JSP, Servlet and RMI

HI,
I have developed a simple interface to start and stop a java application.
In practice I have a command panel (a JSP page) that communicates with a servlet that through RMI is able to start and stop my external java application.
JSP and servlet are under Tomcat.
Here are my codes:
JSP:
<%@ page language="java" session="true" autoFlush="true" isThreadSafe="true"
contentType="text/html; charset=ISO-8859-1" isErrorPage="false" %>
<html>
<head>
<title>Untitled Document</title>
</head>
<body>
<form action="controlpanel" method="get" name="pannello" id="pannello">
<p>
<select name="op" size="1" id="op">
<option value="start" selected>start</option>
<option value="stop">stop</option>
</select>
</p>
<p>
<input type="submit" name="Submit" value="Submit">
</p>
</form>
</body>
</html>
SERVLET:
* Created on 03-Dec-2003
* To change the template for this generated file go to
* Window - Preferences - Java - Code Generation - Code and Comments
package servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.rmi.Naming;
import java.rmi.RMISecurityManager;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import server.Mmce;
* @author root
* To change the template for this generated type comment go to
* Window - Preferences - Java - Code Generation - Code and Comments
public class CommandPanel extends HttpServlet
     protected void doGet(HttpServletRequest request,
               HttpServletResponse response) throws ServletException, IOException
          String operation = request.getParameter("op");
          log("OPERAZIONE="+operation);
          PrintWriter out = response.getWriter();
          if (System.getSecurityManager() == null)
               System.setSecurityManager(new RMISecurityManager());
          try
               Mmce comp=(Mmce)Naming.lookup("rmi://192.168.1.113/Mmce");
               if (operation.equalsIgnoreCase("start"))
                    comp.start();
               else
                    comp.stop();
          catch (Exception e)
               log(e.getMessage());
               StackTraceElement[] el = e.getStackTrace();
               String errore = "";
               for (int g = 0; g < el.length; g++)
                    errore += el[g].toString()+"\n";
               log(errore);
          finally
               response.setContentType("text/html");
               log("Write html");
               RequestDispatcher rd = request.getRequestDispatcher("/panel.jsp");
               rd.forward(request,response);
// Follow part is commented
/**out.println("<html>");
               out.println("<head>");
               out.println("<title>Pannello di comando</title>");
               out.println("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=iso-8859-1\">");
               out.println("</head>");
               out.println("<body>");
               out.println("<form action=\"controlpanel\" method=\"get\" name=\"pannello\" id=\"pannello\">");
               out.println("<p>");
               out.println("<select name=\"op\" size=\"1\" id=\"op\">");
               out.println("<option value=\"start\" selected>start</option>");
               out.println("<option value=\"stop\">stop</option>");
               out.println(" </select>");
               out.println("</p>\n<p>");
               out.println("<input type=\"submit\" name=\"Submit\" value=\"Submit\">\n</p>");
               out.println("</form>\n</body>\n</html>");
All works fine for two times in that I start and stop application. At the third time, when i start my application from jsp, I receive this Tomcat error:
type Status report
message /panel.jsp
description The requested resource (/panel.jsp) is not available.
like the jsp could not be reachble.
If I try to stop and restart the application from Tomcat Manager panel and go to the url of JSP, I have this exception:
org.apache.jasper.JasperException: Unable to compile class for JSP
     org.apache.jasper.JspCompilationContext.load(JspCompilationContext.java:587)
     org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:177)
     org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:296)
     org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
     org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
     sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
     sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     java.lang.reflect.Method.invoke(Method.java:324)
     org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:284)
     java.security.AccessController.doPrivileged(Native Method)
     javax.security.auth.Subject.doAsPrivileged(Subject.java:499)
     org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:306)
     org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:200)
root cause
java.lang.NullPointerException
     sun.misc.URLClassPath$3.run(URLClassPath.java:311)
     java.security.AccessController.doPrivileged(Native Method)
     sun.misc.URLClassPath.getLoader(URLClassPath.java:308)
     sun.misc.URLClassPath.getLoader(URLClassPath.java:285)
     sun.misc.URLClassPath.getResource(URLClassPath.java:155)
     java.net.URLClassLoader$1.run(URLClassLoader.java:190)
     java.security.AccessController.doPrivileged(Native Method)
     java.net.URLClassLoader.findClass(URLClassLoader.java:186)
     org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:192)
     org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:110)
     org.apache.jasper.JspCompilationContext.load(JspCompilationContext.java:582)
     org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:177)
     org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:296)
     org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
     org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
     sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
     sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     java.lang.reflect.Method.invoke(Method.java:324)
     org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:284)
     java.security.AccessController.doPrivileged(Native Method)
     javax.security.auth.Subject.doAsPrivileged(Subject.java:499)
     org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:306)
     org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:200)
note The full stack trace of the root cause is available in the Tomcat logs.
I need to restart Tomcat and then I have the same proble and then that my JSP works fine for two times and at the third time come unreachble.
If I change the servlet's part in which I do the forward to the JSP and put the commented part, the application works fine.
Anybody can tell me why my JSP come unreachble?
Thanks
Emanuele Pecorari

I add this thing:
if I add in java.policy this permission:
permission java.security.AllPermission;
all works fine.
I want to know what exactly permission I must put in my file in order that the application works fine in the same handle.

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// Identify a carriage return character for each output line
int iLf = 10;
char cLf = (*char*)iLf;
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        LOG.debug("InvocationData " + invocationData + ".");
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        LOG.error("Could not invoke method", e);
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        LOG.error("Could not invoke method", e);
        throw new UnhandledException(e);
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        LOG.debug("An error has ocurred when invoking method", e);
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Same JSP/Servlet is executing again and again

Hello,
We have some JSPs which do a lot of processing and is 'alive' for a long period
of time. If we use the JSP with small amouts of data, it is fine. But when we
use the JSP with lot of data, it seems to 'go in a loop'.
It is processing the data again and again and again and brings down our server.
We do not think it is the code that is wrong - as it processes perfectly if the
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Thanks,
Oleg.

Hi Oleg,
Could you tell us how you find out that there is an additional request?
Regards,
Slava Imeshev
"Oleg" <[email protected]> wrote in message
news:[email protected]...
>
Thank you Varad and Slava,
We don't use plagin for iplanet,
but our problem is very similar:
Weblogic generate additional request if the previous request toservlet/jsp is
taking long time.
Where I can configure JSP timeout to fix this problem?
Thank you very much.
Oleg.
"Varadharajan" <[email protected]> wrote:
Hi Oleg,
Are you using weblogic plugin for iplanet webserver ?
In weblogic server 6.1 sp3 there is a problem with this plugin. It would
generate
additional request if the previous request to servlet/jsp is taking more
than
the configurable timeout set in the obj.conf file of iplanet webserver.
This plugin problem is fixed in wls6.1 sp4.
Rgds,
Varad
"Slava Imeshev" <[email protected]> wrote:
Hi Oleg,
See my answers inline.
"Oleg" <[email protected]> wrote in message
news:[email protected]...
Hello,
We have some JSPs which do a lot of processing and is 'alive' for
a
long
period
of time. If we use the JSP with small amouts of data, it is fine.But
when we
use the JSP with lot of data, it seems to 'go in a loop'.I guess you need to figure out if "seems" really "does".
It is processing the data again and again and again and brings downour
server.
How do you know that a JSP goes into a loop?
We do not think it is the code that is wrong - as it processes
perfectly
if the
data is small or when our server is not busy. This problem happensif the
data
is lot and the server is also busy. The JSP seems to be executingagain
and again.
What load is considered to be high/low for you
application? Are you running a load test?
Is there some type of 'refresh' logic in weblogic that refreshes
the
JSP/servlet
and makes it 'execute' again and again.Normally Servlet/JSP enters service() method when
there is an incoming request. It should not be happening
at JSP's will.
Regards,
Slava Imeshev

How can I call EJB from JSP/Servlets in iWS?

Hi!!
My JSP/Servlets are on iWS, and I deploy EJB on iAS.
In this case, I don't know how JSP/Servlet call EJb on iAS.
I'd like to know how I can set JNDI name in JSP/Servlet on iWS.
I will thank you if you give me a simple example source using JSP/Servlet
and EJB.
Thanks in advance!!!
- Park-

Park,
Why Are you running your JSP/Servlets in iWS instead of iAS? For whatever
reason,
look at the Converter sample from iAS. You will be doing RMI/IIOP in this
case and the sample explains in detail what to do.
hth,
-robert
"SungHyun, Park" <[email protected]> wrote in message
news:9jpfmt$[email protected]..
Hi!!
My JSP/Servlets are on iWS, and I deploy EJB on iAS.
In this case, I don't know how JSP/Servlet call EJb on iAS.
I'd like to know how I can set JNDI name in JSP/Servlet on iWS.
I will thank you if you give me a simple example source using JSP/Servlet
and EJB.
Thanks in advance!!!
- Park-

Jsp,servlet,bean question,please help

The Tomcat Web server set up like this.......
The directory structure is
e:/sampleapp/WEB-INF/classes
/lib
And the web.xml is in the WEB-INF for the use of ay potential servlet.
The basic understanding is that all the .java files go into the WEB-INF directory and the .class files go into the classes directory.
All the .jsp files go into the sampleapp directory.Till here is correct I feel.
Now for my qustion......
I plan to use jsp,servlet and beans for a potential web application...,where do all these files go?,just the same as above or is there a difference.
Hope that I have given a reasonable explaination to my question.
Thanks for any replies
AS

All of your compiled servlet and java bean (java
classes in general) will be placed into the following
directory (under a directory structure matching the
java package they are in):
e:/sampleapp/WEB-INF/classesAll of your .jar files that are used as libraries (not
your .jar files for applets):
e:/sampleapp/WEB-INF/libAll of the rest of your JSP files, javascript files,
HTML files, JAR files, images files, etc. will go into
the following directory:
e:/sampleappYou must make sure you put your sampleapp directory
where tomcat can load it. Or use the admin tool to
load it. If you make a .WAR file with a corresponding
web.xml file in it, it will simplify loading it into
tomcat. It also will help you do your servlet
mappings, etc. I hope this helps.Thanks for your timely response.To add to it,let me tell you.
The <b>bean</b> files are put into a package right,so they should be put into the WEB-INF/classes/<package name>
What about The <b> servlet </b> files...... they are just put into the WEB-INF/classes/ directory????
Kindly let me know.
Thanks
AS

Applet-Servlet or RMI - which is better

We are in the process of developing a swing-applet based system that requires regular interaction with multiple databases residing on more than one database server.
The options available before us, as we evaluate are:
a. Use "signed" applets ( as this is going to be essentially an intra-net application) and use JDBC connection to connect to more than one database ( which reside on servers other than the web server).
b. Use applet - servlet communication - basically, the servlet would establish connection to the databases, directly or through EJB, retrieve necessary database information and pass on the objects to the applet - the front end GUI would be controlled by the applet.
c. Use RMI
We would like to have your perspective of the three options, with your experience in this line.
The questions that come to us are:
a. If the system is essentially an intra-net application, is it okay to design with "signed" applet mechanism - how far is this method common in the market and acceptable to the clients? Is it true that the signed applet would be able to establish connection to various "identified servers" that are allowed permissions in the security file?
b. Between applet-servlet and RMI, which is a better method? What should be the factors that need to be considered? Is RMI being widely used or should we be thinking in terms of EJB, eventhough the current project is purely a Java based solution.
Your input is highly appreciated - thanking in advance for any suggestions and inputs that you may provide.
Thanks
Dixie

Dixie,
1) IMHO signed applets are not widely used, but you can use
ordinary applets, which are accessing other resources through
redirector servlet on server side - I mean ordinary applets
are prohibited to establish connect to other than it's own server.
So you will be forced to have special servlet on your server,
which have access to other resources on other servers - this is a
way how to avoid applets limitation.
2) RMI is a heavy solution, because all parameters/objects should
be serialized over net and if network connection is unreliable
working with system will be just a nighmare.
3) If you think that your network connection is unreliable, you can use HTTP protocol between client and server instead of RMI. In this case
you will have following benefits:
i) You can still use all of powerness of thick client
ii) Network unreliability will be defeated
iii) Sometime if you would like to port your application to a thin
client it will be done much more easier than in case of RMI
4) If you would like to use thin client your only problem will
be poorness of UI - if you can go with it - go ahead! Otherwise
use thick client with RMI or HTTP depending on quality of network.
Paul

JSP/Servlets & XML - suggestion needed

Hi everyone,
I don't have any coding issues, I'm really just looking for some help on deciding how to go with a project I want to make. First off, I wrote a Java library that builds messages in a special format. I wanted to come up with a pretty frontend for it, so I decided I'd try my hand at a webapp since I've been interested in them for a while. So far my web app consists of jsps, servlets and my library.
At this point I'd like to add the ability for the webapp to store created messages in an XML file (read / write). The XML library I want to use is JAXB. I have it setup to read/write my XML file fine in a test servlet, however I'd like to implement this in a kind of "best practice" approach. So I'm looking for suggestions on how I should do this.
A few of my ideas:
1) Use a jsp page to call a "MessagesBean" which retrieves my data from my xml file. I could then format this nicely in the jsp page. The problem with this however is that I can't find any way to open a file relative to the webapp from within a Bean. ie. when I try to open "messages.xml", I can see from tomcat errors that it attempts to open it in tomcats bin folder (or if i run from within eclipse, eclipses bin folder). I know I could get around this by using an absolute path but I want this to be portable. Any suggestions?
2) To solve the above problem I found "getServletContext().getRealPath("")" in the Servlet API. Using this method I'm able to open my XML file relative to my webapp. The only issue I have here is that I'm now using a servlet to display the page, making it harder for me to format the output.
I'm very new to JSP/Servlets/etc so I really don't know how I should be doing this. I'm just trying to make sure I don't start out on the wrong foot. Can someone please give some suggestions on what I could do?
Cheers.

I suggested not putting business logic in the servlet, but instead instansiating a business logic object in the servlet and calling one of its functions to do the work.
There is nothing wrong with putting the business logic in the servlet on first try. Just later on, you might want to refactor the code to more conform to the above.
In your code, you mentioned that the MessagesBean in the JSP page doesnt seem to call the constructor. The <useBean> tag first looks to
see if the object is in request scope. If it is, it uses it (doesnt call constructor). If its not, it creates its own (calls constructor). You should always
have it in request scope ready for useBean to use.
I think this line:
<jsp:useBean id="messages" class="my.package.MessagesBean" />
should be changed to something like:
<jsp:useBean id="messages" class="my.package.MessagesBean" scope="request" />
The MessagesBean should only have get/set methods to get data out of its object (its a very simple object that holds data). None of its functions
should perform business logic such as hitting the database.
Therefore these items in your JSP page should be in the servlet or business logic:
messages.setPath( getServletContext().getRealPath("") ); // Pass in relative PATH
messages.processXML(); // Process XML file
While this should be in your JSP:
java.util.List<TEXT> TextFiles = messages.getTEXTFiles(); // Return a List of TEXT objects
Question: The JSP calls my Bean "MessagesBean". It then passes in the current relative path. This seems fairly hackish to me, is there a better way to give the relative path to my bean?
Answer: Hard code the relative path to the JSP page in the servlet or business logic. There is no need for the JSP page to pass its path back to the servlet or business logic. Your servlet
'knows' the path to all the JSP pages it needs to dispatch to.
The best way to learn MVC is to continually refactor your code until it looks more and more like MVC (separation of concerns).

URGENT Servlet with RMI ConnectionException

i have an object with two personalities: Servlet and RMI.
However when i invoke it using the web browser, the following exceptions pop out:

the way i code my program is as follow:

Anyone please help thanks. i have been asking this question here for many time and no one reply may i know at least why?
thanks.

Hi,
I see the java doc of LocateRegsitry and you can read :
LocateRegistry is used to obtain a reference to a bootstrap remote object registry on a particular host (including the local host), or
to create a remote object registry that accepts calls on a specific port.
Note that a getRegistry call does not actually make a
connection to the remote host. It simply creates a local reference to
the remote registry and will succeed even if no registry is running on
the remote host. Therefore, a subsequent method invocation to a remote
registry returned as a result of this method may fail.
So may be the exception, throw when you call rebind, is due to non active registry in local machine. You can try to execute your servlet
after activate your registry via LocateRegistry.createRegistry(int port)
Hope this help

Sample jsp servlet bean (MVC) code

We want to look into the JSP/Servlet/Bean area for our next project. We wish to understand the technology and as such want to hand build simple applications, and as such do not want to use JDeveloper just yet.
We have searched and searched for suitable material but cannot anywhere find a sample application that :
A. Lists contents of a databse table
B. Each item in trhe list is a link to a page that allows that item, to be edited.
C. A new item can be added.
D. Uses the MVC model of JSP/Servlet and bean (preferably with no custom tags)
There are examples that are too simplistic and do not cover the whole picture. Having spent over 100 GBP on books lately, only to be disappointed with the examples provided, we need to see some sample code.
The samples provided by Oracle are too simplistic. They should really have provided ones built around the EMP and DEPT tables.
Anyone know where we can get hold of this sample code.

At the risk of sounding really dumb the examples are just too complex. There does not appear to be anywhere on the web where I can find a simple JSP/servlet/bean example of the type I described. There is enouigh material describing each individual component, but what I need is an example to cement the ideas, but the ones suggested are too much for a newbie. Even the much vaunted Pet Store thingy causes my eyes to glaze over.
I dont expect anyone to have written something with my exact requirements, but surely to goodness there must be something that:
1. On entry presents a search form on a table (e.g. EMP)
2. On submission list all rows in EMp matchiung the criteria.
3. The user can either click the link 'Edit' which opens up a form dispalying the row allowing the user to edit and save the changes, or click the 'New' button to show a blank form to create a new EMP.
All this via a Controller servlet, with the database logic handled by a java bean, and all the presentation done via JSP.
To me this is the most obvious and instructive example of this technology, but after days of trawling the web, and looking through a number of books, I cannot find such a thing.
CGI with Perl DBI/DBD was a breeze to work with compared to this stuff ..... maybe ASP with SQL/Server would be a more fruitful use of time.

Change Drop Down from Other JSP/Servlet/Bean

I am wanting to have a select box populate from a database query based on the information pulled from another select box as the user chooses it (ie a user chooses a state and the city choices populate or something like that). I am using JSP, Servlets and Beans. Seems that I need to us JSF, but I was wondering if there is another way or better way.
Thanks for the thoughts.

user12081556 wrote:
I meant to put in my question above, aren't jsf tags just imbedded in some jsp/html code?Not jsp code no. I don't know whether it's possible to use jsf and jsp together, but I wouldn't try.
While JSP has evolved over time from Html and Java code mixed together to standard tags responsible mostly for displaying the data, it's still an old "hack" that compiles jsp pages into servlets.
JSF at least alleviates some of those problems and works nicely with proper xhtml formatted views too (and there's facelets etc. etc. etc.).
Granted, if you're shown some jsp tags and jsf tags, you might not appreciate the difference in the technologies.

JSP, Servlet and RMI

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