java - 在 Socket.getInputStream 之前向 SocketInputStream 发送一些内容？

Question

这个问题已经有答案了:

ObjectInputStream from socket.getInputStream() (1 个回答)

已关闭 6 年前。

我刚才遇到了一个奇怪的错误。我正在研究可序列化的对象，我使用了两个对象，通过套接字连接相互通信。这两个应用程序是相同的(Peer 2 Peer)，但有两个实例正在运行并尝试通信。

问题似乎围绕着获得ObjectInputStream从 socket InputStream 。我的错误发生在 reader = new ObjectInputSream(cliIn) ，我被抛出了 SocketTimeoutException (这本身很奇怪，我本以为是在 read() 而不是装饰我的流时。下面是我尝试做的事情。

Socket clientSocket;
clientSocket = new Socket(InetAddress.getByName(aHostIP), aPort);
clientSocket.setSoTimeout(3000);

InputStream cliIn = clientSocket.getInputStream();
ObjectInputStream reader = null;
reader = new ObjectInputStream(cliIn); // <--- Error here
ObjectOutputStream writer;
writer = new ObjectOutputStream(new BufferedOutputStream(
     clientSocket.getOutputStream()
));

writer.writeObject(new Request(aPort));
writer.flush();

奇怪的是，如果我移动 ObjectInputStream 的创建直到我写信给OutputStream之后(此时另一个对象将响应该请求)，然后就不再出现错误。

Socket clientSocket;
clientSocket = new Socket(InetAddress.getByName(aHostIP), aPort);
clientSocket.setSoTimeout(3000);   

ObjectOutputStream writer;
writer = new ObjectOutputStream(new BufferedOutputStream(
     clientSocket.getOutputStream()
));

writer.writeObject(new Request(aPort));
writer.flush();

InputStream cliIn = clientSocket.getInputStream();
ObjectInputStream reader = null;
reader = new ObjectInputStream(cliIn); // <--- No more error

另一方(响应方)如下所示:

ObjectInputStream in = new ObjectInputStream(aConnection.getInputStream());
Object req = in.readObject();
SysIO.print("FROM OBJECT! : " + req.toString());
SysIO.print("FROM OBJECT! Port: " + ((Request) req).getPort());

Request res = new Request(15);

ObjectOutputStream out = new ObjectOutputStream(
      new BufferedOutputStream(aConnection.getOutputStream()));
out.writeObject(res);
out.flush();

它现在可以工作了，但我很想知道问题是什么以供将来引用。我可以看到，这可能很难准确地说，但也许您有一些进一步调查的指示，并发问题，我使用的套接字或缓冲区是否错误？

(我省略了一些错误处理以使其更清晰。)

Answer 1

答案就在 ObjectInputStream documentation :

public ObjectInputStream(InputStream in)
                  throws IOException

Creates an ObjectInputStream that reads from the specified InputStream. A serialization stream header is read from the stream and verified. This constructor will block until the corresponding ObjectOutputStream has written and flushed the header.

If a security manager is installed, this constructor will check for the "enableSubclassImplementation" SerializablePermission when invoked directly or indirectly by the constructor of a subclass which overrides the ObjectInputStream.readFields or ObjectInputStream.readUnshared methods.

Parameters:

in - input stream to read from

Throws:

StreamCorruptedException - if the stream header is incorrect

IOException - if an I/O error occurs while reading stream header

SecurityException - if untrusted subclass illegally overrides security-sensitive methods

NullPointerException - if in is null

在构造过程中，流尝试从套接字读取序列化 header ，但套接字读取超时，因为对方尚未发送任何序列化对象。