Jackson - Data Binding With Generics

In simple data binding, we've used Map class which use String as key and Object as a value object. Instead we can have concrete java object and type cast it to be used in JSON binding.

Consider the following example with a class UserData, a class to hold user specific data.

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.Arrays;
import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.type.TypeReference;
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, UserData> userDataMap = new HashMap<String, UserData>();
            UserData studentData = new UserData(); 
            int[] marks = {1,2,3};

            Student student = new Student();
            student.setAge(10);
            student.setName("Mahesh");
            // JAVA Object
            studentData.setStudent(student);
            // JAVA String
            studentData.setName("Mahesh Kumar");
            // JAVA Boolean
            studentData.setVerified(Boolean.FALSE);
            // Array
            studentData.setMarks(marks);
            TypeReference ref = new TypeReference<Map<String,UserData>>() { };
            userDataMap.put("studentData1", studentData);
            mapper.writeValue(new File("student.json"), userDataMap);
            //{
            //   "studentData1":
            //	 {
            //		"student":
            //		{
            //			"name":"Mahesh",
            //			"age":10
            //      },
            //      "name":"Mahesh Kumar",
            //      "verified":false,
            //      "marks":[1,2,3]
            //   }
            //}
            userDataMap = mapper.readValue(new File("student.json"), ref);

            System.out.println(userDataMap.get("studentData1").getStudent());
            System.out.println(userDataMap.get("studentData1").getName());
            System.out.println(userDataMap.get("studentData1").getVerified());
            System.out.println(Arrays.toString(userDataMap.get("studentData1").getMarks()));
      } 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+ " ]";
   }	
}

class UserData {
   private Student student;
   private String name;
   private Boolean verified;
   private int[] marks;

   public UserData(){}

   public Student getStudent() {
      return student;
   }
   public void setStudent(Student student) {
      this.student = student;
   }
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   public Boolean getVerified() {
      return verified;
   }
   public void setVerified(Boolean verified) {
      this.verified = verified;
   }
   public int[] getMarks() {
      return marks;
   }
   public void setMarks(int[] marks) {
      this.marks = marks;
   }		
}

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

Student [ name: Mahesh, age: 10 ]
Mahesh Kumar
false
[1, 2, 3]