I've the following JSON from some upstream api
{
"Id": "",
"Name": "",
"Age": ""
}
And I need to map this above json to a downstream request paylaod (POJO) .
public class Employee
{
#JsonProperty("Id")
private Integer Id;
private User user;
}
public class User {
#JsonProperty("Name")
private String name;
#JsonProperty("Age")
private String age;
}
Right now I'm doing something like
Employee employee = new ObjectMapper().treeToValue(JsonNode node,Employee.class);
But this is giving null in User Object.
The challenge here is , that the json we are getting from upstream can't be changed . So , is there is any way to map the fields into the nested User object , without changing the structure of json received from upstream.
One Solution is : map the fields separately into User object and then set it into the Employee object . But that's not an efficient solution , because for null validations we would need to do validations separately for User and Employee objects. If the nesting is complex then , validation will be hell of replicated code .
Your JSON does not comply with your Employee class.
Because name and age is at the same level as id, but you want to wrapped in a class User.
So either:
Change the json the structure to
{
"id": "",
"user": {
"name": "",
"age": ""
}
}
Or
Unwrap the User class, the Employee class will be:
public class Employee
{
#JsonProperty("Id")
private Integer Id;
#JsonProperty("Name")
private String name;
#JsonProperty("Age")
private String age;
}
Edit
If you can't choose either option 1 or 2, you have only one option left is to create custom deserializer:
Write a deserializer:
public class EmployeeDeserializer extends StdDeserializer<Item> {
public EmployeeDeserializer() {
this(null);
}
public EmployeeDeserializer(Class<?> vc) {
super(vc);
}
#Override
public Employee deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
JsonNode node = jp.getCodec().readTree(jp);
int id = (Integer) ((IntNode) node.get("Id")).numberValue();
String name = node.get("Name").asText();
String age = node.get("Age")).asText();
User user = new User(name, age);
return new Employee(id, user);
}
}
Then register this deserializer:
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Employee.class, new EmployeeDeserializer());
mapper.registerModule(module);
Employee readValue = mapper.readValue(json, Employee.class);
Another way to register deserializer is:
#JsonDeserialize(using = EmployeeDeserializer.class)
public class Employee {
It seems you are not nesting your JSON correctly. Or your Object Structure is wrong.
JSON should be:
{
"Id": "",
"user" : {
"Name": "",
"Age": ""
}
}
The json structure does not match the structure of your classes.
if the json was like;
{
"Id": "an-id,
"user": {
"Name": "Joe",
"Age": "21"
}
}
Then your code to deserialise to an Employee object would work.
Related
I have to use the exchange() method because I pass HttpHeaders there.
ResponseEntity<WeatherResponse> response Entity = restTemplate.exchange(
weather UrlRequest, Http Method.GET, new HttpEntity<>(headers), WeatherResponse.class);
JSON:
{
"geoloc": {
"city": {
"id": 213,
"name": "Boston"
},
"country": {
"id": 213,
"name": "USA"
},
"temp": {
"value": 19.4
}
}
Object to deserialization:
class WeahterResponse{
String country;
String city;
float temp;
}
How to influence deserialization in this case. There are two objects in JSON, and I need one?
class WeahterResponse{
GeoLocation geoloc;
Map<String,String> temp;
}
class GeoLocation {
Map<String,Map<String,Object> geoData;
}
It will deserialize your data to WeatherResponse.
Now if you want to get city data or country Data you can get that as follows.
suppose json is deserialized into weatherResponse.
Map<String,Map<String,Object> geoData = weatherResponse.getGeoLoc();
if(!CollectionUtils.isEmpty(geoData)){
if(geoData.containsKey("city")){
Map<String,Object> cityData = geoData.get("city");
System.out.println(cityData.get("id");
System.out.println(cityData.get("name");
}
//same for other keys of geoLoc
//to get Temp value
Map<String,String> temp = weatherResponse.getTemp();
System.out.println(temp.get("value");
Thanks for João Dias.
I made custom deserializer. https://www.baeldung.com/jackson-deserialization
In my case:
public class WeatherDeserializer extends JsonDeserializer<WeatherResponse> {
#Override
public WeatherResponse deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
JsonNode nodeTree = jsonParser.getCodec().readTree(jsonParser);
JsonNode geoObjectNode = nodeTree.get("geo_object");
JsonNode factNode = nodeTree.get("fact");
String country = geoObjectNode.get("country").get("name").textValue();
String province = geoObjectNode.get("province").get("name").textValue();
String locality = geoObjectNode.get("locality").get("name").textValue();
GeoObject geoObject = new GeoObject(country, province, locality);
Short temp = factNode.get("temp").shortValue();
Long obsTime = factNode.get("uptime").longValue();
return new WeatherResponse(geoObject,temp,obsTime);
}
}
#AllArgsConstructor
#Getter
#JsonDeserialize(using = WeatherDeserializer.class)
public class WeatherResponse {
private GeoObject geoObject;
private Short temp;
private Long uptime;
}
I have a JSON structured like:
{
"id" : "123",
"name" : [ {
"id" : "234",
"stuff" : [ {
"id" : "345",
"name" : "Bob"
}, {
"id" : "456",
"name" : "Sally"
} ]
} ]
}
I want to map to the following data structure:
Class01
#Getter
public class Class01{
private String id;
#JsonDeserialize(using = Class01HashMapDeserialize.class)
private ArrayList<Class02> name;
}
Class02
#Getter
public class Class02{
private String id;
private ArrayList<Class03> stuff;
}
Class03
#Getter
public class Class03{
private String id;
private String name;
}
In my main Method im using an ObjectMapper with objectMapper.readValue(jsonString,new TypeReference<ArrayList<Class02>>(){}) to map this JSON to my Class01. This Class successfully deserealizes the Class02-array into the name array.
When it comes to the second array I don't know how to further deserialize as I am not able to access the json text from the class02 stuff entry.
#Override
public ArrayList<Class02> deserialize(JsonParser parser, DeserializationContext ctxt) throws IOException {
ArrayList<Class02> ret = new ArrayList<Class02>();
ObjectCodec codec = parser.getCodec();
TreeNode classes02 = codec.readTree(parser);
if (classes02.isArray()) {
for (JsonNode class02 : (ArrayNode) classes02) {
if(classe02.get("stuff").isArray()){
ObjectMapper objectMapper = new ObjectMapper();
ArrayList<Class03> classes03 = objectMapper.readValue(class02.get("stuff").asText(), new TypeReference<ArrayList<Class03>>(){});
}
ret.add(new Class02(class02.get("id").asText(), classes03));
}
}
return ret;
}
Why did you put a #JsonDeserialize annotation ? Jackson shall be able to deserialize it just fine without any custom mapping:
#Getter
public class Class01{
private String id;
private ArrayList<Class02> name;
}
Also in a first pass, I would generate the getters/setters/constructor manually for the 3 classes. There may be issues with Lombok & Jackson that you may want to solve later once you made the first version of the code works (Can't make Jackson and Lombok work together)
And your reader shall be more like:
ObjectMapper objectMapper = new ObjectMapper();
String text = ... //Your JSon
Class01 class01 = objectMapper.readValue(text, Class01.class)
I am trying to map my incoming json payload to an arraylist of my model class.
I have a solution but its unintuitive.
I try to do this but get compilation errors-
ObjectMapper mapper = new ObjectMapper();
ArrayList<ModelClass> = mapper.readValue(items, RoleAttribute.class);
FYI I am trying to save this data in a Mongo collection.
Controller-
#PostMapping(value="/resource", consumes="application/json")
public Iterable<ModeClass> createResources(#RequestBody JSONObject requestBody ) throws JsonParseException, JsonMappingException, IOException {
System.out.println(requestBody.getClass());
return serviceImpl.saveResources(requestBody);
}
Model class-
#Data
#AllArgsConstructor
#Document(collection="collection-name")
public
class ModelClass{
#Field
private String ID;
#Field
private String description;
}
The payload is coming in the following format-
{
"data": [
{
"ID": "1",
"description": "desc1"
},
{
"ID": "2",
"description": "desc2"
},
{
"ID": "3",
"description": "desc3"
},
{
"ID": "4",
"description": "desc4"
}
....
]
}
I know I should be using jackson but I can't seem to figure this out. Do I need to change my POJO? Do I need to create custom Jackson config?
You can do it with json annotation. I also notice that your values are represented as data in json so that also needs to be taken care of. Look at below code. That will solve your problem.
import com.fasterxml.jackson.annotation.JsonProperty;
#Data
#AllArgsConstructor
#Document(collection="collection-name")
public class ModelClass{
#Field
#JsonProperty("ID")
private String classID;
#Field
#JsonProperty("description")
private String classDescription;
public String getClassID() {
return classID;
}
public void setClassID(String classID) {
this.classID = classID;
}
public String getClassDescription() {
return classDescription;
}
public void setClassDescription(String classDescription) {
this.classDescription = classDescription;
}
}
And wrapper Data class as below
class Data {
ModelClass[] data;
public ModelClass[] getData() {
return data;
}
public void setData(ModelClass[] data) {
this.data = data;
}
}
And json conversion code as below
ObjectMapper mapper = new ObjectMapper();
// json is your incoming json as a string. You can put inputstream also
Data values = mapper.readValue(json, Data.class);
System.out.println(values.getData().length);
System.out.println(values.getData()[0].getClassID());
You would need a container class for the data field, something like:
#Data
#Document(collection="collection-name")
public class DataClass{
private List<ModelClass> data;
}
Doing it via Jackson should be automatic this way, in controller:
public Iterable<ModeClass> createResources(#RequestBody DataClass requestBody ) {
I have class Admin extends User {}. Admin and User both extends #XmlRootElement
#XmlRootElement
public class User {
....
}
#XmlRootElement
public class Admin extends User {
String statement;
}
I am sending this Json to the right JaxRS service:
{
"id": "84",
"content": "blablah",
"user": {
"id": 1,
"email": "nicolas#robusta.io",
"name": "Nicolas",
"male": true,
"admin": true,
"statement":"hello world"
}
}
Here is the Web service. The comment is supposed to have a User, but we have here an Admin that has a statement field unknown to User.
#POST
#Path("{id}/comments")
public Response createComment(#PathParam("id") long topicId, Comment comment) { ... }
Comment is not accepted as a Commentby Jackson because its User is an Admin:
#XmlRootElement
public class Comment {
String id;
String content;
User user = null;
}
How should I tell Jackson to accept any kind of User ? How to do that the most Java EE compatible (ie with servers that have another Json handler) ?
The jackson approach with polymorphic objects is to add some additional field in your json and use #JsonTypeInfo If you can change your json to something like
"user": {
"type": "Admin",
...
}
Then you can simply use
#JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
#JsonSubTypes({
#JsonSubTypes.Type(name = "User", value = User.class),
#JsonSubTypes.Type(name = "Admin", value = Admin.class)
})
static class User {
public String id;
}
If you can't change your json, then things can get complicated, because there is no default way to handle such a case and you will have to write custom deserializer. And base simple case would look something like this:
public static class PolymorphicDeserializer extends JsonDeserializer<User> {
ObjectMapper mapper = new ObjectMapper();
#Override
public User deserialize(JsonParser p, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
JsonNode tree = p.readValueAsTree();
if (tree.has("statement")) // <= hardcoded field name that Admin has
return mapper.convertValue(tree, Admin.class);
return mapper.convertValue(tree, User.class);
}
}
You can register it on ObjectMapper
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(User.class, new PolymorphicDeserializer());
mapper.registerModule(module);
or with annotation:
#JsonDeserialize(using = PolymorphicDeserializer.class)
class User {
public String id;
}
I have a test.json file with data:
{
"name":"tet",
"id":"1",
"age" : "34"
}
Now when I query select * from test; should show me the result as
name id age
-----------
tet 1 34
Is it possible to directly query a JSON Object as we do for XML?
The popular Jackson XML library supports JsonPointer since version 2.3. This is a query language similar to XPath
Input
[{
"name":"tet",
"id":"1",
"age" : "34"
},{
"name":"tet",
"id":"1",
"age" : "34"
},{
"name":"tet",
"id":"1",
"age" : "34"
},{
"name":"tet",
"id":"1",
"age" : "34"
}]
Example
ObjectMapper objectMapper = new ObjectMapper();
JsonNode root = objectMapper.readTree(new File("foo.json"));
System.out.println(root.at("/0/name").asText());
I would say you can either try looking for a library which allows you to search throught JSON data or to convert your json to JSONObjects and query your data in a Object Oriented way.
Perhaps this thread will help:
Query a JSONObject in java
there is no way to query directly from the Json, if you want you have to create a new class that will do your requirement, OR you can use the ObjectMapper (download and add to your class path) from jackson-all-1.9.0.jar, and create a new transfer Object TestTO.java expose the setters and getters you will get your data like below..
1.create TestTO.java
public class TestTO{
private String name;
private int id;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
2.read your data from the object.
final ObjectMapper mapper = new ObjectMapper();
Test test = mapper.readValue(yourJson.json, TestTO.class);
String name = test.getName();
int id = test.getId();
int age = test.getAge();
if your json contains the multiple test objects, use an test array like below, it will give you the array of tests, you can iterate over and get the data, like below.
final ObjectMapper mapper = new ObjectMapper();
TestTO[] test = mapper.readValue(yourJson.json, TestTO.class[]);
for(Test tst:test){
String name = test.getName();
int id = test.getId();
int age = test.getAge();
}