Map Serialization and Deserialization with Jackson

Just like Java objects, we can serialize and deserialize Java Map by using Jackson. We can easily serialize and deserialize Map<Object, Object>, Map<Object, String>, and Map<String, String> to or from JSON-formatted strings by using Jackson.

Serialization of Java Map

A process of converting Java objects into a stream of bytes is referred to as Serialization. The stream of bytes can be persisted or shared as needed. Java Map is one of the least intuitive objects to serialize.

Let’s take some examples to understand how we can serialize Maps such as Map<Object, Object>, Map<Object, String>, or Map<String, String> by using Jackson.

SerializeMapExample1.java

  import java.util.HashMap;  import java.util.Map;  import java.util.Scanner;    import com.fasterxml.jackson.core.JsonProcessingException;  import com.fasterxml.jackson.databind.ObjectMapper;    //create class SerializeMapExample1 to serialize Java Map  public class SerializeMapExample1 {      //main() methods start    public static void main(String args[]) {      int n;  Map student = new HashMap();    // create an instance of Scanner class  Scanner sc = new Scanner(System.in);    System.out.println(“Enter total number of students: “);  n = Integer.valueOf(sc.nextLine());    for(int i = 0; i < n; i++) {  String id, name;  System.out.println(“Enter student id of “+(i+1)+” student:”);  id = sc.nextLine();  System.out.println(“Enter student name of “+(i+1)+” student:”);  name = sc.nextLine();    // fill student map  student.put(id, name);  }    // create an instance of the ObjectMapper class  ObjectMapper mapper = new ObjectMapper();    try {  // serialize student Map by using Jackson  String jsonString = mapper  .writerWithDefaultPrettyPrinter()  .writeValueAsString(student);  System.out.println(“Java Map after serialize using Jackson: “+jsonString);  } catch (JsonProcessingException e) {  // TODO Auto-generated catch block  e.printStackTrace();  }    // close Scanner class object  sc.close();    }    }  ,>,>

Output:

Map Serialization and Deserialization with Jackson

We can also serialize a Map having a Java object as a value by adding some more lines of code in our previous example.

SerializeMapExample2.java

  import java.util.HashMap;  import java.util.Map;  import java.util.Scanner;    import com.fasterxml.jackson.core.JsonProcessingException;  import com.fasterxml.jackson.databind.ObjectMapper;  import com.fasterxml.jackson.databind.SerializationFeature;    //create class SerializeMapExample2 to serialize Java Map  public class SerializeMapExample2 {      //main() methods start    public static void main(String args[]) {      int n;    Map student = new HashMap();    // create an instance of Scanner class  Scanner sc = new Scanner(System.in);    System.out.println(“Enter total number of students: “);  n = Integer.valueOf(sc.nextLine());    for(int i = 0; i < n; i++) {  String id, fName, lName, course;    Student std = new Student();    System.out.println(“Enter id of “+(i+1)+” student:”);  id = sc.nextLine();    System.out.println(“Enter first name of “+(i+1)+” student:”);  fName = sc.nextLine();  std.setFName(fName);    System.out.println(“Enter last name of “+(i+1)+” student:”);  lName = sc.nextLine();  std.setLName(lName);    System.out.println(“Enter course of “+(i+1)+” student:”);  course = sc.nextLine();  std.setCourse(course);    // fill student map  student.put(id, std);  }    // create an instance of the ObjectMapper class  ObjectMapper mapper = new ObjectMapper();    // enable SerializationFeature in ObjectMapper  mapper.enable(SerializationFeature.INDENT_OUTPUT);    String jsonString;  try {    jsonString = mapper.writeValueAsString(student);  System.out.println(“After converting Map to JSON :”);          System.out.println(jsonString);  } catch (JsonProcessingException e) {  e.printStackTrace();  }    // close Scanner class object  sc.close();    }    }  class Student {        private String fName;      private String lName;      private String course;            public String toString() {          return “Name = “+fName + ” ” +lName+” Course = “+course;      }            public String getFName() {      return fName;      }      public void setFName(String fName) {      this.fName = fName;      }            public String getLName() {      return lName;      }      public void setLName(String lName) {      this.lName = lName;      }            public String getCourse() {      return course;      }      public void setCourse(String course) {      this.course = course;      }        }  ,>,>

Output:

Map Serialization and Deserialization with Jackson

Let’s take another example to understand how we can serialize Map<Object, Object> into JSON String.

SerializeMapExample3.java

  import java.util.HashMap;  import java.util.Map;  import java.util.Scanner;    import com.fasterxml.jackson.core.JsonProcessingException;  import com.fasterxml.jackson.databind.ObjectMapper;  import com.fasterxml.jackson.databind.SerializationFeature;    //create class SerializeMapExample3 to serialize Java Map  public class SerializeMapExample3 {      //main() methods start    public static void main(String args[]) {      int n;    Map student = new HashMap();    // create an instance of Scanner class  Scanner sc = new Scanner(System.in);    System.out.println(“Enter total number of students: “);  n = Integer.valueOf(sc.nextLine());    for(int i = 0; i < n; i++) {  String id, fName, lName;    Student std = new Student();  Course course = new Course();    System.out.println(“Enter id of “+(i+1)+” student:”);  id = sc.nextLine();  std.setId(id);    System.out.println(“Enter first name of “+(i+1)+” student:”);  fName = sc.nextLine();  std.setFName(fName);    System.out.println(“Enter last name of “+(i+1)+” student:”);  lName = sc.nextLine();  std.setLName(lName);    System.out.println(“Enter course of “+(i+1)+” student:”);  course.setName(sc.nextLine());    System.out.println(“Enter Semester: “);  course.setSemester(sc.nextLine());    // fill student map  student.put(course, std);  }    // create an instance of the ObjectMapper class  ObjectMapper mapper = new ObjectMapper();    // enable SerializationFeature in ObjectMapper  mapper.enable(SerializationFeature.INDENT_OUTPUT);    String jsonString;  try {    jsonString = mapper.writeValueAsString(student);  System.out.println(“After converting Map to JSON :”);          System.out.println(jsonString);  } catch (JsonProcessingException e) {  e.printStackTrace();  }    // close Scanner class object  sc.close();    }    }  class Student {    private String id;  private String fName;      private String lName;          public String toString() {          return “Student Id = “+id+” Name = “+fName + ” ” +lName;      }      public String getId() {      return id;      }      public void setId(String id) {      this.id = id;      }            public String getFName() {      return fName;      }      public void setFName(String fName) {      this.fName = fName;      }            public String getLName() {      return lName;      }      public void setLName(String lName) {      this.lName = lName;      }        }  class Course {  private String name;  private String semester;    public String toString() {          return “Course Name = “+name+” Semester = “+semester;      }            public String getName() {      return name;      }      public void setName(String name) {      this.name = name;      }            public String getSemester() {      return semester;      }      public void setSemester(String semester) {      this.semester = semester;      }  }  ,>,>

Output:

Map Serialization and Deserialization with Jackson

Deserialization JSON String to Java Map

A process of converting the stream of bytes into a Java object is referred to as deserialization. We can deserialize the JSON data into Maps of different signatures (Map<String, String>, Map<String, Object>, and Map<Object, Object>).

Let’s take an example to understand how we can deserialize JSON String into Map<String, String>.

DeserializeMapExample1.java

  import java.util.HashMap;  import java.util.Map;  import com.fasterxml.jackson.core.JsonProcessingException;  import com.fasterxml.jackson.core.type.TypeReference;  import com.fasterxml.jackson.databind.JsonMappingException;  import com.fasterxml.jackson.databind.ObjectMapper;  public class DeserializeJsonToMapExample1 {  //main() methods start    public static void main(String args[]) throws JsonMappingException, JsonProcessingException {  // create an instance of ObjectMapper class  ObjectMapper mapper = new ObjectMapper();    // create json string  String studentString = “{“id”: “001”, “fName”:”Nicholas”, “lName”:”Clemens”}”;    // create TypeReference of type HashMap  TypeReference> typeRef = new TypeReference>() {};    // deserialize studentString into Map  Map studentMap = mapper.readValue(studentString, typeRef);    System.out.println(“Student Map======>”+studentMap);    }  }  ,>,>,>

Output:

Map Serialization and Deserialization with Jackson

Let’s take another example to understand how we can deserialize JSON String into Map<Object, String>.

DeserializeMapExample2.java

  import java.util.HashMap;  import java.util.Map;    import com.fasterxml.jackson.core.JsonProcessingException;  import com.fasterxml.jackson.core.type.TypeReference;  import com.fasterxml.jackson.databind.JsonMappingException;  import com.fasterxml.jackson.databind.ObjectMapper;    public class DeserializeJsonToMapExample2 {  //main() methods start    public static void main(String args[]) throws JsonMappingException, JsonProcessingException {  // create an instance of ObjectMapper class  ObjectMapper mapper = new ObjectMapper();    // create json string  String studentString = “{“BCA”: “001 and Nicholas and Clemens”, “MCA”: “002 and Sharon and Lorenz”}”;    // create TypeReference of type HashMap  TypeReference> typeRef = new TypeReference>() {};    // deserialize studentString into Map  Map studentMap = mapper.readValue(studentString, typeRef);    System.out.println(“Student Map======>”+studentMap);    }  }  class Student {    private String id;  private String fName;      private String lName;            Student(String data){      String[] allData = data.split(“and”);          this.id = allData[0].trim();          this.fName = allData[1].trim();          this.lName = allData[2].trim();      }            public String toString() {          return “Student Id = “+id+” Name = “+fName + ” ” +lName;      }            public String getId() {      return id;      }      public String getFName() {      return fName;      }            public String getLName() {      return lName;      }  }  ,>,>,>

Output:

Map Serialization and Deserialization with Jackson

Let’s take another example to understand how we can deserialize JSON String into Map<Object, Object>.

DeserializeMapExample3.java

  import java.util.HashMap;  import java.util.Map;    import com.fasterxml.jackson.core.JsonProcessingException;  import com.fasterxml.jackson.core.type.TypeReference;  import com.fasterxml.jackson.databind.JsonMappingException;  import com.fasterxml.jackson.databind.ObjectMapper;    public class DeserializeMapExample3 {  //main() methods start    public static void main(String args[]) throws JsonMappingException, JsonProcessingException {  // create an instance of ObjectMapper class  ObjectMapper mapper = new ObjectMapper();    // create json string  String studentString = “{“BCA and 2nd Semester”: “001 and Nicholas and Clemens”, “MCA and 4th Semester”: “002 and Sharon and Lorenz”}”;    // create TypeReference of type HashMap  TypeReference> typeRef = new TypeReference>() {};    // deserialize studentString into Map  Map studentMap = mapper.readValue(studentString, typeRef);    System.out.println(“Student Map======>”+studentMap);    }  }  class Student {    private String id;  private String fName;      private String lName;            Student(String data){      String[] allData = data.split(“and”);          this.id = allData[0].trim();          this.fName = allData[1].trim();          this.lName = allData[2].trim();      }            public String toString() {          return “Student Id = “+id+” Name = “+fName + ” ” +lName;      }            public String getId() {      return id;      }      public String getFName() {      return fName;      }            public String getLName() {      return lName;      }  }  class Course {  private String name;  private String semester;    public String toString() {          return “Course Name = “+name+” Semester = “+semester;      }    Course(String data){      String[] allData = data.split(“and”);          this.name = allData[0].trim();          this.semester = allData[1].trim();      }            public String getName() {      return name;      }            public String getSemester() {      return semester;      }  }  ,>,>,>

Output:

Map Serialization and Deserialization with Jackson

Next TopicSerialize Fields Based on Custom Criteria in Jackson

Map Serialization and Deserialization with Jackson

Map Serialization and Deserialization with Jackson

Serialization of Java Map

Deserialization JSON String to Java Map

How to Write a Check

3N+1 Problem in Java

You may also like