and issues. I can assure that this would resolve the above exception. However, it may not be the most appropriate solution.
in my case problem solved . i had entity that i defined :
private JsonNode data;
i changed it to:
private Map<String,String> data;
or this also work :
private Map<Object,String> data;
please let me know if you had any question
I use DAO MVC, and I after some googling I consider to store some variables as Enum in java and String in MySQL. So I create in Item.java (that will be persist into Item table) static initialization and static methods to convert Enum into String and vise versa.
But someone said me that after this static initialization and static methods my Item.java class became NOT POJO.
Question:
Why it became NOT POJO?
And if I'll make those methods not static Item.java class will be POJO?
EDITED: MY code:
package model;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Map;
public class Order {
public enum OrderStatus {
NOT_REVIEWED,
APPROVED,
REJECTED,
RETURNED
}
// ==================
// = Transient =
// ==================
private static final Map<String, OrderStatus> convertStringToOrderStatusMap = new HashMap<String, OrderStatus>(3);
private static final Map<OrderStatus, String> convertOrderStatusToStringMap = new EnumMap<OrderStatus, String>(OrderStatus.class);
static {
convertStringToOrderStatusMap.put("not reviewed", OrderStatus.NOT_REVIEWED);
convertStringToOrderStatusMap.put("approved", OrderStatus.APPROVED);
convertStringToOrderStatusMap.put("rejected", OrderStatus.REJECTED);
convertStringToOrderStatusMap.put("returned", OrderStatus.RETURNED);
convertOrderStatusToStringMap.put(OrderStatus.NOT_REVIEWED, "not reviewed");
convertOrderStatusToStringMap.put(OrderStatus.APPROVED, "approved");
convertOrderStatusToStringMap.put(OrderStatus.REJECTED, "rejected");
convertOrderStatusToStringMap.put(OrderStatus.RETURNED, "returned");
}
// ==================
// = Attributes =
// ==================
private Integer orderId; //Primary key
private OrderStatus status;
private Integer reimbursement;
private String firstName;
private String secondName;
private String passportData;
private String pickUpDate;
private String dropOffDate;
//java.util.Date date = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse("2011-05-18 16:29:31");
private String customerCell;
private String customerAddress;
// ==================
// = Foreign Keys =
// ==================
private User user;
private Car car;
// ==================
// = Public methods =
// ==================
public Integer getOrderId() {
return orderId;
}
public void setOrderId(Integer orderId) {
this.orderId = orderId;
}
public String getStatus() {
return convertOrderStatusToString(status);
}
public void setStatus(OrderStatus status) {
this.status = status;
}
public Integer getReimbursement() {
return this.reimbursement;
}
public void setReimbursement(Integer value) {
this.reimbursement = value;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getSecondName() {
return secondName;
}
public void setSecondName(String secondName) {
this.secondName = secondName;
}
public String getPassportData() {
return passportData;
}
public void setPassportData(String passportData) {
this.passportData = passportData;
}
public String getPickUpDate() {
return pickUpDate;
}
public void setPickUpDate(String pickUpDate) {
this.pickUpDate = pickUpDate;
}
public String getDropOffDate() {
return dropOffDate;
}
public void setDropOffDate(String dropOffDate) {
this.dropOffDate = dropOffDate;
}
public String getCustomerCell() {
return customerCell;
}
public void setCustomerCell(String customerCell) {
this.customerCell = customerCell;
}
public String getCustomerAddress() {
return customerAddress;
}
public void setCustomerAddress(String customerAddress) {
this.customerAddress = customerAddress;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
public Car getCar() {
return car;
}
public void setCar(Car car) {
this.car = car;
}
public static OrderStatus converStringToOrderStatus(String status) {
return convertStringToOrderStatusMap.get(status);
}
public static String convertOrderStatusToString(OrderStatus status) {
return convertOrderStatusToStringMap.get(status);
}
}
Because a Plain Old Java Object only has data. Adding logic and methods means that it's no longer Plain Old Java Object.
That doesn't necessarily make it a bad thing, but you might be able to refactor the logic out into a class of it's own.
Lets ignore POJO.
What they mean is Service Oriented vs Domain Driven.
Service Oriented follows strict separation of behavior from state. They call POJOs data objects which are essentially glorified structs. Thus you would put the static methods in the Service. In fact you probably wouldn't even want the methods static as that is also against the service oriented approach (see dependency injection and evil singleton).
Domain Driven follows the idea of classic OOP (e.g. Rails Active Record) in which they do believe its OK to put behavior in their POJOs. Consequently because state + behavior are coupled there is only one implementation and thus static methods in the domain object are OK.
If your going the DAO route your most likely doing Service Oriented. My opinion is if your going to do the DAO POJO route you should use immutable objects (shameless plug) for those data objects.
Finally putting an inline enum into a class from my knowledge does not violate any definition of POJO. That being said you should know about #Enumerated since your using JPA.
My POJO is :
import org.jongo.marshall.jackson.id.Id;
public class User {
#Id
private String id;
private String name;
private int age;
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;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
I get user from mongo database and want to output him into a file with jackson mapper
ObjectMapper mapper = new ObjectMapper();
mapper.writerWithDefaultPrettyPrinter().writeValue(new File("c:/user.txt"), user);
and I get something like this in my file
{
"name" : "John",
"age" : 23,
"_id" : {
"time" : 1358443593000,
"inc" : 660831772,
"machine" : 2028353122,
"new" : false,
"timeSecond" : 1358443593
}
}
I need id field to be stored into a file as string because when i deserialize this object my id field in pojo looks something like this
{
"time":1358443593000,
"inc":660831772,
"machine":2028353122,
"new":false,
"timeSecond":1358443593
}
Any help will be apreciated
Answering my own question. Found solution here Spring 3.2 and Jackson 2: add custom object mapper
I needed custom object mapper and ObjectId serializer.
public class ObjectIdSerializer extends JsonSerializer<ObjectId> {
#Override
public void serialize(ObjectId value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
jgen.writeString(value.toString());
}
}
public class CustomObjectMapper extends ObjectMapper {
public CustomObjectMapper() {
SimpleModule module = new SimpleModule("ObjectIdmodule");
module.addSerializer(ObjectId.class, new ObjectIdSerializer());
this.registerModule(module);
}
}
I found an easy attempt using springboot 2.5.4.
Just by adding a Jackson2ObjectMapperBuilderCustomizer bean will do the trick.
#Configuration
public class JacksonMapperConfiguration
{
#Bean
public Jackson2ObjectMapperBuilderCustomizer jsonCustomizer() {
return builder -> builder.serializerByType(ObjectId.class, new ToStringSerializer());
}
}
Here is a simple solution for serialization if you don't have a model for the object being stored:
client.getDatabase("db").getCollection("collection").find().onEach { it["_id"] = it["_id"].toString() }
"onEach" is a kotlin function. If you use Java, then change it to a simple foreach.
It's not efficient to iterate over the entire list just for the id. Only use it for small lists where performance is less important than short code.
I have a base class generic with generic type property and several classes inheriting from it. Something like that:
public abstract class BaseClass<T extends Number> {
#XmlAnyElement
public T getId() { return id; }
private T id ; // init for hibernate bug workaround
.....
}
#XmlRootElement
public class A extends BaseClass<Integer> {
private String name;
private String error;
private String url;
public String getError() { return error; }
public void setError(String error) { this.error = error; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public void setUrl(String url) { this.url = url; }
public String getUrl() { return url; }
}
When Jersey tries to marshals it throws:
javax.xml.bind.MarshalException
- with linked exception:
[com.sun.istack.SAXException2: unable to marshal type "java.lang.Integer" as an element because it is missing an #XmlRootElement annotation]
at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:318)
at com.sun.xml.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:172)
at com.sun.jersey.json.impl.JSONMarshallerImpl.marshal(JSONMarshallerImpl.java:94)
at com.sun.jersey.json.impl.BaseJSONMarshaller.marshallToJSON(BaseJSONMarshaller.java:103)
at com.sun.jersey.json.impl.BaseJSONMarshaller.marshallToJSON(BaseJSONMarshaller.java:91)
......
I can't add XmlRootElement annotation to Integer, so what I supposed to do?
You should try to add #XmlRootElement annotation to your BaseClass.