What is the best way to convert a JSON code as this:
{
"data" :
{
"field1" : "value1",
"field2" : "value2"
}
}
in a Java Map in which one the keys are (field1, field2) and the values for those fields are (value1, value2).
Any ideas? Should I use Json-lib for that? Or better if I write my own parser?
This question is related to
java
json
parsing
collections
JSON to Map always gonna be a string/object data type. i haved GSON lib from google.
works very well and JDK 1.5 is the min requirement.
I like google gson library.
When you don't know structure of json. You can use
JsonElement root = new JsonParser().parse(jsonString);
and then you can work with json. e.g. how to get "value1" from your gson:
String value1 = root.getAsJsonObject().get("data").getAsJsonObject().get("field1").getAsString();
import net.sf.json.JSONObject
JSONObject.fromObject(yourJsonString).toMap
My post could be helpful for others, so imagine you have a map with a specific object in values, something like that:
{
"shopping_list":{
"996386":{
"id":996386,
"label":"My 1st shopping list",
"current":true,
"nb_reference":6
},
"888540":{
"id":888540,
"label":"My 2nd shopping list",
"current":false,
"nb_reference":2
}
}
}
To parse this JSON file with GSON library, it's easy : if your project is mavenized
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.3.1</version>
</dependency>
Then use this snippet :
import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
//Read the JSON file
JsonElement root = new JsonParser().parse(new FileReader("/path/to/the/json/file/in/your/file/system.json"));
//Get the content of the first map
JsonObject object = root.getAsJsonObject().get("shopping_list").getAsJsonObject();
//Iterate over this map
Gson gson = new Gson();
for (Entry<String, JsonElement> entry : object.entrySet()) {
ShoppingList shoppingList = gson.fromJson(entry.getValue(), ShoppingList.class);
System.out.println(shoppingList.getLabel());
}
The corresponding POJO should be something like that :
public class ShoppingList {
int id;
String label;
boolean current;
int nb_reference;
//Setters & Getters !!!!!
}
Hope it helps !
If you're using org.json, JSONObject has a method toMap().
You can easily do:
Map<String, Object> myMap = myJsonObject.toMap();
My post could be helpful for others, so imagine you have a map with a specific object in values, something like that:
{
"shopping_list":{
"996386":{
"id":996386,
"label":"My 1st shopping list",
"current":true,
"nb_reference":6
},
"888540":{
"id":888540,
"label":"My 2nd shopping list",
"current":false,
"nb_reference":2
}
}
}
To parse this JSON file with GSON library, it's easy : if your project is mavenized
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.3.1</version>
</dependency>
Then use this snippet :
import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
//Read the JSON file
JsonElement root = new JsonParser().parse(new FileReader("/path/to/the/json/file/in/your/file/system.json"));
//Get the content of the first map
JsonObject object = root.getAsJsonObject().get("shopping_list").getAsJsonObject();
//Iterate over this map
Gson gson = new Gson();
for (Entry<String, JsonElement> entry : object.entrySet()) {
ShoppingList shoppingList = gson.fromJson(entry.getValue(), ShoppingList.class);
System.out.println(shoppingList.getLabel());
}
The corresponding POJO should be something like that :
public class ShoppingList {
int id;
String label;
boolean current;
int nb_reference;
//Setters & Getters !!!!!
}
Hope it helps !
Underscore-java library can convert json string to hash map. I am the maintainer of the project.
Code example:
import com.github.underscore.lodash.U;
import java.util.*;
public class Main {
@SuppressWarnings("unchecked")
public static void main(String[] args) {
String json = "{"
+ " \"data\" :"
+ " {"
+ " \"field1\" : \"value1\","
+ " \"field2\" : \"value2\""
+ " }"
+ "}";
Map<String, Object> data = (Map) U.get((Map<String, Object>) U.fromJson(json), "data");
System.out.println(data);
// {field1=value1, field2=value2}
}
}
JSON to Map always gonna be a string/object data type. i haved GSON lib from google.
works very well and JDK 1.5 is the min requirement.
I like google gson library.
When you don't know structure of json. You can use
JsonElement root = new JsonParser().parse(jsonString);
and then you can work with json. e.g. how to get "value1" from your gson:
String value1 = root.getAsJsonObject().get("data").getAsJsonObject().get("field1").getAsString();
I do it this way. It's Simple.
import java.util.Map;
import org.json.JSONObject;
import com.google.gson.Gson;
public class Main {
public static void main(String[] args) {
JSONObject jsonObj = new JSONObject("{ \"f1\":\"v1\"}");
@SuppressWarnings("unchecked")
Map<String, String> map = new Gson().fromJson(jsonObj.toString(),Map.class);
System.out.println(map);
}
}
Using the GSON library:
import com.google.gson.Gson;
import com.google.common.reflect.TypeToken;
import java.lang.reclect.Type;
Use the following code:
Type mapType = new TypeToken<Map<String, Map>>(){}.getType();
Map<String, String[]> son = new Gson().fromJson(easyString, mapType);
If you're using org.json, JSONObject has a method toMap().
You can easily do:
Map<String, Object> myMap = myJsonObject.toMap();
One more alternative is json-simple which can be found in Maven Central:
(JSONObject)JSONValue.parse(someString); //JSONObject is actually a Map.
The artifact is 24kbytes, doesn't have other runtime dependencies.
java.lang.reflect.Type mapType = new TypeToken<Map<String, Object>>(){}.getType();
Gson gson = new Gson();
Map<String, Object> categoryicons = gson.fromJson(json, mapType );
Use JSON lib E.g. http://www.json.org/java/
// Assume you have a Map<String, String> in JSONObject jdata
@SuppressWarnings("unchecked")
Iterator<String> nameItr = jdata.keys();
Map<String, String> outMap = new HashMap<String, String>();
while(nameItr.hasNext()) {
String name = nameItr.next();
outMap.put(name, jdata.getString(name));
}
Using the GSON library:
import com.google.gson.Gson;
import com.google.common.reflect.TypeToken;
import java.lang.reclect.Type;
Use the following code:
Type mapType = new TypeToken<Map<String, Map>>(){}.getType();
Map<String, String[]> son = new Gson().fromJson(easyString, mapType);
java.lang.reflect.Type mapType = new TypeToken<Map<String, Object>>(){}.getType();
Gson gson = new Gson();
Map<String, Object> categoryicons = gson.fromJson(json, mapType );
Try this code:
public static Map<String, Object> convertJsonIntoMap(String jsonFile) {
Map<String, Object> map = new HashMap<>();
try {
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);
mapper.readValue(jsonFile, new TypeReference<Map<String, Object>>() {
});
map = mapper.readValue(jsonFile, new TypeReference<Map<String, String>>() {
});
} catch (IOException e) {
e.printStackTrace();
}
return map;
}
Use JSON lib E.g. http://www.json.org/java/
// Assume you have a Map<String, String> in JSONObject jdata
@SuppressWarnings("unchecked")
Iterator<String> nameItr = jdata.keys();
Map<String, String> outMap = new HashMap<String, String>();
while(nameItr.hasNext()) {
String name = nameItr.next();
outMap.put(name, jdata.getString(name));
}
Underscore-java library can convert json string to hash map. I am the maintainer of the project.
Code example:
import com.github.underscore.lodash.U;
import java.util.*;
public class Main {
@SuppressWarnings("unchecked")
public static void main(String[] args) {
String json = "{"
+ " \"data\" :"
+ " {"
+ " \"field1\" : \"value1\","
+ " \"field2\" : \"value2\""
+ " }"
+ "}";
Map<String, Object> data = (Map) U.get((Map<String, Object>) U.fromJson(json), "data");
System.out.println(data);
// {field1=value1, field2=value2}
}
}
This way its works like a Map...
JSONObject fieldsJson = new JSONObject(json);
String value = fieldsJson.getString(key);
<dependency>
<groupId>org.codehaus.jettison</groupId>
<artifactId>jettison</artifactId>
<version>1.1</version>
</dependency>
If you need pure Java without any dependencies, you can use build in Nashorn API from Java 8. It is deprecated in Java 11.
This is working for me:
...
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
...
public class JsonUtils {
public static Map parseJSON(String json) throws ScriptException {
ScriptEngineManager sem = new ScriptEngineManager();
ScriptEngine engine = sem.getEngineByName("javascript");
String script = "Java.asJSONCompatible(" + json + ")";
Object result = engine.eval(script);
return (Map) result;
}
}
Sample usage
JSON:
{
"data":[
{"id":1,"username":"bruce"},
{"id":2,"username":"clark"},
{"id":3,"username":"diana"}
]
}
Code:
...
import jdk.nashorn.internal.runtime.JSONListAdapter;
...
public static List<String> getUsernamesFromJson(Map json) {
List<String> result = new LinkedList<>();
JSONListAdapter data = (JSONListAdapter) json.get("data");
for(Object obj : data) {
Map map = (Map) obj;
result.add((String) map.get("username"));
}
return result;
}
The JsonTools library is very complete. It can be found at Github.
I do it this way. It's Simple.
import java.util.Map;
import org.json.JSONObject;
import com.google.gson.Gson;
public class Main {
public static void main(String[] args) {
JSONObject jsonObj = new JSONObject("{ \"f1\":\"v1\"}");
@SuppressWarnings("unchecked")
Map<String, String> map = new Gson().fromJson(jsonObj.toString(),Map.class);
System.out.println(map);
}
}
With google's Gson 2.7 (probably earlier versions too, but I tested 2.7) it's as simple as:
Map map = gson.fromJson(json, Map.class);
Which returns a Map of type class com.google.gson.internal.LinkedTreeMap and works recursively on nested objects.
If you need pure Java without any dependencies, you can use build in Nashorn API from Java 8. It is deprecated in Java 11.
This is working for me:
...
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
...
public class JsonUtils {
public static Map parseJSON(String json) throws ScriptException {
ScriptEngineManager sem = new ScriptEngineManager();
ScriptEngine engine = sem.getEngineByName("javascript");
String script = "Java.asJSONCompatible(" + json + ")";
Object result = engine.eval(script);
return (Map) result;
}
}
Sample usage
JSON:
{
"data":[
{"id":1,"username":"bruce"},
{"id":2,"username":"clark"},
{"id":3,"username":"diana"}
]
}
Code:
...
import jdk.nashorn.internal.runtime.JSONListAdapter;
...
public static List<String> getUsernamesFromJson(Map json) {
List<String> result = new LinkedList<>();
JSONListAdapter data = (JSONListAdapter) json.get("data");
for(Object obj : data) {
Map map = (Map) obj;
result.add((String) map.get("username"));
}
return result;
}
The JsonTools library is very complete. It can be found at Github.
Try this code:
public static Map<String, Object> convertJsonIntoMap(String jsonFile) {
Map<String, Object> map = new HashMap<>();
try {
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);
mapper.readValue(jsonFile, new TypeReference<Map<String, Object>>() {
});
map = mapper.readValue(jsonFile, new TypeReference<Map<String, String>>() {
});
} catch (IOException e) {
e.printStackTrace();
}
return map;
}
import net.sf.json.JSONObject
JSONObject.fromObject(yourJsonString).toMap
With google's Gson 2.7 (probably earlier versions too, but I tested 2.7) it's as simple as:
Map map = gson.fromJson(json, Map.class);
Which returns a Map of type class com.google.gson.internal.LinkedTreeMap and works recursively on nested objects.
One more alternative is json-simple which can be found in Maven Central:
(JSONObject)JSONValue.parse(someString); //JSONObject is actually a Map.
The artifact is 24kbytes, doesn't have other runtime dependencies.
Source: Stackoverflow.com