Develop Reference

How do I use my Jackson KeyDeserializer in nested maps?

Problem
In an existing application, I have to deserialize possibly deeply nested maps, and apply a custom Jackson de-serializer on all keys at all levels.
Since the application handles all kinds of datamodels dynamically, I cannot use an explicit datamodel with clearly typed maps... Instead, I use a Map<String, Object> and checks whether the deserialized Object value itself is a Map.
This causes the custom de-serializer to only apply to the top-level map.
Update: It's important to note that I cannot bind a deserializer to all maps because my datamodel often have more specific maps as well. I typically have fields that are a generic Map<String, Object> for open-ended JSON settings; living together with e.g. Map<EnumType, Double> for more explicit bits of configuration.
Example
To illustrate, I have come up with toy-example below:
ObjectMapper objectMapper = new ObjectMapper().registerModule(new SimpleModule()
.addKeyDeserializer(String.class, new KeyDeserializer() {
#Override
public Object deserializeKey(String s, DeserializationContext deserializationContext) {
return s.toUpperCase();
}
}));
Map<String, Object> value = objectMapper.readValue(
"{\"zero\": 1, \"two\": { \"three\": 4 }}",
new TypeReference<Map<String, Object>>() {}
);
assertThat(value).containsKeys("ZERO", "TWO"); // pass
assertThat((Map) value.get("TWO")).containsKey("THREE"); // fail
The last line of code fails:
java.lang.AssertionError:
Expecting:
<{"three"=4}>
to contain key:
<"THREE">
I cannot declare the type as Map<String, Map<String, Object>> because of the int value that is at the same level. If I try, I get:
Cannot deserialize instance of java.util.LinkedHashMap out of VALUE_NUMBER_INT token
Questions
In this example, what is the best way for me to get upper-cased keys in all nested Maps, even though I need to declare them as Object?
Is there an alternative way to approach this?

Below is a working solution. Though it does not use the KeyDeserializer, as you found out, the KeyDeserializer won't go deep into the JSON to uppercase all the inner JSON field names.
The solution below uses a JsonDeserializer instead of the KeyDeserializer. I took your example and passed a more complicated JSON to test it. It traverses through all the objects in the JSON and uppercases all the field names it comes across.
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper objectMapper = new ObjectMapper().registerModule(
new SimpleModule()
.addDeserializer(Map.class, new JsonDeserializer<>() {
#Override
public Map<String, Object> deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
var map = new HashMap<String, Object>();
while(!p.isClosed()){
JsonToken jsonToken = p.nextToken();
if (JsonToken.FIELD_NAME.equals(jsonToken)) {
String fieldName = p.getCurrentName().toUpperCase();
jsonToken = p.nextToken();
if (JsonToken.START_OBJECT.equals(jsonToken)) {
map.put(fieldName, getObject(p));
} else if (JsonToken.START_ARRAY.equals(jsonToken)) {
map.put(fieldName, getArray(p));
} else {
map.put(fieldName, getScalar(jsonToken, p));
}
}
}
return map;
}
})
);
Map<String, Object> value = objectMapper.readValue(
"{\"zero\": 1, \"two\": { \"three\": 4 }, \"four\": [\"item\", 5], \"five\": \"string\", \"six\": true, \"seven\": 1.2}",
new TypeReference<Map<String, Object>>() {}
);
assertThat(value).containsKeys("ZERO", "TWO"); // pass
assertThat((Map) value.get("TWO")).containsKey("THREE"); // pass
System.out.println("JSON = " + new GsonBuilder().setPrettyPrinting().create().toJson(value));
}
static Map<String, Object> getObject(JsonParser p) throws IOException {
var map = new HashMap<String, Object>();
JsonToken jt = p.nextToken();
while (!JsonToken.END_OBJECT.equals(jt)) {
if (JsonToken.FIELD_NAME.equals(jt)) {
String fieldName = p.getCurrentName().toUpperCase();
jt = p.nextToken();
if (JsonToken.START_OBJECT.equals(jt)) {
map.put(fieldName, getObject(p));
} else if (JsonToken.START_ARRAY.equals(jt)) {
map.put(fieldName, getArray(p));
} else {
map.put(fieldName, getScalar(jt, p));
}
}
jt = p.nextToken();
}
return map;
}
static List<Object> getArray(JsonParser p) throws IOException {
var list = new ArrayList<>();
JsonToken jt = p.nextToken();
while (!JsonToken.END_ARRAY.equals(jt)) {
if (JsonToken.START_OBJECT.equals(jt)) {
list.add(getObject(p));
} else if (JsonToken.START_ARRAY.equals(jt)) {
list.add(getArray(p));
} else {
list.add(getScalar(jt, p));
}
jt = p.nextToken();
}
return list;
}
static Object getScalar(JsonToken jsonToken, JsonParser p) throws IOException {
if (JsonToken.VALUE_NUMBER_INT.equals(jsonToken) || JsonToken.VALUE_NUMBER_FLOAT.equals(jsonToken)) {
return p.getNumberValue();
} else if (JsonToken.VALUE_FALSE.equals(jsonToken)) {
return false;
} else if (JsonToken.VALUE_TRUE.equals(jsonToken)) {
return true;
} else if (JsonToken.VALUE_STRING.equals(jsonToken)) {
return p.getValueAsString();
} else if (JsonToken.VALUE_NULL.equals(jsonToken)) {
return null;
}
throw new RuntimeException("did not find a scalar for JsonToken = " + jsonToken);
}
Right below is the output it generates.
JSON = {
"ZERO": 1,
"FIVE": "string",
"SIX": true,
"FOUR": [
"item",
5
],
"TWO": {
"THREE": 4
},
"SEVEN": 1.2
}
The code assumes the outermost JSON object is a map. So it would need a minor update in the JsonDeserializer to handle an array or scalar as the outer outermost JSON.

serialize map of maps to dyanmodb to json

To attribute Map below in a class that i want to save and read from Dyanmodb, using DynamoDBMapper.
Map<String, Map<String, Transition>> twf;
public class Transition {
public String fst;
public Permission pm;
public List<Action> ac;
}
public class Action {
private String mdl;
private String dsc;
private String nm;
// email address or any other data
private Map<String, String> data;
}
i have tried DynamoDBTypeConverted to convert to String, that results in json string that has " escaped as \" and unreadable in dyanmodb. I wanted to store as json
I implemented with understanding that Dyanmodb supports Map, but i still get error :
Exception processing message: not supported; requires #DynamoDBTyped or #DynamoDBTypeConverted
public class TimeSheetWorkFlowConverter implements
DynamoDBTypeConverter<Map<String, Object>, Map<String, Map<String, Transition>>> {
#Override
public Map convert(Map<String, Map<String, Transition>> object) {
// Map obj = mapper.readValue(object, Map.class);
String newJson = null;
Map objectJson = null;
try {
newJson = mapper.writeValueAsString(object);
objectJson = mapper.readValue(newJson, Map.class);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return objectJson;
}
#SuppressWarnings("unchecked")
#Override
public Map<String, Map<String, Transition>> unconvert(Map<String, Object> object) {
Map<String, Map<String, Transition>> wf = new HashMap<>();
if (object != null && !object.isEmpty())
for (Entry<String, Object> entry : object.entrySet()) {
String key = entry.getKey();
Map<String, Transition> value = mapTransition(entry.getValue());
wf.put(key, value);
}
return wf;
}

JSON String to Java String

I have these JSON String:
{
"Results": {
"output1": {
"type": "table",
"value": {
"ColumnNames": ["userId", "documentId", "Scored Labels", "Scored Probabilities"],
"ColumnTypes": ["String", "String", "Boolean", "Double"],
"Values": [["100213199594809000000", "1Ktol-SWvAh8pnHG2O7HdPrfbEVZWX3Vf2YIPYXA_8gI", "False", "0.375048756599426"], ["103097844766994000000", "1jYsTPJH8gaIiATix9x34Ekcj31ifJMkPNb0RmxnuGxs", "True", "0.753859758377075"]]
}
}
}
}
And I want to have only the ColumnNames and the Values. I have tried it with something like this:
Map<String,Object> map = mapper.readValue(filename, Map.class);
String CN = (String) map.get("ColumnNames");
But then I get the following error:
Exception in thread "main" org.codehaus.jackson.JsonParseException: Unexpected character ('A' (code 65)): expected a valid value (number, String, array, object, 'true', 'false' or 'null')
at [Source: java.io.StringReader#64232b15; line: 1, column: 2]`
I've worked only few times with JSON. Can anybody help me here?
The best case for me would be something like this, which I've done in another case:
String uId = (String) attr.get("userId");
Is it possible?
So now I've done this:
I try it like this:
public class ClientPOJO {
private String userId;
private String documentId;
public String getuserId() {
return userId;
}
public void setuserId(String userId) {
this.userId = userId;
}
public String getdocumentId() {
return documentId;
}
public void setdocumentId(String documentId) {
this.documentId = documentId;
}
}
and then:
ObjectMapper mapper = new ObjectMapper();
ClientPOJO clientes= mapper.readValue(filename, ClientPOJO.class);
String uid = clientes.getuserId();
But now when I make a Prtinout I'll get the same error like before:
Exception in thread "main" org.codehaus.jackson.JsonParseException: Unexpected character ('A' (code 65)): expected a valid value (number, String, array, object, 'true', 'false' or 'null')
at [Source: java.io.StringReader#7a6eb29d; line: 1, column: 2]

Java- Convert JSON string into string / integer / Object
String jsonString = "{"username":"Gajender"}";
org.json.JSONObject jsonObj =new JSONObject(jsonString);
String name = (String) jsonObj.get("username").toString();

Below is an example to illustrate a generic approach to solve your problem ( based on Jackson library). You may like to enhance the solution to meet your all requirements.
Comments inlined.
package com.stackoverflow;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import org.junit.Test;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
// Junit class
public class TableDeserExample {
// sample input
String inputJson = "{\n" +
" \"Results\": {\n" +
" \"output1\": {\n" +
" \"type\": \"table\",\n" +
" \"value\": {\n" +
" \"ColumnNames\": [\"userId\", \"documentId\", \"Scored Labels\", \"Scored Probabilities\"],\n" +
" \"ColumnTypes\": [\"String\", \"String\", \"Boolean\", \"Double\"],\n" +
" \"Values\": [[\"100213199594809000000\", \"1Ktol-SWvAh8pnHG2O7HdPrfbEVZWX3Vf2YIPYXA_8gI\", \"False\", \"0.375048756599426\"], [\"103097844766994000000\", \"1jYsTPJH8gaIiATix9x34Ekcj31ifJMkPNb0RmxnuGxs\", \"True\", \"0.753859758377075\"]]\n"
+
" }\n" +
" }\n" +
" }\n" +
"}";
// POJO to map the Json structure. You may want to make it generalize based
// on field "type"
// (https://github.com/FasterXML/jackson-docs/wiki/JacksonPolymorphicDeserialization)
public static class Result {
private String type;
private TableResult value;
public String getType() {
return this.type;
}
public void setType(String type) {
this.type = type;
}
public void setValue(TableResult value) {
this.value = value;
}
public TableResult getValue() {
return this.value;
}
}
// Pojo for table result
public static class TableResult {
private List<String> columnNames;
private List<String> columnTypes;
private List<Object[]> values;
#JsonProperty("ColumnNames")
public List<String> getColumnNames() {
return this.columnNames;
}
public void setColumnNames(List<String> columnNames) {
this.columnNames = columnNames;
}
#JsonProperty("ColumnTypes")
public List<String> getColumnTypes() {
return this.columnTypes;
}
public void setColumnTypes(List<String> columnTypes) {
this.columnTypes = columnTypes;
}
#JsonProperty("Values")
public List<Object[]> getValues() {
return this.values;
}
public void setValues(List<Object[]> values) {
this.values = values;
}
}
// Top level Json POJO
public static class ResultContainer {
private Map<String, Result> results;
#JsonProperty("Results")
public Map<String, Result> getResults() {
return this.results;
}
public void setResults(Map<String, Result> results) {
this.results = results;
}
}
// A contract to map the result "values" to the expected object
public static interface ResultMapper<T> {
T map(TableResult map, Object[] row);
}
// Basic implementation for mapping user object from json "values[i]" array
public static class UserTableResultMapper implements ResultMapper<User> {
#Override
public User map(TableResult result, Object[] row) {
User user = new User();
// Here use any mapper logic based on column name
// Retrieved from result object.
// Below are for illustration only
user.setId(String.valueOf(row[0]));
user.setDocumentId(String.valueOf(row[1]));
return user;
}
}
// A result reader class
public static class ResultReader<T> implements Iterable<T> {
private TableResult result;
private ResultMapper<T> mapper;
public ResultReader(TableResult result, ResultMapper<T> mapper) {
this.result = result;
this.mapper = mapper;
}
#Override
public Iterator<T> iterator() {
final Iterator<Object[]> itr = result.getValues().iterator();
return new Iterator<T>() {
#Override
public void remove() {
throw new UnsupportedOperationException();
}
#Override
public T next() {
Object[] values = itr.next();
return mapper.map(result, values);
}
#Override
public boolean hasNext() {
return itr.hasNext();
}
};
};
}
public static class User {
private String id;
private String documentId;
// and others
public String getId() {
return this.id;
}
public void setDocumentId(String documentId) {
this.documentId = documentId;
}
public void setId(String id) {
this.id = id;
}
public String getDocumentId() {
return this.documentId;
}
}
#Test
public void simpleTest() throws Exception {
ObjectMapper mapper = new ObjectMapper();
ResultContainer file = mapper.readValue(inputJson, ResultContainer.class);
Result result = file.getResults().get("output1");
ResultReader<User> userResultReader = new ResultReader<>(result.getValue(), new UserTableResultMapper());
for (User user : userResultReader) {
System.out.println(user.getId() + " : " + user.getDocumentId());
}
}
}

If you know exactly the structure of your json (like the json you have post) then you can using Gson to get your object like this:
JsonParser parser = new JsonParser();
JsonObject json = (JsonObject) parser.parse("your_json_string_here");
String column = json.get("Results").getAsJsonObject().get("output1").getAsJsonObject().get("value").getAsJsonObject().get("ColumnNames").getAsJsonArray().toString();
String value = json.get("Results").getAsJsonObject().get("output1").getAsJsonObject().get("value").getAsJsonObject().get("Values").getAsJsonArray().toString();
System.out.println(column);
System.out.println(value);
If you need some things more generic then you can parse your json string to a HashMap<String, Object> then using recursion to read the HashMap and get the value you want.
Example (in my code, the type of Map will corresponding to a Json Object, type of List will corresponding to the Array in Json string):
Type type = new TypeToken<HashMap<String, Object>>() {}.getType();
Gson gson = new Gson();
HashMap<String, Object> map = gson.fromJson("your_json_string_here", type);
for (String key : map.keySet()) {
Object obj = map.get(key);
if (obj instanceof List) {
for (Object o : (List) obj) {
if (o instanceof Map) {
loop((Map) o);
} else {
System.out.println(key + " : " + o);
}
}
} else if (obj instanceof Map) {
loop((Map) obj);
} else {
System.out.println(key + " : " + obj);
}
}
}
private static void loop(Map<String, Object> map) {
for (String key : map.keySet()) {
Object obj = map.get(key);
if (obj instanceof List) {
for (Object o : (List) obj) {
if (o instanceof Map) {
loop((Map) o);
} else {
System.out.println(key + " : " + o);
}
}
} else if (obj instanceof Map) {
loop((Map) obj);
} else {
System.out.println(key + " : " + obj);
}
}
}

Neither Jackson nor any other library will parse the Values array into objects with client data like your POJO. You can achieve this by getting the raw tree of data in this JSON and constructing objects by iterating over the Values array inside this tree. Assuming the order of ColumnNames is fixed then you can parse with Jackson like this:
final ObjectMapper mapper = new ObjectMapper();
final JsonNode tree = mapper.readTree(json);
final JsonNode values = tree.findValue("Values");
final List<ClientPOJO> clients = new ArrayList<>();
for (JsonNode node : values) {
final ClientPOJO client = new ClientPOJO();
client.setUserId(node.get(0).asText());
client.setDocumentId(node.get(1).asText());
client.setScoredLabels(node.get(2).asBoolean());
client.setScoredProbabilities(node.get(3).asDouble());
clients.add(client);
}
Docs for JsonNode. Basically with findValue you can get another node deep into the tree, with get you can get array elements by index and with asText etc you parse a value in JSON into the appropriate type in Java.
Since you seem to be flexible in choice of JSON parsing library I would suggest Jackson 2 from com.fasterxml instead of Jackson 1 from org.codehaus that you tried.

Bind multiple elements to map with attribute as key with java XML annotations, JAXB

I have an XML source from which I unmarshall Objects with JAXB.
The XML source:
<album>
<name>something</name>
<id>003030</id>
<artist>someone</artist>
...
</album>
The java source is like (with the required getter/setters as well):
#XmlRootElement(name="album")
class Album {
String name;
Long id;
String artist;
...
}
So far so good. Now I get some image urls in different sizes within album list:
...
<image size="small">http://.../small.jpg</image>
<image size="medium">http://.../medium.jpg</image>
<image size="large">http://.../large.jpg</image>
...
I want to map it to a java Map something like this:
Map<String,String> imageUrls;
Where the map's key would be the size attribute and the map's value would be the element value.
If it's possible, how should I annotate this variable?

helper class Pair
#XmlAccessorType(XmlAccessType.FIELD)
public class Pair {
#XmlAttribute
private String key;
#XmlValue
private String value;
public Pair() {
}
public Pair(String key, String value) {
this.key = key;
this.value = value;
}
//... getters, setters
}
List of pairs
#XmlAccessorType(XmlAccessType.FIELD)
public class PairList
{
private List<Pair> values = new ArrayList<Pair>();
public PairList() {
}
//...
}
adaptor
public class MapAdaptor extends XmlAdapter<PairList, Map<String, String>>
{
#Override
public Map<String, String> unmarshal(PairList list) throws Exception
{
Map<String, String> retVal = new HashMap<String, String>();
for (Pair keyValue : list.getValues())
{
retVal.put(keyValue.getKey(), keyValue.getValue());
}
return retVal;
}
#Override
public PairList marshal(Map<String, String> map) throws Exception
{
PairList retVal = new PairList();
for (String key : map.keySet())
{
retVal.getValues().add(new Pair(key, map.get(key)));
}
return retVal;
}
}
usage in your entity
#XmlJavaTypeAdapter(value = MapAdaptor.class)
private Map<String, String> imageUrls = new HashMap<String, String>();
PS
You can do it without class PairList using Pair[] instead of PairList
adaptor
public class MapAdaptor extends XmlAdapter<Pair[], Map<String, String>>
{
#Override
public Map<String, String> unmarshal(Pair[] list) throws Exception
{
Map<String, String> retVal = new HashMap<String, String>();
for (Pair keyValue : Arrays.asList(list))
{
retVal.put(keyValue.getKey(), keyValue.getValue());
}
return retVal;
}
#Override
public Pair[] marshal(Map<String, String> map) throws Exception
{
List<Pair> retVal = new ArrayList<Pair>();
for (String key : map.keySet())
{
retVal.add(new Pair(key, map.get(key)));
}
return retVal.toArray(new Pair[]{});
}
}
but in this case you can't control name of every pair. It will be item and you can't change it
<item key="key2">valu2</item>
<item key="key1">valu1</item>
PS2
If you will try use List<Pair> instead of PairList, you will get Exception
ERROR: java.util.List haven't no-arg constructor

How do I access nested HashMaps in Java?

I have a HashMap in Java, the contents of which (as you all probably know) can be accessed by
HashMap.get("keyname");
If a have a HashMap inside another HashMap i.e. a nested HashMap, how would i access the contents? Can i do this like this, inline:
HashMap.get("keyname").get("nestedkeyname");
Thank you.

You can do it like you assumed. But your HashMap has to be templated:
Map<String, Map<String, String>> map =
new HashMap<String, Map<String, String>>();
Otherwise you have to do a cast to Map after you retrieve the second map from the first.
Map map = new HashMap();
((Map)map.get( "keyname" )).get( "nestedkeyname" );

You can get the nested value by repeating .get(), but with deeply nested maps you have to do a lot of casting into Map. An easier way is to use a generic method for getting a nested value.
Implementation
public static <T> T getNestedValue(Map map, String... keys) {
Object value = map;
for (String key : keys) {
value = ((Map) value).get(key);
}
return (T) value;
}
Usage
// Map contents with string and even a list:
{
"data": {
"vehicles": {
"list": [
{
"registration": {
"owner": {
"id": "3643619"
}
}
}
]
}
}
}
List<Map> list = getNestedValue(mapContents, "data", "vehicles", "list");
Map first = list.get(0);
String id = getNestedValue(first, "registration", "owner", "id");

Yes.
See:
public static void main(String args[]) {
HashMap<String, HashMap<String, Object>> map = new HashMap<String, HashMap<String,Object>>();
map.put("key", new HashMap<String, Object>());
map.get("key").put("key2", "val2");
System.out.println(map.get("key").get("key2"));
}

If you plan on constructing HashMaps with variable depth, use a recursive data structure.
Below is an implementation providing a sample interface:
class NestedMap<K, V> {
private final HashMap<K, NestedMap> child;
private V value;
public NestedMap() {
child = new HashMap<>();
value = null;
}
public boolean hasChild(K k) {
return this.child.containsKey(k);
}
public NestedMap<K, V> getChild(K k) {
return this.child.get(k);
}
public void makeChild(K k) {
this.child.put(k, new NestedMap());
}
public V getValue() {
return value;
}
public void setValue(V v) {
value = v;
}
}
and example usage:
class NestedMapIllustration {
public static void main(String[] args) {
NestedMap<Character, String> m = new NestedMap<>();
m.makeChild('f');
m.getChild('f').makeChild('o');
m.getChild('f').getChild('o').makeChild('o');
m.getChild('f').getChild('o').getChild('o').setValue("bar");
System.out.println(
"nested element at 'f' -> 'o' -> 'o' is " +
m.getChild('f').getChild('o').getChild('o').getValue());
}
}

As others have said you can do this but you should define the map with generics like so:
Map<String, Map<String, String>> map = new HashMap<String, Map<String,String>>();
However, if you just blindly run the following:
map.get("keyname").get("nestedkeyname");
you will get a null pointer exception whenever keyname is not in the map and your program will crash. You really should add the following check:
String valueFromMap = null;
if(map.containsKey("keyname")){
valueFromMap = map.get("keyname").get("nestedkeyname");
}

Yes, if you use the proper generic type signature for the outer hashmap.
HashMap<String, HashMap<String, Foo>> hm = new HashMap<String, HashMap<String, Foobar>>();
// populate the map
hm.get("keyname").get("nestedkeyname");
If you're not using generics, you'd have to do a cast to convert the object retrieved from the outer hash map to a HashMap (or at least a Map) before you could call its get() method. But you should be using generics ;-)

I prefer creating a custom map that extends HashMap. Then just override get() to add extra logic so that if the map doesnt contain your key. It will a create a new instance of the nested map, add it, then return it.
public class KMap<K, V> extends HashMap<K, V> {
public KMap() {
super();
}
#Override
public V get(Object key) {
if (this.containsKey(key)) {
return super.get(key);
} else {
Map<K, V> value = new KMap<K, V>();
super.put((K)key, (V)value);
return (V)value;
}
}
}
Now you can use it like so:
Map<Integer, Map<Integer, Map<String, Object>>> nestedMap = new KMap<Integer, Map<Integer, Map<String, Object>>>();
Map<String, Object> map = (Map<String, Object>) nestedMap.get(1).get(2);
Object obj= new Object();
map.put(someKey, obj);

I came to this StackOverflow page looking for a something ala valueForKeyPath known from objc. I also came by another post - "Key-Value Coding" for Java, but ended up writing my own.
I'm still looking for at better solution than PropertyUtils.getProperty in apache's beanutils library.
Usage
Map<String, Object> json = ...
public String getOptionalFirstName() {
return MyCode.getString(json, "contact", "firstName");
}
Implementation
public static String getString(Object object, String key0, String key1) {
if (key0 == null) {
return null;
}
if (key1 == null) {
return null;
}
if (object instanceof Map == false) {
return null;
}
#SuppressWarnings("unchecked")
Map<Object, Object> map = (Map<Object, Object>)object;
Object object1 = map.get(key0);
if (object1 instanceof Map == false) {
return null;
}
#SuppressWarnings("unchecked")
Map<Object, Object> map1 = (Map<Object, Object>)object1;
Object valueObject = map1.get(key1);
if (valueObject instanceof String == false) {
return null;
}
return (String)valueObject;
}

import java.util.*;
public class MyFirstJava {
public static void main(String[] args)
{
Animal dog = new Animal();
dog.Info("Dog","Breezi","Lab","Chicken liver");
dog.Getname();
Animal dog2= new Animal();
dog2.Info("Dog", "pumpkin", "POM", "Pedigree");
dog2.Getname();
HashMap<String, HashMap<String, Object>> dogs = new HashMap<>();
dogs.put("dog1", new HashMap<>() {{put("Name",dog.name);
put("Food",dog.food);put("Age",3);}});
dogs.put("dog2", new HashMap<>() {{put("Name",dog2.name);
put("Food",dog2.food);put("Age",6);}});
//dogs.get("dog1");
System.out.print(dogs + "\n");
System.out.print(dogs.get("dog1").get("Age"));
}
}

Example Map:
{
"data": {
"userData": {
"location": {
"city": "Banja Luka"
}
}
}
}
Implementation:
public static Object getValueFromMap(final Map<String, Object> map, final String key) {
try {
final String[] tmpKeys = key.split("\\.");
Map<String, Object> currentMap = map;
for (int i = 0; i < tmpKeys.length - 1; i++) {
currentMap = (Map<String, Object>) currentMap.get(tmpKeys[i]);
}
return currentMap.get(tmpKeys[tmpKeys.length - 1]);
} catch (Exception exception) {
return null;
}
}
Usage:
final Map<String, Object> data = new HashMap<>();
final Map<String, Object> userData = new HashMap<>();
final Map<String, Object> location = new HashMap<>();
location.put("city", "Banja Luka");
userData.put("location", location);
data.put("userData", userData);
System.out.println(getValueFromMap(data, "userData.location.city"));
Result:
Banja Luka
Process finished with exit code 0

I hit this discussion while trying to figure out how to get a value from a nested map of unknown depth and it helped me come up with the following solution to my problem. It is overkill for the original question but maybe it will be helpful to someone that finds themselves in a situation where you have less knowledge about the map being searched.
private static Object pullNestedVal(
Map<Object, Object> vmap,
Object ... keys) {
if ((keys.length == 0) || (vmap.size() == 0)) {
return null;
} else if (keys.length == 1) {
return vmap.get(keys[0]);
}
Object stageObj = vmap.get(keys[0]);
if (stageObj instanceof Map) {
Map<Object, Object> smap = (Map<Object, Object>) stageObj;
Object[] skeys = Arrays.copyOfRange(keys, 1, keys.length);
return pullNestedVal(smap, skeys);
} else {
return null;
}
}