Singleton in jsp

Hi folks
In a jsp based webapplication is it better to create SingleTon class for making connection?

No. Because of two reasons:
1) you shouldn't be doing database stuff in a JSP
2) you shouldn't even have Java code in a JSP
Lets talk about doing these things from a servlet, where it really belongs. You could create a singleton, but a simple util class with a static method that obtains a datasource from JNDI and creates a Connection using it can be enough.
It all depends on how you are going to structure your code, how you are going to separate tasks and logic, etc. There is no one design that is the best for all applications.

Similar Messages

Can not access the Instance Data of a Singleton class from MBean

I am working against the deadline and i am sweating now. From past few days i have been working on a problem and now its the time to shout out.
I have an application (let's call it "APP") and i have a "PerformanceStatistics" MBean written for APP. I also have a Singleton Data class (let's call it "SDATA") which provides some data for the MBean to access and calculate some application runtime stuff. Thus during the application startup and then in the application lifecysle, i will be adding data to the SDATA instance.So, this SDATA instance always has the data.
Now, the problem is that i am not able to access any of the data or data structures from the PerformanceStatistics MBean. if i check the data structures when i am adding the data, all the structures contains data. But when i call this singleton instance from the MBean, am kind of having the empty data.
Can anyone explain or have hints on what's happening ? Any help will be appreciated.
I tried all sorts of DATA class being final and all methods being synchronized, static, ect.,, just to make sure. But no luck till now.
Another unfortunate thing is that, i some times get different "ServicePerformanceData " instances (i.e. when i print the ServicePerformanceData.getInstance() they are different at different times). Not sure whats happening. I am running this application in WebLogic server and using the JConsole.
Please see the detailed problem at @ http://stackoverflow.com/questions/1151117/can-not-access-the-instance-data-of-a-singleton-class-from-mbean
I see related problems but no real solutions. Appreciate if anyone can throw in ideas.
http://www.velocityreviews.com/forums/t135852-rmi-singletons-and-multiple-classloaders-in-weblogic.html
http://www.theserverside.com/discussions/thread.tss?thread_id=12194
http://www.jguru.com/faq/view.jsp?EID=1051835
Thanks,
Krishna

I am working against the deadline and i am sweating now. From past few days i have been working on a problem and now its the time to shout out.
I have an application (let's call it "APP") and i have a "PerformanceStatistics" MBean written for APP. I also have a Singleton Data class (let's call it "SDATA") which provides some data for the MBean to access and calculate some application runtime stuff. Thus during the application startup and then in the application lifecysle, i will be adding data to the SDATA instance.So, this SDATA instance always has the data.
Now, the problem is that i am not able to access any of the data or data structures from the PerformanceStatistics MBean. if i check the data structures when i am adding the data, all the structures contains data. But when i call this singleton instance from the MBean, am kind of having the empty data.
Can anyone explain or have hints on what's happening ? Any help will be appreciated.
I tried all sorts of DATA class being final and all methods being synchronized, static, ect.,, just to make sure. But no luck till now.
Another unfortunate thing is that, i some times get different "ServicePerformanceData " instances (i.e. when i print the ServicePerformanceData.getInstance() they are different at different times). Not sure whats happening. I am running this application in WebLogic server and using the JConsole.
Please see the detailed problem at @ http://stackoverflow.com/questions/1151117/can-not-access-the-instance-data-of-a-singleton-class-from-mbean
I see related problems but no real solutions. Appreciate if anyone can throw in ideas.
http://www.velocityreviews.com/forums/t135852-rmi-singletons-and-multiple-classloaders-in-weblogic.html
http://www.theserverside.com/discussions/thread.tss?thread_id=12194
http://www.jguru.com/faq/view.jsp?EID=1051835
Thanks,
Krishna

Problem with Configuring Tomcat for running jsp web applications..Plz HELP

I am using Tomcat 5.5 and Jdk 1.5.0_12 and Oracle 10g. I am using jdbc-odbc bridge connection
to connect to the database. I have placed my project folder called
tdm under the webapps folder in Tomcat. This 'tdm' folder consists of
a collection of html pages,jsp pages and images of my project. Also I created a
WEB-INF folderand in that I have lib folder which contains catalina-root.jar
, classes12.jar and nls_charset.jar files. And also in the WEB-INF folder I have the web.xml
file which looks like this
<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app>
<resource-ref>
<description>Oracle Datasource example</description>
<res-ref-name>jdbc/gdn</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
</web-app>
My Server.xml file in Tomcat\conf folder is as follows



<Server port="8005" shutdown="SHUTDOWN">

<Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" />
<Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />

<GlobalNamingResources>

<Environment name="simpleValue" type="java.lang.Integer" value="30"/>

<Resource name="UserDatabase" auth="Container"
type="org.apache.catalina.UserDatabase"
description="User database that can be updated and saved"
factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
pathname="conf/tomcat-users.xml" />
<Resource name="jdbc/gdn" auth="Container"
type="javax.sql.DataSource" driverClassName="sun.jdbc.odbc.JdbcOdbcDriver"
url="jdbc:odbc:gdn"
username="system" password="tiger" maxActive="20" maxIdle="10"
maxWait="-1"/>
</GlobalNamingResources>


<Service name="Catalina">


<Connector
port="5050" maxThreads="150" minSpareThreads="25" maxSpareThreads="75"
enableLookups="false" redirectPort="8443" acceptCount="100"
connectionTimeout="20000" disableUploadTimeout="true" />

     



<Connector port="8009"
enableLookups="false" redirectPort="8443" protocol="AJP/1.3" />






<Engine name="Catalina" defaultHost="localhost">




<Realm className="org.apache.catalina.realm.UserDatabaseRealm"
resourceName="UserDatabase"/>







<Host name="localhost" appBase="webapps"
unpackWARs="true" autoDeploy="true"
xmlValidation="false" xmlNamespaceAware="false">









<Context path="/tdm" docBase="tdm" debug="0" reloadable="true" />
</Host>
</Engine>
</Service>
</Server>
I have set the context path to /tdm in the server.xml file. Should this be placed in context.xml?
My first page in the project is called Homepage.html. To start my project I give http://localhost:5050/tdm/homepage.html
in a browser. Here I accept a username and password from the user and then do the validation in
a valid.jsp file, where I connect to the database and check and use jsp:forward to go to next pages
accordingly. However when I enter the username and password and click Go in the homepage, nothing is
displayed on the next page. The URL in the browser says valid.jsp but a blank screen appears.
WHY DOES IT HAPPEN SO? DOES IT MEAN THAT TOMCAT IS NOT RECOGNIZING JAVA IN MY SYSTEM OR IS IT A PROBLEM
WITH THE DATABASE CONNECTION OR SOMETHING ELSE? I FEEL THAT TOMCAT IS NOT EXECUTING JSP COMMANDS?
IS IT POSSIBLE?WHY WILL THIS HAPPEN?
I set the JAVA_HOME and CATALINA_HOME environment to the jdk and tomcat folders resp.
Is there any other thing that I need to set in classpath? Should I have my project as a
WAR file in the webapps of TOMCAT or just a folder i.e. directory structure will fine?

I am using Tomcat 5.5 and Jdk 1.5.0_12 and Oracle 10g. I am using jdbc-odbc bridge connection
to connect to the database. I have placed my project folder called
tdm under the webapps folder in Tomcat. This 'tdm' folder consists of
a collection of html pages,jsp pages and images of my project. Also I created a
WEB-INF folderand in that I have lib folder which contains catalina-root.jar
, classes12.jar and nls_charset.jar files. And also in the WEB-INF folder I have the web.xml
file which looks like this
<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app>
<resource-ref>
<description>Oracle Datasource example</description>
<res-ref-name>jdbc/gdn</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
</web-app>
My Server.xml file in Tomcat\conf folder is as follows



<Server port="8005" shutdown="SHUTDOWN">

<Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" />
<Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />

<GlobalNamingResources>

<Environment name="simpleValue" type="java.lang.Integer" value="30"/>

<Resource name="UserDatabase" auth="Container"
type="org.apache.catalina.UserDatabase"
description="User database that can be updated and saved"
factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
pathname="conf/tomcat-users.xml" />
<Resource name="jdbc/gdn" auth="Container"
type="javax.sql.DataSource" driverClassName="sun.jdbc.odbc.JdbcOdbcDriver"
url="jdbc:odbc:gdn"
username="system" password="tiger" maxActive="20" maxIdle="10"
maxWait="-1"/>
</GlobalNamingResources>


<Service name="Catalina">


<Connector
port="5050" maxThreads="150" minSpareThreads="25" maxSpareThreads="75"
enableLookups="false" redirectPort="8443" acceptCount="100"
connectionTimeout="20000" disableUploadTimeout="true" />

     



<Connector port="8009"
enableLookups="false" redirectPort="8443" protocol="AJP/1.3" />






<Engine name="Catalina" defaultHost="localhost">




<Realm className="org.apache.catalina.realm.UserDatabaseRealm"
resourceName="UserDatabase"/>







<Host name="localhost" appBase="webapps"
unpackWARs="true" autoDeploy="true"
xmlValidation="false" xmlNamespaceAware="false">









<Context path="/tdm" docBase="tdm" debug="0" reloadable="true" />
</Host>
</Engine>
</Service>
</Server>
I have set the context path to /tdm in the server.xml file. Should this be placed in context.xml?
My first page in the project is called Homepage.html. To start my project I give http://localhost:5050/tdm/homepage.html
in a browser. Here I accept a username and password from the user and then do the validation in
a valid.jsp file, where I connect to the database and check and use jsp:forward to go to next pages
accordingly. However when I enter the username and password and click Go in the homepage, nothing is
displayed on the next page. The URL in the browser says valid.jsp but a blank screen appears.
WHY DOES IT HAPPEN SO? DOES IT MEAN THAT TOMCAT IS NOT RECOGNIZING JAVA IN MY SYSTEM OR IS IT A PROBLEM
WITH THE DATABASE CONNECTION OR SOMETHING ELSE? I FEEL THAT TOMCAT IS NOT EXECUTING JSP COMMANDS?
IS IT POSSIBLE?WHY WILL THIS HAPPEN?
I set the JAVA_HOME and CATALINA_HOME environment to the jdk and tomcat folders resp.
Is there any other thing that I need to set in classpath? Should I have my project as a
WAR file in the webapps of TOMCAT or just a folder i.e. directory structure will fine?

Shared Connection Pool via Singleton

I have just started to learn Java (more jsp & servlets) and have been going through "Core Servlets and Java Server Pages" and in there is stuff on connection pooling. The author provides a good a connection pool servlet that can be shared, but as I'm new and don't fully understand how everything works (got a basic idea).
How do i go about making the following code accessiable via a singleton class?
ConnectionPool Class
package sco;
import java.sql.*;
import java.util.*;
/** A class for preallocating, recycling, and managing
* JDBC connections.
* <P>
* Taken from Core Servlets and JavaServer Pages
* from Prentice Hall and Sun Microsystems Press,
* http://www.coreservlets.com/.
* © 2000 Marty Hall; may be freely used or adapted.
public class ConnectionPool implements Runnable {
private String driver, url, username, password;
private int maxConnections;
private boolean waitIfBusy;
private Vector availableConnections, busyConnections;
private boolean connectionPending = false;
public ConnectionPool(String driver, String url,
                        String username, String password,
                        int initialConnections,
                        int maxConnections,
                        boolean waitIfBusy)
      throws SQLException {
    this.driver = driver;
    this.url = url;
    this.username = username;
    this.password = password;
    this.maxConnections = maxConnections;
    this.waitIfBusy = waitIfBusy;
    if (initialConnections > maxConnections) {
      initialConnections = maxConnections;
    availableConnections = new Vector(initialConnections);
    busyConnections = new Vector();
    for(int i=0; i<initialConnections; i++) {
      availableConnections.addElement(makeNewConnection());
public synchronized Connection getConnection()
      throws SQLException {
    if (!availableConnections.isEmpty()) {
      Connection existingConnection =
        (Connection)availableConnections.lastElement();
      int lastIndex = availableConnections.size() - 1;
      availableConnections.removeElementAt(lastIndex);
      // If connection on available list is closed (e.g.,
      // it timed out), then remove it from available list
      // and repeat the process of obtaining a connection.
      // Also wake up threads that were waiting for a
      // connection because maxConnection limit was reached.
      if (existingConnection.isClosed()) {
        notifyAll(); // Freed up a spot for anybody waiting
        return(getConnection());
      } else {
        busyConnections.addElement(existingConnection);
        return(existingConnection);
    } else {
      // Three possible cases:
      // 1) You haven't reached maxConnections limit. So
      //    establish one in the background if there isn't
      //    already one pending, then wait for
      //    the next available connection (whether or not
      //    it was the newly established one).
      // 2) You reached maxConnections limit and waitIfBusy
      //    flag is false. Throw SQLException in such a case.
      // 3) You reached maxConnections limit and waitIfBusy
      //    flag is true. Then do the same thing as in second
      //    part of step 1: wait for next available connection.
      if ((totalConnections() < maxConnections) &&
          !connectionPending) {
        makeBackgroundConnection();
      } else if (!waitIfBusy) {
        throw new SQLException("Connection limit reached");
      // Wait for either a new connection to be established
      // (if you called makeBackgroundConnection) or for
      // an existing connection to be freed up.
      try {
        wait();
      } catch(InterruptedException ie) {}
      // Someone freed up a connection, so try again.
      return(getConnection());
// You can't just make a new connection in the foreground
// when none are available, since this can take several
// seconds with a slow network connection. Instead,
// start a thread that establishes a new connection,
// then wait. You get woken up either when the new connection
// is established or if someone finishes with an existing
// connection.
private void makeBackgroundConnection() {
    connectionPending = true;
    try {
      Thread connectThread = new Thread(this);
      connectThread.start();
    } catch(OutOfMemoryError oome) {
      // Give up on new connection
public void run() {
    try {
      Connection connection = makeNewConnection();
      synchronized(this) {
        availableConnections.addElement(connection);
        connectionPending = false;
        notifyAll();
    } catch(Exception e) { // SQLException or OutOfMemory
      // Give up on new connection and wait for existing one
      // to free up.
// This explicitly makes a new connection. Called in
// the foreground when initializing the ConnectionPool,
// and called in the background when running.
private Connection makeNewConnection()
      throws SQLException {
    try {
      // Load database driver if not already loaded
      Class.forName(driver);
      // Establish network connection to database
      Connection connection =
        DriverManager.getConnection(url, username, password);
      return(connection);
    } catch(ClassNotFoundException cnfe) {
      // Simplify try/catch blocks of people using this by
      // throwing only one exception type.
      throw new SQLException("Can't find class for driver: " +
                             driver);
public synchronized void free(Connection connection) {
    busyConnections.removeElement(connection);
    availableConnections.addElement(connection);
    // Wake up threads that are waiting for a connection
    notifyAll();
public synchronized int totalConnections() {
    return(availableConnections.size() +
           busyConnections.size());
/** Close all the connections. Use with caution:
   * be sure no connections are in use before
   * calling. Note that you are not <I>required</I> to
   * call this when done with a ConnectionPool, since
   * connections are guaranteed to be closed when
   * garbage collected. But this method gives more control
   * regarding when the connections are closed.
public synchronized void closeAllConnections() {
    closeConnections(availableConnections);
    availableConnections = new Vector();
    closeConnections(busyConnections);
    busyConnections = new Vector();
private void closeConnections(Vector connections) {
    try {
      for(int i=0; i<connections.size(); i++) {
        Connection connection =
          (Connection)connections.elementAt(i);
        if (!connection.isClosed()) {
          connection.close();
    } catch(SQLException sqle) {
      // Ignore errors; garbage collect anyhow
public synchronized String toString() {
    String info =
      "ConnectionPool(" + url + "," + username + ")\n" +
      ", available=" + availableConnections.size() + "\n" +
      ", busy=" + busyConnections.size() + "\n" +
      ", max=" + maxConnections;
    return(info);
ScoPool Class (singleton to access the connection pool)
package sco;
public class ScoPool extends ConnectionPool {
private ScoPool pool = null;
private ScoPool() {
    super(); // Call parent constructor
public static synchronized ScoPool getInstance() {
    if(pool == null) {
      pool = new ScoPool();
    return(pool);
}Please help a newbie.

Figured it out.
package sco;
import java.sql.SQLException;
public class ScoPool extends ConnectionPool {
private static ScoPool pool;
private ScoPool(String driver, String url, String username, String password,
                  int initialConnections, int maxConnections, boolean waitIfBusy) throws SQLException {
    super(driver, url, username, password, initialConnections, maxConnections, waitIfBusy); // Call parent constructor
public static synchronized ScoPool getInstance() {
    if(pool == null) {
      String driver = "com.microsoft.jdbc.sqlserver.SQLServerDriver";
      String url = "jdbc:microsoft:sqlserver://MIM-W0432:1433;DatabaseName=sco";
      String username = "sco_user";
      String password = "123";
      int initCon = 5;
      int maxCon = 10;
      boolean waitIfBusy = true;
      try {
        pool = new ScoPool(driver, url, username, password, initCon, maxCon, waitIfBusy);
      catch(SQLException sqle) {
    return pool;
}

How to populate data before displaying jsp in JSF ?

I have the following situation :
In my app, i have a couple of left-navigation menus, when i click on one of them, i need to show some history data. So, i first need to call a managed bean on click of the link, fetch data and forward to history jsp page.
How do call the managed bean directly (like struts action page) before going to JSP first ? Whenever i give a link to "something.faces", it goes to the jsp directly ?

There are two solutions on my mind. The first is to use the Shale ViewController where you got prerender() method and in it you could fetch the data. The second solution is to fetch the data in the getter method of your property but remember that the getter method could be invoked more than once per request so putting expencive code in it could be dangerous. Use singleton instance of the fetched property, something like:
getMyProperty() {
if (myProperty == null) {
.... fetch the data
return myProperty;
}

Hi how to add new folders under root for jsp in tomcat4.1.18

hi,
previsously i used tomcat3.3 and tomcat4.1.12 run sucessfully.
now i downloed jakartha_tomcat4.1.18,
i am running sample succesfuly direcly under root.
now i want my some jsp appilcationes to run under xyz,pqr folders
here my jsp files are abc.jsp,fgh.jsp while running file url like this
http://localhost:8080/xyz/abc.jsp
http://localhost:8080/pqr/fgh.jsp
while running url server not locate the files.
where i add these xyz and pqr folders in server.xml.
here my server.xml like this any one can modify this



<Server port="8005" shutdown="SHUTDOWN" debug="0">


<Listener className="org.apache.catalina.mbeans.ServerLifecycleListener"
debug="0"/>
<Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener"
debug="0"/>

<GlobalNamingResources>

<Environment name="simpleValue" type="java.lang.Integer" value="30"/>

<Resource name="UserDatabase" auth="Container"
type="org.apache.catalina.UserDatabase"
description="User database that can be updated and saved">
</Resource>
<ResourceParams name="UserDatabase">
<parameter>
<name>factory</name>
<value>org.apache.catalina.users.MemoryUserDatabaseFactory</value>
</parameter>
<parameter>
<name>pathname</name>
<value>conf/tomcat-users.xml</value>
</parameter>
</ResourceParams>
</GlobalNamingResources>


<Service name="Tomcat-Standalone">


<Connector className="org.apache.coyote.tomcat4.CoyoteConnector"
port="8080" minProcessors="5" maxProcessors="75"
enableLookups="true" redirectPort="8443"
acceptCount="100" debug="0" connectionTimeout="20000"
useURIValidationHack="false" disableUploadTimeout="true" />




<Connector className="org.apache.coyote.tomcat4.CoyoteConnector"
port="8009" minProcessors="5" maxProcessors="75"
enableLookups="true" redirectPort="8443"
acceptCount="10" debug="0" connectionTimeout="0"
useURIValidationHack="false"
protocolHandlerClassName="org.apache.jk.server.JkCoyoteHandler"/>












<Engine name="Standalone" defaultHost="localhost" debug="0">



<Logger className="org.apache.catalina.logger.FileLogger"
prefix="catalina_log." suffix=".txt"
timestamp="true"/>


<Realm className="org.apache.catalina.realm.UserDatabaseRealm"
debug="0" resourceName="UserDatabase"/>







<Host name="localhost" debug="0" appBase="webapps"
unpackWARs="true" autoDeploy="true">





<Logger className="org.apache.catalina.logger.FileLogger"
directory="logs" prefix="localhost_log." suffix=".txt"
     timestamp="true"/>


<Context path="" docBase="ROOT" debug="0"/>

<Context path="/examples" docBase="examples" debug="0"
reloadable="true" crossContext="true">
<Logger className="org.apache.catalina.logger.FileLogger"
prefix="localhost_examples_log." suffix=".txt"
     timestamp="true"/>
<Ejb name="ejb/EmplRecord" type="Entity"
home="com.wombat.empl.EmployeeRecordHome"
remote="com.wombat.empl.EmployeeRecord"/>



          
<Environment name="maxExemptions" type="java.lang.Integer"
value="15"/>
<Parameter name="context.param.name" value="context.param.value"
override="false"/>
<Resource name="jdbc/EmployeeAppDb" auth="SERVLET"
type="javax.sql.DataSource"/>
<ResourceParams name="jdbc/EmployeeAppDb">
<parameter><name>username</name><value>sa</value></parameter>
<parameter><name>password</name><value></value></parameter>
<parameter><name>driverClassName</name>
<value>org.hsql.jdbcDriver</value></parameter>
<parameter><name>url</name>
<value>jdbc:HypersonicSQL:database</value></parameter>
</ResourceParams>
<Resource name="mail/Session" auth="Container"
type="javax.mail.Session"/>
<ResourceParams name="mail/Session">
<parameter>
<name>mail.smtp.host</name>
<value>localhost</value>
</parameter>
</ResourceParams>
<ResourceLink name="linkToGlobalResource"
global="simpleValue"
type="java.lang.Integer"/>
</Context>
</Host>
</Engine>
</Service>



</Server>
==========
any one may modify above one
thanks
pullareddyj

As the server.xml is big enough, I took the minimum portion of it. Hope u can proceed with it.

<Context path="" docBase="ROOT" debug="0"/>

<Context path="/xyz" docBase="pathTo_xyz" debug="0" crossContext="true"/>
<Context path="/pqr" docBase="pathTo_pqr" debug="0" crossContext="true"/>

<Context path="/examples" docBase="examples" debug="0"
reloadable="true" crossContext="true">
You should also provide a WEB-INF folder under pqr or xyz folder.
You should also provide a web.xml file under each WEB-INF folder.
The minimal web.xml is
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/j2ee/dtd/web-app_2_3.dtd">
<web-app>
</web-app>
That's it. Try it out. Hope it is OK.
Hafizur Rahman
SCJP

Singleton

I have written a classic Singleton which appears to work fine. One issue bothers me. I wish to collect error messages and return them to the caller rather than throw the error(s). I am concerned that given the single instance of this class, there could be -conflict- in generation of these error messages ....in other words, could caller1 get /see error messages from caller2 ....this code is running in a JAVA class as part of a JSP / Struts environment ....
Rod .
public class SingleClass {
// Sample usage:
// SingleClass.getInstance().setExceptionList();
// X509Certificate cert = SingleClass.getInstance().getCACert ("xxx");
// SingleClass.getInstance().getExceptionList();
private SingleClass() {
// Define our security provider
Security.addProvider(new BouncyCastleProvider());
* A handle to the unique instance.
private static SingleClass _instance = null;
// Errors Collection
private ArrayList EXCEPTIONLIST;
// Our cache of CA Certs
private static HashMap cachedCerts = null;
// How long are cache entries valid - 5 days default
private static long cacheLife = 5 * 24 * 60 * 60 * 1000;
public static void clearCache() {
cachedCerts = null;
public static SingleClass getInstance() {
if ( _instance == null ) {
_instance = new SingleClass();
return _instance;
public ArrayList getExceptionList() {
return EXCEPTIONLIST;
public void setExceptionList() {
EXCEPTIONLIST = new ArrayList();
public X509Certificate getCACert(String caCertDN) {
X509Certificate cert = null;
if ( somecondition ) {
// generate an error message
EXCEPTIONLIST.add(msgParams);
return cert;
etc.

could caller1 get /see error messages from caller2 Well yes. Thats the point of a singleton isn't it? There is only one instance, shared by all the callers. If you want each caller to store their own error messages, a singleton is not the way to do it.
If you are using Struts, why are you not using the Messages/Errors functionality provided there?

JSP tags for managing MBeans??

Hi,
I'm trying to build a GUI for managing a custom MBean. The MBean implementation is a wrapper for a singleton class (specifically, a Configuration class for a web app). I've tried using WebJMX, but the problem there is that it relies heavily on MX4J, and has not kept up with JMX advances in the last two years (MX4J is a bit ahead of weblogic 8.1).
Just as there is a set of console extension jsp tags, I suspect that a set of JSP tags exists for the developers of the Weblogic console to write their JSP pages to manage the weblogic MBeans. I coud just try to figure out the pattern of the INPUT and FORM tags in the html, but that leaves me with a possibly-inaccurate, version-dependent, non-dynamically-generated page to manage one MBean.
Does such a set exist? Could someone point me to any information about how to use such a set of tags?
I would like to be able to have the JSP I use for my console extension display an interface for modifying MBean configurable fields and executing MBean operations. What would the best way be to do this? I do not want to embed the Sun JMX RI in my web-app and launch a separate HtmlAdaptor listening on a different port. I would like the admin to the MBean be accessible through (and only through) the weblogic console.
Thanks in advance for the help,
Matt Geis

Hi,
I'm trying to build a GUI for managing a custom MBean. The MBean implementation is a wrapper for a singleton class (specifically, a Configuration class for a web app). I've tried using WebJMX, but the problem there is that it relies heavily on MX4J, and has not kept up with JMX advances in the last two years (MX4J is a bit ahead of weblogic 8.1).
Just as there is a set of console extension jsp tags, I suspect that a set of JSP tags exists for the developers of the Weblogic console to write their JSP pages to manage the weblogic MBeans. I coud just try to figure out the pattern of the INPUT and FORM tags in the html, but that leaves me with a possibly-inaccurate, version-dependent, non-dynamically-generated page to manage one MBean.
Does such a set exist? Could someone point me to any information about how to use such a set of tags?
I would like to be able to have the JSP I use for my console extension display an interface for modifying MBean configurable fields and executing MBean operations. What would the best way be to do this? I do not want to embed the Sun JMX RI in my web-app and launch a separate HtmlAdaptor listening on a different port. I would like the admin to the MBean be accessible through (and only through) the weblogic console.
Thanks in advance for the help,
Matt Geis

Object living with servlet/jsp container

How do I make an Object live until the servlet container lives? I mean I want an Object to be instantiated once in the lifetime of the webserver session and its has to be singleton and should live alive until the webserver dies? How can I make this possible? I should be able to keep that object alive even if any no references are made to the object. Moreover I should be able to access that object from any java class on that webserver?

You can't do this in memory. The easiest thing to do would be to read/write the persistant data you need from disk.
Anything your JSP or servlet creates in memory will be cleared when it is done serving the request.

Anybody using Hypersonic SQL in JSP?

Hello,
Does anybody use Hypersonic SQL?
I implement a guestbook system with JSP that
saves data in Hypersonic SQL. This system
runs on www.mycgiserver.com. My JSP program
has thread safe option set to false to make
sure one thread is reading and writing the database
at a time. However, every once in a while, the
database will be wiped out mysteriously.
So I am just wondering that this happens to
anyone else? Is this a Hypersonic SQL's bug
or it's the server that goofs up or I did something
wrong with the JSP setting? Any ideas or
comments please? Thanks !!!

Hi there!
I use Hypersonic locally and on mycgiserver.com. Luckilly, I haven't encountered your problems so far. I use a similar approach, I have a bean that handles a singleton-connection to the DB, and that will queue up all requests. But so far , I haven't had that much load on the app, so maybe I'll get back in this matter, with the same problem... Anyone att mycgiserver that had an id�a?
regards
Markus

How to automate task in jsp?

I want to create an sms messaging website using jsp. The sms i believe would be ez, i would just have to use sockets in a bean. However there is a specific functionality i want to implement where my website would send a dummy sms message every 5 minutes to the sms server just to test what speed that server is accepting messages at. This way i can display the server speed to users when the come to my site. My problem is i am not sure how to implement this functionality in jsp. It is a process that needs to happen like a new thread. It should happen whether or not people are visiting the website and it needs to happed every 5 minutes. I am wondering if this functionality could only be setup by my webserver or is there some way in jsp i could use a bean to do this.
Any assistance would be greatly appreciated

could the same thing be done with a jsp page instead of a servlet?The load on startup part, I'm not sure about. If you only wanted to wait til the first person hits a page, or just have a page that must be hit first on startup of the server to get the thread going, you could do that. But that requires direct user interaction to start things off....
As for examples....
In web.xml, you define a servlet and servlet mapping.
<servlet>
     <servlet-name>smsinit</servlet-name>
     <servlet-class>com.pckg.SMSInitServlet</servlet-class>
     <init-param>
          <param-name>config</param-name>
          <param-value>/WEB-INF/sms-config.xml</param-value>
     </init-param>
     <load-on-startup>2</load-on-startup>
</servlet>
<servlet-mapping>
     <servlet-name>smsinit</servlet-name>
     <url-pattern>sms.init</url-pattern>
</servlet-mapping>So that means that if the URL contains "sms.init", the smsinit servlet will be invoked. You probably don't need worry about that, if all you want is something that will load when the server starts. For that, that's what "load-on-startup" is for. The number value has to do with defining load order for multiple servlets. If left out, the servlet isn't initialized til the first time it's called via a URL. Otherwise, any number will do (for all practical purposes). The init-param config is useful if you need to define a file or some parameter that you can use on init to get some other information.
As for the servlet itself
package com.pckg;
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class SMSInitServlet extends HttpServlet {
     private ServletContext application = null;
     public void init(ServletConfig config) throws ServletException {
          super.init(config);
          application = config.getServletContext();
          String config = application.getInitParameter("config");
          File configFile = new File(application.getRealPath(config));
          // read the file or whatever....
          // start your thread class running and maybe put it in application
          // or pass the thread the application object which it could store
          // information in, or just have the thread use static methods/fields
          // or a singleton instance or something like that.
          // the advantage to using the application scope is it limits it to being
          // accessed to JSP pages or other servlets within the web application only
     public void doGet(HttpServletRequest request, HttpServletResponse response)
                   throws ServletException, IOException {
          doPost(request, response);
     public void doPost(HttpServletRequest request, HttpServletResponse response)
                   throws ServletException, IOException {
          // do something here... or nothing, if you want.
}

Declaring public class in JSP environment.

Can anybody please tell me, what technical implication can occur, if we declare a public java class inside JSP.
The scenario is -
I have a JSP file used to display the results in table format.
Before displaying the table, a public class is defined in the same JSP.
Inside the scriptlet, the object is instantiated (using 'new' keyword).
That object is used to populate the table.
I know that according to the MVC architecture, the presentation logic should not be intermingled with the business logic. But I wanted to know whether any 'technical' problems we can face because of this.
For e.g. Synchronization problem or singleton object creation problem etc.

Yes its like a inner class, and will be available only to the current JSP.
The code structure is somewhat like this -
<%!
public class SearchCN{
     String strUserName;
     String strPassword;
     Context context = null;
%>
<%
SearchCN searchObject = new SearchCN();
obj.connect();
%>
Now in such a scenario, I can think of some causes like, if N no of users open the same JSP, then N connections will get created. Connection sharing which could have been implemented for better performance is not possible.
Can you give any additional inputs?

Best way to call EJBs from JavaBeans/JSP

Does anyone have a favorite way for getting EJB data from a JavaBean into
          your JSPs?
          I'm looking for a way of caching the EJBHome references so the beans don't
          have to do a lookup on each page, each time they are called.
          Thanks,
          -TB


How does this HelperClass keep the references cached after it looks them up?
          Is it a singleton object, or does it keep the references in static fields?
          "Argyn Kuketayev" <[email protected]> wrote in message
          news:3b1e468b$[email protected]..
          > make a HelperClass, which will have a method getXXXHome()
          > inside the Helper class you may implement cashing.
          >
          > thanks,
          > Argyn
          >
          > T. Bailey wrote in message <[email protected]>...
          > >Does anyone have a favorite way for getting EJB data from a JavaBean into
          > >your JSPs?
          > >
          > >I'm looking for a way of caching the EJBHome references so the beans
          don't
          > >have to do a lookup on each page, each time they are called.
          > >
          > >Thanks,
          > >-TB
          > >
          > >
          >
          >

Singleton object in clustered enviornment

Hi,
          In my web application which is deployed in clustered enviornment, I am facing problem for singleton object.
          I need to share object among all servers in the clustered.
          I am using weblogic server 9.2. I have tried its Singleton services, but it doesnt work as expected.
          what could be other solution to solve the problem?

No. If you need this type of functionality, use Coherence.
          http://www.tangosol.com/coherence.jsp
          Peace,
          Cameron Purdy
          Tangosol, Inc.
          http://www.tangosol.com/coherence.jsp
          Tangosol Coherence: Clustered Replicated Cache for Weblogic
          "Ferruccio" <[email protected]> wrote in message
          news:[email protected]..
          > Hi,
          > I have a very basic question. In a WebLogic clustered
          > environment, is a Singleton replicated? In other words, if the
          > mySingleton on node A in a cluster is updated with a piece of data,
          > will this show in the mySingleton in node B?
          >
          > Thanks
          >
          > Ciao
          > Ferruccio

Simple caching in singleton DAO

Suppose I was to use a DAO like this in a web application. Different threads would be concurrently accessing this code from different servlets, struts actions, JSP pages, whatever.
import java.util.Map;
import java.util.HashMap;
public class CacheSingletonDAO {
     private static Map items = new HashMap();
     //----- Singleton Methods --------------------------------------------------
     private static final CacheSingletonDAO instance = new CacheSingletonDAO();
     private CacheSingletonDAO() {
          items.put("1","foo");
          items.put("2","bar");
     public static CacheSingletonDAO getInstance() {
          return instance;
     //----- Public Methods -----------------------------------------------------
     public String getItem(String key) {
          Object obj = items.get(key);
          if(obj != null && obj instanceof String) {
               return (String)obj;
          } else {
               return null;
     public Map getItems() {
          return items;
     public void addItem(String key, String item) {
          items.put(key,item);
}The code here is over simplified. For a real implementation of this, there would most likely be a private getItemsFromDB() method that the private constructor would call. I would also have a method like refreshCache() that would call the getItemsFromDB() method, so that I could call that to update the items HashMap with whatever is in the database. The addItem(String, String) method would first store the item in a database, then put item in the HashMap. Assume I would be using this in a single server, single JVM application. Are there any thread-safety or other problems/issues with code like this?

I don't think this logic necessarily follows. I agree
that the user must see all the entries in the
drop-down list, but that doesn't mean that this class
needs to hand the map over to the drop-down list
instance or the UI container. Instead, the UI could
ask this instance to write itself into the drop-down
list.I envisioned the DAO as the model in a MVC app. Writing the drop-down seems like it is a task for the view.
This is a very common sentiment among programmers.
"If you're code is written wrong, then it's not my
problem." I'm not saying that you're wrong to feel
this way, but in general projects get finished faster
when the interfaces between components or classes are
tight. That is, write an interface to your class
that helps people avoid coding mistakes. If
getItems().add() should not be coded then you should
try to make sure that it can't be.That makes sense.
This is a little better. Now when somebody else codes
getItems().add(), their code compiles (as it did
before) but when they run some test case (assuming
they test the right path) they will see an
UnsupportedOperationException instead of seeing some
occasional bad behaviour (as they would have seen
before). But better still, write an interface that
doesn't allow anybody else to code getItems().add() in
the first place. I'm not trying to make your life
more difficult, but in the long run doing this saves
time for everybody on your project.I see your point.
Would it be a reasonable
solution to write String[] getItemValues(), that
returns a copy of all the values currently in the
HashMap? Do you need to supply the user with key-value
pairs instead? Is there a way that you can return an
array of those things rather than the map?You are right, there is no reason I couldn't do that. Would this cause potential performance issues? I would think giving the client the a read-only reference to the hashmap would be faster than generating an array of Object each time.
>>
But then my original question still is do add and
refresh need to be synchronized? I can't think of
anything that would be bad if they weren't
synchronized, but maybe I am overlooking something.
What happens if someone calls the add method while
the refresh method is executing? I guess I need to
show more code to address that:
public void add(String key, String item) {
addItemToDB(key,item);
items.put(key.item);
public void refreshCache() {
items = getItemsFromDB();
}Assume addItemToDB() returns void and inserts myitem
into the database.
Assume getItemsFromDB() queries the DB for all the
items and returns a Map with all of the items.
Do these methods need to be synchronized?
You need to provide synchronization for the map, the
map has no synchronization of it's own.But just synchronizing add and refreshCache won't cut it, right? I think if things happend in this order I would have an issue:
1. Thread A calls refreshCache()
2. refreshCache() calls getItemsFromDB()
3. getItemsFromDB() internally has queried the DB, gotten a ResultSet and is building a collection from the result set, but the method isn't finished yet.
4. Thread B calls add()
5. add() calls addItemtoDB(key,item), which finishes
6. add() puts the item in the items HashMap
7. add() finished executing
8. getItemsFromDB() finishes executing and returns a collection, but the collection doesn't have the item add by Thread B's add()
9. refreshCache replaces the items HashMap with the collection returned from getItemsFromDB() and now the item that was added by Thread B's add() won't end up in the collection until next time refreshCache() is called.
This would be the case even if add() and refreshCache() were synchronized, right?

Singleton in jsp

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