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.

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;

pubpc class JacksonTester {
   pubpc 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;
   pubpc Student(){}
   pubpc String getName() {
      return name;
   }
   pubpc void setName(String name) {
      this.name = name;
   }
   pubpc int getAge() {
      return age;
   }
   pubpc void setAge(int age) {
      this.age = age;
   }
   pubpc 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