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java.net library simplifies network programming.
InetAddress class of java.net.
artima.com)
205.73.4.217)
InetAddress.getByName(String) does DNS lookup (or reverse
lookup) and returns an InetAddress object.
int's).
localhost" allows you to test a
network program without a network.
InetAddress object for localhost:
InetAddress.getByName(null);
InetAddress.getByName("localhost");
InetAddress.getByName("127.0.0.1");
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
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
DatagramSocket on both client and server.
DatagramPacket.
DatagramPacket containing the data.
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
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 marks 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 marks 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 marks
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 }
// 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 represents Uniform Resource Locator (a "pointer" to a
resource on the network).
URLConnection lets you interact with the resource.
URLConnection by invoking
openConnection() on a URL
URLConnection
connect()
on the URLConnection
URLStreamHandlers (for protocols) and
ContentHandlers (for MIME types) are loaded
dynamically when needed.
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 }
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.html
Watch what output your GetServer prints and the web browser prints.
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\n
Run your GetServer application again and look at what the web browser
now prints when you hit 127.0.0.1 URLs.
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.
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/1.0
If 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\n
Finally, 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.
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>
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.
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