I had a need for having Key/Value pairs in the order of my insertion, so I opted to use LinkedHashMap
over HashMap
. But I need to convert the LinkedHashMap
into a JSON String where the order in the LinkedHashMap
is maintained in the string.
But currently I'm achieving it by:
Then converting the JSON into a string.
import java.util.LinkedHashMap;
import java.util.Map;
import org.json.JSONObject;
public class cdf {
public static void main(String[] args) {
Map<String,String > myLinkedHashMap = new LinkedHashMap<String, String>();
myLinkedHashMap.put("1","first");
myLinkedHashMap.put("2","second");
myLinkedHashMap.put("3","third");
JSONObject json = new JSONObject(myLinkedHashMap);
System.out.println(json.toString());
}
}
The output is:
{"3":"third","2":"second","1":"first"} .
But I want it in the order of insertion of the keys, like this:
{"1":"first","2":"second","3":"third"}
Once I convert the LinkedHashMap
into a JSON it loses it order (it's obvious that JSON doesn't have the notion of order) and hence the string too is out of order. Now, how do I generate a JSON string whose order is same as the LinkedHashMap
?
Gson if your friend. This will print the ordered map into an ordered JSON string.
If you want to preserve insertion order, use a LinkedHashMap
.
I used the latest version of Gson (2.8.5), you can can download it via the following options at the bottom of this post.
import java.util.*;
import com.google.gson.Gson;
public class OrderedJson {
public static void main(String[] args) {
// Create a new ordered map.
Map<String,String> myLinkedHashMap = new LinkedHashMap<String, String>();
// Add items, in-order, to the map.
myLinkedHashMap.put("1", "first");
myLinkedHashMap.put("2", "second");
myLinkedHashMap.put("3", "third");
// Instantiate a new Gson instance.
Gson gson = new Gson();
// Convert the ordered map into an ordered string.
String json = gson.toJson(myLinkedHashMap, LinkedHashMap.class);
// Print ordered string.
System.out.println(json); // {"1":"first","2":"second","3":"third"}
}
}
If you want the items to always be inserted at the right place, use a TreeMap
instead.
import java.util.*;
import com.google.gson.Gson;
public class OrderedJson {
public static void main(String[] args) {
// Create a new ordered map.
Map<String,String> myTreeHashMap = new TreeMap<String, String>();
// Add items, in any order, to the map.
myTreeHashMap.put("3", "third");
myTreeHashMap.put("1", "first");
myTreeHashMap.put("2", "second");
// Instantiate a new Gson instance.
Gson gson = new Gson();
// Convert the ordered map into an ordered string.
String json = gson.toJson(myTreeHashMap, TreeMap.class);
// Print ordered string.
System.out.println(json); // {"1":"first","2":"second","3":"third"}
}
}
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.5</version>
</dependency>
compile 'com.google.code.gson:gson:2.8.5'
Or you can visit Maven Central for more download options.