How to get a length of json object saved in local project directory?

I have spring-boot project and my project's structure looks like this...

-src
-target
-pom.xml
-uploaded_json
 -- example.json

and here is my example.json

[
    {
        "Username": "U1",
        "Password": "P1",
    },
    {
        "Username": "U2",
        "Password": "P2",
    },
    {
        "Username": "U3",
        "Password": "P3",
    }  
]
 

Can I read example.json and save it as int type variable? Should I use java.io.File Object? Please help me to figure out how to get the length of JSON file. Thank you in advance.

Edit: I made a method using simple-json.

@GetMapping("getJSON")
	public String testmethod() {
		JSONParser parser = new JSONParser();
		File directory = new File(".");
		JSONArray a;
		try {
			a = (JSONArray) parser.parse(new FileReader(
					directory.getCanonicalPath() + "\\uploaded_json\\example.json"));
			int length = a.size();
			System.out.println(length);
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} catch (ParseException e) {
			e.printStackTrace();
		}
		return null;

	}

I would use the jackson-databind library, using the class JsonNode.

The latest version on the maven repository is 2.11.1

compile group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.11.1'

Here is an example for getting the size with jackson-databind:

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.io.IOException;
import java.nio.file.Paths;

public class GradleApplication {
    public static void main(String[] args) {
    

        try {
            File jsonFile = Paths.get("src", "main", "resources", "example.json").toFile();
            ObjectMapper mapper = new ObjectMapper();
            JsonNode node = mapper.readTree(jsonFile);
            System.out.println("The size of the json is : "+ node.size());
        } catch (IOException e) {
            e.printStackTrace();
        }

     
    }
}