Serializable：writeReplace

如果一个序列化类中含有Object writeReplace()方法，那么实际序列化的对象将是作为writeReplace方法返回值的对象，而且序列化过程的依据是实际被序列化对象的序列化实现。

People定义了writeReplace方法，并且自定义了writeObject/readObject方法。

public class People implements Serializable
{
    /**
     * 
     */
    private static final long serialVersionUID = 2659082826995480601L;
    private int age;
    private String name;

    People(int age,String name)
    {
        this.age = age;
        this.name = name;
    }

    private void writeObject(ObjectOutputStream out)
    {
        System.out.println("是否调用了我？");
    }
    private void readObject(ObjectInputStream in)
    {
        System.out.println("是否调用了我？");
    }   

    private Object writeReplace()
    {
        return new Kong("路人");
    }

}

作为People类writeReplace返回值的Kong对象

public class Kong implements Serializable
{
    /**
     * 
     */
    private static final long serialVersionUID = -7144694309484327560L;

    public String s;

    Kong(String s)
    {
        this.s = s;
    }

    private void writeObject(ObjectOutputStream out) throws IOException
    {
        out.defaultWriteObject();
        System.out.println("出");
    }
    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException
    {
        in.defaultReadObject();
        System.out.println("入");
    }
}

测试程序：

@Test
    public void testOut03() throws FileNotFoundException, IOException
    {
        People p = new People(2,"小白");
        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("D:\\temp01.txt"));
        out.writeObject(p);
        out.flush();
        out.close();
    }

    @Test
    public void testIn03() throws FileNotFoundException, IOException, ClassNotFoundException
    {
        ObjectInputStream in = new ObjectInputStream(new FileInputStream("D:\\temp01.txt"));
        Kong k = (Kong)in.readObject();
        in.close();
        System.out.println(k.s);
    }

可以看到out.writeObject(p);试图序列化一个People对象，但是由于writeReplace方法的存在，实际上序列化了一个Kong 对象，在这个过程中调用了Kong定义的writeObject方法，并且在反序列化过程中，得到了一个Kong对象，并且调用了Kong定义的readObject方法。整个过程与People的writeObject/readObject无关。

这也就是说Kong k = (Kong)in.readObject();这个过程会依赖in中的实际对象，而不是依赖out.writeObject(p);

不知道为什么，就是这么个实现。