We Keep Coding

Simplest way to convert this array in to the specified one using Java

I have this String Json Payload
[
"key1":{
"atr1":"key1",
"atr2":"value1",
"atr3":"value2",
"atr4":"value3,
"atr5":"value4"
},
"key2":{
"atr1":"key2",
"atr2":"value5",
"atr3":"value6",
"atr4":value7,
"atr5":"value8"
}
]
and I want it to be converted in to the following format using Java
[
{
"atr2":"value1",
"atr3":"value2",
"atr4":"value3,
"atr5":"value4"
},
{
"atr2":"value5",
"atr3":"value6",
"atr4": "value7",
"atr5":"value8"
}
]
What would be the simplest way of transforming this ?

You cannot, because the example below is not valid json.
Check it out using this JSON validator.
If you paste this in (I've fixed some basic errors with lack of quotes)
{
{
"atr2":"value1",
"atr3":"value2",
"atr4":"value3",
"atr5":"value4"
},
{
"atr2":"value5",
"atr3":"value6",
"atr4":"value7",
"atr5":"value8"
}
}
You will get these errors ...
It can work if you change the target schema to something like this by using a json-array to contain your data.
[
{
"atr2":"value1",
"atr3":"value2",
"atr4":"value3",
"atr5":"value4"
},
{
"atr2":"value5",
"atr3":"value6",
"atr4":"value7",
"atr5":"value8"
}
]
If this works for you, then this problem can easily be solved by using the ObjectMapper class.
You use it to deserealize the original JSON into a class, which has two fields "key1" and "key2"
Extract the values of these fields and then just store them in an array ...
Serialize the array using the ObjectMapper.
Here a link, which explains how to use the ObjectMapper class to achieve the goals above.
EDIT:
So you'll need the following classes to solve the problem ...
Stores the object data
class MyClass {
String atr2;
String art3;
}
Then you have a container class, which is used to store the initial json.
class MyClassContainer {
MyClass key1;
MyClass key2;
}
Here's how you do the parse from the original json to MyClassContainer
var mapper = new ObjectMapper()
var json = //Get the json String somehow
var myClassContainer = mapper.readValue(json,MyClassContainer.class)
var mc1 = myClassContainer.getKey1();
var mc2 = myClassContainer.getKey2();
var myArray = {key1, key2}
var resultJson = mapper.writeValueAsString(myArray)

Assuming that you will correct the JSON into a valid one (which involves replacing the surrounding square braces with curly ones, and correct enclosure of attribute values within quotes), here's a simpler way which involves only a few lines of core logic.
try{
ObjectMapper mapper = new ObjectMapper();
mapper.configure( DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false );
HashMap<String, Data> map = mapper.readValue( jsonString, new TypeReference<HashMap<String, Data>>(){} );
String json = mapper.writeValueAsString( map.values() );
System.out.println( json );
}
catch( JsonProcessingException e ){
e.printStackTrace();
}
jsonString above is your original JSON corrected and valid JSON input.
Also notice the setting of FAIL_ON_UNKNOWN_PROPERTIES to false to allow atr1 to be ignored while deserializing into Data.
Since we are completely throwing away attr1 and its value, the Data class will represent all fields apart from that.
private static class Data{
private String atr2;
private String atr3;
private String atr4;
private String atr5;
}

How to get json value with jackson?

String url = "https://ko.wikipedia.org/w/api.php?action=query&format=json&list=search&srprop=sectiontitle&srlimit=1&srsearch=grand-theft-auto-v";
String test = restTemplate.getForObject(url, String.class);
Map<String, String> testToJson = objectMapper.readValue(test, Map.class);
testToJson is:
{
batchcomplete: "",
continue: {
sroffset: 1,
continue: "-||",
},
query: {
searchinfo: {
totalhits: 12
},
search: [
{
ns: 0,
title: "그랜드 테프트 오토 V",
pageid: 797633,
}
],
},
}
I want to get title value.
I try
testToJson.get("title")
but it returns null.
How to get title value with jackson?

You can deserialise it to a JsonNode and use JSON Pointer to get required field:
JsonNode node = mapper.readValue(jsonFile, JsonNode.class);
String title = node.at("/query/search/0/title").asText();

you could build a class for this json result then read from it.
public class Result {
private JsonNode searchinfo;
private JsonNode[] searches;
}
// then read:
Result testToJson = objectMapper.readValue(test, Result.class);
System.out.println(testToJson.getSearches(0).get("title"));
refer

It is impossible to read JSON into an instance of a generic class like that because the info about generics are used in compile time and already lost when program is running.
Jackson captures the data about generics using a sub-classed instance of TypeReference<T>.
Map<String, String> testToJson = objectMapper.readValue(test, new TypeReference<Map<String, String>>(){});
The problem with this approach is that Map<String, String> almost never describes complex data (like in the example) correctly. The example contains not only string values, there are numbers and even nested objects.
In situations like that, when you don't want or cannot write a class that describes the structure of the JSON, the better choice is parsing the JSON into a tree structure and traverse it. For example:
JsonNode node = objectMapper.readTree(test);
String title = node.get("query").get("search").get(0).get("title").asText();
Integer offset = node.get("continue").get("strOffset").asInt()

Mapping Json Array to POJO using Jackson

I have a JSON array of the form:
[
[
1232324343,
"A",
"B",
3333,
"E"
],
[
12345424343,
"N",
"M",
3133,
"R"
]
]
I want to map each element of the parent array to a POJO using the Jackson library. I tried this:
ABC abc = new ABC();
ObjectMapper mapper = new ObjectMapper();
JsonNode jsonNode = mapper.readTree(data).get("results");
if (jsonNode.isArray()) {
for (JsonNode node : jsonNode) {
String nodeContent = mapper.writeValueAsString(node);
abc = mapper.readValue(nodeContent,ABC.class);
System.out.println("Data: " + abc.getA());
}
}
where ABC is my POJO class and abc is the object but I get the following exception:
com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of com.demo.json.model.ABC
EDIT:
My POJO looks like this:
class ABC{
long time;
String a;
String b;
int status;
String c;
}
Can someone suggest a solution for this?
EDIT 2: After consulting a lot of answers on StackOverflow and other forums, I came across one solution. I mapped the returned value of readValue() method into an array of POJO objects.
ABC[] abc = mapper.readValue(nodeContent, ABC[].class);
But now I am getting a separate exception
Can not construct instance of ABC: no long/Long-argument constructor/factory method to deserialize from Number value (1552572583232)
I have tried the following but nothing worked:
1. Forcing Jackson to use ints for long values using
mapper.configure(DeserializationFeature.USE_LONG_FOR_INTS, true);
2. Using wrapper class Long instead of long in the POJO
Can anyone help me with this?

You can use ARRAY shape for this object. You can do that using JsonFormat annotation:
#JsonFormat(shape = Shape.ARRAY)
class ABC {
And deserialise it:
ABC[] abcs = mapper.readValue(json, ABC[].class);
EDIT after changes in question.
You example code could look like this:
JsonNode jsonNode = mapper.readTree(json);
if (jsonNode.isArray()) {
for (JsonNode node : jsonNode) {
String nodeContent = mapper.writeValueAsString(node);
ABC abc = mapper.readValue(nodeContent, ABC.class);
System.out.println("Data: " + abc.getA());
}
}
We can use convertValue method and skip serializing process:
JsonNode jsonNode = mapper.readTree(json);
if (jsonNode.isArray()) {
for (JsonNode node : jsonNode) {
ABC abc = mapper.convertValue(node, ABC.class);
System.out.println("Data: " + abc.getA());
}
}
Or even:
JsonNode jsonNode = mapper.readTree(json);
ABC[] abc = mapper.convertValue(jsonNode, ABC[].class);
System.out.println(Arrays.toString(abc));

Your json does not map to the pojo that you have defined. For the pojo that you have defined, the json should be of the form below.
{
"time:1232324343,
"a":"A",
"b":"B",
"status":3333,
"c":"E"
}

Jackson: understand if source JSON is an array or an object

Parsing JSON in Jackson library would require:
for an object
MapType hashMapType = typeFactory.constructMapType(HashMap.class, String.class, Object.class);
Map<String, Object> receivedMessageObject = objectMapper.readValue(messageBody, hashMapType);
for an array of objects
Map[] receivedMessage = objectMapper.readValue(messageBody, HashMap[].class)
What would be the best way to check whether I have array or object in messageBody, in order to route to the correct parsing? Is it just to directly check for array token in MessageBody?

An option is just to treat everything that might be an array as an array. This is often most convenient if your source JSON has just been auto-transformed from XML or has been created using an XML-first library like Jettison.
It's a sufficiently common use case that there's a Jackson switch for this:
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
You can then just deserialize a property into a collection type, regardless of whether it's an array or an object in the source JSON.

If you want to know whether your input is an array or an object, you can simply use the readTree method. A simple example:
ObjectMapper mapper = new ObjectMapper();
String json1 = "{\"key\": \"value\"}";
String json2 = "[\"key1\", \"key2\"]";
JsonNode tree1 = mapper.readTree(json1);
System.out.println(tree1.isArray());
System.out.println(tree1.isObject());
JsonNode tree2 = mapper.readTree(json2);
System.out.println(tree2.isArray());
System.out.println(tree2.isObject());
If you want to be able to deserialize to multiple types, have a look at Polymorphic Deserialization

This is what I did based on the answer from #ryanp :
public class JsonDataHandler {
public List<MyBeanClass> createJsonObjectList(String jsonString) throws JsonMappingException, JsonProcessingException {
ObjectMapper objMapper = new ObjectMapper();
objMapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
List<MyBeanClass> jsonObjectList = objMapper.readValue(jsonString, new TypeReference<List<MyBeanClass>>(){});
return jsonObjectList;
}
}

Java boon JSON parser removing null values from output

I have a small function which takes an input JSON string, parses it using boon into a Map, replaces a value for a particular key, returns back the JSON string of the modified Map.
The code is as follows:
// inputJson = {"key3":"A","key2":"B","key1":null,"keyX":[{"x":2019,"y":123,"z":456},{"x":2017,"y":234,"z":345},{"x":2018,"y":456,"z":567}]}
private static String sorter(String inputJson) {
JsonParserAndMapper mapper = new JsonParserFactory().strict().create();
Map<String, Object> map = mapper.parseMap(inputJson);
List<?> l1 = (List<?>) map.get("keyX");
sort(l1, Sort.sortBy("x"));
map.replace("keyX", l1);
for (String x: map.keySet())
System.out.println(map.get(x));
String outputJson = toJson(map); // problem seems to be here
return outputJson
// outputJson = {"key2":"B","key3":"A","keyX":[{"x":2017,"y":234,"z":345},{"x":2018,"y":456,"z":567},{"x":2019,"y":123,"z":456}]}
The problem is, when I do toJson(map) it removes the key with null values. So, if inputJson contains a key with a null value, it doesn't appear in the output. (Notice: key1 is missing in the output)
How can I parse this without losing the null fields?

Using toJson you are using a default serialiser factory. From boon source code:
public class JsonFactory {
private static ObjectMapper json = JsonFactory.create();
public static ObjectMapper create () {
JsonParserFactory jsonParserFactory = new JsonParserFactory();
jsonParserFactory.lax();
return new ObjectMapperImpl(jsonParserFactory, new JsonSerializerFactory());
}
....
)
Instead of using toJson try using a serialiser factory with includeNulls()
JsonSerializer factory = new JsonSerializerFactory().includeNulls().create();