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How to Parse JSON in Java

+ 4
  tmo9d's Photo
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

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3 Replies

0
  Stuart12345's Photo
Posted Sep 30 2011 10:13 AM

Be sure to add the classifier:

<dependency>
<groupId>net.sf.json-lib</groupId>
<artifactId>json-lib</artifactId>
<version>2.4</version>
<classifier>jdk15</classifier>
</dependency>

see http://stackoverflow...net-sf-json-lib
+ 1
  Adam Musial-Bright's Photo
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.
0
  handark's Photo
Posted Mar 30 2012 07:21 AM

Gson is a very good library.

Thanks Adam