24 Networking.

24 Networking

Protocol is everything.
If the presence of electricity can be made visible in any part of a circuit, I see no reason why intelligence may not be transmitted instantaneously by electricity. Samuel F. B. Morse Protocol is everything. Francois Giuliani What networks of railroads, highways and canals were in another age, the networks of telecommunications, information and computerization … are today. Bruno Kreisky The port is near, the bells I hear, the people all exulting. Walt Whitman

OBJECTIVES In this chapter you will learn:
To understand Java networking with URLs, sockets and datagrams. To implement Java networking applications by using sockets and datagrams. To understand how to implement Java clients and servers that communicate with one another. To understand how to implement network-based collaborative applications. To construct a multithreaded server.

24.1 Introduction 24.2 Manipulating URLs 24.3 Reading a File on a Web Server 24.4 Establishing a Simple Server Using Stream Sockets 24.5 Establishing a Simple Client Using Stream Sockets 24.6 Client/Server Interaction with Stream Socket Connections 24.7 Connectionless Client/Server Interaction with Datagrams 24.8 Client/Server Tic-Tac-Toe Using a Multithreaded Server 24.9 Security and the Network 24.10 Case Study: DeitelMessenger Server and Client DeitelMessengerServer and Supporting Classes DeitelMessenger Client and Supporting Classes 24.11 Wrap-Up

24.1 Introduction Networking package is java.net
Stream-based communications Applications view networking as streams of data Connection-based protocol Uses TCP (Transmission Control Protocol Packet-based communications Individual packets transmitted Connectionless service Uses UDP (User Datagram Protocol)

24.1 Introduction (Cont.) Client-server relationship
Client requests some action be performed Server performs the action and responds to client Request-response model Common implementation: Web browsers and Web servers

Performance Tip 24.1 Connectionless services generally offer greater performance but less reliability than connection-oriented services.

Portability Tip 24.1 TCP, UDP and related protocols enable a great variety of heterogeneous computer systems (i.e., computer systems with different processors and different operating systems) to intercommunicate.

24.2 Manipulating URLs HyperText Transfer Protocol (HTTP)
Uses URIs (Uniform Resource Identifiers) to identify data URLs (Uniform Resource Locators) URIs that specify the locations of documents Refer to files, directories and complex objects HTML document SiteSelector.html (Fig. 24.1) applet element param tag name attribute value attribute

Outline SiteSelector.html Lines 5-12 Declare param tags for the applet, each parameter has a name and a value Fig | HTML document to load SiteSelector applet.

Outline Import classes in package java.net
SiteSelector.java (1 of 5) Lines 3-4 Line 8 Import interface AppletContext from package java.net

Outline (2 of 5) Lines 39-52 Line 45 Line 48 Line 51
SiteSelector.java (2 of 5) Lines 39-52 Line 45 Line 48 Line 51 When the user selects one of the Web sites listed in siteChooser, the program calls method valueChanged Pass the selected site name (the key) to HashMap method get, which locates and returns a reference to the corresponding URL (the value) Get a reference to an AppletContext object that represents the applet container Display in the current browser window the resource associated with URL newDocument

Outline (3 of 5) Line 67 Line 73 Line 77 Lines 81-84
SiteSelector.java (3 of 5) Line 67 Line 73 Line 77 Lines 81-84 Use Applet method getParameter to obtain a Web site title Use Applet method getParameter to obtain the Web site location Use the location as the value of a new URL object If the location passed to the URL constructor is invalid, the URL constructor throws a MalformedURLException

Use Applet method getParameter to obtain the next site title
Outline Use Applet method getParameter to obtain the next site title SiteSelector.java (4 of 5) Line 87 Program output

Outline SiteSelector.java (5 of 5) Program output

24.2 Manipulating URLs HTML frames
Specify target frame in method showDocument _blank _self _top

Error-Prevention Tip 24.1 The applet in Fig. 24.2 must be run from a Web browser, such as Mozilla or Microsoft Internet Explorer, to see the results of displaying another Web page. The appletviewer is capable only of executing applets—it ignores all other HTML tags. If the Web sites in the program contained Java applets, only those applets would appear in the appletviewer when the user selected a Web site. Each applet would execute in a separate appletviewer window.

24.3 Reading a File on a Web Server
Swing GUI component JEditorPane Render both plain text and HTML-formatted text Act as a simple Web browser Retrieves files from a Web server at a given URI HyperlinkEvents Occur when the user clicks a hyperlink Three event types HyperlinkEvent.EventType.ACTIVATED HyperlinkEvent.EventType.ENTERED HyperlinkEvent.EventType.EXITED

Outline ReadServerFile .java (1 of 3) Lines 7, 12 and 13 Line 18 Import JEditPane from package javax.swing, import HyperlinkEvent and HyperlinkListener from package javax.swing.event Declare JEditorPane contentsArea, which will be used to display the contents of the file

Outline (2 of 3) Line 40 Line 41 Lines 42-53 Lines 46-51 Lines 48-49
ReadServerFile .java (2 of 3) Line 40 Line 41 Lines 42-53 Lines 46-51 Lines 48-49 Line 50 Create JEditorPane using the no-argument constructor Set JEditorPane editable property to false Register a HyperlinkListener to handle HyperlinkEvents, which occur when the user clicks a hyperlink in the JEditorPane Method hyperlinkUpdate is called when a HyperlinkEvent occurs Use HyperlinkEvent method getEventType to determine the type of the HyperlinkEvent Use HyperlinkEvent method getURL to obtain the URL represented by the hyperlink

Outline ReadServerFile .java (3 of 3) Line 65 Invoke JEditorPane method setPage to download the document specified by location and display it in the JEditPane

Outline ReadServerFileTest .java (1 of 2) Program output

Outline ReadServerFileTest .java (2 of 2) Program output

Look-and-Feel Observation 24.1
A JEditorPane generates HyperlinkEvents only if it is uneditable.

24.4 Establishing a Simple Server Using Stream Sockets
Five steps to create a simple server in Java Step 1: Create ServerSocket object ServerSocket server = new ServerSocket( portNumber, queueLength ); Register an available port Specify a maximum number of clients Handshake point Binding the server to the port Only one client can be bound to a specific port

Software Engineering Observation 24.1
Port numbers can be between 0 and 65,535. Most operating systems reserve port numbers below 1024 for system services (e.g., and World Wide Web servers). Generally, these ports should not be specified as connection ports in user programs. In fact, some operating systems require special access privileges to bind to port numbers below 1024.

24.4 Establishing a Simple Server Using Stream Sockets (Cont.)
Five steps to create a simple server in Java Step 2: Server listens for client connection Server blocks until client connects Socket connection = server.accept(); Step 3: Sending and receiving data OutputStream to send and InputStream to receive data Method getOutputStream returns Socket’s OutputStream Methods getInputstream returns Socket’s InputStream

24.4 Establishing a Simple Server Using Stream Sockets (Cont.)
Five steps to create a simple server in Java Step 4: Process phase Server and Client communicate via streams Step 5: Close streams and connections Method close

With sockets, network I/O appears to Java programs to be similar to sequential file I/O. Sockets hide much of the complexity of network programming from the programmer.

With Java’s multithreading, we can create multithreaded servers that can manage many simultaneous connections with many clients. This multithreaded-server architecture is precisely what popular network servers use.

A multithreaded server can take the Socket returned by each call to accept and create a new thread that manages network I/O across that Socket. Alternatively, a multithreaded server can maintain a pool of threads (a set of already existing threads) ready to manage network I/O across the new Sockets as they are created. See Chapter 23 for more information on multithreading.

Performance Tip 24.2 In high-performance systems in which memory is abundant, a multithreaded server can be implemented to create a pool of threads that can be assigned quickly to handle network I/O across each new Socket as it is created. Thus, when the server receives a connection, it need not incur the overhead of thread creation. When the connection is closed, the thread is returned to the pool for reuse.

24.5 Establishing a Simple Client Using Stream Sockets
Four steps to create a simple client in Java Step 1: Create a Socket to connect to server Socket connection = new Socket ( serverAddress, port ); Step 2: Obtain Socket’s InputStream and Outputstream Step 3: Process information communicated Step 4: Close streams and connection

24.6 Client/Server Interaction with Stream Socket Connections
Client/server chat application Uses stream sockets Server waits for a client connection attempt Client connects to the server Send and receive messages Client or server terminates the connection Server waits for the next client to connect

Outline (1 of 8) Import ServerSocket and Socket from package java.net
Server.java (1 of 8) Lines 8-9 Line 25 Line 26 Import ServerSocket and Socket from package java.net Declare ServerSocket server which waits for client connection Declare Socket connection which connects to the client

Outline Server.java (2 of 8)

Outline Server.java (3 of 8) Line 62 Line 68 Line 69 Line 70 Create ServerSocket at port with queue of length 100 Wait for a client connection After the connection is established, obtain references to the streams for the connection Send the initial connection message to the client and process all messages received from the client

Outline (4 of 8) Line 93 Line 95 Line 102 Line 103
Server.java (4 of 8) Line 93 Line 95 Line 102 Line 103 Output the host name of the computer that made the connection using Socket method getInetAddress and InetAddress method getHostName Use ServerSocket method accept to wait for a connection from a client Obtain Socket’s OutputStream and use it to initialize ObjectOutputStream Method flush empties output buffer and sends header information

Outline Obtain Socket’s InputStream and use it to initialize ObjectInputStream Server.java (5 of 8) Line 106 Line 124 Use ObjectInputStream method readObject to read a String from client

Outline Method closeConnection closes streams and sockets (6 of 8)
Server.java (6 of 8) Lines Line 145 Line 158 Invoke Socket method close to close the socket Use ObjectOutputStream method writeObject to send a String to client

Outline ServerTest.java

Common Programming Error 24.1
Specifying a port that is already in use or specifying an invalid port number when creating a ServerSocket results in a BindException.

When using an ObjectOutputStream and ObjectInputStream to send and receive data over a network connection, always create the ObjectOutputStream first and flush the stream so that the client’s ObjectInputStream can prepare to receive the data. This is required only for networking applications that communicate using ObjectOutputStream and ObjectInputStream.

Performance Tip 24.3 A computer’s input and output components are typically much slower than its memory. Output buffers typically are used to increase the efficiency of an application by sending larger amounts of data fewer times, thus reducing the number of times an application accesses the computer’s input and output components.

Outline Client.java (1 of 7)

Outline Create a Socket that will connect with port on the server Use InetAddress static method getByName to obtain an InetAdress object containing the IP address specified as a command-line argument to the application Client.java (4 of 7) Line 87 Lines 90-91 Line 98 Line 99 Display a message indicating the name of the server computer to which the client has connected Obtain Socket’s OutputStream and use it to initialize ObjectOutputStream Method flush empties output buffer and sends header information

Outline Read a String object from server (5 of 7) Line 117 Line 138
Client.java (5 of 7) Line 117 Line 138 Invoke Socket method close to close the socket

Use ObjectOutputStream method writeObject to send a String to server
Outline Client.java (6 of 7) Line 151 Use ObjectOutputStream method writeObject to send a String to server

Outline ClientTest.java (1 of 2) Program output

Outline ClientTest.java (2 of 2) Program output

24.7 Connectionless Client/Server Interaction with Datagrams
Connectionless transmission with datagrams No connection maintained with other computer Break message into separate pieces and send as packets Message arrive in order, out of order or not at all Receiver puts messages in order and reads them

Use a DatagramSocket as our server
Outline Server.java (1 of 4) Line 16 Use a DatagramSocket as our server

Outline Use the DatagramSocket constructor that takes an integer port number argument to bind the server to a port where it can receive packets from clients Server.java (2 of 4) Line 30 Lines 47-48 Line 50 Create a DatagramPacket in which a received packet of information can be stored Use DatagramSocket method receive to wait for a packet to arrive at the server

Outline Use DatagramPacket method getAddress to obtain the host name of the computer from which the packet was sent Use DatagramPacket method getPort to obtain the port number through which the host computer sent the packet Use DatagramPacket method getLength to obtain the number of bytes of data sent Server.java (3 of 4) Line 54 Line 55 Line 56 Line 57 Lines 77-79 Use DatagramPacket method getData to obtain an byte array containing the data Create a DatagramPacket, which specifies the data to send, the number of bytes to send, the client computer’s Internet address and the port where the client is waiting to receive packets

Use method send of DatagramSocket to send the packet over the network

Outline ServerTest.java Program ouptut Server window after packet
of data is received from client

Outline (2 of 5) Line 41 Lines 44-45 Line 47
Client.java (2 of 5) Line 41 Lines 44-45 Line 47 Create a DatagramPacket and initialize it with the byte array, the length of the string that was entered by the user, the IP address to which the packet is to be sent and the port number at which the server is waiting Convert the String to a byte array Use DatagramPacket method send to send the packet

Create a DatagramSocket for sending and receiving packets
Outline Client.java (3 of 5) Line 71 Create a DatagramSocket for sending and receiving packets

Create a DatagramPacket to store received information
Outline Client.java (4 of 5) Lines 88-89 Line 95 Line 96 Line 97 Line 98 Create a DatagramPacket to store received information Use DatagramPacket method getAddress to obtain the host name of the computer from which the packet was sent Use DatagramPacket method getPort to obtain the port number through which the host computer sent the packet Use DatagramPacket method getLength to obtain the number of bytes of data sent Use DatagramPacket method getData to obtain an byte array containing the data

Outline ClientTest.java Program output Client window after sending
packet to Server and receiving packet back from Server

Common Programming Error 24.2
Specifying a port that is already in use or specifying an invalid port number when creating a DatagramSocket results in a SocketException.

24.8 Client/Server Tic-Tac-Toe Using a Multithreaded Server
Multiple threads Server uses one thread per player Allow each player to play game independently

Outline TicTacToeServer .java (1 of 12)

Outline Create array players with 2 elements (3 of 12) Line 50 Line 55
TicTacToeServer .java (3 of 12) Line 50 Line 55 Create ServerSocket to listen on port 12345

Execute the Player in the runGame thread pool
Outline Loop twice, blocking at line 79 each time while waiting for a client connection TicTacToeServer .java (4 of 12) Lines 75-87 Line 79 Line 80 Create a new Player object to manage the connection as a separate thread Execute the Player in the runGame thread pool

Get the streams to send and receive data
Outline TicTacToeServer .java (8 of 12) Lines Get the streams to send and receive data

Outline (9 of 12) Lines 213-214 Line 215
TicTacToeServer .java (9 of 12) Lines Line 215 Lines Format output notifying the other player of the move Call Formatter method flush to force the output to the client Send player’s mark

Outline Send message indicating one player connected and waiting for another player to arrive TicTacToeServer .java (10 of 12) Lines Lines Begin the game

Outline Send message indicating player O connected (11 of 12)
TicTacToeServer .java (11 of 12) Lines Line 269 Lines 272 Lines Read a move Check the move Send message indicating the move is valid

Send message indicating the move is invalid
Outline Send message indicating the move is invalid TicTacToeServer .java (12 of 12) Lines

Outline TicTacToeServer Test.java Program output

Outline TicTacToeClient .java (1 of 10)

Outline Connect to the server (4 of 10) Lines 85-86 Lines 89-90
TicTacToeClient .java (4 of 10) Lines 85-86 Lines 89-90 Line 105 Get the streams to send and receive data Read mark character from server

Outline (5 of 10) Lines 121-125 Lines 123-124 Lines 132-136
TicTacToeClient .java (5 of 10) Lines Lines Lines Loop continually Read and process messages from server If valid move, write message and set mark in square

Outline If invalid move, display message
If opponent moves, set mark in square TicTacToeClient .java (6 of 10) Lines Lines

Send the move to the server
Outline TicTacToeClient .java (8 of 10) Lines Send the move to the server

Outline TicTacToeClient Test.java

Fig.24.17 | Sample outputs from the client/server Tic-Tac-Toe program. (Part 1 of 2.)

Fig.24.17 | Sample outputs from the client/server Tic-Tac-Toe program. (Part 2 of 2.)

24.9 Security and the Network
By default, applets cannot perform file processing Applets often limited in machine access Applets can communicate only with the machine from which it was originally downloaded Java Security API Digitally signed applets Applets given more privileges if from trusted source

24.10 Case Study: DeitelMessenger Server and Client
Chat rooms Each user can post a message and read all other messages Multicast Send packets to groups of clients

24.10.1 DeitelMessengerServer and Supporting Classes
Online chat system Classes: Clients connect to this server Interface SocketMessengerConstants Defines constants for port numbers Interface MessageListener Defines method for receiving new chat messages Class MessageReceiver Separate thread listens for messages from clients Class MulticastSender Separate thread delivers outgoing messages to clients

Outline (1 of 3) Line 15 Lines 28-29
DeiterMessenger Server.java (1 of 3) Line 15 Lines 28-29 Implement the MessageListener interface Create a ServerSocket to accept incoming network connections

Outline DeiterMessenger Server.java (2 of 3) Line 38 Lines 41-42 Invoke method accept to wait for and accept a new client connection Create and start a new MessageReceiver for the client

Outline DeiterMessenger Server.java (3 of 3) Lines 62-63 Create and start new MulticastSender to deliver completeMessage to all clients

Outline DeitelMessenger ServerTest.java Program output

Outline Address to send multicast datagrams
SocketMessenger Constants.java Line 9 Line 12 Line 15 Line 18 Line 21 Line 24 Line 27 Address to send multicast datagrams Port listening for multicast datagrams Port for sending multicast datagrams Port for socket connections to server String that indicates disconnect String that separates user name and message Maximum message size in bytes

Outline MessageListener .java Line 9 Method messageReceived allows an implementing class to receive chat messages

Outline MessageReceiver .java (1 of 5)

Attempt to read for five seconds
Outline Attempt to read for five seconds MessageReceiver .java (2 of 5) Line 31

Outline Read line of data from client (3 of 5) Line 53
MessageReceiver .java (3 of 5) Line 53 Line 55 Lines 69-70 A SocketTimeOutException is thrown if the read times out Separate message into two tokens delimited by Message_SEPARATOR

Outline Invoke method messageReceived of interface MessageListener to deliver the new message to the registered MessageListener MessageReceiver .java (4 of 5) Lines 77-79 Lines 84-85 Determine whether message indicates that user wishes to leave chat room

Outline MessageReceiver .java (5 of 5)

Create DatagramSocket for delivering DatagramPackets via multicast
Outline MulticastSender .java (1 of 2) Lines 27-28 Create DatagramSocket for delivering DatagramPackets via multicast

Outline Create an InetAddress object for the multicast address
MulticastSender .java (2 of 2) Line 31 Lines 34-35 Line 37 Line 38 Create the Datagrampacket containing the message Close the DatagramSocket, and the run method returns, terminating the MulticastSender Send the packet with DatagramSocket method send

24.10.1 DeitelMessengerServer and Supporting Classes
Execute DeitelMessengerServerTest Change directories to the proper location Type command java com.deitel.mesenger.sockets.server.DeitelMessengerServerTest

24.10.2 DeitelMessenger Client and Supporting Classes
DeitelMessengerServer client Consists several components Interface MessageManager Class that implements interface MessageManager Manages communication with server Runnable subclass Listens for messages at server’s multicast address Another Runnable subclass Sends messages from client to server JFrame subclass Provides client GUI

Sends new message to DeitelMessengerServer
Outline MessageManager .java Line 10 Line 14 Line 17 Connects MessageManager to DeitelMessengerServer and routes incoming messages to appropriate MessageListener Disconnects MessageManager from DeitelMessengerServer and stops delivering messages to MessageListener Sends new message to DeitelMessengerServer

Outline SocketMessage Manager.java (1 of 4) Line 20 Line 22 Socket for connecting and sending messages to DeitelMessengerServer Runnable listens for incoming messages

Create Socket to communicate with DeitelMessengerServer
Outline SocketMessage Manager.java (2 of 4) Lines 40-41 Line 44 Line 45 Create Socket to communicate with DeitelMessengerServer Create a new packetReceiver, which listens for incoming multicast messages from the server Execute the Runnable

Create a new MessageSender to send DISCONNECT_STRING to the server
Outline Create a new MessageSender to send DISCONNECT_STRING to the server Start the MessageSender to deliver the message using method submit of ExecutorService SocketMessage Manager.java (3 of 4) Lines 63-64 Line 65 Line 66 Invoke Future method get to wait for the disconnect message to be delivered and the Runnable to terminate

Outline SocketMessage Manager.java (4 of 4) Lines 93-94 Create and start a new MessageSender to deliver the new message in a separate thread of execution

Outline MessageSender.java (1 of 2)

Outline Create a new Formatter for the clientSocket’s OutputStream
Invoke Formatter method format to format the message MessageSender.java (2 of 2) Lines 29-30 Line 31 Line 32 Invoke Formatter method flush to ensure that the message is sent immediately

Outline PacketReceiver .java (1 of 4)

Outline MulticastSocket listens for incoming chat messages on port MULTICAST_LISTENING_PORT PacketReceiver .java (2 of 4) Lines 30-31 Line 34 Line 37 Line 40 Line 55 InetAddress object to which DeitelMessengerServer multicasts chat messages Register MulticastSocket to receive messages sent to MULTICAST_ADDRESS Invoke MulticastSocket method setSoTimeout to specify that if no data is received in 5000 milliseconds, the MulticastSocket should issue an InterruptedIOException Create byte array for storing DatagramPacket

Outline Create DatagramPacket for storing message
PacketReceiver .java (3 of 4) Lines 58-59 Line 63 Line 78 Lines 81-82 Receive incoming packet from multicast address Invoke method trim of class String to remove extra white spaces from the end of the message Create a StringTokenizer to separate the message body from the name of the user who sent the message

Invoke MulticastSocket method close to close the MulticastSocket
Outline After parsing message, deliver message to PacketReceiver’s MessageListener PacketReceiver .java (4 of 4) Lines 89-91 Line 97 Line 98 Invoke MulicastSocket method leaveGroup to stop receiving messages from the multicast address Invoke MulticastSocket method close to close the MulticastSocket

Outline ClientGUI.java (1 of 10)

Outline ClientGUI.java (2 of 10) Line 40 Line 41 MessageManager handles communication with chat server MessageListener receives incoming messages from MessageManager

Outline Create an instance of MyMessageListener, which implements interface MessageListener ClientGUI.java (3 of 10) Line 51

Outline ClientGUI.java (4 of 10)

Outline ClientGUI.java (5 of 10) Lines Send user’s name and inputArea’s text to DeitelMessengerServer as a chat message

Disconnect from chat server when user exits client application
Outline ClientGUI.java (6 of 10) Line 155 Disconnect from chat server when user exits client application

Outline When user accesses Connect menu, connect to chat server
ClientGUI.java (7 of 10) Line 169 Lines When user accesses Connect menu, connect to chat server Prompt the user for a user name

Invoke MessageManager method disconnect to disconnect from chat server
Outline ClientGUI.java (8 of 10) Line 195 Invoke MessageManager method disconnect to disconnect from chat server

Display message when MessageListener detects that message was received
Outline ClientGUI.java (9 of 10) Lines Display message when MessageListener detects that message was received

Append the user name, “> ” and messageBody to messageArea
Outline ClientGUI.java (10 of 10) Line 237 Append the user name, “> ” and messageBody to messageArea

Outline (1 of 3) Line 17 Line 20 Line 23
DeitelMessenger .java (1 of 3) Line 17 Line 20 Line 23 Create a client to connect to the localhost Connect to a host supplied by the user Create a ClientGUI for the MessageManager

Outline DeitelMessenger .java (2 of 3)

Outline DeitelMessenger .java (3 of 3)

24.10.2 DeitelMessenger Client and Supporting Classes
Execute DeitelMessenger client application Change directories to the proper location Type command java com.deitel.messenger.sockets.client.DeitelMessenger java com.deitel.messenger.sockets.client.DeitelMessenger localhost java com.deitel.messenger.sockets.client.DeitelMessenger

24 Networking.

Similar presentations

Presentation on theme: "24 Networking."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

24 Networking.

Similar presentations

Presentation on theme: "24 Networking."— Presentation transcript:

Similar presentations

About project

Feedback