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。

try-with-resources try 块可以独立存在，因为它有一个隐含的 finally 块；而传统的try 块后面需要catch 块和/或finally 块。

因此，您的示例代码等效于以下代码（除了资源变量在其各自的 try 块范围之外可见）：

        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 块中，除非您的情况不起作用，因为在请求其 inputStream() 之前，必须在 serverSocket 上调用 accept()。

但是，您的代码示例中仍有适当的机会在您的第二个 try-with-resources 中放置多个资源：

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