Develop Reference

org.json.simple. get unique nested value

I have a json with complex nested. values. But there is one unique key value pair in the json.. without traversing , I need to retrieve the value .
for example:
name : "xyz". In the entire complex nested json , I need to return a json with all the values of name key.
I am currently using org.simple.json. but its very complex as I have to traverse through the entire nested json and build JSONArray etc.

maybe you can use java8 stream，the way is very easy to solve your problem.
example：
[
{
"name":"xyz",
"value":"1"
},
{
"name":"xyz",
"value":"2"
},
{
"name":"xyz",
"value":"3"
}
]
and then，you can create a class:
import lombok.Data;
#Data
public class JsonTest {
private String name;
private String value;
}
finally, like this. btw, I am currently using other json package.
List<JsonTest> jsonArray = JSON.parseArray(json, JsonTest.class);
List<String> valueList = jsonArray.stream()
.filter(e -> "xyz".equals(e.getName()))
.map(JsonTest::getValue)
.collect(Collectors.toList());

Java - Remove Fields from a JSON String recursively without POJOs

How do I remove some fields with a specified name from a JSON string recursively ?
For example, I want to remove the field "secondName" from the following JSON:
INPUT:
{
"name" : "abc",
"secondName": "qwe",
"add" : "abcd",
"moreDetails" : {
"secondName": "qwe",
"age" : "099"
}
}
OUTPUT:
{
"name" : "abc",
"add" : "abcd",
"moreDetails" : {
"age" : "099"
}
}
I have to remove some fields from a lot of different JSONs with different structures/schema, so I won't be able to deserialize/serialize to/from a POJO.

Gson deserializes any valid Json to LinkedTreeMap, like:
LinkedTreeMap<?,?> ltm = new Gson().fromJson(YOUR_JSON, LinkedTreeMap.class);
Then it is just about making some recursive methods to do the clean up:
public void alterEntry(Entry<?, ?> e) {
if(e.getValue() instanceof Map) {
alterMap((Map<?, ?>) e.getValue());
} else {
if(e.getKey().equals("secondName")) { // hard coded but you see the point
e.setValue(null); // we could remove the whole entry from the map
// but it makes thing more complicated. Setting null
// achieves the same.
}
}
}
public void alterMap(Map<?,?> map) {
map.entrySet().forEach(this::alterEntry);
}
Usage:
alterMap(ltm);

You could try storing the JSON as a JSONObject, iterate over the keys using jsonObject.names() and remove the entries using jsonObject.remove(key).

You can do like below if you know the schema and heirarchy:
JsonObject jsonObj= gson.fromJson(json, JsonObject.class);
jsonObj.getAsJsonObject("moreDetails").remove("secondName");
System.out.println(jsonObj.getAsString());
refer this for more info Remove key from a Json inside a JsonObject
else you need to write a dynamic function which will check each and every element of JSON object and try to find the secondName element in it and remove it.
So consider here as you have multiple nested objects then you need to write a function which will iterate over each element and check its type if its again a jsonObject call the same method recursively or iteratively to check against current element, in each check you need to also verify that the key, if it matches with the key which has to be removed then you can remove it and continue the same.
for a hint on how to check a value type of JSON see this How to check the type of a value from a JSONObject?

What is the reasoning on modelling a class to represent JSON data and do I need to?

I have come across this question on StackOverflow which asks about converting JSON to Java. The answer shows that another class is modelled to represent the JSON data as well as an object being created and I don't understand why.
Does that object now contain all the information after Gson reads the content or only one key/value pair? If it only contains 1 key/value pair, I'm assuming I would need to create multiple objects for the JSON that I have below which I can the use a loop to iterate over and add the values to a drop down menu?
{
"1": "Annie",
"2": "Olaf",
"3": "Galio",
"4": "TwistedFate",
"5": "XinZhao",
"6": "Urgot",
"7": "Leblanc",
"8": "Vladimir",
"9": "FiddleSticks",
"10": "Kayle",
"11": "MasterYi",
"12": "Alistar",
"13": "Ryze",
"14": "Sion",
"15": "Sivir",
"16": "Soraka",
"17": "Teemo",
"18": "Tristana",
"19": "Warwick",
"20": "Nunu"
}
Essentially what I am aiming to do is:
1) Create a list of names with the Values.
2) Sort the list of names (as it comes unsorted) in alphabetical order
3) Loop through the list and add each name to a drop down menu
4) When a name in the drop down menu is selected, the key associated with that value is passed to another url which receives more data.
Sorry if this is unclear. I've spent a couple of hours trying to understand how to get elements from JSON and display it, as well as trying to create a list where I can use the key to display information the name but have had no luck except for using a for-each loop.

Let's use Jackson's feature that allows you to map any property to a single method (you don't really need a getter here I believe). Just swap the key and value in this universal setter, and add to a TreeMap, which is already sorted by key (name). Then you can output the keys (names) in the alphabetical order and get an ID by name easily.
public static void main(String[] args) throws IOException {
String json = "....."; // your JSON string here
com.fasterxml.jackson.databind.ObjectMapper mapper =
new com.fasterxml.jackson.databind.ObjectMapper();
ReverseMap pairs = mapper.readValue(json, ReverseMap.class);
for (Map.Entry<Object, String> entry : pairs.getValues().entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
}
public class ReverseMap {
private TreeMap<Object, String> mapping = new TreeMap<>();
#com.fasterxml.jackson.annotation.JsonAnySetter
public void add(String name, Object value) {
mapping.put(value, name);
}
public Map<Object, String> getValues() {
return mapping;
}
}

Gson Bean Mapping Solution
Okay, what you have is a bit unusual for a JSON object; the keys (the numbers in your case) essentially represent properties of their contained object. That's workable, but you have to understand that, for example, when looking for "Annie" in the JSON object, if you use Gson to map to a "bean" class, which we'll call Data (as in the linked example), then you'd have to create a data object like so:
class Data {
private String _1;
// ...
private String _20;
public String get1() { return _1; }
public void set1(String _1) { this._1 = _1; }
// ...
public String get20() { return _20; }
public void set20(String _20) { this._20 = _20; }
}
And by using Data data = new Gson().fromJson(myJsonString, Data.class); on the given string, you'd be able to find "Annie" by calling... uh... data.get1()?
Clearly, this isn't a good solution.
Better Solutions
Since your data doesn't follow the typical format for a JSON object, you have two options:
If you can, refactor your JSON representation to a more verbose, but better representation for parsing.
Use a different approach to parse the existing JSON.
Solution 1: Changing the JSON representation
Refactoring the JSON would result in an object that (preferably) would look like this:
{
"champions" : [
{
"index" : 1,
"name" : "Annie"
},
{
"index" : 2,
"name" : "Olaf"
},
// ...
]
}
This could map easily to a couple of beans that look like this:
class Data {
private List<Champion> champions;
// TODO getters and setters
}
class Champion {
private int index;
private String name;
// TODO getters and setters
}
However, this adds a lot of unnecessary clutter to the JSON object, and isn't really necessary with only two fields per champion (the name, and their index).
You could simplify that further like so:
{
"champions" : [
"Annie",
"Olaf",
// ...
]
}
The bean class for that would then be:
class Data {
private List<String> champions;
// TODO getters and setters
}
Much simpler, but still requires a change to the JSON you're getting, which in some situations isn't possible. If you used this, though, you could also get rid of the "bean" class entirely, via:
List<String> champions = (List<String>) new Gson().fromJson(myJsonString, new TypeToken<List<String>>(){}.getType());
Solution 2: Changing how the JSON is parsed
The arguably better and cleaner solution is just to change how the JSON is parsed.
The goal here (if I understand you correctly) is to parse the JSON and spit out a collection of strings representing each champion's name, accessible by the numeric index of the champion in the JSON representation.
As such, and because of the way the JSON object is laid out as a simple mapping of strings to strings, we can use Gson to pipe directly into a Map<String, Object>, like so:
Map<String, String> mappedValues = new Gson().fromJson(myJsonString, Map.class);
String anniesName = mappedValues.get("1"); // "Annie"
String olafsName = mappedValues.get("2"); // "Olaf"
boolean hasTwentyOneElements = mappedValues.containsKey("21"); // false
This is shorter, requires no "bean" classes, and keeps the original JSON representation. The downside is that you can't easily tell whether the indices of each entry are correct and consistent; ie. if someone types in the wrong number, or deletes one of the entries.
To get a container of all keys, you just use mappedValues.keySet(), and to get a container of all key-value pairs, you use mappedValues.entrySet(), which gives you a Set<Map.Entry<String, String>>. Both of those can be iterated over, and may be in random order (I'm not sure whether the underlying Map implementation preserves insertion order or not).
To get the index for a given name (ie. champ), you'd use something similar to the following:
String index = null;
for (Map.Entry<String, String> entry : mappedValues.entrySet()) {
if (champ.equals(entry.getValue())) {
index = entry.getKey();
break;
}
}
Of course, you'd have to check to see if index is null after this, and handle that appropriately, but it's easily doable.
EDIT: #vempo's answer provides a cleaner, more efficient lookup strategy by means of inverting the map (although the answer is written for Jackson, instead of Gson); an adaptation of this for Gson is as follows (and yes, there is a vastly superior version in java-8, left out for sake of availability):
public Map<String, String> invertMap(Map<String, String> input) {
Map<String, String> newMap = new LinkedTreeMap<String, String>(); // TODO Pick optimal storage class
for (Map.Entry<String, String> entry : input.entrySet()) {
newMap.put(entry.getValue(), entry.getKey());
}
return newMap;
}
// ...
Map<String, String> mappedValues = invertMap(new Gson().fromJson(myJsonString, Map.class));
String annieIndex = mappedValues.get("Annie"); // "1"
String olafIndex = mappedValues.get("Olaf"); // "2"
It's worth noting that this sacrifices efficiency of constructing the map by effectively building it twice (once by Gson and once more to invert), but it makes value lookup much more efficient.

How to translate the Json in to POJO

I have the following JSON I need to be able to present in POJO, how could I
do this ?
The JSON has one key per day and the value for each key is two separate logical arrays, I am using Jackson library.
{
"2014/01/02": [
{"ABC": 2.25, "XYZ": 4.05},
{"amazon.com": 3}
],
"2014/01/03": [
{"ABC": 13.02},
{"amazon.com": 3}
]
}

You don't have much option. That's an ugly looking JSON. There is no consistent format, where you can create POJO.
Things you need to consider. This {} is a JSON object. Im Java mapping terms, it can either map to a POJO, or a Map. In order to map to a POJO, you need to common property names and formatting, of which it doesn't seem like you have. It all seems to be varying. So you may need to use a Map. Here's how I look at it
{ // Start Map
"2014/01/02": [ // Map key: start Array ( List<Map> )
{"ABC": 2.25, "XYZ": 4.05}, // Start another Map
{"amazon.com": 3} // another Map
You can use #JsonAnySetter to simplify, using a POJO wrapper, but you will still have, in the end a Map<String, List<Map<String, Object>> as I pointed out in my comment. If you want POJOs, there needs to be some common formatting.
Here's an example of one way to make it work
POJO
public class Dynamic {
private Map<String, Object> map = new HashMap<>();
public Object get(String key) {
return map.get(key);
}
public Map<String, Object> getMap() {
return map;
}
#JsonAnySetter
public void set(String name, Object value) {
map.put(name, value);
}
}
Test (using your exact JSON in simple.json file)
public class Test {
public static void main(String[] args) throws Exception {
ObjectMapper mapper = new ObjectMapper();
Dynamic dynamic = mapper.readValue(new File("simple.json"), Dynamic.class);
for (String key : dynamic.getMap().keySet()) {
System.out.println("key: " + key);
System.out.println("--------");
List<Map<String, Object>> list = (List<Map<String, Object>>) dynamic.get(key);
for (Map<String, Object> map : list) {
for (Map.Entry<String, Object> entry: map.entrySet()) {
System.out.println("key: " + entry.getKey() + ", value: " + entry.getValue());
}
}
System.out.println("========");
}
}
}
Result
key: 2014/01/03
--------
key: ABC, value: 13.02
key: amazon.com, value: 3
========
key: 2014/01/02
--------
key: ABC, value: 2.25
key: XYZ, value: 4.05
key: amazon.com, value: 3
========

{
"2014/01/02": [
{"ABC": 2.25, "XYZ": 4.05},
{}
],
"2014/01/03": [
{"ABC": 13.02},
{"amazon.com": 3}
]
}
This is even JSON, but not useful. I would make JSON for this like below.
{
[
{date: '2014/01/01',data:[{abc: 13.02, "amazonCom": 3},{abc: 13.02, "amazonCom": 3}},
{date: '2014/01/02',data:[{abc: 13.02, "amazonCom": 3},{abc: 13.02, "amazonCom": 3}},
]
}
Java
public jsonObj {
private String date;
private List<DateData> data;
.... setter//getter
}
public class DateData {
private double abc;
private int amazoneCom;
//constructor and getter/setter
}
You can use JSON libraries like below.
1. Jackson - http://jackson.codehaus.org/
2. Gson - https://code.google.com/p/google-gson/
Those libraries helps you to convert json into Java Object and vise versa as well.
Hope it can help you with solving your problem.

There are many ways to transform json to pojo. Here I am sharing few URL to achieve the same
Google Gson Tutorial : Convert Java Object to / from JSON http://howtodoinjava.com/2014/06/17/google-gson-tutorial-convert-java-object-to-from-json/
Generate Plain Old Java Objects from JSON or JSON-Schema. http://www.jsonschema2pojo.org/

How to perform deeper matching of keys and values with assertj

Say I have a class like this:
public class Character {
public Character(String name){
this.name = name;
}
private String name;
public String getName() { return name; }
}
And later, a Map
Map<Character, Integer> characterAges = new HashMap<Character, Integer>();
characterAges.put(new Character("Frodo"), 34);
Using assertj, what is the best way to test that characterAges includes the "Frodo" character? For the age, I can do:
assertThat(characterAges).hasValue(34);
And I know I could do:
assertThat(characterAges.keySet())
.extracting("name")
.contains("Frodo");
But then I lose my fluency. What I really want it something like this:
assertThat(characterAges)
.hasKey(key.extracting("name").contains("Frodo")
.hasValue(34);
Or even better, so that I can make sure my key and value match:
assertThat(characterAges)
.hasEntry(key.extracting("name").contains("Frodo"), 34);
Is something like this possible?

There is no easy solution for this. One way is to implement a custom Assertion for the character map. Here is a simple custom Assertion example for this problem:
public class CharacterMapAssert extends AbstractMapAssert<MapAssert<Character, Integer>, Map<Character, Integer>, Character, Integer> {
public CharacterMapAssert(Map<Character, Integer> actual) {
super(actual, CharacterMapAssert.class);
}
public static CharacterMapAssert assertThat(Map<Character, Integer> actual) {
return new CharacterMapAssert(actual);
}
public CharacterMapAssert hasNameWithAge(String name, int age) {
isNotNull();
for (Map.Entry<Character, Integer> entrySet : actual.entrySet()) {
if (entrySet.getKey().getName().contains(name) && (int) entrySet.getValue() == age) {
return this;
}
}
String msg = String.format("entry with name %s and age %s does not exist", name, age);
throw new AssertionError(msg);
}
}
In the test case:
assertThat(characterAges).hasNameWithAge("Frodo", 34);
Be aware that you have for every custom data structure to write your own assertion. For you Character class you can generate a assertion with the AssertJ assertions generator.
Update Java 8
With Java 8 can also the Lambda Expression used
assertThat(characterAges).matches(
(Map<Character, Integer> t)
-> t.entrySet().stream().anyMatch((Map.Entry<Character, Integer> t1)
-> "Frodo".equals(t1.getKey().getName()) && 34 == t1.getValue()),
"is Frodo and 34 years old"
);

You can also do something like this:
assertThat(characterAges).contains(entry("Frodo", 34), ...);
See https://github.com/joel-costigliola/assertj-core/wiki/New-and-noteworthy#new-map-assertions

The following methods of AbstractMapAssert will work for you:
containsExactlyEntriesOf Verifies that the actual map contains only the entries of the given map and nothing else, in order. This should be used with TreeMap. HashMap will not guarantee order and your test will randomly fail.
containsExactlyInAnyOrderEntriesOf Verifies that the actual map contains only the given entries and nothing else, in any order. This will work with HashMap.
import java.util.Map;
import org.assertj.core.api.Assertions;
import org.junit.jupiter.api.Test;
public class TestMapAssertions {
#Test
public void testCreateMap() {
//Call
Map<String, String> actual = ClassUnderTest.createMap();
//Assert
Assertions.assertThat(actual).containsExactlyInAnyOrderEntriesOf(
Map.of("Key1", "Value1", "Key2", "Value2")
);
}
public static class ClassUnderTest {
public static Map<String, String> createMap() {
return Map.of("Key1", "Value1", "Key2", "Value2");
}
}
}

Since 3.6.0, you can use hasEntrySatisfying:
assertThat(characterAges)
.hasSize(1)
.hasEntrySatisfying(aKey, e ->
assertThat(e)
.isEqualTo(99.99)
);
In your case, if you cannot use the key for lookup you can use Condition-based hasEntrySatisfying (more verbose).

I am not sure about the date/version of introduction, but there are a bunch of assertions in MapAssert now. From http://joel-costigliola.github.io/assertj/core-8/api/org/assertj/core/api/MapAssert.html:
contains(Map.Entry... entries)
- Verifies that the actual map contains the given entries, in any order.
containsAnyOf(Map.Entry... entries)
- Verifies that the actual map contains at least one of the given entries.
containsExactly(Map.Entry... entries)
- Verifies that the actual map contains only the given entries and nothing else, in order.
containsKeys(KEY... keys)
- Verifies that the actual map contains the given keys.
containsOnly(Map.Entry... entries)
- Verifies that the actual map contains only the given entries and nothing else, in any order.
containsOnlyKeys(KEY... keys)
- Verifies that the actual map contains only the given keys and nothing else, in any order.
containsValues(VALUE... values)
- Verifies that the actual map contains the given values.
doesNotContain(Map.Entry... entries)
- Verifies that the actual map does not contain the given entries.
doesNotContainKeys(KEY... keys)
- Verifies that the actual map does not contain any of the given keys.
extracting(Function,Object>... extractors)
- Uses the given Functions to extract the values from the object under test into a list, this new list becoming the object under test.
For your example, containsExactly() should do the trick.

If you didn't want to go down the custom assert route, and could access the instances of the characters in the SUT (system under test) in the test, another option could be
In the SUT:
Character frodo = new Character("Frodo");
characterAges.put(frodo, 34);
And in the test
MapEntry frodoAge34 = MapEntry.entry(frodo, 34);
assertThat(characterAges).contains(frodoAge34);

What about using .entrySet() with .extracting()?
assertThat(characterAges.entrySet())
.extracting(
entry -> entry.getKey().getName(),
Map.Entry::getValue)
.contains(tuple("Frodo", 34));

Below is my example for asserting the nested map of response from actuator endpoint.
Below is the sample response from actuator endpoint. Response is a json response with two root level keys named "git" and "build" both of them are nested json. Below is an example of testing the build json structure
{
"git": {
"branch": "my-test-branch",
"build": {
"time": "2022-03-08T12:43:00Z",
"version": "0.0.1-SNAPSHOT",
"user": {
"name": "gituser",
"email": "gituseremail#domain.com"
},
"host": "hostName"
}
},
"build": {
"artifact": "test-project",
"name": "test-name",
"time": "2022-03-08T12:45:07.389Z",
"version": "0.0.1-SNAPSHOT",
"group": "com.exmaple"
}
}
Below is the test.
#SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyApplicationTest {
#Autowired
private TestRestTemplate restTemplate;
#Test
void testInfoActuatorEndpoint() {
Map responseMap = this.restTemplate.getForObject("/actuator/info", Map.class);
assertThat(responseMap)
.hasSize(2)
.containsKey("git")
.containsKey("build")
.extracting("build")
.hasFieldOrPropertyWithValue("artifact", "test-project")
.hasFieldOrPropertyWithValue("name", "test-name")
.hasFieldOrPropertyWithValue("version", "0.0.1-SNAPSHOT")
.hasFieldOrPropertyWithValue("group", "com.example");
}
}