Objects and Java Seminar by Bill Venners Network Programming Lecture Handout --------------------------------------------------------------------------------Seminars | Objects & Java | Design Workshop | Jini & Distrib | Objects & Patterns | Modules Agenda Introduce network programming, IP, and sockets Give a client/server code example Compare TCP and UDP Introduce datagrams and give a code example Touch on multicast protocol Introduce URLs and give a code example --------------------------------------------------------------------------------Network Programming Java's architecture is network-oriented. The java.net library simplifies network programming. You use Java I/O streams to communicate via sockets. Java's built-in support for multi-threading simplifies creating server programs that must handle multiple client requests concurrently. --------------------------------------------------------------------------------IP and Sockets IP (internet protocol) breaks communication into packets. Packets routed and delivered separately No delivery guarantee Max packet size: 65535 (less a 20 byte header) Sockets enable two machines to communicate via IP. Other protocols layered on top of IP: TCP (Transmission Control Protocol) UDP (User Datagram Protocol) --------------------------------------------------------------------------------IP Addresses IP requires that each machine have a unique IP address. Represented by the InetAddress class of java.net. IP Addresses are 32-bit numbers, often represented in these two forms: host name (A DNS name such as artima.com) quad form (205.73.4.217) InetAddress.getByName(String) does DNS lookup (or reverse lookup) and returns an InetAddress object. --------------------------------------------------------------------------------Client/Server Computing A socket connects a client and a server. The server listens on a port for client requests. Clients must specify the server's host IP Address and port number to make the request. Once connected, the client/server distinction goes away from the sockets' perspective. --------------------------------------------------------------------------------Port Number Port numbers are 16-bit unsigned integers (represented in Java by int's). Each port represents a "service" offered by the host. Ports 0 - 1024 are reserved for well-known services. You should use parts above 1024 for your own servers. Clients must specify both port and IP Address when making a connection request. --------------------------------------------------------------------------------Localhost The reserved host name "localhost" allows you to test a network program without a network. Server and clients can all exist on the same computer. Three ways to get an InetAddress object for localhost: InetAddress.getByName(null); InetAddress.getByName("localhost"); InetAddress.getByName("127.0.0.1"); --------------------------------------------------------------------------------The Summer Server Application 1 // In file network/ex1/SummerServer.java 2 import java.net.*; 3 import java.io.*; 4 import java.util.StringTokenizer; 5 6 public class SummerServer { 7 8 public static final int PORT = 2000; 9 10 private static class InvalidLongException 11 extends Exception { 12 13 private String message; 14 15 InvalidLongException(String s) { 16 message = s; 17 } 18 19 public String getMessage() { 20 return message; 21 } 22 } 23 24 public static void main(String[] args) 25 throws IOException { 26 27 ServerSocket listener = 28 new ServerSocket(PORT); 29 30 try { 31 32 for (;;) { 33 34 Socket sock = listener.accept(); 35 36 try { 37 38 serveClient(sock); 39 } 40 finally { 41 sock.close(); 42 } 43 } 44 } 45 finally { 46 listener.close(); 47 } 48 } 49 50 private static void serveClient(Socket sock) 51 throws IOException { 52 53 BufferedReader reader = new BufferedReader( 54 new InputStreamReader( 55 sock.getInputStream())); 56 57 BufferedWriter writer = new BufferedWriter( 58 new OutputStreamWriter( 59 sock.getOutputStream())); 60 61 for (;;) { 62 63 String s = reader.readLine(); 64 65 if (s == null) { 66 break; 67 } 68 69 String outString; 70 try { 71 outString = 72 Long.toString(sumString(s)); 73 } 74 catch(InvalidLongException e) { 75 outString = e.getMessage(); 76 } 77 writer.write(outString); 78 writer.newLine(); 79 writer.flush(); 80 } 81 } 82 83 private static long sumString(String s) 84 throws InvalidLongException { 85 86 long sum = 0; 87 88 StringTokenizer st = new StringTokenizer(s); 89 String token; 90 while (st.hasMoreTokens()) { 91 token = st.nextToken(); 92 try { 93 sum += Long.parseLong(token); 94 } 95 catch (NumberFormatException e) { 96 throw new InvalidLongException( 97 "Invalid number: " + token); 98 } 99 } 100 101 return sum; 102 } 103 } 104 1 // In file network/ex1/SummerClient.java 2 import java.net.*; 3 import java.io.*; 4 5 public class SummerClient { 6 7 public static void main(String[] args) 8 throws IOException { 9 10 InetAddress ia = InetAddress.getByName(null); 11 12 Socket sock = new Socket(ia, SummerServer.PORT); 13 14 try { 15 16 BufferedReader serverReader = 17 new BufferedReader( 18 new InputStreamReader( 19 sock.getInputStream())); 20 21 BufferedWriter serverWriter = 22 new BufferedWriter( 23 new OutputStreamWriter( 24 sock.getOutputStream())); 25 26 LineNumberReader stdinReader = 27 new LineNumberReader( 28 new BufferedReader( 29 new InputStreamReader( 30 System.in))); 31 32 for (;;) { 33 34 String userLine = stdinReader.readLine(); 35 36 if (userLine == null || 37 userLine.length() == 0) { 38 39 break; 40 } 41 42 serverWriter.write(userLine); 43 serverWriter.newLine(); 44 serverWriter.flush(); 45 46 String serverLine = serverReader.readLine(); 47 System.out.println(serverLine); 48 } 49 } 50 finally { 51 sock.close(); 52 } 53 } 54 } 55 --------------------------------------------------------------------------------Handling Multiple Clients Concurrently 1 // In file network/ex2/SummerServer.java 2 import java.net.*; 3 import java.io.*; 4 import java.util.StringTokenizer; 5 6 public class SummerServer { 7 8 public static final int PORT = 2000; 9 10 private static class InvalidLongException 11 extends Exception { 12 13 private String message; 14 15 InvalidLongException(String s) { 16 message = s; 17 } 18 19 public String getMessage() { 20 return message; 21 } 22 } 23 24 private static class SummerService 25 extends Thread { 26 27 private Socket sock; 28 29 public SummerService(Socket sock) { 30 this.sock = sock; 31 } 32 33 public void run() { 34 35 try { 36 37 BufferedReader reader = 38 new BufferedReader( 39 new InputStreamReader( 40 sock.getInputStream())); 41 42 BufferedWriter writer = 43 new BufferedWriter( 44 new OutputStreamWriter( 45 sock.getOutputStream())); 46 47 for (;;) { 48 49 String s = reader.readLine(); 50 51 if (s == null) { 52 break; 53 } 54 55 String outString; 56 try { 57 outString = 58 Long.toString(sumString(s)); 59 } 60 catch(InvalidLongException e) { 61 outString = e.getMessage(); 62 } 63 writer.write(outString); 64 writer.newLine(); 65 writer.flush(); 66 } 67 } 68 catch (IOException e) { 69 } 70 finally { 71 try { 72 sock.close(); 73 } 74 catch (IOException e) { 75 } 76 } 77 } 78 } 79 80 public static void main(String[] args) 81 throws IOException { 82 83 ServerSocket listener = new ServerSocket(PORT); 84 85 try { 86 87 for (;;) { 88 89 Socket sock = listener.accept(); 90 91 SummerService ss = 92 new SummerService(sock); 93 ss.start(); 94 } 95 } 96 finally { 97 listener.close(); 98 } 99 } 100 101 private static long sumString(String s) 102 throws InvalidLongException { 103 104 long sum = 0; 105 106 StringTokenizer st = new StringTokenizer(s); 107 String token; 108 while (st.hasMoreTokens()) { 109 token = st.nextToken(); 110 try { 111 sum += Long.parseLong(token); 112 } 113 catch (NumberFormatException e) { 114 throw new InvalidLongException( 115 "Invalid number: " + token); 116 } 117 } 118 119 return sum; 120 } 121 } 122 1 // In file network/ex2/SummerClient.java 2 import java.net.*; 3 import java.io.*; 4 5 public class SummerClient { 6 7 public static void main(String[] args) 8 throws IOException { 9 10 InetAddress ia = InetAddress.getByName(null); 11 12 Socket sock = new Socket(ia, 13 SummerServer.PORT); 14 15 try { 16 17 BufferedReader serverReader = 18 new BufferedReader( 19 new InputStreamReader( 20 sock.getInputStream())); 21 22 BufferedWriter serverWriter = 23 new BufferedWriter( 24 new OutputStreamWriter( 25 sock.getOutputStream())); 26 27 LineNumberReader stdinReader = 28 new LineNumberReader( 29 new BufferedReader( 30 new InputStreamReader( 31 System.in))); 32 33 for (;;) { 34 35 String userLine = 36 stdinReader.readLine(); 37 38 if (userLine == null || 39 userLine.length() == 0) { 40 41 break; 42 } 43 44 serverWriter.write(userLine); 45 serverWriter.newLine(); 46 serverWriter.flush(); 47 48 String serverLine = 49 serverReader.readLine(); 50 System.out.println(serverLine); 51 } 52 } 53 finally { 54 sock.close(); 55 } 56 } 57 } 58 --------------------------------------------------------------------------------TCP versus UDP The Summer Server examples use TCP. TCP (Transmission Control Protocol): "reliable" (the packets are guaranteed to get there) packets arrive in the order they were sent slower than UDP (reliability has overhead) UDP (User Data Protocol): "unreliable" (the packets aren't guaranteed to get there) packets may arrive out of order packets may arrive faster than they can be consumed faster than TCP (because less overhead) --------------------------------------------------------------------------------Datagrams Datagrams (UDP packets) are like letters: You put the recipient's and your own return address (IP Address & Port Number) on the envelope. You send it, but don't know if whether it will actually get there. If you send a second letter tomorrow, that might get there first. UDP is used for: Clock tickers, game player position announcers, etc... Streaming protocals such as RealAudio Designing a faster reliable protocol than TCP --------------------------------------------------------------------------------Using Datagrams Need a DatagramSocket on both client and server. To send, place the data (up to 65535 bytes less 20-byte header) into a DatagramPacket. On receiving end, get a DatagramPacket containing the data. There is no "connection" as with TCP. --------------------------------------------------------------------------------The Clock Server 1 // In file network/ex3/ClockServer.java 2 import java.net.*; 3 import java.io.*; 4 import java.util.StringTokenizer; 5 import java.util.Vector; 6 import java.util.Date; 7 8 public class ClockServer { 9 10 public static final int REGISTRATION_PORT = 2001; 11 private final static int ADDR_BYTE_SIZE = 4; 12 13 private Vector mailingList = new Vector(); 14 15 public static class AddressAndPort 16 implements Serializable { 17 18 private InetAddress addr; 19 private int port; 20 21 public AddressAndPort(InetAddress addr, int port) { 22 23 this.addr = addr; 24 this.port = port; 25 } 26 27 public InetAddress getAddress() { 28 return addr; 29 } 30 31 public int getPort() { 32 return port; 33 } 34 35 public boolean equals(Object o) { 36 37 if (o == null) { 38 return false; 39 } 40 41 AddressAndPort anp; 42 43 try { 44 anp = (AddressAndPort) o; 45 } 46 catch (ClassCastException e) { 47 return false; 48 } 49 50 if (addr.equals(anp.addr) && port == anp.port) { 51 return true; 52 } 53 else { 54 return false; 55 } 56 } 57 } 58 59 private class RegistrationService extends Thread { 60 61 private Socket sock; 62 63 public void run() { 64 65 ServerSocket listener; 66 try { 67 listener = 68 new ServerSocket(REGISTRATION_PORT); 69 } 70 catch (IOException e) { 71 // Need to signal main thread that 72 // no one is getting registered. 73 return; 74 } 75 try { 76 77 for (;;) { 78 79 Socket sock; 80 try { 81 sock = listener.accept(); 82 } 83 catch (IOException e) { 84 System.out.println(e.toString()); 85 e.printStackTrace(); 86 continue; 87 } 88 89 System.out.println("Got a connection."); 90 registerClient(sock); 91 } 92 } 93 finally { 94 try { 95 listener.close(); 96 } 97 catch (IOException e) { 98 } 99 } 100 } 101 102 private void registerClient(Socket sock) { 103 104 AddressAndPort anp; 105 106 // Grab the data from the client. 107 try { 108 109 ObjectInputStream ois = 110 new ObjectInputStream( 111 new BufferedInputStream( 112 sock.getInputStream())); 113 114 anp = (AddressAndPort) ois.readObject(); 115 } 116 catch (ClassNotFoundException e) { 117 // Just abort registering this client 118 System.out.println(e.toString()); 119 e.printStackTrace(); 120 return; 121 } 122 catch (InvalidClassException e) { 123 // Just abort registering this client 124 System.out.println(e.toString()); 125 e.printStackTrace(); 126 return; 127 } 128 catch (StreamCorruptedException e) { 129 // Just abort registering this client 130 System.out.println(e.toString()); 131 e.printStackTrace(); 132 return; 133 } 134 catch (OptionalDataException e) { 135 // Just abort registering this client 136 System.out.println(e.toString()); 137 e.printStackTrace(); 138 return; 139 } 140 catch (IOException e) { 141 // Just abort registering this client 142 System.out.println(e.toString()); 143 e.printStackTrace(); 144 return; 145 } 146 finally { 147 try { 148 sock.close(); 149 } 150 catch (IOException e) { 151 } 152 } 153 154 synchronized (ClockServer.this) { 155 156 int len = mailingList.size(); 157 158 boolean found = false; 159 for (int i = 0; i < len; ++i) { 160 161 Object o = mailingList.elementAt(i); 162 163 if (anp.equals(o)) { 164 found = true; 165 System.out.println( 166 "Already registered: (" + 167 anp.getAddress().getHostAddress() + 168 ", " + anp.getPort() + ")"); 169 break; 170 } 171 } 172 173 if (!found) { 174 mailingList.addElement(anp); 175 System.out.println("Registering: (" + 176 anp.getAddress().getHostAddress() + ", " 177 + anp.getPort() + ")"); 178 } 179 } 180 } 181 } 182 183 private class TickerService extends Thread { 184 185 public void run() { 186 187 DatagramSocket sock; 188 189 try { 190 sock = new DatagramSocket(); 191 } 192 catch (SocketException e) { 193 System.out.println(e.toString()); 194 e.printStackTrace(); 195 return; 196 } 197 198 for (;;) { 199 200 // Create the Datagram 201 Date date = new Date(); 202 203 ByteArrayOutputStream baos = 204 new ByteArrayOutputStream(); 205 ObjectOutputStream oos; 206 try { 207 oos = new ObjectOutputStream(baos); 208 oos.writeObject(date); 209 oos.close(); 210 } 211 catch (IOException e) { 212 return; 213 } 214 215 byte[] data = baos.toByteArray(); 216 217 Vector ml; 218 synchronized (this) { 219 ml = (Vector) mailingList.clone(); 220 } 221 222 int len = ml.size(); 223 224 for (int i = 0; i < len; ++i) { 225 226 AddressAndPort anp = 227 (AddressAndPort) ml.elementAt(i); 228 229 InetAddress ia = anp.getAddress(); 230 int port = anp.getPort(); 231 232 DatagramPacket dp = 233 new DatagramPacket(data, 234 data.length, ia, port); 235 236 try { 237 sock.send(dp); 238 } 239 catch (IOException e) { 240 } 241 System.out.println("Sending to port: " + 242 port); 243 } 244 245 try { 246 Thread.sleep(1000); 247 } 248 catch (InterruptedException e) { 249 } 250 } 251 } 252 } 253 254 private void start() { 255 RegistrationService rs = new RegistrationService(); 256 rs.start(); 257 TickerService ts = new TickerService(); 258 ts.start(); 259 } 260 261 public static void main(String[] args) 262 throws IOException { 263 264 ClockServer cs = new ClockServer(); 265 cs.start(); 266 } 267 } 268 --------------------------------------------------------------------------------The Clock Applet 1 // In file network/ex3/ClockApplet.java 2 import java.applet.*; 3 import java.net.*; 4 import java.io.*; 5 import java.awt.*; 6 import java.util.Date; 7 8 public class ClockApplet extends Applet { 9 10 private int myPort = 4000; 11 private Runner runner; 12 private CoolClockCanvas clock = 13 new CoolClockCanvas(); 14 15 private class Runner extends Thread { 16 17 private boolean stopRequested; 18 19 void requestStop() { 20 stopRequested = true; 21 } 22 23 public void run() { 24 25 for (;;) { 26 27 if (stopRequested) { 28 return; 29 } 30 31 try { 32 InetAddress ia = 33 InetAddress.getByName(null); 34 35 ClockServer.AddressAndPort myANP = 36 new ClockServer.AddressAndPort( 37 ia, myPort); 38 39 Socket sock = new Socket(ia, 40 ClockServer.REGISTRATION_PORT); 41 42 try { 43 44 ObjectOutputStream oos = 45 new ObjectOutputStream( 46 new BufferedOutputStream( 47 sock.getOutputStream())); 48 49 try { 50 oos.writeObject(myANP); 51 } 52 finally { 53 oos.close(); 54 } 55 } 56 finally { 57 sock.close(); 58 } 59 60 DatagramSocket dgsock; 61 62 try { 63 dgsock = new DatagramSocket(myPort); 64 } 65 catch (SocketException e) { 66 System.out.println(e.toString()); 67 e.printStackTrace(); 68 return; 69 } 70 71 for (;;) { 72 73 int packetSize = 1000; 74 byte[] buf = new byte[packetSize]; 75 76 DatagramPacket dp = 77 new DatagramPacket( 78 buf, packetSize); 79 80 dgsock.receive(dp); 81 System.out.println("Datagram received"); 82 83 byte[] data = dp.getData(); 84 85 ByteArrayInputStream bais = 86 new ByteArrayInputStream(data); 87 88 ObjectInputStream ois; 89 Date date; 90 try { 91 ois = new ObjectInputStream(bais); 92 date = (Date) ois.readObject(); 93 ois.close(); 94 } 95 catch (IOException e) { 96 System.out.println(e.toString()); 97 e.printStackTrace(); 98 continue; 99 } 100 catch (ClassNotFoundException e) { 101 System.out.println(e.toString()); 102 e.printStackTrace(); 103 continue; 104 } 105 106 clock.setTime(date); 107 } 108 } 109 catch (IOException e) { 110 System.out.println(e.toString()); 111 e.printStackTrace(); 112 return; 113 } 114 } 115 } 116 } 117 118 public void init() { 119 120 String portStr = getParameter("port"); 121 if (portStr != null) { 122 try { 123 myPort = Integer.parseInt(portStr); 124 } 125 catch (NumberFormatException e) { 126 // Use default port number 127 } 128 } 129 130 setLayout(new BorderLayout()); 131 add("Center", clock); 132 } 133 134 public synchronized void start() { 135 136 if (runner == null) { 137 138 runner = new Runner(); 139 runner.start(); 140 } 141 } 142 143 public synchronized void stop() { 144 145 if (runner != null) { 146 147 runner.requestStop(); 148 runner = null; 149 } 150 } 151 } 152 1 // In file network/ex3/CoolClockCanvas.java 2 import java.awt.*; 3 import java.awt.event.*; 4 import java.util.*; 5 6 class CoolClockCanvas extends Canvas { 7 8 private Color backgroundColor = Color.lightGray; 9 private Color shadowColor = Color.gray; 10 private Color tickShadowColor = Color.darkGray; 11 private int xCircleCenter; 12 private int yCircleCenter; 13 private int xSecondHandTip; 14 private int ySecondHandTip; 15 private int secondHandRadius; 16 private Date latestDate = new Date(); 17 18 Thread runner; 19 20 CoolClockCanvas() { 21 22 setBackground(backgroundColor); 23 } 24 25 public void setTime(Date date) { 26 27 latestDate = date; 28 repaint(); 29 } 30 31 private Point getHandTip(int radius, int minutePos) { 32 33 double thetaInDegrees; 34 35 if (minutePos <= 15) { 36 37 thetaInDegrees = (15.0 - (double) minutePos) * 6.0; 38 } 39 else { 40 41 thetaInDegrees = 360.0 - (6.0 * 42 ((double) minutePos - 15.0)); 43 } 44 45 double thetaInRadians = (thetaInDegrees / 180.0) * Math.PI; 46 47 double radiusDouble = (double) radius; 48 49 int x = (int) Math.round(radiusDouble * 50 Math.cos(thetaInRadians)); 51 int y = (int) Math.round(radiusDouble * 52 Math.sin(thetaInRadians)); 53 54 Point point = new Point(xCircleCenter + x, 55 yCircleCenter - y); 56 57 return point; 58 } 59 60 public void update(Graphics g) { 61 62 // Don't erase background because 63 // double buffering in paint() 64 // to reduce flicker. 65 paint(g); 66 } 67 68 synchronized public void paint(Graphics g) { 69 70 Dimension canvasSize = getSize(); 71 72 // Double buffer to reduce flicker 73 Image offscreenImage = createImage( 74 canvasSize.width, canvasSize.height); 75 Graphics og = offscreenImage.getGraphics(); 76 77 // Take smaller of width and height of canvas, and subtract 78 // ten from it. That will be the diameter of the clock's 79 // face (the outer circle). 80 int outerCircleDiameter = canvasSize.width; 81 if (canvasSize.width > canvasSize.height) { 82 outerCircleDiameter = canvasSize.height; 83 } 84 outerCircleDiameter -= 8; 85 86 int xOuterCircle = (canvasSize.width - 87 outerCircleDiameter) / 2; 88 int yOuterCircle = (canvasSize.height - 89 outerCircleDiameter) / 2; 90 91 // Paint with background color first 92 og.setColor(backgroundColor); 93 og.fillRect(0, 0, canvasSize.width, canvasSize.height); 94 95 // Draw lines around the edge of the canvas, to give 96 // it the appearance of a sunken panel. 97 og.setColor(shadowColor); 98 og.drawLine(0, 0, 0, canvasSize.height - 1); 99 og.drawLine(0, 0, canvasSize.width - 1, 0); 100 101 og.setColor(Color.white); 102 og.drawLine(0, canvasSize.height - 1, 103 canvasSize.width - 1, canvasSize.height - 1); 104 og.drawLine(canvasSize.width - 1, 0, 105 canvasSize.width - 1, canvasSize.height - 1); 106 107 108 // Draw arcs around the face of the clock 109 // to give it a raised appearance. 110 og.setColor(Color.white); 111 og.drawArc(xOuterCircle, yOuterCircle, 112 outerCircleDiameter, outerCircleDiameter, 45, 180); 113 og.setColor(shadowColor); 114 og.drawArc(xOuterCircle, yOuterCircle, 115 outerCircleDiameter, outerCircleDiameter, 45, -180); 116 117 // Radius of tick s is 4 pixels less than radius 118 // of outer circle 119 int fullRadius = (outerCircleDiameter / 2) - 4; 120 121 // Radius of tip of the second hand 122 secondHandRadius = fullRadius + 1; 123 124 int minuteHandRadius = secondHandRadius; 125 int hourHandRadius = (fullRadius * 2) / 3; 126 127 xCircleCenter = xOuterCircle + (outerCircleDiameter / 2); 128 yCircleCenter = yOuterCircle + (outerCircleDiameter / 2); 129 130 // Calculate the absolute x and y positions for the 131 // tick s that aren't at 12, 3, 6, or 9:00. 132 double shortSideDouble = ((double) fullRadius) * 133 Math.cos(Math.PI / 6.0); 134 double longSideDouble = ((double) fullRadius) * 135 Math.sin(Math.PI / 6.0); 136 int shortSide = (int) (shortSideDouble + 0.5); 137 int longSide = (int) (longSideDouble + 0.5); 138 139 // Put up 12 tick s 140 // 12:00 141 drawTickMark(og, xCircleCenter, yCircleCenter - fullRadius); 142 143 // 1:00 144 drawTickMark(og, xCircleCenter + shortSide, 145 yCircleCenter - longSide); 146 147 // 2:00 148 drawTickMark(og, xCircleCenter + longSide, 149 yCircleCenter - shortSide); 150 151 // 3:00 152 drawTickMark(og, xCircleCenter + fullRadius, yCircleCenter); 153 154 // 4:00 155 drawTickMark(og, xCircleCenter + longSide, 156 yCircleCenter + shortSide); 157 158 // 5:00 159 drawTickMark(og, xCircleCenter + shortSide, 160 yCircleCenter + longSide); 161 162 // 6:00 163 drawTickMark(og, xCircleCenter, yCircleCenter + fullRadius); 164 165 // 7:00 166 drawTickMark(og, xCircleCenter - shortSide, 167 yCircleCenter + longSide); 168 169 // 8:00 170 drawTickMark(og, xCircleCenter - longSide, 171 yCircleCenter + shortSide); 172 173 // 9:00 174 drawTickMark(og, xCircleCenter - fullRadius, yCircleCenter); 175 176 // 10:00 177 drawTickMark(og, xCircleCenter - longSide, 178 yCircleCenter - shortSide); 179 180 // 11:00 181 drawTickMark(og, xCircleCenter - shortSide, 182 yCircleCenter - longSide); 183 184 Calendar cal = new GregorianCalendar(); 185 cal.setTime(latestDate); 186 187 // Calculate the hour hand tip position 188 int hours = cal.get(Calendar.HOUR); 189 int minutes = cal.get(Calendar.MINUTE); 190 if (hours == 12) { 191 hours = 0; 192 } 193 int minPosOfHourHand = (hours * 5) + (minutes / 12); 194 Point hourHandTip = getHandTip(hourHandRadius, 195 minPosOfHourHand); 196 197 // Calculate the minute hand tip position 198 Point minuteHandTip = getHandTip(minuteHandRadius, minutes); 199 200 // Calculate the second hand tip position 201 int secs = cal.get(Calendar.SECOND); 202 Point secondHandTip = getHandTip(secondHandRadius, secs); 203 204 // Draw shadow of the 3 by 3 square in the center. 205 og.setColor(Color.black); 206 og.fillRect(xCircleCenter - 1, yCircleCenter - 1, 3, 3); 207 208 // Draw the hour hand 209 og.setColor(Color.blue); 210 og.drawLine(xCircleCenter, yCircleCenter, 211 hourHandTip.x, hourHandTip.y); 212 213 // Draw the minute hand 214 og.drawLine(xCircleCenter, yCircleCenter, 215 minuteHandTip.x, minuteHandTip.y); 216 217 // Draw a 2 by 2 square in the center on top 218 // of the shadow and hour and minute hands. 219 og.setColor(Color.red); 220 og.fillRect(xCircleCenter - 1, yCircleCenter - 1, 2, 2); 221 222 // Draw the second hand 223 og.drawLine(xCircleCenter, yCircleCenter, 224 secondHandTip.x, secondHandTip.y); 225 226 xSecondHandTip = secondHandTip.x; 227 ySecondHandTip = secondHandTip.y; 228 229 g.drawImage(offscreenImage, 0, 0, this); 230 } 231 232 private void drawTickMark(Graphics g, int x, int y) { 233 234 g.setColor(tickShadowColor); 235 g.fillRect(x, y, 2, 2); 236 g.setColor(Color.white); 237 g.fillRect(x, y, 1, 1); 238 } 239 } --------------------------------------------------------------------------------Multicast Protocol TCP and UDP are unicast protocols: there is only one sender and one receiver. Multicast packets are UDP packets that can take an arbitrary number of receivers. Multicast uses "class D" IP addresses: 224.0.0.1 to 239.255.255.255. Receivers "subscribe" to the multicast group (IP address). Anyone can send to the group (not just subscribers). All subscribers are eligible to receive the packet. // Join a Multicast group. InetAddress group = InetAddress.getByName("225.6.7.8"); MulticastSocket ms = new MulticastSocket(7000); ms.joinGroup(group); // Send the group a datagram. (Don't need to be a // member to send to the group.) byte[] msg = {'H', 'o', 'w', 'd', 'y'}; DatagramPacket dp = new DatagramPacket(msg, msg.length, group, 7000); ms.send(dp); // Get a datagram from the group. byte[] buf = new byte[1000]; DatagramPacket recv = new DatagramPacket(buf, buf.length); ms.receive(recv); // Leave the group. ms.leaveGroup(group); --------------------------------------------------------------------------------URL and URLConnection URL represents Uniform Resource Locator (a "pointer" to a resource on the network). URLConnection lets you interact with the resource. Create URLConnection by invoking openConnection() on a URL Set up the URLConnection Make the actual connection by invoking connect() on the URLConnection Interact with the header fields and contents of the resource. URLStreamHandlers (for protocols) and ContentHandlers (for MIME types) are loaded dynamically when needed. --------------------------------------------------------------------------------The Resource Grabber 1 // In file network/ex5/ResourceGrabber.java 2 import java.net.*; 3 import java.io.*; 4 import java.util.Date; 5 import java.util.StringTokenizer; 6 7 public class ResourceGrabber { 8 9 public static void main(String[] args) { 10 11 if (args.length < 1) { 12 System.out.println( 13 "Need URL and optional local filename."); 14 return; 15 } 16 17 try { 18 19 URL url = new URL(args[0]); 20 21 System.out.println( 22 "Connecting to resource..."); 23 URLConnection conn = url.openConnection(); 24 InputStream is = url.openStream(); 25 26 try { 27 28 // Get info about the resource 29 String type = conn.getContentType(); 30 Date date = new Date(conn.getLastModified()); 31 String lastMod = date.toLocaleString(); 32 33 // Print the info 34 System.out.println( 35 "Grabbing resource\n type: " + type 36 + "\n last modified: " + lastMod); 37 38 FileOutputStream fos; 39 if (args.length < 2) { 40 41 String localFile = null; 42 43 // Grab the simple file name from the 44 // URL String 45 String fullPath = url.getFile(); 46 StringTokenizer st = 47 new StringTokenizer(fullPath, "/"); 48 while (st.hasMoreTokens()) { 49 localFile = st.nextToken(); 50 } 51 fos = new FileOutputStream(localFile); 52 } 53 else { 54 fos = new FileOutputStream(args[1]); 55 } 56 57 try { 58 59 BufferedOutputStream bos = 60 new BufferedOutputStream(fos); 61 BufferedInputStream bis = 62 new BufferedInputStream(is); 63 64 int c; 65 int count = 0; 66 67 while ((c = bis.read()) != -1) { 68 bos.write(c); 69 ++count; 70 } 71 72 if (count != 1) { 73 System.out.println(count 74 + " bytes downloaded."); 75 } 76 else { 77 System.out.println( 78 "1 byte downloaded."); 79 } 80 } 81 finally { 82 fos.close(); 83 } 84 } 85 finally { 86 is.close(); 87 } 88 } 89 catch (MalformedURLException e) { 90 System.err.println(e.toString()); 91 e.printStackTrace(); 92 } 93 catch (IOException e) { 94 System.err.println(e.toString()); 95 e.printStackTrace(); 96 } 97 } 98 } --------------------------------------------------------------------------------Exercises Problem 1. Write an application named GetServer.java that creates a ServerSocket on port 80. When a client request comes in, get an InputStream from the socket returned by read lines from the ServerSocket's accept() method, and wrap the InputStream in an InputStreamReader and a BufferedReader. Read one line at a time from the BufferedReader while the length of the line read does not equal 0 and the first character is not '\r' or '\n'. Each time you read a line from the BufferedReader, print the line out to the standard output. Once you are done reading lines, just close the socket by closing the BufferedReader. What you'll end up printing out is HTTP requests sent by a web browser, which are always terminated by a blank line, as in: GET /jvm/index.html HTTP/1.0 Referer: http://minovia/subscribe.html Connection: Keep-Alive User-Agent: Mozilla/4.7 [en] (Win98; I) Host: minovia Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */* Accept-Encoding: gzip Accept-Language: en Accept-Charset: iso-8859-1,*,utf-8 <BLANK LINE>Start your GetServer application and then open a web browser. Type in URLs into your browser's address bar such as: http://127.0.0.1or http://127.0.0.1/this/is/a/longer/pathname/filename.htmlWatch what output your GetServer prints and the web browser prints. Problem 2. Change your GetServer application from Problem 1 so that it also sends a response back to the client. First, get an OutputStream from the socket, and wrap that in a BufferedOutputStream and a DataOutputStream. Write the following line out to the client after reading in the HTTP request lines, and before closing the socket: HTTP/1.0 404 Not found\r\n\r\nRun your GetServer application again and look at what the web browser now prints when you hit 127.0.0.1 URLs. Problem 3. Change your GetServer application from Problem 2 so that each time a client request comes in, it fires off a new thread to handle the client. Name the thread class ServerThread. Test your application again with a web browser. Problem 4. Create a private instance method getFile() that returns a String and takes no arguments in your ServerThread class, and call the method from your run() method right after getting the DataOutputStream from the socket. Wrap the getFile() invocation in a try block that has a catch (Exception e) clause. In the catch clause, print the 404 Not Found response back to the client. Move the code that gets a BufferedReader from the socket to the getFile() method. After getting the BufferedReader, make sure that the first three characters of the first line is "GET," as in: GET /jvm/index.html HTTP/1.0If the first three lines is not a GET, just throw an IOException back to the run() method. Finally, parse out the second token of that line, which in the above case would be, "/jvm/index.html," and return that value from getFile(). Back in the main run() method of ServerThread, format an HTTP request that indicates an HTML document is being returned: HTTP/1.1 200 OK\r\n Content-Type: text/html\r\n\r\nFinally, format the file name returned by getFile() into an HTML page like this: <HTML> <HEAD> <TITLE>Requested File</TITLE> </HEAD> <BODY> <H1>The requested file was: /jvm/index.html</H1> </BODY> </HTML>Write this HTML page out to the client after the 200 OK response. Start your GetServer once again and hit 127.0.0.1 URLs with your web browser. Problem 5. Please enhance your GetServer application yet again. Change the return value of getFile() to a java.io.File. Modify getFile() so that it returns an actual full path to the file requested in the GET, based on a hard-coded base directory. For your hard-coded base directory, select some directory that has web pages in it, such as the directory in which you installed your javadoc documentation. If the requested path turns out to be a directory, just append index.html to the path. Back in the run() method, adjust the code so that the full path is printed out in the web page sent back to the client, such as: <HTML> <HEAD> <TITLE>Requested File</TITLE> </HEAD> <BODY> <H1>The requested file was: d:\hard\coded\dir\jvm\index.html</H1> </BODY> </HTML>Problem 6. Lastly, change the run() method such that it actually sends back an approprite MIME type and the actual file contents. First, create a new java.util.HashMap in the GetServer's main() method, and add to it the MIME types for several file extensions: htm text/html html text/html txt text/plain jpg image/jpeg gif image/gif Pass a reference to this HashMap to the constructor of every ServerThread. In the ServerThread's run() method, figure out the appropriate MIME type by looking up the file's extension in the Map passed to the ServerThread's constructor. Send that MIME type back to the client in the Content-Type header rather than just text/html. If you don't recognize the file extension, just use the MIME type text/plain. In addition to Content-Type, send back a Content-Length header that indicates the length of the file to follow, as in: HTTP/1.1 200 OK\r\n Content-Length: 92\r\n Content-Type: image/gif\r\n\r\nLastly, create a FileInputStream for the File returned by getFile(), and wraps the FileInputStream in a BufferedInputStream. Then read bytes from the file and write them to the socket. When your done, just close both the socket and the file, and return from the run() method.
如果数组不能序列化,建议使用Vector,就是烦一点
创建一个包含该数组的类实现Serializable接口: class dataObj implements Serializable { public short t1_full = 0; public byte[] t2 = new byte[18]; public float t3 = 0f; public double t4 = 0d; } 利用ObjectOutputStream/ObjectInputStream创建一个sin/sout,利用readObject/writeObject读写该类,肯定可以搞定
import java.io.*;
import java.net.*;
import java.sql.*;
import java.util.Vector;
class ServerThread extends Thread{//继承线程
private Socket socket;//定义套接口
private BufferedReader in;//定义输入流
private PrintWriter out;//定义输出流
int no;//
public ServerThread(Socket s) throws IOException {//线程构造函数
socket=s;//取得传递参数
in=new BufferedReader(new InputStreamReader(socket.getInputStream()));//创建输入流
out=new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())),true);//创建输出流
start();//启动线程
}public void run(){//线程监听函数
try{ while(true){
String str=in.readLine();//取得输入字符串
if(str.equals("end"))break;//如果是结束就关闭连接
//***************************
}
public class Server{//主服务器类
public static void main(String args[])throws IOException{
ServerSocket s=new ServerSocket(8080);//在8080端口创建套接口
System.out.println("Server start.."+s);
try{
while(true){Socket socket=s.accept();//无限监听客户的请求
System.out.println("Connectino accept:"+socket);
try{new ServerThread(socket);//创建新线程
}catch(IOException e){socket.close();}
}
}finally{s.close();}//捕或异常
}
}//服务器程序结束
InputStream.read(byte[])
和
OutputStream.write(byte[])
注意:
read方法需要检测返回值。至于为什么?请查考JDK API文档。
Network Programming
Lecture Handout
--------------------------------------------------------------------------------Seminars | Objects & Java | Design Workshop | Jini & Distrib | Objects & Patterns | Modules
Agenda
Introduce network programming, IP, and sockets
Give a client/server code example
Compare TCP and UDP
Introduce datagrams and give a code example
Touch on multicast protocol
Introduce URLs and give a code example --------------------------------------------------------------------------------Network Programming
Java's architecture is network-oriented.
The java.net library simplifies network programming.
You use Java I/O streams to communicate via sockets.
Java's built-in support for multi-threading simplifies creating server programs that must handle multiple client requests concurrently. --------------------------------------------------------------------------------IP and Sockets
IP (internet protocol) breaks communication into packets.
Packets routed and delivered separately
No delivery guarantee
Max packet size: 65535 (less a 20 byte header)
Sockets enable two machines to communicate via IP.
Other protocols layered on top of IP:
TCP (Transmission Control Protocol)
UDP (User Datagram Protocol) --------------------------------------------------------------------------------IP Addresses
IP requires that each machine have a unique IP address.
Represented by the InetAddress class of java.net.
IP Addresses are 32-bit numbers, often represented in these two forms:
host name (A DNS name such as artima.com)
quad form (205.73.4.217)
InetAddress.getByName(String) does DNS lookup (or reverse lookup) and returns an InetAddress object. --------------------------------------------------------------------------------Client/Server Computing
A socket connects a client and a server.
The server listens on a port for client requests.
Clients must specify the server's host IP Address and port number to make the request.
Once connected, the client/server distinction goes away from the sockets' perspective. --------------------------------------------------------------------------------Port Number
Port numbers are 16-bit unsigned integers (represented in Java by int's).
Each port represents a "service" offered by the host.
Ports 0 - 1024 are reserved for well-known services.
You should use parts above 1024 for your own servers.
Clients must specify both port and IP Address when making a connection request. --------------------------------------------------------------------------------Localhost
The reserved host name "localhost" allows you to test a network program without a network.
Server and clients can all exist on the same computer.
Three ways to get an InetAddress object for localhost:
InetAddress.getByName(null);
InetAddress.getByName("localhost");
InetAddress.getByName("127.0.0.1"); --------------------------------------------------------------------------------The Summer Server Application
1 // In file network/ex1/SummerServer.java
2 import java.net.*;
3 import java.io.*;
4 import java.util.StringTokenizer;
5
6 public class SummerServer {
7
8 public static final int PORT = 2000;
9
10 private static class InvalidLongException
11 extends Exception {
12
13 private String message;
14
15 InvalidLongException(String s) {
16 message = s;
17 }
18
19 public String getMessage() {
20 return message;
21 }
22 }
23
24 public static void main(String[] args)
25 throws IOException {
26
27 ServerSocket listener =
28 new ServerSocket(PORT);
29
30 try {
31
32 for (;;) {
33
34 Socket sock = listener.accept();
35
36 try {
37
38 serveClient(sock);
39 }
40 finally {
41 sock.close();
42 }
43 }
44 }
45 finally {
46 listener.close();
47 }
48 }
49
50 private static void serveClient(Socket sock)
51 throws IOException {
52
53 BufferedReader reader = new BufferedReader(
54 new InputStreamReader(
55 sock.getInputStream()));
56
57 BufferedWriter writer = new BufferedWriter(
58 new OutputStreamWriter(
59 sock.getOutputStream()));
60
61 for (;;) {
62
63 String s = reader.readLine();
64
65 if (s == null) {
66 break;
67 }
68
69 String outString;
70 try {
71 outString =
72 Long.toString(sumString(s));
73 }
74 catch(InvalidLongException e) {
75 outString = e.getMessage();
76 }
77 writer.write(outString);
78 writer.newLine();
79 writer.flush();
80 }
81 }
82
83 private static long sumString(String s)
84 throws InvalidLongException {
85
86 long sum = 0;
87
88 StringTokenizer st = new StringTokenizer(s);
89 String token;
90 while (st.hasMoreTokens()) {
91 token = st.nextToken();
92 try {
93 sum += Long.parseLong(token);
94 }
95 catch (NumberFormatException e) {
96 throw new InvalidLongException(
97 "Invalid number: " + token);
98 }
99 }
100
101 return sum;
102 }
103 }
104 1 // In file network/ex1/SummerClient.java
2 import java.net.*;
3 import java.io.*;
4
5 public class SummerClient {
6
7 public static void main(String[] args)
8 throws IOException {
9
10 InetAddress ia = InetAddress.getByName(null);
11
12 Socket sock = new Socket(ia, SummerServer.PORT);
13
14 try {
15
16 BufferedReader serverReader =
17 new BufferedReader(
18 new InputStreamReader(
19 sock.getInputStream()));
20
21 BufferedWriter serverWriter =
22 new BufferedWriter(
23 new OutputStreamWriter(
24 sock.getOutputStream()));
25
26 LineNumberReader stdinReader =
27 new LineNumberReader(
28 new BufferedReader(
29 new InputStreamReader(
30 System.in)));
31
32 for (;;) {
33
34 String userLine = stdinReader.readLine();
35
36 if (userLine == null ||
37 userLine.length() == 0) {
38
39 break;
40 }
41
42 serverWriter.write(userLine);
43 serverWriter.newLine();
44 serverWriter.flush();
45
46 String serverLine = serverReader.readLine();
47 System.out.println(serverLine);
48 }
49 }
50 finally {
51 sock.close();
52 }
53 }
54 }
55
--------------------------------------------------------------------------------Handling Multiple Clients Concurrently
1 // In file network/ex2/SummerServer.java
2 import java.net.*;
3 import java.io.*;
4 import java.util.StringTokenizer;
5
6 public class SummerServer {
7
8 public static final int PORT = 2000;
9
10 private static class InvalidLongException
11 extends Exception {
12
13 private String message;
14
15 InvalidLongException(String s) {
16 message = s;
17 }
18
19 public String getMessage() {
20 return message;
21 }
22 }
23
24 private static class SummerService
25 extends Thread {
26
27 private Socket sock;
28
29 public SummerService(Socket sock) {
30 this.sock = sock;
31 }
32
33 public void run() {
34
35 try {
36
37 BufferedReader reader =
38 new BufferedReader(
39 new InputStreamReader(
40 sock.getInputStream()));
41
42 BufferedWriter writer =
43 new BufferedWriter(
44 new OutputStreamWriter(
45 sock.getOutputStream()));
46
47 for (;;) {
48
49 String s = reader.readLine();
50
51 if (s == null) {
52 break;
53 }
54
55 String outString;
56 try {
57 outString =
58 Long.toString(sumString(s));
59 }
60 catch(InvalidLongException e) {
61 outString = e.getMessage();
62 }
63 writer.write(outString);
64 writer.newLine();
65 writer.flush();
66 }
67 }
68 catch (IOException e) {
69 }
70 finally {
71 try {
72 sock.close();
73 }
74 catch (IOException e) {
75 }
76 }
77 }
78 }
79
80 public static void main(String[] args)
81 throws IOException {
82
83 ServerSocket listener = new ServerSocket(PORT);
84
85 try {
86
87 for (;;) {
88
89 Socket sock = listener.accept();
90
91 SummerService ss =
92 new SummerService(sock);
93 ss.start();
94 }
95 }
96 finally {
97 listener.close();
98 }
99 }
100
101 private static long sumString(String s)
102 throws InvalidLongException {
103
104 long sum = 0;
105
106 StringTokenizer st = new StringTokenizer(s);
107 String token;
108 while (st.hasMoreTokens()) {
109 token = st.nextToken();
110 try {
111 sum += Long.parseLong(token);
112 }
113 catch (NumberFormatException e) {
114 throw new InvalidLongException(
115 "Invalid number: " + token);
116 }
117 }
118
119 return sum;
120 }
121 }
122 1 // In file network/ex2/SummerClient.java
2 import java.net.*;
3 import java.io.*;
4
5 public class SummerClient {
6
7 public static void main(String[] args)
8 throws IOException {
9
10 InetAddress ia = InetAddress.getByName(null);
11
12 Socket sock = new Socket(ia,
13 SummerServer.PORT);
14
15 try {
16
17 BufferedReader serverReader =
18 new BufferedReader(
19 new InputStreamReader(
20 sock.getInputStream()));
21
22 BufferedWriter serverWriter =
23 new BufferedWriter(
24 new OutputStreamWriter(
25 sock.getOutputStream()));
26
27 LineNumberReader stdinReader =
28 new LineNumberReader(
29 new BufferedReader(
30 new InputStreamReader(
31 System.in)));
32
33 for (;;) {
34
35 String userLine =
36 stdinReader.readLine();
37
38 if (userLine == null ||
39 userLine.length() == 0) {
40
41 break;
42 }
43
44 serverWriter.write(userLine);
45 serverWriter.newLine();
46 serverWriter.flush();
47
48 String serverLine =
49 serverReader.readLine();
50 System.out.println(serverLine);
51 }
52 }
53 finally {
54 sock.close();
55 }
56 }
57 }
58
--------------------------------------------------------------------------------TCP versus UDP
The Summer Server examples use TCP.
TCP (Transmission Control Protocol):
"reliable" (the packets are guaranteed to get there)
packets arrive in the order they were sent
slower than UDP (reliability has overhead)
UDP (User Data Protocol):
"unreliable" (the packets aren't guaranteed to get there)
packets may arrive out of order
packets may arrive faster than they can be consumed
faster than TCP (because less overhead) --------------------------------------------------------------------------------Datagrams
Datagrams (UDP packets) are like letters:
You put the recipient's and your own return address (IP Address & Port Number) on the envelope.
You send it, but don't know if whether it will actually get there.
If you send a second letter tomorrow, that might get there first.
UDP is used for:
Clock tickers, game player position announcers, etc...
Streaming protocals such as RealAudio
Designing a faster reliable protocol than TCP --------------------------------------------------------------------------------Using Datagrams
Need a DatagramSocket on both client and server.
To send, place the data (up to 65535 bytes less 20-byte header) into a DatagramPacket.
On receiving end, get a DatagramPacket containing the data.
There is no "connection" as with TCP. --------------------------------------------------------------------------------The Clock Server
1 // In file network/ex3/ClockServer.java
2 import java.net.*;
3 import java.io.*;
4 import java.util.StringTokenizer;
5 import java.util.Vector;
6 import java.util.Date;
7
8 public class ClockServer {
9
10 public static final int REGISTRATION_PORT = 2001;
11 private final static int ADDR_BYTE_SIZE = 4;
12
13 private Vector mailingList = new Vector();
14
15 public static class AddressAndPort
16 implements Serializable {
17
18 private InetAddress addr;
19 private int port;
20
21 public AddressAndPort(InetAddress addr, int port) {
22
23 this.addr = addr;
24 this.port = port;
25 }
26
27 public InetAddress getAddress() {
28 return addr;
29 }
30
31 public int getPort() {
32 return port;
33 }
34
35 public boolean equals(Object o) {
36
37 if (o == null) {
38 return false;
39 }
40
41 AddressAndPort anp;
42
43 try {
44 anp = (AddressAndPort) o;
45 }
46 catch (ClassCastException e) {
47 return false;
48 }
49
50 if (addr.equals(anp.addr) && port == anp.port) {
51 return true;
52 }
53 else {
54 return false;
55 }
56 }
57 }
58
59 private class RegistrationService extends Thread {
60
61 private Socket sock;
62
63 public void run() {
64
65 ServerSocket listener;
66 try {
67 listener =
68 new ServerSocket(REGISTRATION_PORT);
69 }
70 catch (IOException e) {
71 // Need to signal main thread that
72 // no one is getting registered.
73 return;
74 }
75 try {
76
77 for (;;) {
78
79 Socket sock;
80 try {
81 sock = listener.accept();
82 }
83 catch (IOException e) {
84 System.out.println(e.toString());
85 e.printStackTrace();
86 continue;
87 }
88
89 System.out.println("Got a connection.");
90 registerClient(sock);
91 }
92 }
93 finally {
94 try {
95 listener.close();
96 }
97 catch (IOException e) {
98 }
99 }
100 }
101
102 private void registerClient(Socket sock) {
103
104 AddressAndPort anp;
105
106 // Grab the data from the client.
107 try {
108
109 ObjectInputStream ois =
110 new ObjectInputStream(
111 new BufferedInputStream(
112 sock.getInputStream()));
113
114 anp = (AddressAndPort) ois.readObject();
115 }
116 catch (ClassNotFoundException e) {
117 // Just abort registering this client
118 System.out.println(e.toString());
119 e.printStackTrace();
120 return;
121 }
122 catch (InvalidClassException e) {
123 // Just abort registering this client
124 System.out.println(e.toString());
125 e.printStackTrace();
126 return;
127 }
128 catch (StreamCorruptedException e) {
129 // Just abort registering this client
130 System.out.println(e.toString());
131 e.printStackTrace();
132 return;
133 }
134 catch (OptionalDataException e) {
135 // Just abort registering this client
136 System.out.println(e.toString());
137 e.printStackTrace();
138 return;
139 }
140 catch (IOException e) {
141 // Just abort registering this client
142 System.out.println(e.toString());
143 e.printStackTrace();
144 return;
145 }
146 finally {
147 try {
148 sock.close();
149 }
150 catch (IOException e) {
151 }
152 }
153
154 synchronized (ClockServer.this) {
155
156 int len = mailingList.size();
157
158 boolean found = false;
159 for (int i = 0; i < len; ++i) {
160
161 Object o = mailingList.elementAt(i);
162
163 if (anp.equals(o)) {
164 found = true;
165 System.out.println(
166 "Already registered: (" +
167 anp.getAddress().getHostAddress() +
168 ", " + anp.getPort() + ")");
169 break;
170 }
171 }
172
173 if (!found) {
174 mailingList.addElement(anp);
175 System.out.println("Registering: (" +
176 anp.getAddress().getHostAddress() + ", "
177 + anp.getPort() + ")");
178 }
179 }
180 }
181 }
182
183 private class TickerService extends Thread {
184
185 public void run() {
186
187 DatagramSocket sock;
188
189 try {
190 sock = new DatagramSocket();
191 }
192 catch (SocketException e) {
193 System.out.println(e.toString());
194 e.printStackTrace();
195 return;
196 }
197
198 for (;;) {
199
200 // Create the Datagram
201 Date date = new Date();
202
203 ByteArrayOutputStream baos =
204 new ByteArrayOutputStream();
205 ObjectOutputStream oos;
206 try {
207 oos = new ObjectOutputStream(baos);
208 oos.writeObject(date);
209 oos.close();
210 }
211 catch (IOException e) {
212 return;
213 }
214
215 byte[] data = baos.toByteArray();
216
217 Vector ml;
218 synchronized (this) {
219 ml = (Vector) mailingList.clone();
220 }
221
222 int len = ml.size();
223
224 for (int i = 0; i < len; ++i) {
225
226 AddressAndPort anp =
227 (AddressAndPort) ml.elementAt(i);
228
229 InetAddress ia = anp.getAddress();
230 int port = anp.getPort();
231
232 DatagramPacket dp =
233 new DatagramPacket(data,
234 data.length, ia, port);
235
236 try {
237 sock.send(dp);
238 }
239 catch (IOException e) {
240 }
241 System.out.println("Sending to port: " +
242 port);
243 }
244
245 try {
246 Thread.sleep(1000);
247 }
248 catch (InterruptedException e) {
249 }
250 }
251 }
252 }
253
254 private void start() {
255 RegistrationService rs = new RegistrationService();
256 rs.start();
257 TickerService ts = new TickerService();
258 ts.start();
259 }
260
261 public static void main(String[] args)
262 throws IOException {
263
264 ClockServer cs = new ClockServer();
265 cs.start();
266 }
267 }
268
--------------------------------------------------------------------------------The Clock Applet
1 // In file network/ex3/ClockApplet.java
2 import java.applet.*;
3 import java.net.*;
4 import java.io.*;
5 import java.awt.*;
6 import java.util.Date;
7
8 public class ClockApplet extends Applet {
9
10 private int myPort = 4000;
11 private Runner runner;
12 private CoolClockCanvas clock =
13 new CoolClockCanvas();
14
15 private class Runner extends Thread {
16
17 private boolean stopRequested;
18
19 void requestStop() {
20 stopRequested = true;
21 }
22
23 public void run() {
24
25 for (;;) {
26
27 if (stopRequested) {
28 return;
29 }
30
31 try {
32 InetAddress ia =
33 InetAddress.getByName(null);
34
35 ClockServer.AddressAndPort myANP =
36 new ClockServer.AddressAndPort(
37 ia, myPort);
38
39 Socket sock = new Socket(ia,
40 ClockServer.REGISTRATION_PORT);
41
42 try {
43
44 ObjectOutputStream oos =
45 new ObjectOutputStream(
46 new BufferedOutputStream(
47 sock.getOutputStream()));
48
49 try {
50 oos.writeObject(myANP);
51 }
52 finally {
53 oos.close();
54 }
55 }
56 finally {
57 sock.close();
58 }
59
60 DatagramSocket dgsock;
61
62 try {
63 dgsock = new DatagramSocket(myPort);
64 }
65 catch (SocketException e) {
66 System.out.println(e.toString());
67 e.printStackTrace();
68 return;
69 }
70
71 for (;;) {
72
73 int packetSize = 1000;
74 byte[] buf = new byte[packetSize];
75
76 DatagramPacket dp =
77 new DatagramPacket(
78 buf, packetSize);
79
80 dgsock.receive(dp);
81 System.out.println("Datagram received");
82
83 byte[] data = dp.getData();
84
85 ByteArrayInputStream bais =
86 new ByteArrayInputStream(data);
87
88 ObjectInputStream ois;
89 Date date;
90 try {
91 ois = new ObjectInputStream(bais);
92 date = (Date) ois.readObject();
93 ois.close();
94 }
95 catch (IOException e) {
96 System.out.println(e.toString());
97 e.printStackTrace();
98 continue;
99 }
100 catch (ClassNotFoundException e) {
101 System.out.println(e.toString());
102 e.printStackTrace();
103 continue;
104 }
105
106 clock.setTime(date);
107 }
108 }
109 catch (IOException e) {
110 System.out.println(e.toString());
111 e.printStackTrace();
112 return;
113 }
114 }
115 }
116 }
117
118 public void init() {
119
120 String portStr = getParameter("port");
121 if (portStr != null) {
122 try {
123 myPort = Integer.parseInt(portStr);
124 }
125 catch (NumberFormatException e) {
126 // Use default port number
127 }
128 }
129
130 setLayout(new BorderLayout());
131 add("Center", clock);
132 }
133
134 public synchronized void start() {
135
136 if (runner == null) {
137
138 runner = new Runner();
139 runner.start();
140 }
141 }
142
143 public synchronized void stop() {
144
145 if (runner != null) {
146
147 runner.requestStop();
148 runner = null;
149 }
150 }
151 }
152 1 // In file network/ex3/CoolClockCanvas.java
2 import java.awt.*;
3 import java.awt.event.*;
4 import java.util.*;
5
6 class CoolClockCanvas extends Canvas {
7
8 private Color backgroundColor = Color.lightGray;
9 private Color shadowColor = Color.gray;
10 private Color tickShadowColor = Color.darkGray;
11 private int xCircleCenter;
12 private int yCircleCenter;
13 private int xSecondHandTip;
14 private int ySecondHandTip;
15 private int secondHandRadius;
16 private Date latestDate = new Date();
17
18 Thread runner;
19
20 CoolClockCanvas() {
21
22 setBackground(backgroundColor);
23 }
24
25 public void setTime(Date date) {
26
27 latestDate = date;
28 repaint();
29 }
30
31 private Point getHandTip(int radius, int minutePos) {
32
33 double thetaInDegrees;
34
35 if (minutePos <= 15) {
36
37 thetaInDegrees = (15.0 - (double) minutePos) * 6.0;
38 }
39 else {
40
41 thetaInDegrees = 360.0 - (6.0 *
42 ((double) minutePos - 15.0));
43 }
44
45 double thetaInRadians = (thetaInDegrees / 180.0) * Math.PI;
46
47 double radiusDouble = (double) radius;
48
49 int x = (int) Math.round(radiusDouble *
50 Math.cos(thetaInRadians));
51 int y = (int) Math.round(radiusDouble *
52 Math.sin(thetaInRadians));
53
54 Point point = new Point(xCircleCenter + x,
55 yCircleCenter - y);
56
57 return point;
58 }
59
60 public void update(Graphics g) {
61
62 // Don't erase background because
63 // double buffering in paint()
64 // to reduce flicker.
65 paint(g);
66 }
67
68 synchronized public void paint(Graphics g) {
69
70 Dimension canvasSize = getSize();
71
72 // Double buffer to reduce flicker
73 Image offscreenImage = createImage(
74 canvasSize.width, canvasSize.height);
75 Graphics og = offscreenImage.getGraphics();
76
77 // Take smaller of width and height of canvas, and subtract
78 // ten from it. That will be the diameter of the clock's
79 // face (the outer circle).
80 int outerCircleDiameter = canvasSize.width;
81 if (canvasSize.width > canvasSize.height) {
82 outerCircleDiameter = canvasSize.height;
83 }
84 outerCircleDiameter -= 8;
85
86 int xOuterCircle = (canvasSize.width -
87 outerCircleDiameter) / 2;
88 int yOuterCircle = (canvasSize.height -
89 outerCircleDiameter) / 2;
90
91 // Paint with background color first
92 og.setColor(backgroundColor);
93 og.fillRect(0, 0, canvasSize.width, canvasSize.height);
94
95 // Draw lines around the edge of the canvas, to give
96 // it the appearance of a sunken panel.
97 og.setColor(shadowColor);
98 og.drawLine(0, 0, 0, canvasSize.height - 1);
99 og.drawLine(0, 0, canvasSize.width - 1, 0);
100
101 og.setColor(Color.white);
102 og.drawLine(0, canvasSize.height - 1,
103 canvasSize.width - 1, canvasSize.height - 1);
104 og.drawLine(canvasSize.width - 1, 0,
105 canvasSize.width - 1, canvasSize.height - 1);
106
107
108 // Draw arcs around the face of the clock
109 // to give it a raised appearance.
110 og.setColor(Color.white);
111 og.drawArc(xOuterCircle, yOuterCircle,
112 outerCircleDiameter, outerCircleDiameter, 45, 180);
113 og.setColor(shadowColor);
114 og.drawArc(xOuterCircle, yOuterCircle,
115 outerCircleDiameter, outerCircleDiameter, 45, -180);
116
117 // Radius of tick s is 4 pixels less than radius
118 // of outer circle
119 int fullRadius = (outerCircleDiameter / 2) - 4;
120
121 // Radius of tip of the second hand
122 secondHandRadius = fullRadius + 1;
123
124 int minuteHandRadius = secondHandRadius;
125 int hourHandRadius = (fullRadius * 2) / 3;
126
127 xCircleCenter = xOuterCircle + (outerCircleDiameter / 2);
128 yCircleCenter = yOuterCircle + (outerCircleDiameter / 2);
129
130 // Calculate the absolute x and y positions for the
131 // tick s that aren't at 12, 3, 6, or 9:00.
132 double shortSideDouble = ((double) fullRadius) *
133 Math.cos(Math.PI / 6.0);
134 double longSideDouble = ((double) fullRadius) *
135 Math.sin(Math.PI / 6.0);
136 int shortSide = (int) (shortSideDouble + 0.5);
137 int longSide = (int) (longSideDouble + 0.5);
138
139 // Put up 12 tick s
140 // 12:00
141 drawTickMark(og, xCircleCenter, yCircleCenter - fullRadius);
142
143 // 1:00
144 drawTickMark(og, xCircleCenter + shortSide,
145 yCircleCenter - longSide);
146
147 // 2:00
148 drawTickMark(og, xCircleCenter + longSide,
149 yCircleCenter - shortSide);
150
151 // 3:00
152 drawTickMark(og, xCircleCenter + fullRadius, yCircleCenter);
153
154 // 4:00
155 drawTickMark(og, xCircleCenter + longSide,
156 yCircleCenter + shortSide);
157
158 // 5:00
159 drawTickMark(og, xCircleCenter + shortSide,
160 yCircleCenter + longSide);
161
162 // 6:00
163 drawTickMark(og, xCircleCenter, yCircleCenter + fullRadius);
164
165 // 7:00
166 drawTickMark(og, xCircleCenter - shortSide,
167 yCircleCenter + longSide);
168
169 // 8:00
170 drawTickMark(og, xCircleCenter - longSide,
171 yCircleCenter + shortSide);
172
173 // 9:00
174 drawTickMark(og, xCircleCenter - fullRadius, yCircleCenter);
175
176 // 10:00
177 drawTickMark(og, xCircleCenter - longSide,
178 yCircleCenter - shortSide);
179
180 // 11:00
181 drawTickMark(og, xCircleCenter - shortSide,
182 yCircleCenter - longSide);
183
184 Calendar cal = new GregorianCalendar();
185 cal.setTime(latestDate);
186
187 // Calculate the hour hand tip position
188 int hours = cal.get(Calendar.HOUR);
189 int minutes = cal.get(Calendar.MINUTE);
190 if (hours == 12) {
191 hours = 0;
192 }
193 int minPosOfHourHand = (hours * 5) + (minutes / 12);
194 Point hourHandTip = getHandTip(hourHandRadius,
195 minPosOfHourHand);
196
197 // Calculate the minute hand tip position
198 Point minuteHandTip = getHandTip(minuteHandRadius, minutes);
199
200 // Calculate the second hand tip position
201 int secs = cal.get(Calendar.SECOND);
202 Point secondHandTip = getHandTip(secondHandRadius, secs);
203
204 // Draw shadow of the 3 by 3 square in the center.
205 og.setColor(Color.black);
206 og.fillRect(xCircleCenter - 1, yCircleCenter - 1, 3, 3);
207
208 // Draw the hour hand
209 og.setColor(Color.blue);
210 og.drawLine(xCircleCenter, yCircleCenter,
211 hourHandTip.x, hourHandTip.y);
212
213 // Draw the minute hand
214 og.drawLine(xCircleCenter, yCircleCenter,
215 minuteHandTip.x, minuteHandTip.y);
216
217 // Draw a 2 by 2 square in the center on top
218 // of the shadow and hour and minute hands.
219 og.setColor(Color.red);
220 og.fillRect(xCircleCenter - 1, yCircleCenter - 1, 2, 2);
221
222 // Draw the second hand
223 og.drawLine(xCircleCenter, yCircleCenter,
224 secondHandTip.x, secondHandTip.y);
225
226 xSecondHandTip = secondHandTip.x;
227 ySecondHandTip = secondHandTip.y;
228
229 g.drawImage(offscreenImage, 0, 0, this);
230 }
231
232 private void drawTickMark(Graphics g, int x, int y) {
233
234 g.setColor(tickShadowColor);
235 g.fillRect(x, y, 2, 2);
236 g.setColor(Color.white);
237 g.fillRect(x, y, 1, 1);
238 }
239 }
--------------------------------------------------------------------------------Multicast Protocol
TCP and UDP are unicast protocols: there is only one sender and one receiver.
Multicast packets are UDP packets that can take an arbitrary number of receivers.
Multicast uses "class D" IP addresses: 224.0.0.1 to 239.255.255.255.
Receivers "subscribe" to the multicast group (IP address).
Anyone can send to the group (not just subscribers). All subscribers are eligible to receive the packet. // Join a Multicast group.
InetAddress group = InetAddress.getByName("225.6.7.8");
MulticastSocket ms = new MulticastSocket(7000);
ms.joinGroup(group);
// Send the group a datagram. (Don't need to be a
// member to send to the group.)
byte[] msg = {'H', 'o', 'w', 'd', 'y'};
DatagramPacket dp = new DatagramPacket(msg,
msg.length, group, 7000);
ms.send(dp);
// Get a datagram from the group.
byte[] buf = new byte[1000];
DatagramPacket recv = new DatagramPacket(buf,
buf.length);
ms.receive(recv);
// Leave the group.
ms.leaveGroup(group);
--------------------------------------------------------------------------------URL and URLConnection
URL represents Uniform Resource Locator (a "pointer" to a resource on the network).
URLConnection lets you interact with the resource.
Create URLConnection by invoking openConnection() on a URL
Set up the URLConnection
Make the actual connection by invoking connect() on the URLConnection
Interact with the header fields and contents of the resource.
URLStreamHandlers (for protocols) and ContentHandlers (for MIME types) are loaded dynamically when needed. --------------------------------------------------------------------------------The Resource Grabber
1 // In file network/ex5/ResourceGrabber.java
2 import java.net.*;
3 import java.io.*;
4 import java.util.Date;
5 import java.util.StringTokenizer;
6
7 public class ResourceGrabber {
8
9 public static void main(String[] args) {
10
11 if (args.length < 1) {
12 System.out.println(
13 "Need URL and optional local filename.");
14 return;
15 }
16
17 try {
18
19 URL url = new URL(args[0]);
20
21 System.out.println(
22 "Connecting to resource...");
23 URLConnection conn = url.openConnection();
24 InputStream is = url.openStream();
25
26 try {
27
28 // Get info about the resource
29 String type = conn.getContentType();
30 Date date = new Date(conn.getLastModified());
31 String lastMod = date.toLocaleString();
32
33 // Print the info
34 System.out.println(
35 "Grabbing resource\n type: " + type
36 + "\n last modified: " + lastMod);
37
38 FileOutputStream fos;
39 if (args.length < 2) {
40
41 String localFile = null;
42
43 // Grab the simple file name from the
44 // URL String
45 String fullPath = url.getFile();
46 StringTokenizer st =
47 new StringTokenizer(fullPath, "/");
48 while (st.hasMoreTokens()) {
49 localFile = st.nextToken();
50 }
51 fos = new FileOutputStream(localFile);
52 }
53 else {
54 fos = new FileOutputStream(args[1]);
55 }
56
57 try {
58
59 BufferedOutputStream bos =
60 new BufferedOutputStream(fos);
61 BufferedInputStream bis =
62 new BufferedInputStream(is);
63
64 int c;
65 int count = 0;
66
67 while ((c = bis.read()) != -1) {
68 bos.write(c);
69 ++count;
70 }
71
72 if (count != 1) {
73 System.out.println(count
74 + " bytes downloaded.");
75 }
76 else {
77 System.out.println(
78 "1 byte downloaded.");
79 }
80 }
81 finally {
82 fos.close();
83 }
84 }
85 finally {
86 is.close();
87 }
88 }
89 catch (MalformedURLException e) {
90 System.err.println(e.toString());
91 e.printStackTrace();
92 }
93 catch (IOException e) {
94 System.err.println(e.toString());
95 e.printStackTrace();
96 }
97 }
98 }
--------------------------------------------------------------------------------Exercises
Problem 1.
Write an application named GetServer.java that creates a ServerSocket on port 80. When a client request comes in, get an InputStream from the socket returned by read lines from the ServerSocket's accept() method, and wrap the InputStream in an InputStreamReader and a BufferedReader. Read one line at a time from the BufferedReader while the length of the line read does not equal 0 and the first character is not '\r' or '\n'. Each time you read a line from the BufferedReader, print the line out to the standard output. Once you are done reading lines, just close the socket by closing the BufferedReader. What you'll end up printing out is HTTP requests sent by a web browser, which are always terminated by a blank line, as in: GET /jvm/index.html HTTP/1.0
Referer: http://minovia/subscribe.html
Connection: Keep-Alive
User-Agent: Mozilla/4.7 [en] (Win98; I)
Host: minovia
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */*
Accept-Encoding: gzip
Accept-Language: en
Accept-Charset: iso-8859-1,*,utf-8
<BLANK LINE>Start your GetServer application and then open a web browser. Type in URLs into your browser's address bar such as: http://127.0.0.1or
http://127.0.0.1/this/is/a/longer/pathname/filename.htmlWatch what output your GetServer prints and the web browser prints. Problem 2.
Change your GetServer application from Problem 1 so that it also sends a response back to the client. First, get an OutputStream from the socket, and wrap that in a BufferedOutputStream and a DataOutputStream. Write the following line out to the client after reading in the HTTP request lines, and before closing the socket:
HTTP/1.0 404 Not found\r\n\r\nRun your GetServer application again and look at what the web browser now prints when you hit 127.0.0.1 URLs. Problem 3.
Change your GetServer application from Problem 2 so that each time a client request comes in, it fires off a new thread to handle the client. Name the thread class ServerThread. Test your application again with a web browser. Problem 4.
Create a private instance method getFile() that returns a String and takes no arguments in your ServerThread class, and call the method from your run() method right after getting the DataOutputStream from the socket. Wrap the getFile() invocation in a try block that has a catch (Exception e) clause. In the catch clause, print the 404 Not Found response back to the client. Move the code that gets a BufferedReader from the socket to the getFile() method. After getting the BufferedReader, make sure that the first three characters of the first line is "GET," as in: GET /jvm/index.html HTTP/1.0If the first three lines is not a GET, just throw an IOException back to the run() method. Finally, parse out the second token of that line, which in the above case would be, "/jvm/index.html," and return that value from getFile(). Back in the main run() method of ServerThread, format an HTTP request that indicates an HTML document is being returned: HTTP/1.1 200 OK\r\n
Content-Type: text/html\r\n\r\nFinally, format the file name returned by getFile() into an HTML page like this: <HTML>
<HEAD>
<TITLE>Requested File</TITLE>
</HEAD>
<BODY>
<H1>The requested file was: /jvm/index.html</H1>
</BODY>
</HTML>Write this HTML page out to the client after the 200 OK response. Start your GetServer once again and hit 127.0.0.1 URLs with your web browser. Problem 5.
Please enhance your GetServer application yet again. Change the return value of getFile() to a java.io.File. Modify getFile() so that it returns an actual full path to the file requested in the GET, based on a hard-coded base directory. For your hard-coded base directory, select some directory that has web pages in it, such as the directory in which you installed your javadoc documentation. If the requested path turns out to be a directory, just append index.html to the path. Back in the run() method, adjust the code so that the full path is printed out in the web page sent back to the client, such as: <HTML>
<HEAD>
<TITLE>Requested File</TITLE>
</HEAD>
<BODY>
<H1>The requested file was: d:\hard\coded\dir\jvm\index.html</H1>
</BODY>
</HTML>Problem 6.
Lastly, change the run() method such that it actually sends back an approprite MIME type and the actual file contents. First, create a new java.util.HashMap in the GetServer's main() method, and add to it the MIME types for several file extensions: htm text/html
html text/html
txt text/plain
jpg image/jpeg
gif image/gif Pass a reference to this HashMap to the constructor of every ServerThread. In the ServerThread's run() method, figure out the appropriate MIME type by looking up the file's extension in the Map passed to the ServerThread's constructor. Send that MIME type back to the client in the Content-Type header rather than just text/html. If you don't recognize the file extension, just use the MIME type text/plain. In addition to Content-Type, send back a Content-Length header that indicates the length of the file to follow, as in: HTTP/1.1 200 OK\r\n
Content-Length: 92\r\n
Content-Type: image/gif\r\n\r\nLastly, create a FileInputStream for the File returned by getFile(), and wraps the FileInputStream in a BufferedInputStream. Then read bytes from the file and write them to the socket. When your done, just close both the socket and the file, and return from the run() method.
class dataObj implements Serializable
{
public short t1_full = 0;
public byte[] t2 = new byte[18];
public float t3 = 0f;
public double t4 = 0d;
}
利用ObjectOutputStream/ObjectInputStream创建一个sin/sout,利用readObject/writeObject读写该类,肯定可以搞定
import java.awt.*;
import java.net.*;
import java.io.*;public class Server extends Frame{
TextArea display;
public Server()
{
display=new TextArea(20,5);
add("Center",display);
resize(300,150);
show();
} public void runServer()
{
ServerSocket server;
Socket connection;
DataOutputStream output;
try{
display.setText("Connecting ...\n");
server=new ServerSocket(5000,100);
connection=server.accept() ;
display.setText("Connection received...\n");
display.append("Sending data...\n");
output=new DataOutputStream(connection.getOutputStream());
String s=new String("连接成功!\n");
byte buf[]=new byte[1024];
buf=s.getBytes() ;
output.write(buf,0,buf.length );
display.append(
"Transmission complete.Closing socket.\n");
connection.close() ;
}
catch(IOException e){
e.printStackTrace();
}
} public boolean handleEvent(Event e)
{
if(e.id==Event.WINDOW_DESTROY){
hide();
dispose();
System.exit(0);
} return super.handleEvent(e);
} public static void main(String args[])
{
Server s=new Server(); s.runServer();
}
}//Client.javaimport java.awt.*;
import java.net.*;
import java.io.*;public class Client extends Frame{
TextArea display; public Client()
{
super("Client");
display=new TextArea(20,10);
add("Center",display);
resize(300,150);
show();
} public void runClient()
{
Socket client;
DataInputStream input;
char c;
byte buf[]=new byte[1024];
int i;
String str; try{
client=new Socket(InetAddress.getLocalHost(),
5000);
display.append("Created Socket\n"); input=new DataInputStream(client.getInputStream());
display.append("Created input stream\n");
display.append(
"The text from the server is:\n\t");
i=input.read(buf);
str=new String(buf);
display.appendText(str);
client.close() ;
}
catch(IOException e){
e.printStackTrace() ;
} } public boolean handleEvent(Event e)
{
if(e.id==Event.WINDOW_DESTROY){
hide();
dispose();
System.exit(0);
} return super.handleEvent(e);
} public static void main(String args[])
{
Client c=new Client(); c.runClient() ;
}
}可以显示中文