Modernas Programmeanas Tehnologijas Advanced Programming Technologies

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Modernas Programmeanas Tehnologijas (Advanced
Programming Technologies)

• Edgars Celms, Martin Opmanis
• (askola_at_mii.lu.lv)

Latvijas Universitates Matematikas un
informatikas instituts 2007, Riga, Latvija
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Tikloanas iespejas valoda Java (networking)

• Java How to Program, Sixth Edition
• Chapter 24. Networking
• Darboanas ar URL
• Datu lasiana no Web Servera
• Vienkara servera izveidoana izmantojot stream
  sockets
• Vienkara klienta izveidoana izmantojot stream
  sockets
• Klienta/Servera sadarbiba izmantojot stream
  sockets savienojumu
• Bezsavienojuma (connectionless) Klienta/Servera
  sadarbiba izmantojot datagrams
• Klienta/Servera Tic-Tac-Toe izmantojot
  daudzpavedienu (multithreading) serveri

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Ievads

• Pakotne java.net satur klases, kuras nodroina
  darbu ar tikla servisiem
• Plusmas bazeta sadarbiba (stream-based
  communications)
• Lietojumprogrammas tikloanos uztver ka datu
  plusmas (streams of data)
• Konekciju bazeti protokoli
• Izmanto TCP (Transmission Control Protocol)
• Pakeu bazeta sadarbiba (packet-based
  communications)
• Tiek sutitas individualas paketes
• Bezkonekciju servisi (connectionless service)
• Izmanto UDP (User Datagram Protocol)
• Klienta-servera attieciba (client-server
  relationship)
• Klients pieprasa veikt kadas darbibas
• Serveris izpilda darbibas un atbild klientam
• Pieprasijuma-atbildes modelis (request-response
  model)
• Popularaka implementacija timekla
  parlukprogrammas (web browsers) un timekla
  serveri (web servers)

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Daas piezimes I (Software Engineering
Observation)

• Performance tip. Connectionless services
  generally offer greater performance but less
  reliability than connection-oriented services.
• Portability tip. 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.

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Darboanas ar URLiem (manipulating URLs)

• HyperText Transfer Protocol (HTTP)
• Izmanto URI (Uniform Resource Identifiers) lai
  identificetu datus
• URL (Uniform Resource Locators)
• URI specifice dokumentu atraanas vietu
• Var referencet failus, folderus, ka ari daadus
  saliktus (complex) objektus.
• HTML dokuments SiteSelector.html
• applet elements
• param birka (tag)
• name atributs
• value atributs

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HTML document to load SiteSelector applet
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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
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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
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Darboanas ar URLiem (manipulating URLs)

• HTML freimi (frames)
• Ir ari iespeja specificet freimu showDocument
  metode
• _blank
• _self
• _top

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Daas piezimes II (Software Engineering
Observation)

• The applet in example 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.

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Datu lasiana no Web Servera

• Swing GUI komponente JEditorPane
• Spej apstradat gan parastu tekstu (plain text),
  gan ari HTML-formatetu tekstu
• Piemers, ReadServerFile.java darbojas ka
  vienkara timekla parlukprogramma (web browser)
• Attelo failus no timekla servera pec uzdota URI
• HyperlinkEvents notikumi
• Notiek bridi, kad lietotajs uzklikkina uz
  hipersaites (hyperlink)
• Tris notikumu tipi
• HyperlinkEvent.EventType.ACTIVATED
• HyperlinkEvent.EventType.ENTERED
• HyperlinkEvent.EventType.EXITED
• JEditorPane genere HyperlinkEvents tikai un
  vienigi tad, ja ta ir nemodificejama
  (uneditable).

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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
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Vienkara servera izveidoana izmantojot stream
sockets

• Pieci soli vienkara servera izveidoanai valoda
  Java
• 1. Solis Jaizveido ServerSocket objekts
• ServerSocket server new ServerSocket(
  portNumber, queueLength )
• Japieregistre pieejamais (brivais) ports
• Jaspecifice maksimalais klientu skaits (queue
  length).
• Porta numuru klients izmanto, lai atrastu servera
  aplikaciju uz servera, tiek saukts ari par
  Handshake point
• Jasasaista serveris ar portu (binding the server
  to the port)
• Tikai viena servera aplikacija var but
  piesaistits specifiskam portam
• 2. Solis Serveris klausas klienta pieslegumus
• Serveris nepartraukti (indefinitely) klausas
  potencialos klienta pieslegumus
• Socket connection server.accept()
• Izmantojot Socket objektu serveris sadarbojas ar
  klientu
• The interactions with the client actually occur
  at a different server port from the handshake
  point. This allows the port specified in Step 1
  to be used again in a multithreaded server to
  accept another client connection.
• 3. Solis Datu sutiana un sanemana
• OutputStream datu sutianai un InputStream datu
  sanemanai
• Metode getOutputStream atgrie Socketa
  OutputStream
• Metode getInputstream atgrie Socketa
  InputStream
• 4. Solis Procesa faze
• Serveris un klients sadarbojas izmantojot plusmas

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Daas piezimes III (Software Engineering
Observation)

• Port numbers can be between 0 and 65,535. Most
  operating systems reserve port numbers below 1024
  for system services (e.g., e-mail 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.
• 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 Javas 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.
• Performance tip.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.

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Vienkara klienta izveidoana izmantojot stream
sockets

• Cetri soli vienkara klienta izveidoanai valoda
  Java
• 1. Solis Lai pieslegtos serverim ir jaizveido
  Socket objekts
• Socket connection new Socket ( serverAddress,
  port )
• 2. Solis Datu sutiana un sanemana
• OutputStream datu sutianai un InputStream datu
  sanemanai
• Metode getOutputStream atgrie Socketa
  OutputStream
• Metode getInputstream atgrie Socketa
  InputStream
• 4. Solis Procesa faze
• Klients un serveris sadarbojas izmantojot plusmas
• 4. Solis Sledz plusmas un savienojumus

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Klienta/Servera sadarbiba izmantojot stream
sockets savienojumu

• Klienta/servera chat lietojumprogramma
• Izmanto stream sockets
• Serveris gaida klienta piesleguma meginajumu
• Klients piesledzas serverim
• Suta un sanem zinojumus
• Klients vai serveris izbeidz savienojumu
• Serveris gaida nakamo klienta pieslegumu

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Import ServerSocket and Socket from package
java.net
Declare ServerSocket server which waits for
client connection
Declare Socket connection which connects to the
client
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Wait for a client connection
Create ServerSocket at port 12345 with queue of
length 100
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
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Use ServerSocket method accept to wait for a
connection from a client
Output the host name of the computer that made
the connection using Socket method getInetAddress
and InetAddress method getHostName
Obtain Sockets OutputStream and use it to
initialize ObjectOutputStream
Method flush empties output buffer and sends
header information
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Popularakas programmeanas kludas I (Common
Programming Error)

• Specifying a port that is already in use or
  specifying an invalid port number when creating a
  ServerSocket results in a BindException.

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Daas piezimes IV (Software Engineering
Observation)

• 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 clients ObjectInputStream can prepare
  to receive the data. This is required only for
  networking applications that communicate using
  ObjectOutputStream and ObjectInputStream.
• Performance tip.A computers 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 computers input and output
  components.

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Use InetAddress static method getByName to obtain
an InetAdress object containing the IP address
specified as a command-line argument to the
application
Create a Socket that will connect with port 12345
on the server
Display a message indicating the name of the
server computer to which the client has connected
Obtain Sockets OutputStream and use it to
initialize ObjectOutputStream
Method flush empties output buffer and sends
header information
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Bezsavienojuma (connectionless) klienta/servera
sadarbiba izmantojot datagrams

• Bezsavienojuma sadarbiba izmantojot datagrams
• Netiek uzturets savienojums starp datoriem
• Sadala zinojumus atsevikas dalas un suta ka
  paketes
• Zinojumi var pienakt noteikta seciba, bez
  secibas, vai ari nepienakt vispar
• Sanemejam ir javar sakartot paketes pareiza
  seciba un izlasit

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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
Create a DatagramPacket, which specifies the data
to send, the number of bytes to send, the client
computers Internet address and the port where
the client is waiting to receive packets
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Use method send of DatagramSocket to send the
packet over the network
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Server window after packet of data is received
from client
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Convert the String to a byte array
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
Use DatagramPacket method send to send the packet
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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
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Client window after sending packet to Server
and receiving packet back from Server
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Popularakas programmeanas kludas II (Common
Programming Error)

• Specifying a port that is already in use or
  specifying an invalid port number when creating a
  DatagramSocket results in a SocketException.

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Klienta/Servera Tic-Tac-Toe izmantojot
daudzpavedienu (multithreading) serveri

• Tuvak neapskatisim.
• Sikak skat. Java How to Program, Sixth Edition
  
• 24.8. Client/Server Tic-Tac-Toe Using a
  Multithreaded Server
• With Javas 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.
• Ja ir interese, tad varat izpetit ari ka ir
  realizets DeitelMessenger Serveris un Klients
• Sikak skat. Java How to Program, Sixth Edition
  
• 24.10. Case Study DeitelMessenger Server and
  Client

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Klienta/Servera Tic-Tac-Toe izmantojot
daudzpavedienu (multithreading) serveri
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Jautajumi ?