How to read json file into java with simple JSON library?

To read a JSON file in Java using the Simple JSON library, you can follow these steps. The Simple JSON library provides an easy-to-use API for parsing JSON data.

1. Add the Simple JSON Library to Your Project

Using Maven:

Add the following dependency to your pom.xml file:

<dependency>
    <groupId>com.googlecode.json-simple</groupId>
    <artifactId>json-simple</artifactId>
    <version>1.1.1</version>
</dependency>

Using Gradle:

Add this to your build.gradle:

implementation 'com.googlecode.json-simple:json-simple:1.1.1'

If you’re not using a build tool, download the JAR file from Maven Repository and add it to your project manually.

2. Example JSON File

Let’s assume you have a JSON file named data.json:

{
  "name": "John Doe",
  "age": 30,
  "isEmployed": true,
  "skills": ["Java", "Python", "JavaScript"]
}

3. Code to Read and Parse the JSON File

Here’s how you can read and parse the JSON file using the Simple JSON library:

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

import java.io.FileReader;
import java.io.IOException;

public class ReadJsonExample {
    public static void main(String[] args) {
        // Create a JSONParser instance
        JSONParser jsonParser = new JSONParser();

        try {
            // Read the JSON file
            FileReader reader = new FileReader("data.json");

            // Parse the JSON file into a JSONObject
            JSONObject jsonObject = (JSONObject) jsonParser.parse(reader);

            // Extract data from the JSON object
            String name = (String) jsonObject.get("name");
            long age = (long) jsonObject.get("age");
            boolean isEmployed = (boolean) jsonObject.get("isEmployed");
            JSONArray skills = (JSONArray) jsonObject.get("skills");

            // Print the extracted data
            System.out.println("Name: " + name);
            System.out.println("Age: " + age);
            System.out.println("Is Employed: " + isEmployed);
            System.out.println("Skills: " + skills);

            // Close the reader
            reader.close();
        } catch (IOException | ParseException e) {
            e.printStackTrace();
        }
    }
}

Explanation of the Code

1. JSONParser:
   • The JSONParser class is used to parse JSON data into Java objects.
2. FileReader:
   • Used to read the JSON file.
3. JSONObject:
   • Represents the JSON object after parsing.
4. Extracting Values:
   • Use the get method to retrieve values by their key.
   • For arrays, cast the value to a JSONArray.
5. Exception Handling:
   • Handle IOException for file operations and ParseException for parsing errors.

Output

If data.json contains the provided JSON, the output will be:

Name: John Doe
Age: 30
Is Employed: true
Skills: [Java, Python, JavaScript]

Key Points

• Ensure the file path (data.json) is correct.
• If the JSON structure is complex (nested objects, arrays), you can cast values to JSONObject or JSONArray and iterate through them.
• The Simple JSON library is lightweight and easy to use but lacks some features provided by modern libraries like Jackson or Gson.

This is how you can read and parse a JSON file using the Simple JSON library in Java!