Parsing String to JsonNode Jackson

In this section, we will understand how we can use Jackson 2.0 for converting a JSON String to a JsonNode. JsonNode is one of the most used classes of Jackson. It is an immutable class; means we cannot actually build an object graph of JsonNode instances. Instead, we can create an object graph of the subclass of JsonNode, i.e., ObjectNode.

The process of parsing JsonString into JsonNode is very simple. We simply create an instance of ObjectMapper class and use its readTree() method in the following way:

  String str = “{“proId”:”001″,”proName”:”MX Pro 20″,”price”:”25k”}”;  ObjectMapper map = new ObjectMapper();  JsonNode node = map.readTree(str);  

Let’s take an example to understand how the readTree() method is used for parsing.

StringToJsonNodeExample.java

  //import required classes and package if any  import java.io.IOException;  import java.text.ParseException;  import com.fasterxml.jackson.core.JsonParseException;  import com.fasterxml.jackson.databind.JsonMappingException;  import com.fasterxml.jackson.databind.JsonNode;  import com.fasterxml.jackson.databind.ObjectMapper;  //create class StringToJsonNodeExample to understand how to parse string to JsonNode  public class StringToJsonNodeExample {  //main method start   public static void main(String args[]) throws ParseException {  // create instance of the ObjectSerialization class  ObjectMapper obj = new ObjectMapper();  try {  String jsonString = “{“proId”:”001″,”proName”:”MX Pro 20″,”price”:”25k”}”;   System.out.println(jsonString);  System.out.println();  JsonNode node = obj.readTree(jsonString);  System.out.println(“After parsing String to JsonNode: “+node);  System.out.println();  JsonNode node1 = node.get(“proId”);  System.out.println(“Product Id = “+node1.textValue());  JsonNode node2 = node.get(“proName”);  System.out.println(“Product Name = “+node2.textValue());  JsonNode node3 = node.get(“price”);  System.out.println(“Product Price = “+node3.textValue());  } catch (JsonParseException e) {  e.printStackTrace();  } catch (JsonMappingException e) {  e.printStackTrace();  } catch (IOException e) {  e.printStackTrace();  }   }  }  

Output:

Many times, we need to go lower level for accessing the data from the JsonString. For this purpose, we use the JsonFactory, JsonParser, JsonNode and getFactory(), createParser() and readTree() methods in the following way:

  String str = “{“proId”:”001″,”proName”:”MX Pro 20″,”price”:”25k”}”;  ObjectMapper mapper = new ObjectMapper();  JsonFactory factory = mapper.getFactory();  JsonParser parser = factory.createParser(str);   JsonNode node = mapper.readTree(parser);  

Let’s take an example to understand how these three classes and their methods are used for parsing.

LowLevelParsingExample.java

  //import required classes and package if any  import java.io.IOException;  import java.text.ParseException;  import com.fasterxml.jackson.core.JsonFactory;  import com.fasterxml.jackson.core.JsonParseException;  import com.fasterxml.jackson.core.JsonParser;  import com.fasterxml.jackson.databind.JsonMappingException;  import com.fasterxml.jackson.databind.JsonNode;  import com.fasterxml.jackson.databind.ObjectMapper;  //create class LowLevelParsingExample to understand how to perform low level parsing  public class LowLevelParsingExample {  //main method start   public static void main(String args[]) throws ParseException {  // create instance of the ObjectSerialization class  ObjectMapper obj = new ObjectMapper();  try {  String jsonString = “{“proId”:”001″,”proName”:”MX Pro 20″,”price”:”25k”}”;   System.out.println(jsonString);  System.out.println();  // create instance of getFactory() method  JsonFactory factory = obj.getFactory();  // create parser by using the createParser() method  JsonParser parser = factory.createParser(jsonString);  // create JsonNode from parser  JsonNode node = obj.readTree(parser);  System.out.println(“After parsing String to JsonNode: “+node);  System.out.println();  JsonNode node1 = node.get(“proId”);  System.out.println(“Product Id = “+node1.textValue());  JsonNode node2 = node.get(“proName”);  System.out.println(“Product Name = “+node2.textValue());  JsonNode node3 = node.get(“price”);  System.out.println(“Product Price = “+node3.textValue());  } catch (JsonParseException e) {  e.printStackTrace();  } catch (JsonMappingException e) {  e.printStackTrace();  } catch (IOException e) {  e.printStackTrace();  }   }  }  

Output:

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