Jackson Streaming API

Jackson Streaming API is a widely used APIs. It is used for reading and writing JSON data as a discrete event. The API provides JsonParser and JsonGenerator classes for reading and writing data simultaneously. Streaming API is the most powerful, fastest and lowest overhead approach for reading and writing JSON data. The concept of the token is used by this approach and handle each and every information of JSON carefully.

Let's take examples to understand how Streaming API is used for writing and reading JSON.

Creating JSON Using JsonGenerator Class

JsonGenerator is one of the most important class for writing JSON. It is very easy to use in our code. In order to use JsonGenerator class, first we create an instance of JsonGenerator class with the help of JsonFactory.createJsonGenerator(). We write the JSON value by using the write() method of the JsonGenerator class.

Syntax of using JsonGenerator class is as follows:

JsonFactory factory = new JsonFactory();
JsonGenerator generator = factory.createGenerator(new File(
   "product.json"), JsonEncoding.UTF8);
jsonGenerator.writeStartObject();
jsonGenerator.writeStringField("proName", "MX Pro 20");

Let's create a program that demonstrate the same.

StreamingAPIExample1.java

// import required classes and package if any
import java.io.File;
import java.io.IOException;
import java.util.Map;
import java.util.Scanner;
import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.databind.JsonMappingException;
// create class StreamingAPIExample1 to understand Streaming API
public class StreamingAPIExample1 {	
	// main() method start
	public static void main(String args[]){
		// use try-catch block 
		try {         		
			// create an instance of JsonFactory 
			JsonFactory jsonFactory = new JsonFactory();
			
			// create an instance of JsonGenerator by using the createGenerator() method of JsonFactory
			JsonGenerator jsonGenerator = jsonFactory.createGenerator(new File("C:\\Users\\rastogi ji\\Desktop\\product.json"), JsonEncoding.UTF8);
			// create an instance of Scanner class
			Scanner sc = new Scanner(System.in);
			// use writeStartObject()
			jsonGenerator.writeStartObject();
			// write name field to product.json file
			System.out.println("Enter Product Name:");
			String name = sc.nextLine();
			jsonGenerator.writeStringField("name", name); 
			// write price field to product.json file
			System.out.println("Enter Product Price:");
			String price = sc.nextLine();
			jsonGenerator.writeStringField("price", price);
			// write expire field to product.json
			System.out.println("Is product expire(Yes/No)?:");
			String expire = sc.nextLine();
			jsonGenerator.writeStringField("expire", expire);
			// "variation" : [X1, X2, X3]
			jsonGenerator.writeFieldName("variations"); 			
			// use writeStartArray() method to write values in an array
			jsonGenerator.writeStartArray(); 			
			System.out.println("Total number of variations:");
			int size = Integer.parseInt(sc.nextLine());			
			for(int i = 0; i < size; i++) {
				System.out.println("Enter "+(i+1)+" variation name:");
				jsonGenerator.writeString(sc.nextLine()); 
			}			
			// use writeEndArray() method to stop writing values in the array
			jsonGenerator.writeEndArray(); 
			// use writeStartObject()
			jsonGenerator.writeEndObject(); 			
			// close JsonGenerator using close() method
			jsonGenerator.close();        			
			// close Scanner class
			sc.close();		
			// create an instance of the ObjectMapper class
			ObjectMapper mapper = new ObjectMapper();
			@SuppressWarnings("unchecked")
			Map<String,Object> mapData = mapper.readValue(new File("C:\\Users\\rastogi ji\\Desktop\\product.json"), Map.class);
			System.out.println(mapData.get("name"));
			System.out.println(mapData.get("price"));
			System.out.println(mapData.get("expire"));
			System.out.println(mapData.get("variations"));
		} 
		catch (JsonParseException e) { 
			e.printStackTrace(); 
		} catch (JsonMappingException e) {
			e.printStackTrace(); 
		} catch (IOException e) { 
			e.printStackTrace(); 
		}
	}
}

Output:

Reading JSON Using JsonParser Class

JsonParser is another most important class that is used for reading JSON data. It is also very simple to use in our code. In order to use JsonParser class, first we create an instance of JsonParser with the help of JsonFactory.createJsonParser(). We read each JSON string as a token by using the nextToken() method.

Syntax of using JsonParser class is as follows:

JsonFactory factory = new JsonFactory();
JsonParser parser = factory.createJsonParser(new File("product.json"));
while (parser.nextToken() != JsonToken.END_OBJECT) {
   //getting current token
   String fieldname = parser.getCurrentName();
   if ("name".equals(fieldname)) {
      //switch to next token
      parser.nextToken();
      System.out.println(parser.getText());        	 
   }
}

Let's create a program that demonstrate the same.

StreamingAPIExample2.java

//import required classes and package if any
import java.io.File;
import java.io.IOException;
import java.util.Scanner;
import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.databind.JsonMappingException;
//create class StreamingAPIExample2 to understand Streaming API
public class StreamingAPIExample2 {	
	// main() method start
	public static void main(String args[]){
		// use try-catch block 
		try {         
			
			// create an instance of JsonFactory 
			JsonFactory jsonFactory = new JsonFactory();
			// create an instance of JsonGenerator by using the createGenerator() method of JsonFactory
			JsonGenerator jsonGenerator = jsonFactory.createGenerator(new File("C:\\Users\\rastogi ji\\Desktop\\product.json"), JsonEncoding.UTF8);
			// create an instance of Scanner class
			Scanner sc = new Scanner(System.in);			
			// use writeStartObject()
			jsonGenerator.writeStartObject();
			// write name field to product.json file
			System.out.println("Enter Product Name:");
			String name = sc.nextLine();
			jsonGenerator.writeStringField("name", name); 

			// write price field to product.json file
			System.out.println("Enter Product Price:");
			String price = sc.nextLine();
			jsonGenerator.writeStringField("price", price);

			// write expire field to product.json
			System.out.println("Is product expire(Yes/No)?:");
			String expire = sc.nextLine();
			jsonGenerator.writeStringField("expire", expire);

			// "variation" : [X1, X2, X3]
			jsonGenerator.writeFieldName("variations"); 
			
			// use writeStartArray() method to write values in an array
			jsonGenerator.writeStartArray(); 
			
			System.out.println("Total number of variations:");
			int size = Integer.parseInt(sc.nextLine());
			
			for(int i = 0; i < size; i++) {
				System.out.println("Enter "+(i+1)+" variation name:");
				jsonGenerator.writeString(sc.nextLine()); 
			}
			
			// use writeEndArray() method to stop writing values in the array
			jsonGenerator.writeEndArray(); 
			// use writeStartObject()
			jsonGenerator.writeEndObject(); 
			// close JsonGenerator using close() method
			jsonGenerator.close();        			
			// close Scanner class
			sc.close();
			// create an instance of JsonParser by using createParser
			JsonParser parser = jsonFactory.createParser(new File("C:\\Users\\rastogi ji\\Desktop\\product.json"));
			
			// read each json string as a token
			while (parser.nextToken() != JsonToken.END_OBJECT) {
	            //getting current token
	            String fieldname = parser.getCurrentName();
	            if ("name".equals(fieldname)) {
	               //switch to next token
	               parser.nextToken();
	               System.out.println("Product Name: "+parser.getText());        	 
	            }
	            if("price".equals(fieldname)){
	               //switch to next token
	               parser.nextToken();
	               System.out.println("Price: "+parser.getText());        	 
	            }
	            if("expire".equals(fieldname)){
	               //switch to next token
	               parser.nextToken();
	               System.out.println("Is expire?: "+parser.getText());        	 
	            }
	            if("variations".equals(fieldname)){
	               //switch to next token "["
	               parser.nextToken();
	               // loop till token equal to "]"
	               while (parser.nextToken() != JsonToken.END_ARRAY) {
	                  System.out.println("Product Variations: "+parser.getText()); 
	               }
	            }
	         }
		} 
		catch (JsonParseException e) { 
			e.printStackTrace(); 
		} catch (JsonMappingException e) {
			e.printStackTrace(); 
		} catch (IOException e) { 
			e.printStackTrace(); 
		}
	}
}

Output: