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Handle JSON object Tag(s): Networking XML/RSS/JSON


JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is used primarily to transmit data between a server and web application, as an alternative to XML.

JSON structures are easy to manipulate from Java. The required libraries are now included in the Java EE 7 specification.

Create a JSON object from a String
In this HowTo, we create a JSON object from a String.

In a MAVEN project, add this dependency 


  <dependency>

    <groupId>org.glassfish</groupId>

    <artifactId>javax.json</artifactId>

    <version>1.0.4</version>

  </dependency>
or download the jars from https://jsonp.java.net/download.html 

import java.io.StringReader;

import javax.json.Json;

import javax.json.JsonObject;

import javax.json.JsonReader;



// https://jsonp.java.net/download.html

public class Json1 {

   String jsonString = "{" +

      "     \"firstName\": \"John\", \"lastName\": \"Smith\", \"age\": 25," +

      "     \"address\" : { " +

      "     \"streetAddress\": \"21 2nd Street\"," +

      "     \"city\": \"New York\"," +

      "     \"state\": \"NY\"," +

      "     \"postalCode\": \"10021\"" +

      "     }," +

      "     \"phoneNumber\": [" +

      "         { \"type\": \"home\", \"number\": \"212 555-1234\" }," +

      "         { \"type\": \"fax\", \"number\": \"646 555-4567\" }" +

      "     ]" +

      "}";



   public static void main(String args[]) {

      Json1 x = new Json1();

      x.doit();

   }



   public void doit() {

      JsonReader reader = Json.createReader(new StringReader(jsonString));

      JsonObject object = reader.readObject();

      reader.close();

      System.out.println(object.getString("firstName") + " " + object.getString("lastName")) ;

      System.out.println(object.getJsonObject("address").getString("city")) ;

      /*

          output :

            John Smith

            New York

      */

   }

}
Create a JSON object from a File
To use a file, replace the StringReader by a FileReader.
Create a JSON object from code

Now, we want to create the JSON object from code. 


import javax.json.Json;

import javax.json.JsonObject;



public class Json2 {

   public static void main(String args[]) {

      Json2 x = new Json2();

      x.doit();

   }



   public void doit() {

      JsonObject object = Json.createObjectBuilder()

        .add("firstName", "John")

        .add("lastName", "Smith")

        .add("age", 25)

        .add("address", Json.createObjectBuilder()

           .add("streetAddress", "21 2nd Street")

           .add("city", "New York")

           .add("state", "NY")

           .add("postalCode", "10021"))

        .add("phoneNumber", Json.createArrayBuilder()

           .add(Json.createObjectBuilder()

           .add("type", "home")

           .add("number", "212 555-1234"))

           .add(Json.createObjectBuilder()

           .add("type", "fax")

           .add("number", "646 555-4567")))

        .build();



      System.out.println(object.getString("firstName") + " " + object.getString("lastName")) ;

      System.out.println(object.getJsonObject("address").getString("city")) ;

   }

}
Create a JSON object from a REST service response
To call the REST service, we will use the HTTPClient module from Apache.

In a MAVEN project, add these dependencies 


  <dependency>

    <groupId>org.glassfish</groupId>

    <artifactId>javax.json</artifactId>

    <version>1.0.4</version>

  </dependency>



  <dependency>

    <groupId>org.apache.httpcomponents</groupId>

    <artifactId>httpclient</artifactId>

    <version>4.3.5</version>

  </dependency>
or download the required jars from : For the demonstration, we call http://jsonplaceholder.typicode.com/ which is Fake Online REST API for Testing and Prototyping.

The first example calls jsonplaceholder.typicode.com/posts/1 to get the first message. From the response, we extract the id and the title.

The raw response looks like 


{

  "userId": 1,

  "id": 1,

  "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",

  "body": "quia et suscipit ...eveniet architecto"

}




import java.io.InputStreamReader;



import javax.json.Json;

import javax.json.JsonObject;

import javax.json.JsonReader;



import org.apache.http.HttpHost;

import org.apache.http.HttpStatus;

import org.apache.http.client.methods.CloseableHttpResponse;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.impl.client.CloseableHttpClient;

import org.apache.http.impl.client.HttpClientBuilder;



public class Json3 {

   public static void main(String args[]) throws Exception {

      Json3 x = new Json3();

      x.doit();

   }



   public void doit() throws Exception {

      JsonReader reader = null;

      CloseableHttpClient client = HttpClientBuilder.create().build();

      HttpHost target = new HttpHost("jsonplaceholder.typicode.com", 80, "http");

      HttpGet request = new HttpGet("/posts/1");

      request.addHeader("accept", "application/json");

      CloseableHttpResponse response = null;

      try {

         response = client.execute(target, request);

         if (response.getStatusLine().getStatusCode() != HttpStatus.SC_OK) {

            throw new Exception("Failed : HTTP error code : "

               + response.getStatusLine().getStatusCode());

         }



         reader = Json.createReader(new InputStreamReader((response.getEntity().getContent())));

         JsonObject object = reader.readObject();



         // System.out.println("raw : " + object.toString()) ;

         System.out.println("id : " + object.getJsonNumber("id")) ;

         System.out.println("title : " + object.getString("title")) ;

         /*

            output

              id : 1

              title : sunt aut facere repellat provident occaecati excepturi optio reprehenderit

              Done.

         */

        }

     finally {

        if (reader != null) reader.close();

        if (client != null) client.close();

        if (response != null) response.close();

        System.out.println("Done.");

     }

   }

}

Now we call jsonplaceholder.typicode.com/posts which returns a message list of 100 elements. From the response, we iterate the returned array to display the id and the title.

The raw response looks like 


[

  {

    "userId": 1,

    "id": 1,

    "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",

    "body": "quia et suscipit ...eveniet architecto"

  }

...

  {

    "userId": 10,

    "id": 100,

    "title": "at nam consequatur ea labore ea harum",

    "body": "cupiditate quo est a modi nesciunt ... ratione error aut"

  }

]




import java.io.InputStreamReader;



import javax.json.Json;

import javax.json.JsonArray;

import javax.json.JsonObject;

import javax.json.JsonReader;



import org.apache.http.HttpHost;

import org.apache.http.HttpStatus;

import org.apache.http.client.methods.CloseableHttpResponse;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.impl.client.CloseableHttpClient;

import org.apache.http.impl.client.HttpClientBuilder;



public class Json4 {

   public static void main(String args[]) throws Exception {

      Json4 x = new Json4();

      x.doit();

   }



   public void doit() throws Exception {

      JsonReader reader = null;

      CloseableHttpClient client = HttpClientBuilder.create().build();

      HttpHost target = new HttpHost("jsonplaceholder.typicode.com", 80, "http");

      HttpGet request = new HttpGet("/posts");

      request.addHeader("accept", "application/json");

      CloseableHttpResponse response = null;

      try {

         response = client.execute(target, request);

         if (response.getStatusLine().getStatusCode() != HttpStatus.SC_OK) {

            throw new Exception("Failed : HTTP error code : "

                + response.getStatusLine().getStatusCode());

         }



         reader = Json.createReader(new InputStreamReader((response.getEntity().getContent())));

         JsonArray array = reader.readArray();



         for (int j = 0; j < array.size(); j++  ) {

            JsonObject jo = array.getJsonObject(j);

            System.out.println("id : " + jo.getJsonNumber("id")) ;

            System.out.println("title : " + jo.getString("title")) ;

         }

         /*

            output

              id : 1

              title : sunt aut facere repellat provident occaecati excepturi optio reprehenderit

              ...

              id : 100

              title : at nam consequatur ea labore ea harum

              Done.

         */

      }

      finally {

         if (reader != null) reader.close();

         if (client != null) client.close();

         if (response != null) response.close();

         System.out.println("Done.");

      }

   }

}
The same operation using JsonParser and InputStream 

import java.io.InputStream;



import javax.json.Json;

import javax.json.stream.JsonParser;

import javax.json.stream.JsonParser.Event;



import org.apache.http.HttpHost;

import org.apache.http.HttpStatus;

import org.apache.http.client.methods.CloseableHttpResponse;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.impl.client.CloseableHttpClient;

import org.apache.http.impl.client.HttpClientBuilder;





//https://jsonp.java.net/download.html

//http://hc.apache.org/downloads.cgi



public class Json5 {



   public static void main(String args[]) throws Exception {

      Json5 x = new Json5();

      x.doit();

   }



   public void doit() throws Exception {

      CloseableHttpClient client = HttpClientBuilder.create().build();

      HttpHost target = new HttpHost("jsonplaceholder.typicode.com", 80, "http");

      HttpGet request = new HttpGet("/posts");

      request.addHeader("accept", "application/json");

      CloseableHttpResponse response = null;

      try {

         response = client.execute(target, request);

         if (response.getStatusLine().getStatusCode() != HttpStatus.SC_OK) {

            throw new Exception("Failed : HTTP error code : "

                  + response.getStatusLine().getStatusCode());

         }



         InputStream is = response.getEntity().getContent();

         JsonParser parser = Json.createParser(is);

         while (parser.hasNext()) {

            Event e = parser.next();

            if (e == Event.KEY_NAME) {

               switch (parser.getString()) {

               case "id":

                  parser.next();

                  System.out.print(parser.getString());

                  System.out.print(": ");

                  break;

               case "title":

                  parser.next();

                  System.out.println(parser.getString());

                  System.out.println("---------");

                  break;

               }

            }

         }

         /*

           output :

           1: sunt aut facere repellat provident occaecati excepturi optio reprehenderit

           -------------

           2: qui est esse

           ---------

           ...

           99: temporibus sit alias delectus eligendi possimus magni

           ---------

           100: at nam consequatur ea labore ea harum

           ---------

           Done.

          */

      }

      finally {

         if (client != null) client.close();

         if (response != null) response.close();

         System.out.println("Done.");

      }

   }

}
Create a Java object from a JSON object
It's possible to do it by hand by calling the jasonobject.get[type] and the corresponding DTO/POJO set methods. But it is easier to use a library to handle the finer details. One library which is nice is GSON.

In Maven project, use 


<dependency>

    <groupId>com.google.code.gson</groupId>

    <artifactId>gson</artifactId>

    <version>2.3.1</version>

</dependency>
or download the jar from here

Again from our REST example at jsonplaceholder.typicode.com/posts/1 , we define a DTO/POJO as : 


public class JsonPlaceHolderPosts {

   int userid;

   int id;

   String title;

   String body;



   public int getUserid() {

      return userid;

   }

   public void setUserid(int userid) {

      this.userid = userid;

   }

   public int getId() {

      return id;

   }

   public void setId(int id) {

      this.id = id;

   }

   public String getTitle() {

      return title;

   }

   public void setTitle(String title) {

      this.title = title;

   }

   public String getBody() {

      return body;

   }

   public void setBody(String body) {

      this.body = body;

   }

}
and then from a JSON stream, we create the Java object 

import java.io.InputStreamReader;



import org.apache.http.HttpHost;

import org.apache.http.HttpStatus;

import org.apache.http.client.methods.CloseableHttpResponse;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.impl.client.CloseableHttpClient;

import org.apache.http.impl.client.HttpClientBuilder;



import com.google.gson.Gson;



// https://jsonp.java.net/download.html

// http://hc.apache.org/downloads.cgi

// http://search.maven.org/#artifactdetails|com.google.code.gson|gson|2.3.1|jar



public class Json6 {



     public static void main(String args[]) throws Exception {

        Json6 x = new Json6();

        x.doit();

     }



     public void doit() throws Exception {

        CloseableHttpClient client = HttpClientBuilder.create().build();

        HttpHost target = new HttpHost("jsonplaceholder.typicode.com", 80, "http");

        HttpGet request = new HttpGet("/posts/1");

        request.addHeader("accept", "application/json");

        CloseableHttpResponse response = null;

        try {

           response = client.execute(target, request);

           if (response.getStatusLine().getStatusCode() != HttpStatus.SC_OK) {

               throw new Exception("Failed : HTTP error code : "

                  + response.getStatusLine().getStatusCode());

           }



           Gson gson = new Gson();

           JsonPlaceHolderPosts jphp = gson.fromJson(new InputStreamReader

                 (response.getEntity().getContent()), JsonPlaceHolderPosts.class);

           System.out.println("id : " + jphp.getId()) ;

           System.out.println("title : " + jphp.getTitle()) ;

           /*

              ouput:

              id : 1

              title : sunt aut facere repellat provident occaecati excepturi optio reprehenderit

              Done.

           */

        }

        finally {

           if (client != null) client.close();

           if (response != null) response.close();

           System.out.println("Done.");

        }

     }

}
Create a JSON string from a Java object
Finally, from a Java object, create a JSON string. 

import com.google.gson.Gson;



// http://search.maven.org/#artifactdetails|com.google.code.gson|gson|2.3.1|jar



public class Json7 {



   public static void main(String args[]) throws Exception {

      Json7 x = new Json7();

      x.doit();

   }



   public void doit() throws Exception {

      JsonPlaceHolderPosts jphp = new JsonPlaceHolderPosts();

      jphp.setUserid(1111);

      jphp.setId(2222);

      jphp.setTitle("foo");

      jphp.setBody("bar");



      Gson gson = new Gson();

      String json = gson.toJson(jphp, JsonPlaceHolderPosts.class);

      System.out.println("json : " + json) ;

      System.out.println("Done.");

      /*

       output :

       json : {"userid":1111,"id":2222,"title":"foo","body":"bar"}

       Done.

      */

   }

}