Oas9i AS and Servlet

Dear OTN Readers and Oracle Support,
I am using OAS9i AS with Oracle 8i Database. I have some basic
questions:
1. Is there a way to deploy applications without using sess_sh
tool like some GUI frontend.
2. OAS9i has many ways to run servlets: JServ, OSE and
OC4J/J2EE.
Jserv do not even implement the current Servlet Specs although
OAS 4.8 used to and Apache have not updated it for a long
time. Is this okay to use Jserv or we should move to other
technology like OSE/OC4J.
3. How do we set session time outs in Servlets in OSE?
I did not find a way to read the config variables found
in wedcontexts. The only config value that I can read from
servlets is the ones defines while using publishservlet
command in sess_sh.
Please help. My email is: [email protected]
Thanks a lot,
Surendra

Anatoly,
You can request for AS but I am not sure if you will get IPv4 public space or not. Which location are you from? If Asia then you will need to contact APNIC and looks difficult to get IPv4 space since it is exausted. You will have to take IPv6 public space for the Internet connectivity. Time to upgrade your network to support IPv6 internet now. Also you will need to make sure that your hosts(PC) are capable of supporting IPv4 & IPv6 both stacks.
Also I assume that you want to do 6to4 NAT because NAT-PT has already been deprecated. NAT64 mechanism is generally used for the site-site communication or VPN traffic. I am not sure if you can use this for the Internet. Internet will have native IPv4 or IPv6 connectivity whether you perform private V4 to Internet V4 NAT or Site-local V6 to Internet V6 NAT.
I don't think you can do private V4 to public V6 NAT. Mean while you can have a small V4 subnet from your ISP and PAT all of your internal traffic to the Internet.
Regards,
Deepak Ambotkar

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Hello, I have a problem with my web service.
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The problem is that after I tried to integrate this service in an existing project. This project contains servlets. In these servlets, I'm using sessions.
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Hello, I have a problem with my web service.
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The problem is that after I tried to integrate this service in an existing project. This project contains servlets. In these servlets, I'm using sessions.
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But of course, it's not working by itself. I know there's something to do with the web.xml files.
The thing is that I created a web.xml file for the service, and another for the servlets.
I was thinking of joining both of them in one xml file, but everything crashes then...
Could someone tell me how to create a project with a web service and servlets, and mostly how to configure the xml file??
Thanks for any help
Philippe

Deploying a WAR file containing .jsp and servlets (also uses JNI)

Deploying a WAR file containing .jsp and servlets (also uses JNI) on Windows 2000
We had problems making it initially work on Sun ONE Web Server 6.0 Service Pack 1 because of lack of good iPlanet Web
Server documentation on deploying such files.
This is how we went about it:
1) Make one of the servlet and JSP (must call another Java Class) web application (.war) examples work with iPlanet Web
Server.
C:\iPlanet\Servers\plugins\servlets\examples\web-apps\HelloWorld\HelloWorld.war
and
C:\iPlanet\Servers\plugins\servlets\examples\web-apps\jakarta-examples\jarkarta-examples.war
a) Go to your Web Server Administration to deploy the application using GUI Web Application Deploy.
(We usually use command line, we experienced some issues with the GUI version, but maybe it is fixed in the new Web Server
service packs)
From browser, open http://yourserver:8888/
Click on Select a Server:Manage
Click on Virtual Server Class
Click on https-yourserver
Click on the Web Applications Tab
Then, click on Deploy Web Application
Enter the following -
WAR File On: Local
WAR File Path: C:\iPlanet\Servers\plugins\servlets\examples\web-apps\jakarta-examples\jarkarta-examples.war
Application URI: /jakarta
Installation Directory: c:\iPlanet\examples\jakarta-examples
By clicking on OK it deployed the application.
I can verify that it is deployed by selecting "Edit Web Applications" and I see the following entry:
Edit     /jakarta     c:/iPlanet/examples/jakarta-examples
Also, c:/iPlanet/examples/jakarta-examples should have the similar following directory structure ..
- [images]
- [jsp]
- index.html
- [servlets]
- [META-INF]
- [WEB-INF]
- [classes]
- [tlds]
- web.xml
- index.html
I restarted the server and accessed it using the following URL from my IE browser:
http://yourserver/jakarta/index.html
Then I clicked on the JSP Examples and tried some JSP examples.
b) Alternatively, you can also deploy the same example from the command-line.
Make sure C:\iPlanet\Servers\bin\https\httpadmin\bin\ is in your path
wdeploy deploy      -u /jakarta
          -i yourserver
          -v https-yourserver
          -d c:\iplanet\examples\jakarta-examples
          C:\iPlanet\Servers\plugins\servlets\examples\web-apps\jakarta-examples\jarkarta-examples.war
Restart the web server (I don't think you have to restart, but .. might as well).
2)Deploy your web-application
My Foo.war has the following structure.
You can use jar tf Foo.war to look at the file contents from command line (assuming you have JDK installed and the bin is
in your PATH)
Foo.war
- [META-INF]
- [WEB-INF]
- web.xml
- [classes]
- Bar.class
- MoServlet.class
- [lib]
- ThirdParty.jar
- [natlib]
- extlib.dll
- foo.jsp
Here is our application scenario:
foo.jsp uses a class call Bar (it is not in any package). The Bar java class uses classes from ThirdParty.jar. The
ThirdParty.jar in turn uses JNI to load library extlib.dll. foo.jsp also calls /servlet/Mo as well.
Now to deploy it, do the following:
(a) Make sure that within foo.jsp, you import the Bar class ( I don't know why you have to do it, but if you don't you get
JSP compile error).
<%@page language="java" import="Bar" contentType="text/html"%>
(b) Check web.xml (for Servlets)
Within web.xml, make sure you have the following mappings:
<servlet>
<servlet-name> MoLink </servlet-name>
<servlet-class> MoServlet </servlet-class>
</servlet>
<servlet-mapping>
<servlet-name> MoLink </servlet-name>
<url-pattern> /servlet/Mo </url-pattern>
</servlet-mapping>
(c) Deploy the application
Using command line:
wdeploy deploy      -u /foo
          -i yourserver
          -v https-yourserver
          -d c:\iplanet\examples\foo-dir
          Foo.war
(d) Change web-apps.xml file (for picking up ThirdParty.jar)
It is located in
C:\iPlanet\Servers\https-yourserver\config
You should see something similar to following after successful deployment.
<web-app uri="/foo" dir="C:\iPlanet\examples\foo-dir" enable="true"/>
Change it to look like following to pick up the ThirdParty.jar
<web-app uri="/foo" dir="C:\iPlanet\examples\foo-dir" enable="true">
<class-loader reload-interval="300"
          classpath="C:/iPlanet/examples/foo-dir/WEB-INF/lib/ThirdParty.jar"
          delegate="false"/>
</web-app>
(e) Change jvm12.conf file (for JNI)
It is located in
C:\iPlanet\Servers\https-yourserver\config
Add or uncomment the following lines:
#optional - just helps with instrumenting the jsp and servlet code
jvm.include.CLASSPATH=1
jvm.enableDebug=1
nes.jsp.enabledebug=1
jvm.trace=7
jvm.verboseMode=1
#required for JNI
java.compiler=NONE
jvm.classpath=.;C:\JDK1.3.1\lib\tools.jar;C:/iPlanet/Servers/plugins/servlets/examples/legacy/beans.10/SDKBeans10.jar;
jvm.option=-Xrs
jvm.option=-Xnoagent
# not sure if this is needed for iPlanet web server
jvm.option=-Djava.library.path=C:/iPlanet/examples/foo-dir/natlib/ -Djava.compiler=NONE
(f) Change magnus.conf file (for JNI)
We HAD to change this file in order for ThirdParty.jar file to pick up the native C++ code using JNI. Apparently, the
iPlanet Web Server doesn't pick the Environment Variable Path. Because when we had the directory containing the DLL just
in Path, it didn't work.
Change Extrapath directive:
ExtraPath C:/iPlanet/Servers/bin/https/bin;${NSES_JRE_RUNTIME_LIBPATH}
to
ExtraPath c:/iPlanet/examples/foo-dir/natlib;C:/iPlanet/Servers/bin/https/bin;${NSES_JRE_RUNTIME_LIBPATH}
(g) Apply changes from the Web Server Administration Console and Restart the web server.
You should be able to see the behaviour that you want from your application.
http://yourserver/foo/foo.jsp
Hope this was helpful!!!
Sonu

Deploying a WAR file containing .jsp and servlets (also uses JNI) on Windows 2000
We had problems making it initially work on Sun ONE Web Server 6.0 Service Pack 1 because of lack of good iPlanet Web
Server documentation on deploying such files.
This is how we went about it:
1) Make one of the servlet and JSP (must call another Java Class) web application (.war) examples work with iPlanet Web
Server.
C:\iPlanet\Servers\plugins\servlets\examples\web-apps\HelloWorld\HelloWorld.war
and
C:\iPlanet\Servers\plugins\servlets\examples\web-apps\jakarta-examples\jarkarta-examples.war
a) Go to your Web Server Administration to deploy the application using GUI Web Application Deploy.
(We usually use command line, we experienced some issues with the GUI version, but maybe it is fixed in the new Web Server
service packs)
From browser, open http://yourserver:8888/
Click on Select a Server:Manage
Click on Virtual Server Class
Click on https-yourserver
Click on the Web Applications Tab
Then, click on Deploy Web Application
Enter the following -
WAR File On: Local
WAR File Path: C:\iPlanet\Servers\plugins\servlets\examples\web-apps\jakarta-examples\jarkarta-examples.war
Application URI: /jakarta
Installation Directory: c:\iPlanet\examples\jakarta-examples
By clicking on OK it deployed the application.
I can verify that it is deployed by selecting "Edit Web Applications" and I see the following entry:
Edit     /jakarta     c:/iPlanet/examples/jakarta-examples
Also, c:/iPlanet/examples/jakarta-examples should have the similar following directory structure ..
- [images]
- [jsp]
- index.html
- [servlets]
- [META-INF]
- [WEB-INF]
- [classes]
- [tlds]
- web.xml
- index.html
I restarted the server and accessed it using the following URL from my IE browser:
http://yourserver/jakarta/index.html
Then I clicked on the JSP Examples and tried some JSP examples.
b) Alternatively, you can also deploy the same example from the command-line.
Make sure C:\iPlanet\Servers\bin\https\httpadmin\bin\ is in your path
wdeploy deploy      -u /jakarta
          -i yourserver
          -v https-yourserver
          -d c:\iplanet\examples\jakarta-examples
          C:\iPlanet\Servers\plugins\servlets\examples\web-apps\jakarta-examples\jarkarta-examples.war
Restart the web server (I don't think you have to restart, but .. might as well).
2)Deploy your web-application
My Foo.war has the following structure.
You can use jar tf Foo.war to look at the file contents from command line (assuming you have JDK installed and the bin is
in your PATH)
Foo.war
- [META-INF]
- [WEB-INF]
- web.xml
- [classes]
- Bar.class
- MoServlet.class
- [lib]
- ThirdParty.jar
- [natlib]
- extlib.dll
- foo.jsp
Here is our application scenario:
foo.jsp uses a class call Bar (it is not in any package). The Bar java class uses classes from ThirdParty.jar. The
ThirdParty.jar in turn uses JNI to load library extlib.dll. foo.jsp also calls /servlet/Mo as well.
Now to deploy it, do the following:
(a) Make sure that within foo.jsp, you import the Bar class ( I don't know why you have to do it, but if you don't you get
JSP compile error).
<%@page language="java" import="Bar" contentType="text/html"%>
(b) Check web.xml (for Servlets)
Within web.xml, make sure you have the following mappings:
<servlet>
<servlet-name> MoLink </servlet-name>
<servlet-class> MoServlet </servlet-class>
</servlet>
<servlet-mapping>
<servlet-name> MoLink </servlet-name>
<url-pattern> /servlet/Mo </url-pattern>
</servlet-mapping>
(c) Deploy the application
Using command line:
wdeploy deploy      -u /foo
          -i yourserver
          -v https-yourserver
          -d c:\iplanet\examples\foo-dir
          Foo.war
(d) Change web-apps.xml file (for picking up ThirdParty.jar)
It is located in
C:\iPlanet\Servers\https-yourserver\config
You should see something similar to following after successful deployment.
<web-app uri="/foo" dir="C:\iPlanet\examples\foo-dir" enable="true"/>
Change it to look like following to pick up the ThirdParty.jar
<web-app uri="/foo" dir="C:\iPlanet\examples\foo-dir" enable="true">
<class-loader reload-interval="300"
          classpath="C:/iPlanet/examples/foo-dir/WEB-INF/lib/ThirdParty.jar"
          delegate="false"/>
</web-app>
(e) Change jvm12.conf file (for JNI)
It is located in
C:\iPlanet\Servers\https-yourserver\config
Add or uncomment the following lines:
#optional - just helps with instrumenting the jsp and servlet code
jvm.include.CLASSPATH=1
jvm.enableDebug=1
nes.jsp.enabledebug=1
jvm.trace=7
jvm.verboseMode=1
#required for JNI
java.compiler=NONE
jvm.classpath=.;C:\JDK1.3.1\lib\tools.jar;C:/iPlanet/Servers/plugins/servlets/examples/legacy/beans.10/SDKBeans10.jar;
jvm.option=-Xrs
jvm.option=-Xnoagent
# not sure if this is needed for iPlanet web server
jvm.option=-Djava.library.path=C:/iPlanet/examples/foo-dir/natlib/ -Djava.compiler=NONE
(f) Change magnus.conf file (for JNI)
We HAD to change this file in order for ThirdParty.jar file to pick up the native C++ code using JNI. Apparently, the
iPlanet Web Server doesn't pick the Environment Variable Path. Because when we had the directory containing the DLL just
in Path, it didn't work.
Change Extrapath directive:
ExtraPath C:/iPlanet/Servers/bin/https/bin;${NSES_JRE_RUNTIME_LIBPATH}
to
ExtraPath c:/iPlanet/examples/foo-dir/natlib;C:/iPlanet/Servers/bin/https/bin;${NSES_JRE_RUNTIME_LIBPATH}
(g) Apply changes from the Web Server Administration Console and Restart the web server.
You should be able to see the behaviour that you want from your application.
http://yourserver/foo/foo.jsp
Hope this was helpful!!!
Sonu

Need help in JSP and Servlets

Hi friends,
[please forgive me if i am posting this in the wrong forum, all seems same to a fresher]
Now, to my problem..i need a suggestion, a way or a method to implement the following!
I am supposed to create a servlet that reads data from oracle database. Once i retrive the data (for example: 6 rows of a table having 4 attributes), i am supposed to pass this data to a JSP page where the data has to be formatted and displayed properly. If i call the same servlet from a different JSP, i should be able to access the data in that JSP and format it in a different way. How do i pass the data to JSP? what method i can use to achieve this task?
Note: I already know about PrintWriter pw = response.getWriter(); and then printing the formated HTML page..but i want to keep the formatting to JSP part and send only the data part that i can access in JSP
Thanks in adavance

arun_ramachandran wrote:
[please forgive me if i am posting this in the wrong forum, all seems same to a fresher]Then you should learn to be more observant - after all, we have JSP and Servlet fora, further down the list. :)
I am supposed to create a servlet that reads data from oracle database. Once i retrive the data (for example: 6 rows of a table having 4 attributes), i am supposed to pass this data to a JSP page where the data has to be formatted and displayed properly. If i call the same servlet from a different JSP, i should be able to access the data in that JSP and format it in a different way. How do i pass the data to JSP? what method i can use to achieve this task? You can store the data in your session object. You can even use JavaBeans and the jsp:usebean tag.
[http://java.sun.com/products/jsp/tags/11/syntaxref11.fm14.html]
Note: I already know about PrintWriter pw = response.getWriter(); and then printing the formated HTML page..but i want to keep the formatting to JSP part and send only the data part that i can access in JSPA wise approach - I wish more prople woiuld be as thoughtful.

How to upload a file into server using j2ee jsp and servlet with bean?

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mani

hi,
soory for late reply.
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Hi all,
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files of the war file and the class files in the war file are not reaching to
the EJBs. Please let me know at the earliest.
Atanu

Hi.
You might try looking at the petstore example which combines webapps (war files) with
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Regards,
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Atanu Dey wrote:
Hi all,
How can I add a classpath to EJB and Servlets in Weblogic 6.1, so that that classpath
can be achieved by both EJB jar and war file? I have deployed a .ear file having
the jar and war files. Now the EJBs inside the jar file are not reaching the class
files of the war file and the class files in the war file are not reaching to
the EJBs. Please let me know at the earliest.
Atanu--
Michael Young
Developer Relations Engineer
BEA Support

How to setup my computer to run JSP and Servlets

I want to setup my computer to run JSP and Servlets.
What kind of Servers and other tool i need to install to run JSP and Servlets.
Plz, Help me to start my work on JSP.
Regards,
Usman Ali

hello
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1st, you should have two computers: one is server and the other is local workstation. This server should have a static IP address, that other people can go into your server. Workstation is any computer normal you use it.
2nd, you need to setup your server in: OS(linux or windows 2000), web server (jrun, apach or Tomcat etc. ), as well as install JDK, servlet.
3rd, your local workstation just use as programming editor and open a browser to testing, anytime you write your code, then ftp to server to test.
Reality, you have many technical thing to solve, eg setup web server etc. However, you can write your source code and test it, then open to outside people.
hope to helpness, if anything don't uderstand, you can post again or send email to me [email protected] Since I just have setup this configuration in my university for my project.

Load balancing for JSPs and servlets

Hi:
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          cluster. This provides round robin load balancing just fine. Will it
          provide weight based load balancing if I set 'weblogic.system.weight'
          differently on each server, or is that not relevant for clustering JSPs
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          Sincerely,
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Currently the plugins ( for NES, IIS and Apache) just use the round robin
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          To use this property for your JSP/Servlet load balancing you have to use
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          Ashish Vimal wrote:
          > Hi:
          > I am using IIS as the proxy server, with the WLS plug-in, to a WLS
          > cluster. This provides round robin load balancing just fine. Will it
          > provide weight based load balancing if I set 'weblogic.system.weight'
          > differently on each server, or is that not relevant for clustering JSPs
          > and servlets?
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Which tutorials may you suggest for JDBC and servlets?

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e.g. How to make a servlet etc.
Thanks, in advance!

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Here is a tutorial that has both concepts in it at the same time. Site is down now, but is usually up. http://www.roseindia.net/jdbc/jdbcconnectivity.shtml
Also, you will eventually want to download a J2EE container such as Tomcat or Jboss.
- Saish

Basic jsp and servlet question (JSP Model 2)

Hi
I want to make an website where i use JSP Model 2 architecture. However I got a basic question
1. I need to separate business logic from presentation with the use of jsp and servlets. Meaning I want no html code in the servlet. Can you give a simple example of how this can be done? If I map my implementation of httpServlet to a jsp page in web.xml and override doPost() and doGet(). The calls to the jsp page comes to the servlet as it should. I want to process some methods (calling sessionbeans or similar which in turn calls entitybeans) and then show the jsp page.
How do I show the jsp page without mixing html in the servlet as I've done below:
doGet(HttpServletRequest req, HttpServletResponse res)
PrintWriter p = response.getWriter();
p.print("<html><body>Hello world</body></html>"); //I dont want to do //this, I want to display the JSP site
doPost(HttpServletRequest req, HttpServletResponse res)
//doSomething
}Message was edited by:
CbbLe

You should treat your servlet class much like a controller, where you can then use JSP as the view. The way you achieve this is to use the forward() method in RequestDispatcher.
Say you've got a servlet class org.yoursite.controller.YourController:
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
//Set some value for use in the JSP file associated wth me
req.setAttribute("greeting", "Hello world!");
//Done with our business logic, off we go to the JSP file
ServletContext app = getServletContext();
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    disp = app.getRequestDispatcher("/some/jsp/file.jsp);
    disp.forward(req, resp);
}Now in your JSP file:
<h1>Example</h1>
<div>
I just want to say <%= request.getAttribute("greeting") %>
</div>Going to that servlet now executes business logic and then points to the JSP file for the view. You can forward from servlet to servlet too if needs be. The string you pass to forward() is whatever would be in the URI of the request so any <servlet-mapping> configurations in web.xml are used ;)
There is some pretty in-depth documentation on the J2EE blueprints website, namely service-to-worker and front-controller patterns. I dare say if you're looking for this sort of code you'll want to look at the composite view pattern too (also on blueprints).

EJB and Servlets

Hi there,
A frontend processing of HTTP request that pass thru WebLogic server that make
API calls thru tuxedo to the application servers that eventually running C, C++
that retrieve data from a backend database of Oracle.
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Thanks
Neo

Sorry, wrong question, just ignore it.

Third-party jars not visible to EJB's and servlets.

Hi, This is an unanswered post in an newsgroup which exactly displays our
current problem,
Extract Begins -->
"I've got a WebApp with classloading issues while running WebLogic 5.1.
According to the JSDK 2.2 API, if I include third-party classes in
WEB-INF/lib, my EJBs and servlets should be able to load any jar'ed classes
inside. In practice, however, it seems to make no difference. My EJB always
comes back with a NoClassDefFound error for xerces.jar that's in WEB-INF/lib
(and I've even tried adding it to the EJB JAR itself with no change).Of
course, if I put Xerces in the server's classpath, there are no problems but
that's a road I don't want to go down.How can I tell my EJB's to load
third-party classes from the WEB-INF/lib directory of the WAR file? I'd
appreciate your insight. <-- End
We are busy migrating one of our apps from 5.1 to 6.1, What we have done
thus far and fairly successfully is the following,
We packaged all the jsps, WEB-INF, html, images into a WAR file and then
packed all EJB's, META-INF and classes to which the ejbs refer, into an EAR
file.
EMARKET_APPS/
+myjsp.jsp
+myhtml.html
+images
+WEB-INF/+
|
+classes/+
|
+myclass1.class
+myclass2.class
|
+lib/+
|
+OReily.jar
+jts.jar
+xerces-1_4_1.jar
+junit.jar
+jcschart110Kwl.jar
|
+web.xml
+weblogic.xml
+META-INF/+
|
+applications.xml
+ejbs/+
|
+myejb1.jar
+myejb2.jar
+lib/+
|
+classes.jar
Please advise.
Rgs Roly

Have you tried to include the jars in the Class path entry in the manifest file.
That should work eventhough I haven't tried it yet (fighting with ear deployement
and I must say WLS seems to be winning). I'll get back to when I've tried it.
There is a VERY good article on theserverside.com regarding class loaders and
EAR/WAR/EJBs at http://www.theserverside.com/resources/articles/J2EE-Deployment/chapter.html
Good luck
/erik

MVC JSP and Servlets

I'm creating JSP pages to represent the view of the site and servlets to get the request and decide which JSP page to load next.
When the servlet recibes a request it generally has to query the database to get some data and then show it back to the client. To do this the servlet calls other object that is responsible to query the database and fill a ResultSet.
My question is: what is better, to load a Vector with special objects containing the data in the ResultSet and then return this vector to the jsp page for it to use it, or may a return directly the ResultSet to the jsp page? With the first option I have to cycle in the resultSet to load the vector and then cycle through the vector to show the results. With the second option I cycle only once, but I isolate from the database (column names, order in which the things are returned...)
I hope anybody can give me an opinion.
Thanks

There are a few things wrong with this:
1) MVC -> The View should have no Model work init.
For the MVC pattern, the database is Model. Use
a
a ResultSet in JSP, and now your View is lockedto
a
database with a specific column format.
Huh? I think that's backwards. The View willalmost
always require Model data unless it is a staticpage.
The Model, however, should be agnostic about what
t View technology it serves. (The Controllerbridges
the two). Also, I would call the database the
Persistence or Integration tier, a separateconcept
from the Model, though intimately coupled to it.I meant the work of the model (gathering the data to
a presentable form) is moved to the View. Yes, the
View needs to know the Model to be able to display
its data. But the Model should handle the data
collection.
Fair enough. I might have read it backwards as well.
>>
2) Any web application (or any application in
general) wether it uses MVC or not, should still
follow a 3 tier approach: Persistance (Data),Domain
(logic), Presentation (View, output) (note, thisis
different then MVC.) By moving the ResultSet inthe
JSP you would be dragging the Persistancemechanism
up two layers. Generally, a layer should only
see
the layer just below it (Presentation seesDomain.
Domain sees Persistance. Persistance never sees
s Domain or Presentation. Domain never sees
Presentation. Presentation never seesPersistance).
>
I agree that Persistence and View should not seeeach
other. However, Model and Persistence must. How
else do you write a DAO? Or even use a mapperlike
Hibernate?First the Model doesn't fit into just one of the
three tiers (Persistance Domain and Presentation).
The Model of MVC is both the Domain logic and the
e Persistance mechanism.
To me, at least, Domain logic = model. The terms I have normally read is either "business tier" or "model domain". "Patterns of Enterprise Application Architecture", M. Fowler. Though, I will concede that this tier has the least well defined set of terms.
But for the three tier architecture: the domain sees
the persistance. You always see one layer down. So
Domain sees the persistance and pulls the data into
the model. So a DAO would be part of the Domain, the
logic of collecting the data from the database to be
used in the application (in the correct object graph
and all that). The persistance though, doesn't see
the domain.
Hmm, I'm not sure which direction 'down' is. And even if 'down' meant towards the back-end or away from it, what about the controller? It parses view requests and delegates them to the model. The results are then normally returned to the controller for dispatch to a view. So, the controller seems to have its fingers in all the tiers except integration and persistence, at least to me. I think of the controller as the 'middle man' between model and view that lets the model be agnostic to the view. The view and controller will to some extent always be coupled. However, the model theoretically exists on its own.
Half of me thinks that I have a different view on
where the Domain and Persistance border is. I
thought the DAO or the Data Mapper would be in the
Domain, whereas you seem to be saying they are in the
Persistance layer?
That's interesting. I don't know if there is an absolute answer. We are dealing with the O/R boundary, and the DAO straddles the boundary. However, one could, at least theoretically, change persistence strategies. What would change? Not your model objects, but your persistence tier objects. Though, again, the definition is nebulous.
3) From a Practical matter:
In many DBs, if you close the connection fromwhich
the ResultSet was derived, the ResultSet is
closed
and you get errors if you try to access it. Ifyou
don't close the connection in the Servlet beforeyour
JSP, then you have to do it in the JSP. Thatmeans
even more DB bleed through to the JSP, and theM->V.
Or, you could just not close the Connection and
d allow it to hang around and create memory
leaks.
>
Yepper.
4) Also practical:
To use the ResultSet in JSP is going to require
scriptlet code. This is ugly and hard to manageand
update later. You have to wrap your code in
try{}catch(SQLException e) {} finally {}, so
the
code is even uglier and harder to manage(especially
if you end up not touching the thing for monthsand
forget what you had done - or god forbid someoneelse
has to keep up your code). You could make acustom
tag to handle it, which makes the JSP easier toread,
but does further damage of spreading the dataaccess
code all over the application.
Definitely!
5) Practical:
When you do this sort of thing, then later
decide
to
change the way the database is set up, digging
all
the places affected by the simple renaming of a
column, or refactoring of which columns are inwhich
tables becomes a heavy effort. Keep it all in a
DataAccessObject, and changes in DB becomestrivial
to keep track of in your code. It is all in one
place, and can be tested off line. Harder stillis
if you change persistance from a database to anXML
library, or some directory lookup or something.You
would have to completely refactor your Servlet
and
your JSP. Put it in a DataAccessObject and allyou
have to do is switch out the DAO instance. The
change is transparent to the Servlet and the JSPas
long as you maintain an interface.
Just keep in mind that for the vast majority of
projects, the RDBMS technology is rarely switched.I
generally program to interfaces in my Model, butmy
Persistence tier is always so tightly coupled thatI
simply use POJO's without an interface.
6) Practical:
I have elluded to this several times, but I will
state it specifically. When you isolate the
persistance and data access to its own layer
then
you
can swap out the presentation (the View and the
Controller) when testing all your persistance
operations. This means the data is independent
of
the container. You can run it out of theServlet/JSP
environment and it will behave EXACTLY as it
will
inside the JSP environment. You can designrobust
tests, debug, redesign, re-edit, etc... muchquicker.
Then, when all done, plug it into your web app
p without worry.
Great point.
Of course, Numbers 3 -> 6 are the reasons why
following 1->2 (MVC and the 3 Tier architecture)are
such good ideas.- Saish
BTW, please take all the above just in the interest of having a good discussion. I have been wrong many times before! ;^)
- Saish

Oas9i AS and Servlet

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