#students.json

[
  {
    "rollno": "R001",
    "fullname": "Tran Van A",
    "email": "a@gmail.com"
  },
  {
    "rollno": "R002",
    "fullname": "Tran Van B",
    "email": "a@gmail.com"
  },
  {
    "rollno": "R003",
    "fullname": "Tran Van C",
    "email": "a@gmail.com"
  },
  {
    "rollno": "R004",
    "fullname": "Tran Van D",
    "email": "a@gmail.com"
  },
  {
    "rollno": "R005",
    "fullname": "Tran Van E",
    "email": "a@gmail.com"
  },
  {
    "rollno": "AAA",
    "fullname": "AAA",
    "email": "AAA"
  },
  {
    "rollno": "BBB",
    "fullname": "BBB",
    "email": "BBB"
  }
]

#students.xml

<?xml version="1.0" encoding="UTF-8"?>
<students>
	<student>
		<rollno>R001</rollno>
		<fullname>Tran Van A</fullname>
		<email>a@gmail.com</email>
	</student>
	<student>
		<rollno>R002</rollno>
		<fullname>Tran Van B</fullname>
		<email>a@gmail.com</email>
	</student>
	<student>
		<rollno>R003</rollno>
		<fullname>Tran Van C</fullname>
		<email>a@gmail.com</email>
	</student>
	<student>
		<rollno>R004</rollno>
		<fullname>Tran Van D</fullname>
		<email>a@gmail.com</email>
	</student>
	<student>
		<rollno>R005</rollno>
		<fullname>Tran Van E</fullname>
		<email>a@gmail.com</email>
	</student>
	<student>
		<rollno>AAA</rollno>
		<fullname>AAA</fullname>
		<email>AAA</email>
	</student>
	<student>
		<rollno>BBB</rollno>
		<fullname>BBB</fullname>
		<email>BBB</email>
	</student>
</students>

#Student.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package lesson09;

import java.util.Scanner;

/**
 *
 * @author QTA
 */
public class Student {
    String rollno;
    String fullname;
    String email;

    public Student() {
    }

    public Student(String rollno, String fullname, String email) {
        this.rollno = rollno;
        this.fullname = fullname;
        this.email = email;
    }

    public String getRollno() {
        return rollno;
    }

    public void setRollno(String rollno) {
        this.rollno = rollno;
    }

    public String getFullname() {
        return fullname;
    }

    public void setFullname(String fullname) {
        this.fullname = fullname;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
    
    public void input() {
        Scanner scan = new Scanner(System.in);
        
        System.out.println("Nhap msv: ");
        rollno = scan.nextLine();
        System.out.println("Nhap ten: ");
        fullname = scan.nextLine();
        System.out.println("Nhap email: ");
        email = scan.nextLine();
    }

    @Override
    public String toString() {
        return "Student{" + "rollno=" + rollno + ", fullname=" + fullname + ", email=" + email + '}';
    }
    
    public void display() {
        System.out.println(this);
    }
    
    public String toXML() {
        return "<student>\n" +
"				<rollno>"+rollno+"</rollno>\n" +
"				<fullname>"+fullname+"</fullname>\n" +
"				<email>"+email+"</email>\n" +
"			</student>";
    }
}

#StudentHandler.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package lesson09;

import java.util.ArrayList;
import java.util.List;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

/**
 *
 * @author QTA
 */
public class StudentHandler extends DefaultHandler{
    List<Student> studentList = null;
    Student std = null;
    
    boolean isRollno = false;
    boolean isFullname = false;
    boolean isEmail = false;
    
    public StudentHandler() {
        studentList = new ArrayList<>();
    }

    @Override
    public void startElement(String uri, String localName, String qName, Attributes attr) throws SAXException {
        if(qName.equalsIgnoreCase("student")) {
            std = new Student();
        } else if(qName.equalsIgnoreCase("rollno")) {
            isRollno = true;
        } else if(qName.equalsIgnoreCase("fullname")) {
            isFullname = true;
        } else if(qName.equalsIgnoreCase("email")) {
            isEmail = true;
        }
    }

    @Override
    public void endElement(String uri, String localName, String qName) throws SAXException {
        if(qName.equalsIgnoreCase("student")) {
            studentList.add(std);
            std = null;
        } else if(qName.equalsIgnoreCase("rollno")) {
            isRollno = false;
        } else if(qName.equalsIgnoreCase("fullname")) {
            isFullname = false;
        } else if(qName.equalsIgnoreCase("email")) {
            isEmail = false;
        }
    }

    @Override
    public void characters(char[] chars, int start, int length) throws SAXException {
        String value = new String(chars, start, length);
        
        if(isRollno) {
            std.setRollno(value);
        } else if(isFullname) {
            std.setFullname(value);
        } else if(isEmail) {
            std.setEmail(value);
        }
    }

    public List<Student> getStudentList() {
        return studentList;
    }

    public void setStudentList(List<Student> studentList) {
        this.studentList = studentList;
    }
}

#Test.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package lesson09;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import static lesson09.Test2.readText;
import org.xml.sax.SAXException;

/**
 *
 * @author QTA
 */
public class Test {
    static List<Student> studentList = null;
    static InputStreamReader reader = null;
    static BufferedReader bReader = null;
    
    public static void main(String[] args) throws IOException {
        studentList = new ArrayList<>();
        int choose;
        reader = new InputStreamReader(System.in);
        bReader = new BufferedReader(reader);
        
        do {
            showMenu();
            choose = Integer.parseInt(bReader.readLine());
            
            switch(choose) {
                case 1:
                    inputStudent();
                    break;
                case 2:
                    displayStudent();
                    break;
                case 3:
                    readXML();
                    break;
                case 4:
                    saveXML();
                    break;
                case 5:
                    readJSON();
                    break;
                case 6:
                    saveJSON();
                    break;
                case 7:
                    System.out.println("Exit!!!");
                    break;
                default:
                    System.out.println("Input failed!!!");
                    break;
            }
        } while(choose != 7);
    }
    
    static void showMenu() {
        System.out.println("1. Input Student");
        System.out.println("2. Display Student");
        System.out.println("3. Read XML");
        System.out.println("4. Save XML");
        System.out.println("5. Read JSON");
        System.out.println("6. Save JSON");
        System.out.println("7. Exit");
        System.out.println("Choose: ");
    }
    
    static void readXML() {
        SAXParserFactory factory = SAXParserFactory.newInstance();
        try {
            SAXParser parser = factory.newSAXParser();
            
            StudentHandler handler = new StudentHandler();
            parser.parse(new File("students.xml"), handler);
            
            studentList = handler.getStudentList();
            
            for (Student student : studentList) {
                student.display();
            }
        } catch (ParserConfigurationException ex) {
            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
        } catch (SAXException ex) {
            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    private static void inputStudent() {
        System.out.println("Nhap so sinh vien can them: ");
        int n = 0;
        try {
            n = Integer.parseInt(bReader.readLine());
        } catch (IOException ex) {
            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
        }
        
        for (int i = 0; i < n; i++) {
            Student std = new Student();
            std.input();
            studentList.add(std);
        }
    }

    private static void displayStudent() {
        System.out.println("Danh sach sinh vien: ");
        for (Student student : studentList) {
            student.display();
        }
    }

    private static void saveXML() {
        String xml = toXML();
        saveFile(xml, "students.xml");
    }
    
    static String toXML() {
        StringBuilder builder = new StringBuilder();
        for (Student student : studentList) {
            builder.append(student.toXML());
        }
        
        return "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                "\n" +
                "<students>\n" +
                builder.toString() +
                "</students>";
    }

    private static void readJSON() {
        Gson gson = new Gson();
        String content = readText("students.json");
        Type type = new TypeToken<List<Student>>(){}.getType();
        
        studentList = gson.fromJson(content, type);
        
        for (Student student : studentList) {
            student.display();
        }
    }

    private static void saveJSON() {
        //Convert studentList -> JSON String
        Gson gson = new Gson();
        Type type = new TypeToken<List<Student>>(){}.getType();
        String json = gson.toJson(studentList, type);
        
        //save json -> file
        saveFile(json, "students.json");
    }
    
    static void saveFile(String content, String filename) {
        FileWriter writer = null;
        BufferedWriter bWriter = null;
        
        try {
            writer = new FileWriter(filename);
            bWriter = new BufferedWriter(writer);
            
            bWriter.write(content);
        } catch (IOException ex) {
            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            if(bWriter != null) {
                try {
                    bWriter.close();
                } catch (IOException ex) {
                    Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
            if(writer != null) {
                try {
                    writer.close();
                } catch (IOException ex) {
                    Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
    }
    
    static String readText(String filename) {
        FileReader reader = null;
        BufferedReader bReader = null;
        
        StringBuilder builder = new StringBuilder();
        
        try {
            reader = new FileReader(filename);
            bReader = new BufferedReader(reader);
            String line;
            
            while((line = bReader.readLine()) != null) {
                builder.append(line);
            }
        } catch (FileNotFoundException ex) {
            Logger.getLogger(Test2.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(Test2.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            if(bReader != null) {
                try {
                    bReader.close();
                } catch (IOException ex) {
                    Logger.getLogger(Test2.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
            if(reader != null) {
                try {
                    reader.close();
                } catch (IOException ex) {
                    Logger.getLogger(Test2.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
        
        return builder.toString();
    }
}

#Test2.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package lesson09;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.lang.reflect.Type;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author QTA
 */
public class Test2 {
    public static void main(String[] args) {
        readJSON();
    }
    
    static void readJSON() {
        List<Student> studentList = null;
        
        Gson gson = new Gson();
        String content = readText("students.json");
        Type type = new TypeToken<List<Student>>(){}.getType();
        
        studentList = gson.fromJson(content, type);
        
        for (Student student : studentList) {
            student.display();
        }
    }
    
    static String readText(String filename) {
        FileReader reader = null;
        BufferedReader bReader = null;
        
        StringBuilder builder = new StringBuilder();
        
        try {
            reader = new FileReader(filename);
            bReader = new BufferedReader(reader);
            String line;
            
            while((line = bReader.readLine()) != null) {
                builder.append(line);
            }
        } catch (FileNotFoundException ex) {
            Logger.getLogger(Test2.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(Test2.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            if(bReader != null) {
                try {
                    bReader.close();
                } catch (IOException ex) {
                    Logger.getLogger(Test2.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
            if(reader != null) {
                try {
                    reader.close();
                } catch (IOException ex) {
                    Logger.getLogger(Test2.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
        
        return builder.toString();
    }
}