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1 import java.net.*;
2 import java.io.*;
3
6 public class UDPEcho implements Runnable  {
7
8 private int port;
9 private InetAddress hostIP;
10 private DatagramSocket sock;
11
12 private static final int BUF_SIZE = 1024;
13
14
15 public UDPEcho(String host,int port)
16 throws IOException,UnknownHostException{
17 this.hostIP = InetAddress.getByName(host);
18 this.port = port;
19 sock = new DatagramSocket();
20 System.out.println("UDP: "+sock.getLocalAddress()+":"+
21 sock.getLocalPort());
22 }
24
25 public void send(String s) throws IOException{
26 System.out.println("Sending:"+s);
27 DatagramPacket packet = new DatagramPacket(s.getBytes(),
28 s.length(),
29 hostIP,
30 port);
31 sock.send(packet);
32 }
33
34 public void run(){
35 byte[] buf = new byte[BUF_SIZE];
36 DatagramPacket incomingData = new DatagramPacket(buf,buf.length);
37 try{
38 while(true){
39 sock.receive(incomingData);
40 System.out.println("UDP From:"+
41 incomingData.getAddress().getHostAddress()+":"+
42 incomingData.getPort());
43 System.out.println(new String (incomingData.getData(),
44 0,incomingData.getLength()));
45 System.out.flush();
46 incomingData.setLength(buf.length);
47 }
48 }catch(IOException io_ex){
49 io_ex.printStackTrace();
50 }
51 }
52
53 public static void usage(){
54 System.err.print(
55 "Usage: java UDPEcho host port\n"+
56 "OR\n"+
57 "Usage: java UDPEcho port\n");
58 }
59
60 public static void doEcho(int port)throws IOException{
61 byte[] buf = new byte[BUF_SIZE];
62 DatagramPacket packet = new DatagramPacket(buf,buf.length);
63 DatagramSocket sock = new DatagramSocket(port);
64
65 System.out.println("Starting UDP echo on"+
66 sock.getLocalAddress().getHostAddress()+
67 ":"+sock.getLocalPort());
68 while(true){
69 try{
70 sock.receive(packet);
71 sock.send(packet);
72 System.out.print(
73 "UDP From: "+packet.getAddress().getHostAddress()+":"+
74 packet.getPort()+
75 "\n"+
76 new String (packet.getData(),0,packet.getLength())+
77 "\n"
78 );
79 System.out.flush();
80
81 packet.setLength(buf.length);
82 }catch(IOException io_ex){
84 }
85 }
86 }
87
88 public static void main(String args[]){
89 int port;
90 String host;
91
92 if(args.length == 1){
93 try{
94 port = Integer.parseInt(args[0]);
95
96 doEcho(port);
97
98 }catch(IOException io_ex){
99 io_ex.printStackTrace();
100 System.exit(1);
101
102 }catch(NumberFormatException num_ex){
103 num_ex.printStackTrace();
104 System.exit(1);
105 }
106 }else if(args.length == 2){
107 try{
108 host = args[0];
109 port = Integer.parseInt(args[1]);
110
111 UDPEcho ut = new UDPEcho(host,port);
112 Thread thread = new Thread (ut);
113 thread.start();
114
115 BufferedReader in = new BufferedReader(
116 new InputStreamReader(System.in));
117 String s;
118 System.out.print("Enter datagram:");
119 s = in.readLine();
120 while(s != null){
121 ut.send(s);
122 try{
123 Thread.currentThread().sleep(100);
124 }catch(InterruptedException i_ex){
125 }
126 System.out.print("Enter datagram:");
127 s = in.readLine();
128 }
129 System.exit(1);
130
131 }catch(IOException io_ex){
132 io_ex.printStackTrace();
133 System.exit(1);
134 }catch(NumberFormatException num_ex){
135 num_ex.printStackTrace();
136 System.exit(1);
137 }
138
139 }else{
140 usage();
141 }
142 }
143
144 }
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Java API By Example, From Geeks To Geeks.