First of all, serialization is to convert an object or set of these bits to treat them in different computer applications, either to store them in files, or send them through sockets (roughly, by the network). You can serialize any object, as long as it is inherited from the Serializable interface.
The advantage of HashMap is that it has already implemented Serializable , so we can serialize all the HashMap at once, with all its data and internal attributes, so when you open the program, just is to open the flow, read and assign, close the flows and the buffer and you're done.
An example in Java code is the following:
private HashMap<Integer, Persona> personas = new HashMap<Integer, Persona>();
We have a HashMap , which the primary key will be of the class Integer or integer, and the content will be of the class Persona . To save you can use the following:
public boolean add(int edad, String nombre){
Persona p = new Persona(edad, nombre);
return personas.put(personas.size()+1, p) != null;
}
Up to this point it only saves in memory, to save in the file do the following:
public void guardar(){
try {
fos = new FileOutputStream(file);
oos = new ObjectOutputStream(fos);
oos.writeObject(this.personas);
oos.close();
fos.close();
} catch (FileNotFoundException ex) {
Logger.getLogger(Gestion.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException ex) {
Logger.getLogger(Gestion.class.getName()).log(Level.SEVERE, null, ex);
}
}
The add and save method can be merged if you want. The whole class where all the serialization is is as follows:
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.HashMap;
import java.util.logging.Level;
import java.util.logging.Logger;
/*
* 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.
*/
/**
*
* @author Carlos
*/
public class Gestion {
private HashMap<Integer, Persona> personas = new HashMap<Integer, Persona>();
private File file;
private FileInputStream fis;
private FileOutputStream fos;
private ObjectInputStream ois;
private ObjectOutputStream oos;
public Gestion(String ruta) {
this.file = new File(ruta);
this.crearArchivo();
}
public boolean add(int edad, String nombre){
Persona p = new Persona(edad, nombre);
return personas.put(personas.size()+1, p) != null;
}
public HashMap<Integer, Persona> obtenerTodo() {
try {
HashMap<Integer, Persona> personasTemp = new HashMap<>();
boolean buffer = false;
fis = new FileInputStream(file);
while (fis.available() > 0) {
ois = new ObjectInputStream(fis);
Persona p = (Persona) ois.readObject();
if (p != null) {
personasTemp.put(personasTemp.size() + 1, p);
}
buffer = true;
}
if (buffer) {
ois.close();
}
fis.close();
return personasTemp;
} catch (IOException | ClassNotFoundException e) {
System.out.println(e);
return null;
}
}
public void obtener(){
try {
fis = new FileInputStream(file);
boolean buffer = false;
while(fis.available() > 0){
ois = new ObjectInputStream(fis);
HashMap<Integer, Persona> personasTemp = (HashMap<Integer, Persona>) ois.readObject();
if (personasTemp != null){
this.personas = personasTemp;
}
buffer = true;
}
if (buffer){
ois.close();
}
fis.close();
} catch (FileNotFoundException ex) {
Logger.getLogger(Gestion.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException | ClassNotFoundException ex) {
Logger.getLogger(Gestion.class.getName()).log(Level.SEVERE, null, ex);
}
}
public void guardar(){
try {
fos = new FileOutputStream(file);
oos = new ObjectOutputStream(fos);
oos.writeObject(this.personas);
oos.close();
fos.close();
} catch (FileNotFoundException ex) {
Logger.getLogger(Gestion.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException ex) {
Logger.getLogger(Gestion.class.getName()).log(Level.SEVERE, null, ex);
}
}
private void crearArchivo() {
if(!this.file.exists()){
try {
file.createNewFile();
} catch (IOException ex) {
Logger.getLogger(Gestion.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
public void imprimirTodo(){
if(this.personas.isEmpty()){
System.out.println("No hay nada...");
return;
}
for(int i = 0 ; i < this.personas.size(); i++){
System.out.println(personas.get(i+1));
}
}
}
The people class is the following:
import java.io.Serializable;
import java.util.Objects;
/*
* 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.
*/
/**
*
* @author Carlos
*/
public class Persona implements Serializable{
private static final long serialVersionUID = 1L;
private int edad;
private String nombre;
public Persona(int edad, String nombre) {
this.edad = edad;
this.nombre = nombre;
}
public int getEdad() {
return edad;
}
public void setEdad(int edad) {
this.edad = edad;
}
public String getNombre() {
return nombre;
}
public void setNombre(String nombre) {
this.nombre = nombre;
}
@Override
public int hashCode() {
int hash = 7;
hash = 59 * hash + this.edad;
hash = 59 * hash + Objects.hashCode(this.nombre);
return hash;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final Persona other = (Persona) obj;
if (this.edad != other.edad) {
return false;
}
if (!Objects.equals(this.nombre, other.nombre)) {
return false;
}
return true;
}
@Override
public String toString() {
return "Persona{" + "edad=" + edad + ", nombre=" + nombre + '}';
}
}
And finally the Main or main class, which is where the Main is, is the following:
/*
* 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.
*/
/**
*
* @author Carlos
*/
public class Main {
private final Gestion gestion;
public Main() {
this.gestion = new Gestion("ejemplo.bin");
/*this.gestion.add(25, "Carlos");
this.gestion.add(20, "Juan");
this.gestion.add(19, "Pepe");
this.gestion.guardar();*/
this.gestion.imprimirTodo();
this.gestion.obtener();
this.gestion.imprimirTodo();
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
Main m = new Main();
}
}