Jackson Streaming API – read and write json

Java JSON Tutorial Content:

• JSON Introduction
• JSON.simple example-read and write JSON
• GSON example-read and write
• JSONJackson example – read and write JSON
• Jackson Streaming API – read and write JSON

• JsonGenerator : To write json
• JsonParser : To read json

In this post,we will read and write JSON using Jackson Streaming API.
1). Create a java project named “JacksonStreamingAPIExample”

2) Add following maven dependency for jackson.
Pom.xml :

 
 4.0.0

 com.arpit.java2blog
 JacksonStreamingAPIExample
 0.0.1-SNAPSHOT
 jar

 JacksonStreamingAPIExample
 http://maven.apache.org

 
 UTF-8
 

 
 
 junit
 junit
 3.8.1
 test
 
 
 org.codehaus.jackson
 jackson-xc
 1.9.13
 
 

3) create a pojo named “Country.java”

package org.arpit.java2blog.pojo;

import java.util.ArrayList;
import java.util.List;

public class Country {

 String name;
 int population;
 private List listOfStates;

 //getter and setter methods

 public String getName() {
      return name;

 public void setName(String name) {
  this.name = name;
 }

 public int getPopulation() {
  return population;
 }

 public void setPopulation(int population) {
  this.population = population;
 }

 public List getListOfStates() {
  return listOfStates;
 }

 public void setListOfStates(List listOfStates) {
 this.listOfStates = listOfStates;
 }

}

Write JSON to file:

4) Create a new class named “JacksonWriteToFileStreamingAPIExample.java” in src->org.arpit.java2blog.JacksonStreamingAPIExample

package com.arpit.java2blog.JacksonStreamingAPIExample;

import java.io.File;
import java.io.IOException;

import org.codehaus.jackson.JsonEncoding;
import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.util.DefaultPrettyPrinter;

/**
 * 
 * @author Arpit Mandliya
 *
 */
public class JacksonWriteToFileStreamingAPIExample 
{
    public static void main( String[] args )
    {
       try {
     JsonFactory jfactory = new JsonFactory();

     // Write json to a file
     JsonGenerator jsonGenerator = jfactory.createJsonGenerator(new File("//Users//Arpit//countryStreaming.json"), JsonEncoding.UTF8);
     jsonGenerator.setPrettyPrinter(new DefaultPrettyPrinter());
     jsonGenerator.writeStartObject(); // {
     //"name" : "India"
     jsonGenerator.writeStringField("name", "India");
     // "population" : "10000"
     jsonGenerator.writeNumberField("population", 10000);

     // "listOfStates" :
     // This is an array object
     jsonGenerator.writeFieldName("listOfStates");
     // Create start of array tag  [
     jsonGenerator.writeStartArray();

     jsonGenerator.writeString("Madhya Pradesh");

     jsonGenerator.writeString("Maharashtra");

     jsonGenerator.writeString("Rajasthan");
     // Create End of array tag  ]
     jsonGenerator.writeEndArray();
     // end of JSON Object tag }
     jsonGenerator.writeEndObject();

     jsonGenerator.close();

    } catch (JsonGenerationException e) {

     e.printStackTrace();

    } catch (IOException e) {

     e.printStackTrace();

    }
    }
}

Run above program and content of file countryStreaming.json will be as below :

{
  "name" : "India",
  "population" : 10000,
  "listOfStates" : [ "Madhya Pradesh", "Maharashtra", "Rajasthan" ]
}

Read JSON to file:

Here we will read above created JSON file.
5) Create a new class named “JacksonJsonReadFromFileExample.java” in src->org.arpit.java2blog.JacksonStreamingAPIExample

package com.arpit.java2blog.JacksonStreamingAPIExample;

import java.io.File;
import java.io.IOException;
import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.JsonToken;

public class JacksonStreamingReadFromFileExample {

 public static void main(String[] args)
 {
  try {

   JsonFactory jfactory = new JsonFactory();

   System.out.println("Reading data from json file");
                        System.out.println("--------------------------");
   JsonParser jParser = jfactory
     .createJsonParser(new File("//Users//Arpit//countryStreaming.json"));

   // We need to loop until we reach to the end object.
   while (jParser.nextToken() != JsonToken.END_OBJECT) {

    String fieldname = jParser.getCurrentName();
    if ("name".equals(fieldname)) {

     jParser.nextToken();
     System.out.println("Name of Country:"+jParser.getText());
    }

    if ("population".equals(fieldname)) {
     jParser.nextToken();
     System.out.println("Population: "+jParser.getText());
    }
    // reading the listOfStates which is an array
    if ("listOfStates".equals(fieldname)) {
     // current token is "[" beginning of array. So we wii go to  next
     jParser.nextToken();
     System.out.println("List of states:");
     // iterate through the array until token equal to "]"
     while (jParser.nextToken() != JsonToken.END_ARRAY) {

      System.out.println(jParser.getText());
     }
    }

   }
   jParser.close();

  } catch (JsonGenerationException e) {

   e.printStackTrace();

  } catch (IOException e) {

   e.printStackTrace();

  }
 }
}

Run above program and you will get following output:

Reading data from json file
--------------------------
Name of Country:India
Population: 10000
List of states:
Madhya Pradesh
Maharashtra
Rajasthan

6) Project Structure: