Transcript Developing the Beamline Video System Software Solutions using

Developing the Beamline Video System
Software Solutions using Java Technology
Kenneth R. Sharp
Stanford Synchrotron Radiation Laboratory
January 8, 2002
Introduction
The simple user interface of the
Beamline Video System (left)
requires a complex n-tiered
client-server architecture to link
the user’s web browser to the
Axis Video Servers at the
beamlines.
This presentation examines the
implementation of that
architecture.
Component Architecture
HTML
Java
Applet
Java
Applet
JavaScript
JavaScript
Java
Applet
Java
Applet
Internet
SMB
Beamlines
Axis Server
(Hutch)
Axis Server
(Control)
Web Server
Java Servlets
Video System Goals and Challenges
Goals
•Web browser interface – no additional software for user to install
•Display selected views from multiple Axis servers in a single web page
•Limit beamline access to current user or staff
•Simple UI to change Presets, Image Size and Resolution
•Ability to Enable/Disable Camera View and Date/Time Stamp
•Display Current Preset Name as Video Caption
•Snapshot feature to capture images of user’s current crystal
Challenges
•Limited JPEG streams available from each Axis server
•“Server Push” works only with Netscape browsers
•Inability to use Apache web server Rewrite Rules
•Need to hide all Axis CGI calls from user-accessible HTML
•Need to synchronize User Authentication with BLU-ICE/DCS and Unix
•Mix of root and non-root Axis CGI calls
•Poor performance of Linux firmware on Axis servers
Video System Solutions
Java Servlets
•Middleware runs on SMB web server, uses Apache Tomcat
•Uses session objects to manage user access
•Proxies all requests from web browsers to Axis Servers
•Hides Axis Server IP Address and CGI Commands from User
•Has root access to Axis Servers
•Uses multiple threads to match image streams to user requests
Java Applets and Java Script
•Client software runs on web browsers
•Applets, compiled Java programs, use Client Pull to request
and display video images at up to 4 frames per second
•JavaScript, Java source code included in the HTML, handles
user interface events such as changing a preset from a dropdown menu
Video System n-tiered Architecture
Web Browser
SMB
MySQL Beamline
Configuration
Database
HTML &
JavaScript
Java Applets
Tomcat (Servlet
Container)
Video System
Servlets
Beamline 1
Axis Server
(Hutch)
Axis Server
(Control)
.
.
.
Apache
Internet
(User Authentication
and SSL)
Beamline n
Axis Server
(Hutch)
Axis Server
(Control)
BLU-ICE/DCS
•Video System directly calls Axis Server CGI to control
cameras and images. Video System does not use DCS.
•Video System and BLU-ICE/DCS both query Beamline
Configuration Database (MySQL) to match user to beamline.
•BLU-ICE retrieves images and controls camera presets by
direct calls to Axis Server CGI. BLU-ICE does not use DCS
for these purposes.
•BLU-ICE calls Java Servlet to update the image caption to
the new preset.
•Future versions of Video System may use DCS to provide
more sophisticated levels of control over the cameras.
Java and TCL
BLU-ICE is written in TCL (Tool Command Language) and C
In the Olden Days (Mid to Late 90’s)
•Scripting Languages (Perl, TCL, Python, etc.) were for “quick and dirty”
jobs connecting existing processes, rapid GUI development for Unix, or
simple CGI.
•Traditional Languages (C, C++, Java, etc.) were for applications that
implemented complex algorithms and data structures or were more
resource intensive. Users of these languages tended towards a more formal
approach to programming.
•TCL was Unix-only, extensible only with C, and did not implement such
things as multi-threaded applications.
Currently:
•The lines have blurred.
•Scripting languages are approaching traditional languages in terms of
broad application development capabilities.
•Traditional languages have tools that assist in rapid application
development.
•Java/TCL integrations (TCL-Blend and JACL) are available.
•Language selection is to some degree becoming a matter of personal
choice and experience
Advantages to Java
•Complete Object-Oriented Programming Language with
features such as: Strong-Typing, Encapsulation, Inheritance,
Exception Handling, etc. Syntax similar to C++, but simpler
•One language can be used for both client and server
applications.
•Fully featured Integrated Development Environments (IDEs)
available for editing, compiling, and debugging. Examples:
Webgain’s Visual Café, Borland’s JBuilder, IBM’s Visual Age
•APIs for: GUI, standard I/O, SQL Database queries, multithreading, socket/networking, etc.
•Portable – Java code is compiled to “bytecode” which is run
on various computers by system-specific Java Virtual Machines
(JVMs). Video System code was developed and tested on
Windows 2000 computer and ran untouched on SMB Irix
system. MySQL class library driver downloaded once and runs
on both Windows and Unix
Visual Café IDE
Types of Java Programs
•Command Line Applications
•Stand-Alone GUI Applications
•Servlets (applications running within web server
context)
•Applets (applications running within web browser
context)
•JavaScript (language variant with source code
included in HTML; run by web browser)
A Simple Command Line Application
public class HelloWorld {
public static void main(String[] args){
System.out.println("Hello World");
try {
System.out.println("Hello: " + args[0]);
} catch (ArrayIndexOutOfBoundsException e) {}
}
}
A Simple Stand-Alone GUI
import java.awt.*;
public class Frame1 extends Frame
{
public Frame1()
{
//{{INIT_MENUS
//}}
//{{REGISTER_LISTENERS
SymWindow aSymWindow = new SymWindow();
this.addWindowListener(aSymWindow);
SymAction lSymAction = new SymAction();
button1.addActionListener(lSymAction);
//}}
//{{INIT_CONTROLS
setLayout(null);
setSize(405,305);
setVisible(false);
label1.setText("Hello World?");
add(label1);
label1.setFont(new Font("Dialog", Font.BOLD, 16));
label1.setBounds(132,24,108,40);
checkbox1.setState(true);
checkbox1.setLabel("World");
add(checkbox1);
checkbox1.setFont(new Font("Dialog", Font.BOLD, 12));
checkbox1.setBounds(132,65,100,40);
textField1.setBounds(156,108,100,36);
label2.setText("Custom:");
add(label2);
label2.setFont(new Font("Dialog", Font.BOLD, 12));
label2.setBounds(96,108,60,40);
button1.setLabel("Say Hello");
add(button1);
button1.setBackground(java.awt.Color.lightGray);
button1.setFont(new Font("Dialog", Font.BOLD, 12));
button1.setBounds(132,184,84,40);
add(label3);
label3.setForeground(java.awt.Color.blue);
label3.setFont(new Font("Dialog", Font.PLAIN, 20));
label3.setBounds(120,225,192,40);
setTitle("AWT Application");
//}}
Java Servlets
•Execution controlled by Servlet Container (Tomcat)
•Simple implementation: by writing responses to HTTP GET and
POST requests
•Servlet responses can be HTML, images, or any other data that
would normally be returned by a web server
•Includes use of unique 128-bit session keys created for each
browser session. Session keys passed from browser via
“cookies” for each request from the server
•Servlet engine stores session data for each current session.
When user logs in, determine which beam lines are available to
that user and store data in session object. Each subsequent
request is matched against that object.
•Requests from browser contain no Axis-specific URLs or CGI
with which user might try to directly access video servers.
A Simple Servlet (code)
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class SimpleServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) {
try {
PrintWriter out = response.getWriter();
out.println("<HTML><HEAD><TITLE>A Simple Servlet</TITLE></HEAD>");
out.println("<BODY>");
out.println("<p><img src=/examples/ssrl.gif></p>");
out.println("Hello, World!");
out.println("</BODY>");
out.println("</HTML>");
} catch (IOException e) {
System.err.println("Error writing to web browser.");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response) {
doGet(request, response);
}
}
A Simple Servlet (result)
Applets
•Compiled Java Code
•Execution controlled by containing web page
•Generally, can only output to its graphic context within
its web page, and can receive input only from its web
page or from the user
•Generally, can only establish communications socket
with originating web server
•Appropriate security certificates can be created to allow
operations “outside the sandbox” with user permission
•Efficiency of operation depends on JVM implementation
of web browser
A Simple Applet
public class VidApplet extends Applet implements Runnable
{
public void start()
{
if (myThread == null && initOK)
public void run() {
{
int imageLen = 0;
myThread = new Thread(this);
while (true) {
myThread.start();
try {
}
myThread.sleep(1000);
}
} catch (InterruptedException e) {
System.out.println("unable to sleep.");
public void stop()
}
{
imageOK = false;
if (myThread != null)
okToPaint = false;
{
if (currImage != null) currImage.flush();
try {
mt.removeImage(currImage);
myThread.stop();
currImage = getImage(url);
} catch (SecurityException e) {}
mt.addImage(currImage, 0);
myThread = null;
try {
}
mt.waitForAll(5000);
}
if (!mt.isErrorAny()) {
imageOK = true;
<HTML><HEAD><TITLE><APPLET TEST></TITLE></HEAD>
}
<BODY>
} catch (InterruptedException e)
Hello World!<BR>
{System.out.println("ERROR!");}
<APPLET code="VidApplet.class" width="352" height="240"></APPLET>
repaint();
</BODY>
</HTML>
}
}
JavaScript
•Java Source code included with an HTML file
•Executed as page is loading or upon a programmed event
(such as Mouse Click or Keyboard Press)
•Syntax varies from standard Java to include web documents
•JavaScript and Java Applets within a single page may crosscommunicate with the appropriate programming
A Simple JavaScript Example
<HTML><HEAD><TITLE><JavaScript Example></TITLE>
<SCRIPT Language=JavaScript>
var userinput = prompt("To whom do you wish to say Hello?");
</SCRIPT>
</HEAD>
<BODY>
Here is your message:<BR>
<SCRIPT Language=JavaScript>
document.write("Hello <B>" + userinput + "!</B>");
</SCRIPT>
</BODY>
</HTML>
Video Stream Handling
1
1
1
Tomcat
1
n
n
n
n
1
1
1
1
n
n
n
n
Separate threads
handle each video
stream, storing the
latest image from
each stream in a
buffer. Requests from
applets running in
client web browsers
return individual
images from the
buffers.
A specific video
stream (beamline,
camera, size,
resolution) is created
on the first request
and runs until no
request has been
made for it for 10
seconds.
Beamline 1
Axis Server
(Hutch)
Axis Server
(Control)
.
.
.
Beamline n
Axis Server
(Hutch)
Axis Server
(Control)
Authentication Flow (1)
This is the control flow between the user’s browser and the server for authentication and page selection
Browser (HTML)
Browser (HTML)
Authentication
User Name
Apache
Tomcat
UserName
Tomcat
Browser (HTML)
Browser (HTML)
Browser (HTML)
Avail.
Beamlines
Beamline
Request
Video Page
Tomcat
Tomcat
Tomcat
Avail.
Beamlines
MySQL
Configuration
Database
Image Flow (2)
This is the control flow from each Java applet. Multiple applets are running concurrently from any number
of current users. Each applet displays a different video image.
Browser (Java)
Image
Request
Tomcat
Tomcat
Stream
Request
Axis Video
Server
Browser (Java)
Video
Frame
Tomcat
Video
Stream
Axis Video
Server
Browser (Java)
Image
Request
Video
Frame
Tomcat
Video
Stream
Axis Video
Server
Browser (Java)
No Request for
10 seconds
Tomcat
Video
Stream
Axis Video
Server
Tomcat
Terminate
Video
Stream
Axis Video
Server
Camera Control Flow (3)
This is the control flow from the user’s browser for Preset changes, Camera enable/disable, and
Date/Time enable disable. These requests are processed concurrently with the previous Image flow.
Browser
(JavaScript)
Control
Request
Tomcat
Tomcat
Tomcat
Browser
Request
Response
Tomcat
Control
Request (as
root)
Control
Response
Axis Video
Server
Axis Video
Server
Java and Bioinformatics
The following articles from Sun’s Java website illustrate ways
that Java is being used in the fields of Computational Biology
and Bioinformatics.
http://java.sun.com/features/2001/09/genome.html
http://java.sun.com/features/2001/10/genome2.html
Glossary
Apache – Commonly used web server software developed by the Apache Software Foundation and distributed for free
as “open source”.
CGI – “Common Gateway Interface”. Specification for programs called by web servers to return dynamic data. CGI
programs tend to be written in scripting languages such as Perl or TCL.
Client Pull – Typical web browser operation where all data from the server must be explicitly requested by the web
browser. Opposite of Server Push.
Client-Server – Software/Network architecture that separates executable elements into two or more connected tiers
which may run on different hardware resources.
CLI – “Command Line Interface”. A software program’s user interface made up of commands typed into a console
display.
GUI – “Graphical User Interface”. A software program’s user interface made up of windows and control elements, as
opposed to a CLI.
IDE – “Integrated Development Environment”. Software development tool used to code, compile, and debug programs.
Java – Software programming language developed by Sun Microsystems.
JVM – “Java Virtual Machine”. System software needed to run Java programs.
Java Servlets – Java-based alternative to CGI, used to return dynamically created html, images and data to web
servers. Requires a “Servlet Container” such as Apache Tomcat.
Java Applets – Java programs run within the context of a web browser.
JavaScript – Java code included within an HTML file to be run by a web browser.
Java Plug-Ins – Java Applets that are run by Sun’s Java Run Time JVM instead of a web browser’s built-in JVM.
JPEG – “Joint Photographic Experts Group”. A digital image format commonly used in web pages. The format of
images returned by Axis Video Servers.
Middleware – A middle tier of a client-server architecture which retrieves data from a server and passes it on to a client.
Typically handles business logic for a database server.
MySQL – Open Source relational database software that supports Stuctured Query Language (SQL) queries.
Server Push – Protocol in which a continuous data stream from a server can be processed by a web browser with no
programming needed. Resource heavy and works only with Netscape. Opposite of Client Pull.
Tomcat – An open source Java Servlet Container from the Apache Software Foundation. Integrates with the Apache
web server.
Thread – Execution of a portion of a software program that runs independently and that may run concurrently with
other portions of the same program.