Jackson - Data Binding

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

• Simple Data Binding − It converts JSON to and from Java Maps, Lists, Strings, Numbers, Booleans, and null objects.
• Full Data Binding − It converts JSON to and from any Java type.

ObjectMapper reads/writes JSON for both types of data bindings. Data binding is analogous to JAXB parser for XML.
We will cover simple data binding in this chapter. Full data binding is discussed separately in the next chapter.

Simple Data Binding

Simple data binding refers to mapping of JSON to JAVA core data types. The following table illustrates the relationship between JSON types versus Java types.

S.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

Simple Data Binding Example

Let us take a simple example to understand simple data binding in detail. 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 org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.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);
         
         // result student.json
         // {
         //    "student":{"name":"Mahesh","age":10},
         //    "marks":[1,2,3],
         //    "verified":false,
         //    "name":"Mahesh Kumar"
         // }
         
         
         mapper.writeValue(new File("student.json"), studentDataMap);

         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]