I have the following json data (patients.json):
{
"A" : {
"name" : "Tom",
"age" : 12
},
"B" : {
"name" : "Jim",
"age" : 54
}
}
Using the Jackson JSON library, how can I get something like the following:
HashMap<String, ???> patients = objectMapper.readValue(new File("patients.json"), ???);
String Aname = patients.get("A").get("name");
int Aname = patients.get("A").get("age");
Deserialize your JSON into Jackson's JSON Object type, ObjectNode. You can then traverse it as you see fit.
For example
ObjectNode patients = objectMapper.readValue(new File("test.json"), ObjectNode.class);
// you can check if it is actually an ObjectNode with JsonNode#isObject()
ObjectNode nodeA = (ObjectNode)patients.get("A");
String name = nodeA.get("name").asText();
int age = (int) nodeA.get("age").asLong();
Note that the methods asXyz() return default values if the target node cannot be converted to that type. You can check with the corresponding isXyz() methods before invoking them.
You could create a class to map your patients to;
private static class Patient {
#JsonProperty("name")
private String name;
#JsonProperty("age")
private int age;
public Patient() { }
public String getName() {
return name;
}
public int getAge() {
return age;
}
}
Then read your json into it via jackson
HashMap<String, Patient> patients = objectMapper.readValue(new File("patients.json"), new TypeReference<HashMap<String,Patient>>() {});
Patient patientA = patients.get("A");
String patientAName = patientA.getName();
int pateintAAge = patientA.getAge();
Related
i don't arrive to get the name of the containerStatuses.
I tried this (regarding a precedent post), the error is reported on the get("name") with "The method get(String) is undefined for the type JsonElement".
Thanks for help
JsonObject data = new Gson().fromJson(myjsoncontent, JsonObject.class);
JsonArray items = data .get("items").getAsJsonArray();
for(JsonElement element : items){
JsonObject object = element.getAsJsonObject();
String containerstatusesname = object.get("status").getAsJsonObject().get("containerStatuses").getAsJsonArray().get(0).get("name").getAsString();
}
// My Json Content
{
"kind": "Space",
"apiVersion": "v1",
"metadata": {
"selfLink": "something",
"resourceVersion": "something"
},
"items": [
{
"status": {
"containerStatuses": [
{
"name": "thisismyname"
}
]
}
}
]
}
Why are you using gson emulating JSON.parse? Is using a sledgehammer to crack a nut.
If you want to use gson it's better to create a class that matches your json data as:
public class ApiResponse {
private String kind;
private String apiVersion;
private Metadata metadata;
private List<Item> items;
public List<String> getAllNames() {
List<String> allNames = new ArrayList();
for (Item item: items) {
allNames.add(item.getStatus().get(0).getName());
}
return allNames;
}
public String getFirstName() {
if (items.length == 0 || items.get(0).getStatus().length == 0) {
return "";
}
return items.get(0).getStatus().get(0).getName();
}
class Metadata {
private String selfLink;
private String resourceVersion;
}
class Item {
private List<StatusContainer> status;
List<StatusContainer> getStatus() {
return status;
}
}
class StatusContainer {
private String name;
String getName() {
return name;
}
}
}
And then execute:
ApiResponse response = gson.fromJson(myjsoncontent, ApiResponse.class);
String firstName = response.getFirstName();
And this way the response object will contain all the data of the parsed json. Notice you'll need to add the getters to access this properties if are kept private.
No need to emulate the result of JSON.parse and have JsonObject, JsonArray...
You have to change
.get(0).get("name")
to
.get(0).getAsJsonObject().get("name")
JsonArray returns JsonElements when you iterate over it
Get the Array Element as Object cause its structured as Object
.getAsJsonArray().get(0).getAsJsonObject().get("name").getAsString();
public class Baseproperties
{
#JsonProperty("id")
private String id ;
private Integer ccode;
//...set and geters
}
public class Person
{
#JsonProperty("name")
private String name ;
private Integer age;
#JsonProperty("props")
private Baseproperties bprop;
//...set and geters
}
public class Cars
{
#JsonProperty("model")
private String Model ;
private Integer yearOfMake;
#JsonProperty("props")
private Baseproperties bprop;
//...set and geters
}
public MessageWrapper
{
#JsonProperty("ct")
private String classType;
private Object data;
//...set and geters
}
I need to serialise MessageWrapper class to json, but the approach fails due to unable to desearialize the Object data;
here i am reading the classType and desearializing it to either Person or CarType
//Person
{
"name": "arnold",
"age": 21
}
//car
{
"model": "Moriz",
"yearOfMake": 1892
}
//example MessageWrapper
String s= "{
"ct": "<packagename>.car",
"data": {
"model": "Moriz",
"yearOfMake": 1892
"props":{
"id" : "12312",
"ccode" :33
}
}
}"
mapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);
MessageWrapper mw = mapper.readValue(s, MessageWrapper.class);
if(mw.getclassType().toString().equals("<packagename>.car"))
Cars cw = mapper.readValue(mw.getData(), Cars.class);
but cw is wrong // serialise fails.
This is because there is no ObjectMapper::readValue method that takes Object as first argument.
By default with your approach Jackson will deserialize your data field to LinkedHashMap because you have given it Object type.
To then deserialize this value manually you will have to use ObjectMapper::convertValue and passing Cars.class as argument :
Cars cw = mapper.convertValue(mw.getData(), Cars.class);
And also get rid of :
mapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);
as it does not seem to be needed here.
And just to add, I am not sure that approach with such dynamic data is good because, if you will be creating more and more types of objects you will end up with a tower of ifs or colosal switch statement.
I intend to create a JSON Array with the following structure. The metadata tag is going to constant in all the entries. I am stumped.
[{
"metadata": {
"Value": "String"
},
"name": "String",
"id": "String"
},
{
"metadata": {
"Value": "String"
},
"name": "String",
"id": "String"
}
]
public class yourJsonObject {
private Map<String, String> metadata;
private String name;
private string id;
public yourJsonObject() {
}
public Map<String, String> getMetadata(){
return metadata;
}
public void setMetadata(Map<String, String> metadata){
this.metadata = metadata;
}
public String getName(){
return name;
}
public void setName(String name) {
this.name = name;
}
public String getId(){
return id;
}
public void setId(String id){
this.id = id;
}
}
Then somewhere else you can just do this:
ObjectMapper mapper = new ObjectMapper(); // create once, reuse
yourJsonObject example = new yourJsonObject(); // have your POJO you want to save
mapper.writeValue(new File("result.json"), example);
To read you can just use:
ObjectMapper mapper = new ObjectMapper(); // create once, reuse
yourJsonObject value = mapper.readValue(new File("data.json"), yourJsonObject .class);
Both snippets are taken from my linked wiki article from jackson themselves.
Jackson should automatically be able to parse this POJO to an equivalent JSON if configured correctly.
Note: Jackson has to be globally registered and has to know about it. Please read the wiki of what you use to know about it... Jackson in 5 Minutes
Else you could just manually build the JSON like Neeraj said.
JSONArray array = new JSONArray(); // Create JSONArray Object
JSONObject jsonObject = new JSONObject(); // Your JSONObject which gets added into array
jsonObject.put("metadata",new MetaDataCustomClass("SomeRandomStringValue"));
jsonObject.put("name", "Neeraj");
jsonObject.put("id", "123");
array.add(jsonObject); // Here you push the jsonObject into Array.
Note: MetaDataCustomClass is just a custom Class having a Value instance variable of type String.
Class MetaDataCustomClass {
private String value;
public MetaDataCustomClass(String value){
this.value = value;
}
}
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();
}
I am trying to load my Json into my class
public User() {
this.fbId = 0;
this.email = "";
this.name = "";
this.thumb = "";
this.gender = "";
this.location = "";
this.relationship = null;
this.friends = new ArrayList();
}
{
users:{
user:{
name:'the name',
email:'some#email.com',
friends:{
user:{
name:'another name',
email:'this#email.com',
friends:{
user:{
name:'yet another name',
email:'another#email.com'
}
}
}
}
}
}
}
I am struggling to get GSON to load the user details into the above Java object with the following code
User user = gson.fromJson(this.json, User.class);
The JSON is invalid. A collection is not to be represented by {}. It stands for an object. A collection/array is to be represented by [] with commaseparated objects.
Here's how the JSON should look like:
{
users:[{
name: "name1",
email: "email1",
friends:[{
name: "name2",
email: "email2",
friends:[{
name: "name3",
email: "email3"
},
{
name: "name4",
email: "email4"
}]
}]
}]
}
(note that I added one more friend to the deepest nested friend, so that you understand how to specify multiple objects in a collection)
Given this JSON, your wrapper class should look like this:
public class Data {
private List<User> users;
// +getters/setters
}
public class User {
private String name;
private String email;
private List<User> friends;
// +getters/setters
}
and then to convert it, use
Data data = gson.fromJson(this.json, Data.class);
and to get the users, use
List<User> users = data.getUsers();