Jackson - Data Binding

Data Binding API is used to convert JSON to and from POJO (Plain Old Java Object) using property accessor or using annotations. It is of two type.

• Simple Data Binding - Converts JSON to and from Java Maps, Lists, Strings, Numbers, Booleans and null objects.
• Full Data Binding - Converts JSON to and from any JAVA type.

ObjectMapper reads/writes JSON for both types of data bindings. Data Binding is most convenient way and is analogus to JAXB parer for XML.

Simple Data Binding

Simple data binding refers to mapping of JSON to JAVA Core data types. Following table illustrates the relationship between JSON types vs Java Types.

Sr. No.	JSON Type	Java Type
1	object	LinkedHashMap<String,Object>
2	array	ArrayList<Object>
3	string	String
4	complete number	Integer, Long or BigInteger
5	fractional number	Double / BigDecimal
6	true | false	Boolean
7	null	null

Let's see simple data binding in action. Here we'll map JAVA basic types directly to JSON and vice versa.

Create a java class file named JacksonTester in C:\>Jackson_WORKSPACE.

File: JacksonTester.java

import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonTester {
   public static void main(String args[]){
      JacksonTester tester = new JacksonTester();
         try {
            ObjectMapper mapper = new ObjectMapper();

            Map<String,Object> studentDataMap = new HashMap<String,Object>(); 
            int[] marks = {1,2,3};

            Student student = new Student();
            student.setAge(10);
            student.setName("Mahesh");
            // JAVA Object
            studentDataMap.put("student", student);
            // JAVA String
            studentDataMap.put("name", "Mahesh Kumar");     
            // JAVA Boolean
            studentDataMap.put("verified", Boolean.FALSE);
            // Array
            studentDataMap.put("marks", marks);

            mapper.writeValue(new File("student.json"), studentDataMap);
            //result student.json
   //{ 
            //   "student":{"name":"Mahesh","age":10},
            //   "marks":[1,2,3],
            //   "verified":false,
            //   "name":"Mahesh Kumar"
            //}
            studentDataMap = mapper.readValue(new File("student.json"), Map.class);

            System.out.println(studentDataMap.get("student"));
            System.out.println(studentDataMap.get("name"));
            System.out.println(studentDataMap.get("verified"));
            System.out.println(studentDataMap.get("marks"));
      } catch (JsonParseException e) {
         e.printStackTrace();
      } catch (JsonMappingException e) {
         e.printStackTrace();
      } catch (IOException e) {
            e.printStackTrace();
      }
   }
}

class Student {
   private String name;
   private int age;
   public Student(){}
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   public int getAge() {
      return age;
   }
   public void setAge(int age) {
      this.age = age;
   }
   public String toString(){
      return "Student [ name: "+name+", age: "+ age+ " ]";
   } 
}

Verify the result

Compile the classes using javac compiler as follows:

C:\Jackson_WORKSPACE>javac JacksonTester.java

Now run the jacksonTester to see the result:

C:\Jackson_WORKSPACE>java JacksonTester

Verify the Output

{name=Mahesh, age=10}
Mahesh Kumar
false
[1, 2, 3]

Full Data Binding

Data Binding with Generics