java - 我对嵌套 try-with-resource 的使用是否正确？

Question

我有一个简单的 TCP 服务器，它打印客户端发送的消息。我正在尝试修改它以使用 try-with-resource 功能。在我的示例中使用嵌套的 try-with-resource 语句是否正确？

public static void main(String args[]) throws IOException {
    String receivedMessage;

    try (ServerSocket serverSocket = new ServerSocket(777)) {
        while (true) {
            Socket socket = serverSocket.accept();
            System.out.println("Client connected");
            try (BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()))) {
                while ((receivedMessage = in.readLine()) != null) {
                    System.out.println(receivedMessage);
                }
                System.out.println("Client disconnected");
            }
        }
    }
}

Answer 1

是的，你的例子是正确的。

资源尝试 try block 可以独立，因为它有一个隐式 finally堵塞;而传统的 try block 后面必须跟一个 catch block 和/或 finally block 。

因此，您的示例代码等同于以下内容(除了资源变量在其各自 try block 的范围之外可见):

        final ServerSocket serverSocket = new ServerSocket(777);
        try {
            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("Client connected");
                final BufferedReader in = new BufferedReader(new InputStreamReader(
                        socket.getInputStream()));
                try {
                    while ((receivedMessage = in.readLine()) != null) {
                        System.out.println(receivedMessage);
                    }
                    System.out.println("Client disconnected");
                } finally {
                    in.close();
                }
            }
        } finally {
            serverSocket.close();
        }

我会建议您将这两个资源放在同一个 try block 中，除非在您的情况下不起作用，因为有必要调用 accept()在请求其 inputStream() 之前在 serverSocket 上.

但是，在您的代码示例中仍然有适当的机会将多个资源放入您的第二次 try-with-resources 中:

try (Reader stream = new InputStreamReader(socket.getInputStream());
     BufferedReader in = new BufferedReader(stream)) {
  // do stuff, still preferring to use 'in' here rather than 'stream'
}