Serialisierung - readObject writeObject überschreibt

Question

Nachdem ich den folgenden Code geschrieben habe, muss ich jetzt die benutzerdefinierten readObject() - und writeObject() - Überschreibungsmethoden in StudentData verwenden, um die Variablen des Objekts zu lesen und zu schreiben. Ohne hierfür die Methoden defaultWriteObject oder defaultReadObject zu verwenden.

Das Problem ist, dass ich nicht vollständig verstehe, was ich tun soll. Ich habe gelesen Uses of readObject/writeObject in Serialization, aber ich kann nicht meinen Kopf drumherum. Kann mir jemand in die richtige Richtung zeigen?

Mein Code:

import java.io.*; //importing input-output files 

class Student implements java.io.Serializable { 

    String name; // declaration of variables 
    String DOB; 
    int id; 

    Student(String naam, int idno, String dob) // Initialising variables to user 
               // data 
    { 
     name = naam; 
     id = idno; 
     DOB = dob; 
    } 

    public String toString() { 
     return name + "\t" + id + "\t" + DOB + "\t"; 
    } 

} 

import java.io.BufferedReader; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.io.ObjectInputStream; 
import java.io.ObjectOutputStream; 

class StudentData      //main class 
{ 
    public static void main(String args[]) throws IOException     //exception handling 
    { 
     System.out.println("Enter the numbers of students:"); 
     BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); 
     int n = Integer.parseInt(in.readLine()); 

     Student[] students = new Student[n]; 

     //Student[] S=new Student[n];      // array of objects declared and defined 
     for (int i = 0; i < students.length; i++) { 
      System.out.println("Enter the Details of Student no: " + (i + 1));    //reading data form the user 
      System.out.println("Name: "); 
      String naam = in.readLine(); 
      System.out.println("ID no: "); 
      int idno = Integer.parseInt(in.readLine()); 
      System.out.println("DOB: ");    
      String dob = (in.readLine()); 

      students[i] = new Student(naam, idno, dob);       

      File studentFile = new File("StudentData.txt"); 
      try { 
       FileOutputStream fileOutput = new FileOutputStream(studentFile); 
       ObjectOutputStream objectOutput = new ObjectOutputStream(fileOutput); 
       objectOutput.writeObject(students); 

       students = null; 

       FileInputStream fileInput = new FileInputStream(studentFile); 
       ObjectInputStream objectInputStream = new ObjectInputStream(fileInput); 

       students = (Student[]) objectInputStream.readObject(); 
      } catch (ClassNotFoundException e) { 
       e.printStackTrace(); 
      } 

      for (Student student : students) { 
       System.out.println(student); 
      } 
     } 
    } 
} 

Answer 1

Sie haben es, wie dies zu tun:

import java.io.IOException; 

class Student implements java.io.Serializable { 

    String name; 
    String DOB; 
    int id; 

    Student(String naam, int idno, String dob) { 
     name = naam; 
     id = idno; 
     DOB = dob; 
    } 

    private void writeObject(java.io.ObjectOutputStream stream) 
      throws IOException { 
     stream.writeObject(name); 
     stream.writeInt(id); 
     stream.writeObject(DOB); 
    } 

    private void readObject(java.io.ObjectInputStream stream) 
      throws IOException, ClassNotFoundException { 
     name = (String) stream.readObject(); 
     id = stream.readInt(); 
     DOB = (String) stream.readObject(); 
    } 

    public String toString() { 
     return name + "\t" + id + "\t" + DOB + "\t"; 
    } 

} 

Die readObject- aufgerufen kurz nach einer Instanz von Studenten zu schaffen (unter Umgehung des normalen Konstruktor).