Serialization and data generic binding of objects in the Jackson library in Java

Jackson object serialization
Here we will introduce serializing Java objects to a JSON file, and then reading the JSON file to get converted to an object. In this example, the Student class is created. Create a student object that will be represented in JSON in a student.json file.

Create a Java class file named JacksonTester in C:/> Jackson_WORKSPACE.

File: JacksonTester.java

 import java.io.File;import java.io.IOException;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 { Student student = new Student(); student.setAge(10); student.setName("Mahesh"); tester.writeJSON(student); Student student1 = tester.readJSON(); System.out.println(student1); } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } private void writeJSON(Student student) throws JsonGenerationException, JsonMappingException, IOException{ ObjectMapper mapper = new ObjectMapper(); mapper.writeValue(new File("student.json"), student); } private Student readJSON() throws JsonParseException, JsonMappingException, IOException{ ObjectMapper mapper = new ObjectMapper(); Student student = mapper.readValue(new File("student.json"), Student.class); return student; }}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+ " ]"; } }

Verification results

Use javac to compile the following class:
The code copy is as follows:
C:/Jackson_WORKSPACE>javac JacksonTester.java

Now run jacksonTester to see the result:
The code copy is as follows:
C:/Jackson_WORKSPACE>java JacksonTester

The verification output result is copied as follows:
Student [ name: Mahesh, age: 10 ]

Jackson Data Binding Generics
In simple data binding, we use String as the key object and map the class as a value object. Instead, we can use specific Java objects and types to cast to JSON.

Consider the following example using a class UserData to save user-specific data.

Create a directory called JacksonTester in the Java class file C:/> Jackson_WORKSPACE.

File name: 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 userDataMap = new HashMap(); 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>() { }; 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 output

Use javac to compile the following class:
The code copy is as follows:
C:/Jackson_WORKSPACE>javac JacksonTester.java

Now run jacksonTester to see the result:
The code copy is as follows:
C:/Jackson_WORKSPACE>java JacksonTester

Verify the output

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