Fall Semester, 2002
Object Databases, Distributed Objects, WWW
© 2002, All Rights Reserved, SDSU & Roger Whitney
San Diego State University -- This page last updated 10-Dec-02
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CS 580 Client-Server Programming Fall Semester, 2002 Object Databases, Distributed Objects, WWW |
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© 2002, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 10-Dec-02 |
Object Databases
Store and retrieve objects from the database
Examples
Example – OmniBase for VW
Creating the database
reservations := OmniBase openOn: 'reservationsDB'. addRoom :=reservations newTransaction. addRoom root at: 'ba121' put: (OrderedCollection new). addRoom commit. reservations close.Adding a Request newRequest :=Reservation startTime: (Time readFrom: '9:00 am' readStream) endTime: (Time readFrom: '10:00 am' readStream) date: (Date readFrom: '12/7/02' readStream). reservations := OmniBase openOn: 'reservationsDB'. [currentReservations := OmniBase root at: 'ba121'. currentReservations detect: [:each | each intersects: newRequest] ifNone: [currentReservations add: newRequest. currentReservations markDirty]] evaluateAndCommitIn: reservations newTransaction
Distributed Objects
RMI Example - Hello World Modified from "Getting Started Using RMI"
The Remote Interface
public interface Hello extends java.rmi.Remote { String sayHello() throws java.rmi.RemoteException; }
The Server Implementation
// Required for Remote Implementation import java.rmi.*; import java.rmi.server.UnicastRemoteObject; // Used in method getUnixHostName import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class HelloServer extends UnicastRemoteObject implements Hello { public HelloServer() throws RemoteException { } // The actual remote sayHello public String sayHello() throws RemoteException { return "Hello World from " + getUnixHostName(); }
// Works only on UNIX machines
protected String getUnixHostName() { try { Process hostName; BufferedReader answer; hostName = Runtime.getRuntime().exec( "hostname" ); answer = new BufferedReader( new InputStreamReader( hostName.getInputStream()) ); hostName.waitFor(); return answer.readLine().trim(); } catch (Exception noName) { return "Nameless"; } }
// Main that registers with Server with Registry
public static void main(String args[]) { // Create and install a security manager System.setSecurityManager(new RMISecurityManager()); try { HelloServer serverObject = new HelloServer (); Naming.rebind("//roswell.sdsu.edu/HelloServer", serverObject ); System.out.println("HelloServer bound in registry"); } catch (Exception error) { System.out.println("HelloServer err: "); error.printStackTrace(); } } }
The Client Code
import java.rmi.*; import java.net.MalformedURLException; public class HelloClient { public static void main(String args[]) { try { Hello remote = (Hello) Naming.lookup( "//roswell.sdsu.edu/HelloServer"); String message = remote.sayHello(); System.out.println( message ); } catch ( Exception error) { error.printStackTrace(); } } }Note there are four different types of exception thrown, but shown to save space
WWW as a Client-Server System
Many people use WWW to implement client-server systems
Advantages:
Generating HTML pages dynamically
WWW client-server systems need more interaction than static web pages
Main Issues in Dynamically generating HTML
How to map an HTTP request to a program to generate HTML?
Keeping the display separate from the business logic
Mapping an HTTP request to a program
Special Web Servers
Basic HTTP is not hard to implement
Write your own server to produce dynamic responses
Not common
Examples
Special API for Web servers
Web servers allow you to link code to extend their functionality
Examples
Servlets
Background
Started by Sun
Sun controls the Servlet API ( http://java.sun.com/products/servlet/2.2/javadoc/index.html)
Tomcat - Apache module that supports servlets & Java Server pages
JRun - commercial product supporting servlets & Java Server pages
VisualWorks supports the Servlet API
What are Servlets?
Java programs that are
Sample Servlet Program import java.io.*; import java.util.Date; import javax.servlet.*; public class SimpleDateServlet extends GenericServlet { public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException { InputStream rawIn; DataInputStream parsedInput; rawIn = request.getInputStream(); parsedInput = new DataInputStream(rawIn); ServletOutputStream out = response.getOutputStream(); String inputLine = parsedInput.readLine(); if (inputLine.startsWith("date")) { Date now = new Date(); out.println( now.toString() ); } else out.println( "Invalid Input" ); } }
Common Gateway Interface (CGI)
Standard for calling external programs
The basic idea
The basic questions
Finding and running the CGI program
Web server is configured to treat files in particular directories as programs
Often cgi-bin indicates a such a CGI directory
All files in a CGI directory and subdirectories are treated as programs
A URL that references a program in a CGI directory will cause the Web server to run that program as a CGI program
Sending a Response to the server
CGI program writes the response on the standard output
The server reads the output and forms http response
CGI defines headers for communication from CGI program to server
The CGI Return Headers (CGI/1.1)
The output of scripts begins with a small header. This header consists of text lines, in the same format as an HTTP header, terminated by a blank line (a line with only a linefeed or CR/LF).
Any headers that are not server directives are sent directly back to the client. Currently, this specification defines three server directives:
Content-type
CGI Example
File: hiMomFancy
Location: /net/www/www-eli/cgi-bin/cgiExamples
CGI directory : /net/www/www-eli/cgi-bin
File Contents:
#!/bin/sh echo Content-type: text/html echo echo "<B>Hi Mom</B>", echo echo "<BIG>How is Dad?</BIG>" echo "<CENTER>I am fine</CENTER>".
URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/hiMomFancy
Information from the Web server to the CGI Program
Web server sends data to the CGI Program via:
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AUTH_TYPE |
CONTENT_LENGTH |
CONTENT_TYPE |
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DOCUMENT_ROOT |
GATEWAY_INTERFACE |
HTTP_ACCEPT |
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HTTP_USER_AGENT
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PATH_INFO |
PATH_TRANSLATED
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QUERY_STRING
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REMOTE_ADDR |
REMOTE_HOST |
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REMOTE_IDENT |
REMOTE_USER |
REQUEST_METHOD |
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SCRIPT_NAME |
SERVER_NAME |
SERVER_PORT |
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SERVER_PROTOCOL |
SERVER_SOFTWARE |
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Example of CGI Environment Variables
File: variables
Location: /net/www/www-eli/cgi-bin/cgiExamples
URL:
http://www.eli.sdsu.edu/cgi-bin/cgiExamples/variables
File Contents:
#!/bin/sh # Code from http://hoohoo.ncsa.uiuc.edu/cgi/test-cgi.txt echo Content-type: text/plain echo echo CGI/1.0 test script report: echo echo argc is $#. argv is "$*". echo echo CONTENT_LENGTH = $CONTENT_LE echo CONTENT_TYPE = $CONTENT_TYPE echo GATEWAY_INTERFACE = $GATEWAY_INTERFACE echo HTTP_ACCEPT = "$HTTP_ACCEPT" echo PATH_INFO = $PATH_INFO echo PATH_TRANSLATED = $PATH_TRANSLATED echo QUERY_STRING = $QUERY_STRING echo REMOTE_ADDR = $REMOTE_ADDR echo REMOTE_HOST = $REMOTE_HOST echo REMOTE_USER = $REMOTE_USER echo REQUEST_METHOD = $REQUEST_METHOD echo SCRIPT_NAME = $SCRIPT_NAME echo SERVER_NAME = $SERVER_NAME echo SERVER_PORT = $SERVER_PORT echo SERVER_PROTOCOL = $SERVER_PROTOCOL echo SERVER_SOFTWARE = $SERVER_SOFTWARE
CGI, Java, & Smalltalk
Java and Smalltalk are not good candidates for CGI programs
Expensive to start up VM for each request
Problems reading environment variables
Java’s classpath can cause problems
FastCGI
Background
Languages supported:
Fast CGI
Pros:
Active Web Pages
Basic Idea
Imbed code in html pages
When the web server reads a page the imbedded code is run
Examples
Java Server Pages (JSP)
Active Server Pages (ASP)
Smalltalk Server Pages (SSP)
PHP
Pros
Allows graphic designers to design web pages with dynamic content
Scripting languages designed for text manipulation
Cons Testing
Some scripting languages are owned by one company
Can result in a code mess with business logic and display code mixed together
Smalltalk Server Page Example
<html> <head> <title> Smalltalk Server Page Example </title> </head> <body> <% theHour := Time now hours. %> <%= theHour > 18 ifTrue: ['Good evening.'] ifFalse: [theHour > 12 ifTrue:['Good afternoon.'] ifFalse: ['Good morning.']]. %> </body> </html>
Copyright ©, All rights reserved.
2002 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA.
OpenContent license defines the copyright on this document.
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