关于用ObjectInputStream封装socket输入流后程序阻塞的问题

下面的代码运行后在(2)和(3)处会阻塞住

public class Server {
public static void main(String[] args)throws Exception{
ServerSocket ssock=new ServerSocket(3000);
Socket sock=ssock.accept();

ObjectInputStream in=new ObjectInputStream(sock.getInputStream()); //(2)
ObjectOutputStream out=new ObjectOutputStream(sock.getOutputStream()); //(1)
while(true){
out.writeObject("s");
out.flush();
}
}
}

public class Client {
public static void main(String[] args)throws Exception{
Socket sock=new Socket("127.0.0.1",3000);
ObjectOutputStream out=new ObjectOutputStream(sock.getOutputStream());//(3)
ObjectInputStream in=new ObjectInputStream(sock.getInputStream()); //(4)
while(true){
out.writeObject("s");
System.out.println((String)in.readObject());
}
}
}

而把(1)和(2)，(3)和(4)对调后程序运行正常。

原因如下：
使用缺省的serializetion的实现时,一个ObjectOutputStream的构造和一个ObjectInputStream的构造必须一一对应.ObjectOutputStream的构造函数会向输出流中写入一个标识头,而ObjectInputStream会首先读入这个标识头!

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