把一个对象存储到硬盘上——Externalizable

Java的对象不仅可以在内存中调用，还可以在硬盘中存取，需要实现一个Externalizable接口，下面介绍其简单用法

首先，写一个类实现Externalizable接口

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

public class Car implements Externalizable{
	public Car(){}
	public Car(int id,int price){
		this.id = id;
		this.price = price;
	}
 private int id;
 public int getId() {
	return id;
}
public void setId(int id) {
	this.id = id;
}
public int getPrice() {
	return price;
}
public void setPrice(int price) {
	this.price = price;
}
private int price;

//写入硬盘的方法
@Override
public void writeExternal(out) throws IOException {
	// TODO Auto-generated method stub
	System.out.println("开始写入");
	out.writeObject(id);//ObjectOutput这个东西也就只有在这能用到了把 
	out.writeObject(price);
        out.flush();
        out.close();

 }
//从硬盘读出的方法
 @Override
public void readExternal(ObjectInput in) throws IOException,
		ClassNotFoundException {
	// TODO Auto-generated method stub
	System.out.println("开始读出");
	this.id = (int)in.readObject();
	this.price = (int)in.readObject();
	return;
}
}

调用方法

		Externalizable car1 = new Car(8,2);
		car1.writeExternal(new ObjectOutputStream(new FileOutputStream(new File("d:/exteral.txt"))));
		Car car2 = new Car();
		car2.readExternal(new ObjectInputStream(new FileInputStream(new File("d:/exteral.txt"))));
		System.out.println(car2.getId()+" "+car2.getPrice());

不过目测Serializable也可以实现相同的功能，代码如下

import java.io.Serializable;

public class Person implements Serializable {
	private String name;
	private int age;
	private int id;
	
	public Person(){}
	public Person(String name,int age,int id){
		this.name = name;
		this.age=age;
		this.id=id;
	}
	
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	
	
	
}

调用

ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("d:/person1.txt")));
		objectOutputStream.writeObject(new Person("haha",25,1));
		objectOutputStream.close();
		
		ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(new File("d:/person1.txt")));
		Person p1 = (Person) objectInputStream.readObject();
		objectInputStream.close();
		System.out.println(p1.getName()+p1.getAge()+p1.getId());