How to parse JSON in Java

How to Parse JSON in Java

+
3

Submitted
by tmo9d
Posted Sep
23 2009 12:25 PM

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.

This sample project is available on GitHub here: http://github.com/to...le-json-parsing

For more information about the json-lib project, see JSON-LIB project page

Cover of Java Web Services: Up and Running

Learn more about this topic from Java Web Services: Up and Running.

This quick, practical, and thorough introduction to Java web services -- the JAX-WS and JAX-RS APIs -- offers a mix of architectural overview, complete working code examples, and short yet precise instructions for compiling, deploying, and executing a sample
application. You'll not only learn how to write web services from scratch, but also how to integrate existing services into your Java applications.

Tags:

2 Replies

Alternative
solution by Stuart12345
Posted Sep
30 2011 10:13 AM

Be sure to add the classifier:

see http://stackoverflow...net-sf-json-lib

Alternative
solution by Adam Musial-Bright
Posted Oct
03 2011 09:39 AM

Gson, the Google JSON library is also very nice.

You will need a simple POJOs for the JSON representation:

// JSON representation
class MyJson {

  public MyJson() {}

  private String foo;
  private float coolness;
  // other attributes

  public void setFoo(String foo) {
    this.foo = foo;
  }

  public String getFoo() {
    return foo;
  }

  public void setCoolness(float coolness) {
    this.coolness = coolness;
  }

  public float getCoolness() {
    return coolness;
  }

}

Now you can convert a JSON representation into a JSON object:

  Gson gson = new Gson();
  MyJson myJson = new gson.fromJson(jsonTxt, MyJson.class);

  // now you have a real java object
  System.out.println(myJson.getFoo());

done.

学步园