Java Client Server Computing

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JavaClient Server Computing
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C/S Computing on the Web
Client
Server
HTTP Server
Server API
Form
Post/Get
Applet
RMI
Servlets
JDBC/ODBC
CGI
Direct Socket Operations
DatabaseServer
ApplicationServer
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Client-Server Programming in Java

• Programming network sockets
• Invoking distributed objects using Remote Method
  Invocation (RMI)
• Communicating with HTTP server
• Accessing remote databases using JDBC
• CGI programming

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Programming Network Sockets

• A TCP/IP Socket is the Java object that connects
  a client to a network server that is listening on
  a numbered network port for a connection.
• Sockets are used to implement reliable
  bi-directional point-to-point, stream-based
  connections between clients and servers on the
  Internet.

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Programming Network Sockets

• Client-side
• (1) Create a Socket object
• InetAddress address
• InetAddress.getByName(IP Address)
• Socket client new Socket(address,
• portNumber)

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Programming Network Sockets

• (2) Create an output stream that can be used to
  send info to the Socket.
• PrintStream out new
• PrintStream(client.getOutputStream()
• (3) Create an input stream to read the response
  from the server.
• DataInputStream in new
• DataInputStream(client.getInputStream()

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Programming Network Sockets

• (4) Process input and output with
  handleConnection() method and other I/O methods.
• ...
• (5) Close the socket when done.
• client.close()

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Programming Network Sockets

• Server-side
• (1) Create a SocketServer object
• ServerSocket listenSocket new
• ServerSocket(portName)
• (2) Create a Socket object (multiple
  connectionspossible) from the ServerSocket
• Socket server listenSocket.accept()

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Programming Network Sockets

• (3) Create an input stream to read input from the
  client
• DataInputStream in new
• DataInputStream(server.getInputStream)
• (4) Create an output stream that can be used to
  send info back to the client
• PrintStream out new
• PrintStream(server.getOutputStream())

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Programming Network Sockets

• (5) Process input and output with
  handleConnection() method and other I/O methods.
• ...
• (6) Close the socket when done.
• server.close()

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Remote Method Invocation

• RMI (Remote Method Invocation) is Javas
  implementation of CORBA (Common Object Request
  Broker Architecture).
• RMI is an object-oriented version of RPC (Remote
  Procedure Call).

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Remote Method Invocation

• The client requests an object from the server
  using a simple high-level language. Once it has
  the object, it invokes its methods as though it
  were a normal local object. (Behind the scene the
  requests for the method are rerouted to the
  server.)
• Neither the client nor the server have to do
  anything explicitly with input/output streams or
  client/server sockets.

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Remote Method Invocation

• Why Socket not RMI?
• (1) RMI only works among Java systems, not HTTP.
• (2) RMI requires common code to be installed on
  both client and server.
• (3) RMI requires Java VM to be run at both end.

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Communicating with HTTP Server

• A HTML page can gather user input in two ways
  (1) FORMs and (2) Java applets. Both can use
  HTTP GET and POST methods for server interaction.
• Java supports a much richer interface than do
  HTML forms, but building interfaces in Java is
  often more difficult than in HTML.

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Using Java applets to send GET data to CGI
programs

• (1) The showDocument() method can be used to
  request the browser to display a particular URL.
• The URLEncoder.encode method can be used to code
  the string being send into HTTP readable form.
• (SearchService.java)

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Sending Data via GET and Processing the Results

• If you are developing both the client and the
  server end of the process, you can then have the
  server CGI return data in non-HTML format and
  have the client CGI process the data and present
  it in graph or some other custom format.
• (ShowFile.java)

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Using Java Applets to Send POST Data to CGI
Programs

• If you are developing both the client and the
  server end of the process, you can then have the
  client CGI send POST data to the server CGI.

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Java Database Connectivity

• JDBC is another API provided by Java for database
  connectivity.
• There are 7 steps to query database
• (1) Load the JDBC driver.
• String driver
• (connect.microsoft.microsoftDriver)
  
• Class.forName(driver)

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Java Database Connectivity

• (2) Define the connection URL
• String url jdbcff-sybase//host/database)
• (3) Establish the connection
• String user username
• String password password
• Connection connection
• DriverManager.getConnection(url, user,
  
• password)

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Java Database Connectivity

• (4) Create a Statement intance for query.
• Statement statement
• connection.createStatement()
• (5) Execute a statement.
• String query SELECT FROM table
• ResultSet results
• statement.executeQuery(query)
• (6) Process the resutls.
• (7) Close the connection.

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Common Gateway Interface

• The CGI lets HTML pages communicate with database
  or other programs on a system running an HTTP
  server.
• Instead of treating a CGI program as a file whose
  content should be returned, the HTTP server
  treats it as a program whose output should be
  returned.

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Common Gateway Interface

• So, a CGI program processes data from the client
  and return the results.
• A CGI program should perform 4 steps
• (1) Read the data.
• (2) Output HTTP headers.
• (3) Send a blank line.
• (4) Generate a HTML document.