How to Parse JSON in Java

Use json-lib, a library which adds JSON support to any Java program. json-lib can take a String and turn it into a JSONObject which can then be used to retrieve specific attributes.

1. Add this dependency to your project:

<dependency>
      <groupId>net.sf.json-lib</groupId>
      <artifactId>json-lib</artifactId>
      <version>2.3</version>
      <scope>compile</scope>
    </dependency>





What does this mean? See How to Add a Dependency to a Java Project

2. Put the following JSON sample in your classpath:

{'foo':'bar',
 'coolness':2.0,
 'altitude':39000,
 'pilot':{'firstName':'Buzz',
          'lastName':'Aldrin'},
 'mission':'apollo 11'}



3. Load the resource from the classpath and parse this JSON as follows:

package com.discursive.answers;

import java.io.InputStream;

import net.sf.json.JSONObject;
import net.sf.json.JSONSerializer;

import org.apache.commons.io.IOUtils;

public class JsonParsing {

    public static void main(String[] args) throws Exception {
        InputStream is =
                JsonParsing.class.getResourceAsStream( "sample-json.txt");
        String jsonTxt = IOUtils.toString( is );
       
        JSONObject json = (JSONObject) JSONSerializer.toJSON( jsonTxt );       
        double coolness = json.getDouble( "coolness" );
        int altitude = json.getInt( "altitude" );
        JSONObject pilot = json.getJSONObject("pilot");
        String firstName = pilot.getString("firstName");
        String lastName = pilot.getString("lastName");
       
        System.out.println( "Coolness: " + coolness );
        System.out.println( "Altitude: " + altitude );
        System.out.println( "Pilot: " + lastName );
    }
}



Note that JSONSerializer returns a JSON object. This is a general object which could be a JSONObject or a JSONArray depending on the JSON you are trying to parse. In this example, since I know that the JSON is a JSONObject, I can cast the result directly to a JSONObject. If you are dealing with JSON that could return a JSONArray, you'll likely want to check the type of the object that is returned by toJSON.