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首页 > 解决方案 > 检查端口是否已绑定并在 Java 中侦听；“重置”一个 SocketChannel？

java - 检查端口是否已绑定并在 Java 中侦听；“重置”一个 SocketChannel？

问题描述

class CheckServerStarted implements Closeable
    {
        private final SocketChannel channel;
        private final InetSocketAddress address;
        private boolean connStarted = false;

        public CheckServerStarted(InetSocketAddress address) throws IOException
        {
            channel = SocketChannel.open();
            channel.configureBlocking(false);

            this.address = address;
        }

        /**
         * @throws IOException 
         * 
         */
        private void startConn() throws IOException
        {
            channel.connect(address);
            connStarted = true;
        }

        private boolean check(int timeout, boolean retry)
        {
            for (int i = 0; i < timeout; i++)
            {
                try
                {
                    final boolean justStarted = !connStarted;
                    if (justStarted)
                    {
                        startConn();
                    }

                    if (justStarted || (i > 0))
                    {
                        // Wait a second between attempts/give the connection some time to get established.
                        try
                        {
                            Thread.sleep(1000);
                        }
                        catch (InterruptedException e)
                        {
                            throw new RuntimeException(e);
                        }
                    }

                    if (channel.finishConnect())
                    {
                        System.out.println("Server started - accepting connections on " + address.toString());
                        return true;
                    }
                }
                catch (IOException e)
                {
                    System.out.println("Connect attempt failed : " + e.getMessage());
                    if (!retry)
                    {
                        break;
                    }

                    // Try to start the connection again if it failed.
                    connStarted = false;
                }
            }

            System.out.println("Connect attempt to " + address.toString() + " failed, ran out of time/attempts");
            return false;
        }

        /* (non-Javadoc)
         * @see java.io.Closeable#close()
         */
        public void close()
        {
            try
            {
                channel.close();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }
        }
    }

我有以下代码，旨在用于等待/检查服务器是否启动并监听给定的地址/端口。

这个想法是，例如，我可以调用

new CheckServerStarted(addr).check(60, true);

尝试连接到它长达 60 秒（如果连接失败，则重试，因为服务器尚未绑定套接字）

或者

new CheckServerStarted(addr).check(1, false);

检查服务器当前是否正在接受连接。

当我现在运行第一个示例时，我得到如下输出

Connect attempt failed : Connection refused: no further information
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt failed : null
14-Jun-2018 10:55:42    Connect attempt to /192.168.223.68:59695 failed, ran out of time/attempts

两次尝试之间显然没有等待 1 秒。

我猜我需要在尝试之间“重置”频道？我需要每次都创建一个新的吗？

标签： javanio

解决方案

即使连接尝试失败，您也无法重新连接已连接的套接字。必须关闭它并创建一个新的。

其他问题：

  • 您正在泄漏套接字。
  • 摆脱睡眠并使用Selector.
  • 打印e而不是e.getMessage(). 如果您一开始就正确地做到了这一点，而不是整天盯着“null”，您可能会自己解决问题。
  • 调用是致命的IOException，finishConnect()而不是重试的信号。

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