Java Tips and Tricks: Creating & Parsing JSON data with Java

JSON.org has provided libraries to create/parse JSON data through Java code.

LIBRARY 1 :- json-rpc library

Download JAR file json-rpc-1.0.jar (75 kb)

JSONObject class :-

· to create JSON data in Java.

· It is an unordered collection of name/value pairs

· Its external form is a string wrapped in curly braces with colons between the names and values, and commas between the values and names

· Its internal form is an object having get() and opt() methods for accessing the values by name, and put() methods for adding or replacing values by name.

· The values can be any of these types: Boolean, JSONArray, JSONObject, Number, and String, or the JSONObject.NULL object.

Example

import org.json.JSONObject;

...

JSONObject json = new JSONObject();

json.put("city", "Mumbai");

json.put("country", "India");

...

String output = json.toString();

...

Thus by using toString() method you can get the output in JSON format.

JSONArray class :-

· It is an ordered sequence of values.

· Its external text form is a string wrapped in square brackets with commas separating the values.

· The internal form is an object having get and opt methods for accessing the values by index, and put methods for adding or replacing values.

· The values can be any of these types: Boolean, JSONArray, JSONObject, Number, String, or the JSONObject.NULL object

LIBRARY 2 :- json-lib library

JSON-lib is a java library for transforming beans, maps, collections, java arrays and XML to JSON and back again to beans and DynaBeans.

Download: json-lib.jar

Json-lib requires (at least) the following dependencies in your classpath:

Example

package net.viralpatel.java;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import net.sf.json.JSONObject;

public class JsonMain {

public static void main(String[] args) {

        Map<String,
  Long> map = new

HashMap<String, Long>();

        map.put("A",
  10L);

        map.put("B",
  20L);

        map.put("C",
  30L);

        JSONObject
  json = new

JSONObject();

json.accumulateAll(map);

System.out.println(json.toString());

List<String> list = new ArrayList<String>();

list.add("Sunday");

list.add("Monday");

list.add("Tuesday");

        json.accumulate("weekdays",
  list);

System.out.println(json.toString());

}

Output:

{"A":10,"B":20,"C":30}

{"A":10,"B":20,"C":30,"weekdays":["Sunday","Monday","Tuesday"]}

LIBRARY 3:- Google Gson library

· Gson is a Java library that can be used to convert Java Objects into their JSON representation.

· It can also be used to convert a JSON string to an equivalent Java object.

· Gson can work with arbitrary Java objects including pre-existing objects that you do not have source-code of.

Gson Goals :

Provide simple toJson() and fromJson() methods to convert Java objects to JSON and vice-versa
Allow pre-existing unmodifiable objects to be converted to and from JSON
Extensive support of Java Generics
Allow custom representations for objects
Support arbitrarily complex objects (with deep inheritance hierarchies and extensive use of generic types).

Example

import java.util.List;

import com.google.gson.Gson;

public class Test {

public static void main(String... args) throws Exception {

        String
  json =

"{"

                +
  "'title': 'Computing and Information systems',"

                +
  "'id' : 1,"

                +
  "'children' : 'true',"

                +
  "'groups' : [{"

                    +
  "'title' : 'Level one CIS',"

                    +
  "'id' : 2,"

                    +
  "'children' : 'true',"

                    +
  "'groups' : [{"

                        +
  "'title' : 'Intro To Computing and Internet',"

                        +
  "'id' : 3,"

                        +
  "'children': 'false',"

                        +
  "'groups':[]"

                    +
  "}]"

                +
  "}]"

            +
  "}";

        //
  Now do the magic.

        Data
  data = new

Gson().fromJson(json,
  Data.class);

        //
  Show it.

System.out.println(data);

}

class Data {

private String title;

private Long id;

private Boolean children;

private

List<Data>
  groups;

public

String getTitle() {
  return

title;
  }

public Long getId() { return id; }

public

Boolean getChildren()
  { return

children;
  }

public

List<Data>
  getGroups() { return

groups; }

public void

setTitle(String title) { this.title =
  title; }

public void setId(Long id) { this.id = id; }

public void

setChildren(Boolean children) {
  this.children = children; }

public void

setGroups(List<Data> groups) {
  this.groups = groups; }

public String toString() {

return

String.format("title:%s,id:%d,children:%s,groups:%s",
  title, id, children, groups);

}

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Tuesday, 12 March 2013

Creating & Parsing JSON data with Java

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