Objectivity/DB and JAVA
Objectivity/Java
Installation on NT and access on AFS
Objectivity/Java
Documentation
Interesting information: tools, applets, ... implemented using Objectivity/DB and Java (including code):
Objectivity/Java
- The platforms supported for Objectivity 5.0/JAVA are indicated here.
NOTE: SOLARIS AND NT ONLY !
Objectivity for Java requires that you have access to following software:
Objectivity/DB
Objectivity for Java
Java Development Kit
(JDK) Release 1.1.3 or higher.
You can access to the Objectivity/JAVA product directly (via NICE or AFS).
If you do not have access to the previous installations you have to
install the Objectivity product locally:
- To install the complete product click here
.
- To install the Objectivity/JAva click here
.
Check that the installation is fine by running
an example.
- 1. If you have already a local installation of the Objectivity/DB
product but not the Java API you just have to run the setup.exe
installation program and choose from the menu window the following option:
- Objectivity for Java
2. Add the Objectivity for Java library path
- CLASSPATH installDir\lib\oojava.jar
from NICE: at the moment Objectivity
5.0 with the Java API is not installed . You should install
Objectivity/DB locally in your NT system. You can access to JDK 1.1.5
from NICE.
from AFS in Solaris:
You can access to Objectivity/JAVA 5.0 -Solaris directly by calling the RD45 scripts, they set also the access to JDK1.1.6.
Bourne Shell syntax:
-
export OBJY_VERS=5.0;
- source /afs/cern.ch/rd45/objy/objyenv.sh
- C Shell Syntax:
- setenv OBJY_VERS 5.0
source /afs/cern.ch/rd45/objectivity/objyenv.csh
- C Shell Syntax
- #JAVA settings to use another version of JDK different
from JDK1.1.6
setenv JAVA_HOME "/usr/local/libexec/jdk/<version>"
setenv PATH "${JAVA_HOME}/bin:${PATH}"
setenv CLASSPATH ".:/afs/cern.ch/sw/lhcxx/specific/sun/Objectivity/5.0/java/lib/
oojava.jar:${JAVA_HOME}/lib/classes.zip:${CLASSPATH}"
setenv LD_LIBRARY_PATH "${JAVA_HOME}/lib:${LD_LIBRARY_PATH}"
- Note: Make sure that the path to JDK
and Objectivity class library for Java are set properly.
1.Compile the files Vehicle.java , Fleet.java , VrcInit.java
, and Vrc.java located in the GettingStarted subdirectory of the programming
samples directory.
- javac VrcInit.java
javac Vrc.java
Note: you may get the error:
- SIGSEGV 11*
segmentation violation
si_signo [11]: SIGSEGV 11* segmentation violation
si_errno [0]: Error 0
si_code [1]: SEGV_MAPERR [addr: 0xad7ae2bc]
stackbase=EFFFE9A0, stackpointer=EFFFE6E0
Objectivity for java in Solaris uses the system native threads, while the java virtual machine, by default, starts using green threads. To specify to the virtual machine that you want to use native threads, you should specify following flag:
> java -native YourClass
The bytecodes will be generated and stored on the .class files. In GettingStarted
directory you will have following files :
- Fleet.class
Fleet.java
Vehicle.class
Vehicle.java
Vrc.class
Vrc.java
VrcInit.class
VrcInit.java
- d:\installDir\java\samples\GettingStarted\oolockserver
- d:\installDir\java\samples\GettingStarted\oonewfd -fdfilepath
D:\objy50\docs\java\samples\GettingStarted\Vrc.fdb
-lockserverhost <your host> Vrc
- Objectivity/DB (TM) Create Federated Database Utility, Version
5.0 Build: 58
Copyright (c) Objectivity, Inc 1993, 1998. All rights reserved.
Federated Database "Vrc" created.
- D:\objy50\docs\java\samples\GettingStarted>oodumpcatalog Vrc
Objectivity/DB (TM) List Database Files Utility, Version 5.0 Build:
58
Copyright (c) Objectivity, Inc 1990, 1998. All rights reserved.
FD Name = Vrc
FD ID = 1
FD File = pc-01::D:\objy50\docs\java\samples\GettingStarted\Vrc.fdb
Boot File = pc-01::D:\objy50\docs\java\samples\GettingStarted\Vrc
Jnl Dir = pc-01::D:\objy50\docs\java\samples\GettingStarted
Lock Host = pc-01
4.Execute VrcInit to initialize the federated database.
- d:\installDir\java\samples\GettingStarted\java VrcInit
Created database
"VehiclesDB".
Created container "VehiclesContainer".
Added vehicle: License:CA1234 Class:G Doors:4
MANUAL Rate:40
Added vehicle: License:CA7654 Class:H Doors:4
AUTOMATIC Rate:40
Note: You can find more information about this
example in the "Getting Started" chapter of the Objectivity for Java doucmentation.
You will find other examples as indicated in
the "Programming Examples" chapter.
5. Use oobrowse (in NT) or ootoolmgr (in UNIX) to browse
the database VehiclesDB.
- d:\installDir\java\samples\GettingStarted\oobrowse Vrc
Documentation
You can find all java documentation on html and pdf in following directories of the Objectivity installation:- java/index.html
java/api/*.html
java/guide.pdf
- java/samples/GettingStarted/*.java
Tools
DRO-TOOL- It is a Federated Database Configuration Management tool for
Objectivity/DB written in java.
Developed at CERN/IT/ASD/RD45
Applets
- You cannot open a Objectivity/DB federated database directly
from an applet due to a security exception with the browser.
In principle, it should be possible to open a federated database from a browser if you specify a boot file archive and an autonomous partition residing in the web server host, you only try to open a socket connection between the applet and the web server, but it crashes when loading the oojava.jar file. If you use the appletviewer instead the applet is working perfectly.
There are some others methods to access to a federated database from
an applet that helps you to solve this security problem. Two of them (agents
and servlets) are discused in following
agents section. The third method is using CORBA. Anyway the
philosofy is the same. You have a program running in the web server that
communicates with the applet and accesses to the federated database.
Agents
- Another use of agents is to access to an Objectivity/DB from the web
but it is not possible to do this directly from an applet,
The other type of agent we have developed is to access to Objectivity/DB federated databases from the web. From a Java Applet, you cannot open a federated database and work with it due to security restrictions in the browser, but using agents it is possible!
The structure of an application using agents would be the following one:
You could force your application to communicate with the federation
only using the AMS server, but even in this case, you will get a security
exception in the browser.
In this case, the agent implements all the methods for accessing the database. The Java applet starts a voyager server, and sends an agent to the host where the database resides. An applet can only communicate with the server in which the web page resides. To avoid this limitation, voyager implements a router service. All the messages sent to any agent will pass through this server. With it, you can create a voyager server in the same host as the web server, and use it as a router. Agents created in applets will have no address limitation, and can be sent and communicate with any host without any special restriction.
As the applet need to have access to the Objectivity for Java bindings, the agent must implement all those methods. Objectivity/DB for Java binding must be installed in the host where the agent will be sent (but it is not needed in the host where the applet is running or even in the web server host).
With Objectspace’s Voyager 2.0, the Java classes that will be used as agents don’t need to specify any special voyager code. Once you create a class, you must create an interface for this class. To do that, you can use the ‘igen’ program that comes with voyager. It will automatically generate the interface. In the applet, once you have created the agent with the Factory.create() method, you can access to the remote class as if it was local.
The clients need only a Java capable browser, where they execute an applet. In the client side, you don’t need any special software to access to Objectivity Databases, or any agent packages. All the classes required by the applet will be loaded from the web server.
The main steps of the application are:
1. Applet bytecodes are loaded from the web server into the browser.
2. The applet starts an agent, and send it to a remote host.
3. Depending of the agent task, it will check for the status of one
of the servers or both, or to retrieve the data of a database locally and
perform some analysis to this data.
While the agent is doing a task, the client doesn’t need to stay connected
to the network. The client can connect later to monitor the task, or to
retrieve the final result, once the task is done.
More information about agents you can find it here:
Commented code
example of an applet that retrieves information from a
federated database. Requirements to run following code: Objectivity
5.0, Voyager 2.0.0 and jdk1.1.7
Servlets
- The original standard for server-side scripts is CGI or Common Gateway
Interface. CGI is simple and widely supported. The main problem with CGIs
is that is not very efficient because the server launches one copy of the
script per request and the overhead can be significant. Vendors have developed
proprietary alternatives such ISAPI (Microsoft) and NSAPI (Netscape) to
address the performance issue. JavaSoft proposed the Java servlets as a
standard efficient alternative to CGI.
Servlets are server-side Java programs that provide a means of generating dynamic Web content. They are not standalone applications that can be executed from the command line; instead, they run within Web servers. In order to run servlets inside a Web server the server must have a Java Virtual Machine running within itself. Unlike applets, servlets are not constrained by security restrictions. They have the capabilities of a full-fledged Java program and can access files for reading and writing, load classes, change system properties, etc. They are restricted only by the file system permissions, just like other Java application programs.
A servlet is loaded the first time it is used, and it remains in memory
for later requests. It has an init method, where you can initialise the
state of the servlet, and different methods for the different calls (doGet,
doPost, doPut, doDelete). There is also a destroy method to manage the
resources that are held by the servlet.
You can use a servlet to perform typical server-side processing. The
servlet can communicate with the client computer and it can also communicate
with other remote, networked computers.
Java servlets have full access to Java's networking features. The servlets can connect with other networked computers using sockets or Remote Method Invocation (RMI). Also, the servlet can easily connect to an Objectivity/DB using the Objectivity Java bindings. The main restriction using Objectivity federated databases is that you can only work with one federated database. As the Java bindings from Objectivity/DB uses static methods keep the information about the federated database currently opened, only one federated database can be opened per virtual machine. But the servlets are all executed in the same VM, so you can only have one federation per server.
One possible solution for this restriction can be done with the help of agents. As said before, a servlet has no special restrictions, so it can begin a new VM, and start there an agent server. Then the servlet can send there an agent that will open the federated database, and work with it. This solution let you open more than a federation using the same servlet, but you will have the same performance problem than using CGIs: start a new shell (in our case, a new VM) per request.
Follows an example code of a servlet that shows the database information
of a federated database. When you first call the servlet, it shows you
a form and asks for the boot file of the federation. Then, the servlet
tries to open the federated database, and retrieve the information concerning
the autonomous partitions, databases and containers of the federation.
Atention: Once you specify a boot file, it will always show the information
of the same federated database, even if you specify a different boot file
later.
Example
code of a servlet here !
Requirements to run following code: Objectivity 5.0,
Voyager 2.0.0 and jdk1.1.7
Java
Analysis Studio
Developed at SLAC/BaBar.
WIRED
Developed at CERN/IT/IPT.
Your comments about this page are welcome ! Please send us a mail.
If you have any applet that you think would be useful
for the physics community and you would like to share it please send it
to us, we will make it accessible to everybody.