Java创建一个新的ObjectInputStream块

Question

我正在尝试使用从Socket检索的InputStream创建一个新的ObjectInputStream.这是我的代码:

这是我的MessageGetterSender类的构造函数.该程序没有到达Checkpoint 4.

public MessageGetterSender(Socket socket) {

    System.out.println("MessageGetterSender: Checkpoint 1");

    this.socket = socket;

    // Get input and output streams
    try {
        System.out.println("MessageGetterSender: Checkpoint 2");

        InputStream is = socket.getInputStream();

        System.out.println("MessageGetterSender: Checkpoint 3");

        this.in = new ObjectInputStream(is);

        System.out.println("MessageGetterSender: Checkpoint 4");

    } catch (IOException ioe) {
        System.out.println("Could not get ObjectInputStream on socket: " + socket.getLocalPort());
    }

    try {
        this.out = new ObjectOutputStream(socket.getOutputStream());
    } catch (IOException ioe) {
        System.out.println("Could not get ObjectOutputStream on socket: " + socket.getLocalPort());
    }

    System.out.println("MessageGetterSender: Checkpoint 5");
}

我正在从我连接到服务器以获取套接字的类中实例化一个新的MessageGetterSender对象.这是相关的代码.它是InstantMessageClass的构造函数,即实例化MessageGetterSender对象的类:

public InstantMessageClient(String username) {

try {
    socket = new Socket("localhost", 5555);
} catch (IOException ioe) {
    System.out.println("Error: Could not connect to socket on port: " + serverPort);
}

messageGetterSender = new MessageGetterSender(socket);

...

由于代码没有执行到Checkpoint 4但它确实到达了Checkpoint 3,我很确定ObjectInputStream的实例化是罪魁祸首.我无法弄清楚为什么.有任何想法吗？谢谢您的帮助.

Answer 1

只是为了扩展FatGuy对其他发现这一点的Google员工的回答; 这个"鸡和鸡蛋问题"的解决方案是让每一方首先打开输出流,刷新输出流,然后打开输入流.

ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
out.flush();
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());

Answer 2

在构造函数中构造一个ObjectInputStream类时,该类会尝试读取ObjectOutputStream连接另一端关联的头文件.在读取该标题之前,它不会返回.因此,如果您看到构造函数"挂起",那是因为套接字的另一端未使用过ObjectOutputStream,或者尚未刷新数据.