使用UDP实现广播发送

小灰灰 2022-11-21 01:20 182阅读 0赞

### 目录 ###

*  需求描述：
 *  参考代码
 *  代码描述
 *   *  ClientA代码描述：
     *  ClientB代码描述
 *  运行结果

# 需求描述： #

第一步：现在有ClientA向网络中的所有设备的8888端口发送广播，ClientB需要监听8888端口来收到广播信息  
第二步：ClientB在收到广播信息后需要给予回执。需要将消息回复过去

# 参考代码 #

/** * 广播出去，并接受收到信息的回执 */
    public class ClientA { 
        private static final Integer BroadCast_Port = 8888;//广播端口
        private static final Integer Receive_Port = 9999;//别人的回执端口
        private static final String SENDSTR = "明天都来家里吃饭啊！";
        public static void main(String[] args) throws Exception { 
            System.out.println("准备好我要广播了-------");
            MyLisener lisener = lisener();
            sendBroadCast();
            List<InetAddress> inetAddresses = null;
            while(true){ 
                if(99 == System.in.read()){ //如果按了c就退出
                    inetAddresses = lisener.closeAndGetAddress();
                    break;
                }
            }
            inetAddresses = lisener.closeAndGetAddress();
            System.out.println("收到参加聚会的人员信息----------------------");
            for (InetAddress inetAddress : inetAddresses) { 
                System.out.println("人员信息->>>>>"+inetAddress.getHostAddress());
            }
            System.out.println("------------------------------------------");
            System.out.println("所有都结束了");
        }
    
        private static void sendBroadCast() throws IOException { 
            //发送广播
            DatagramSocket datagramSocket = new DatagramSocket();
            DatagramPacket datagramPacket = new DatagramPacket(SENDSTR.getBytes("UTF-8"),SENDSTR.getBytes().length);
            datagramPacket.setPort(BroadCast_Port);
            datagramPacket.setAddress(InetAddress.getByName("255.255.255.255"));
            datagramSocket.send(datagramPacket);
        }
    
        private static MyLisener lisener() throws InterruptedException { 
            CountDownLatch countDownLatch = new CountDownLatch(1);
            MyLisener myLisener = new MyLisener(countDownLatch);
            myLisener.start();
            countDownLatch.await();
            return myLisener;
    
        }
    
        private static class MyLisener extends Thread{ 
            private DatagramSocket ds;
            private boolean finished = false;
            private final CountDownLatch countDownLatch;
            private final List<InetAddress> devices = new ArrayList<>();
            private MyLisener(CountDownLatch countDownLatch) { 
                this.countDownLatch = countDownLatch;
            }
    
            @Override
            public void run() { 
                try { 
                    ds = new DatagramSocket(Receive_Port);
                    countDownLatch.countDown();
                    while(!finished){ 
                        byte[] bytes = new byte[100];
                        DatagramPacket datagramPacket = new DatagramPacket(bytes, bytes.length);
                        ds.receive(datagramPacket);
                        devices.add(datagramPacket.getAddress());
                        System.out.println("获得数据 ->>>> "+new String(datagramPacket.getData(),0,datagramPacket.getLength()));
                    }
                }catch (Exception e){ 
    // e.printStackTrace();
                }
    
            }
    
            public List<InetAddress> closeAndGetAddress(){ 
                if(ds != null){ 
                    ds.close();
                    ds = null;
                }
                this.finished = true;
                //我不允许外面的更改
                return Collections.unmodifiableList(devices);
            }
        }
    }

/** * 用来接收数据 */
    public class ClientB { 
        private static final Integer Receive_Port = 8888;//广播端口
        private static final Integer Send_Port = 9999;//别人的回执端口
        private final static String SENDSTR = "好的，我要吃八碗<QAQ>";
        public static void main(String[] args) throws IOException { 
            System.out.println("开始启动");
            MyCustomer myCustomer = new MyCustomer();
            myCustomer.start();
            while(true){ 
                if(99 == System.in.read()){ //如果按了c就退出
                    myCustomer.exit();
                    break;
                }
            }
        }
    
        private static class MyCustomer extends Thread{ 
            private DatagramSocket ds = null;
            private boolean finished = false;
            @Override
            public void run() { 
                try { 
                    ds = new DatagramSocket(Receive_Port);
                    while(!finished){ 
                        byte[] bytes = new byte[100];
                        DatagramPacket receivePacket = new DatagramPacket(bytes, bytes.length);
                        ds.receive(receivePacket);
                        System.out.println(new String(receivePacket.getData(),0,receivePacket.getLength()));
                        //发送数据
                        System.out.println("发送回执");
                        DatagramPacket sendPacket = new DatagramPacket(SENDSTR.getBytes(), SENDSTR.getBytes().length);
                        //发送到广播的那个地址
                        sendPacket.setAddress(receivePacket.getAddress());
                        sendPacket.setPort(Send_Port);
                        ds.send(sendPacket);
                    }
                }catch (Exception e){ 
    
                }
            }
            public void exit(){ 
                if(ds != null){ 
                    ds.close();
                    ds = null;
                    finished = true;
                }
            }
        }
    }

# 代码描述 #

## ClientA代码描述： ##

此类中创建了一个lisener线程。因为需要开启一个端口来监听别人发来的消息，而且不想阻塞主线程，所以就新开了个线程。  
在线程中使用到了countdownLatch，因为现在的设计思路是：先开启监听端口（接受消息的端口）再进行广播发送。也就是说在没有监听的时候让主线程阻塞，当监听了就不阻塞线程，就是使用CountDownLatch来实现的。

## ClientB代码描述 ##

此客户端为接受广播消息的一段，并给出回执  
这边也创建一个线程。这里代码比较简单，暂无可说。。。

# 运行结果 #

clientA运行结果  
![在这里插入图片描述][20201029153956512.png_pic_center]

clientB运行结果  
![在这里插入图片描述][20201029153940335.png_pic_center]

[20201029153956512.png_pic_center]: /images/20221120/893c6b3eaeb54ebf9101a3c34aed7934.png
[20201029153940335.png_pic_center]: /images/20221120/40307aca299348a09a8a25376a155ce7.png