Jackson - Data Binding With Generics

In simple data binding, we have used Map class which uses String as key and Object as a value object. Instead, we can have a concrete Java object and type cast it to use it 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.List;
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;
import org.codehaus.jackson.type.TypeReference;

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]