反序列化对象

       下面程序为Singleton类提供了readResolve()方法，当JVM反序列化地恢复一个新对象时，系统会自动调用这个readResolve()方法返回指定好的对象，从而保证系统通过反序列化机制不会产生多个对象。运行下面程序，程序判断singleton == singleton2 是否相同将输出true，这表明反序列化机制恢复出来的Java对象依然是原来的Java对象。通过这种方式可保证反序列化时Singleton依然是单例类。

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamException;
import java.io.Serializable;

class Singleton implements Serializable {
	private static final long serialVersionUID = 327838450350496302L;

	private static Singleton instance;
	private String name;

	private Singleton(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public static Singleton getInstance(String name) {
		if (instance == null) {
			instance = new Singleton(name);
		}
		return instance;
	}

	// 提供readResolve()方法
	private Object readResolve() throws ObjectStreamException {
		return instance;
	}

}

public class SingletonTest {

	public static void main(String[] args) throws Exception {
		// 调用静态方法来获取wolf实例
		Singleton singleton = Singleton.getInstance("NorhtWolf");
		System.out.println("Wolf对象创建完成~~~");
		Singleton singleton2 = null;
		ObjectOutputStream objectOutputStream = null;
		ObjectInputStream objectInputStream = null;
		try {
			// 创建对象输出流
			objectOutputStream = new ObjectOutputStream(new FileOutputStream(
					"b.bin"));
			// 创建对象输入流
			objectInputStream = new ObjectInputStream(new FileInputStream(
					"b.bin"));
			// 序列化输入Java对象
			objectOutputStream.writeObject(singleton);
			objectOutputStream.flush();
			// 反序列化恢复Java对象
			singleton2 = (Singleton) objectInputStream.readObject();
			System.out.println(singleton2.getName());
			// 两个对象的实例变量值完全相等
			System.out.println(singleton.equals(singleton2));
			// 两个对象不相同
			System.out.println(singleton == singleton2);

		} catch (Exception e) {
		} finally {
			if (objectOutputStream != null) {
				objectOutputStream.close();
			}
			if (objectInputStream != null) {
				objectInputStream.close();
			}
		}

	}

}