Q: What version of JBoss AS do I need to run Seam? A: For Seam 1.3: Seam was developed against JBoss 4.2. Seam can still be run against JBoss 4.0. The seam documentation contains instructions for configuring JBoss 4.0. A: For Seam 1.2: Since Seam requires the latest edition of EJB3, you need to install [...]

Tomcat Interview Questions – 1 How do you create multiple virtual hosts? If you want tomcat to accept requests for different hosts e.g., www.myhostname.com then you must 0. create ${catalina.home}/www/appBase , ${catalina.home}/www/deploy, and ${catalina.home}/conf/Catalina/www.myhostname.com 1. add a host entry in the server.xml file 1 <Host appBase="www/appBase" name="www.myhostname.com"/> 2. Create the the following file under conf/Catalina/www.myhostname.com/ROOT.xml [...]

Tomcat Interview Questions – 1

How do you create multiple virtual hosts?

If you want tomcat to accept requests for different hosts e.g., www.myhostname.com then you must 0. create ${catalina.home}/www/appBase , ${catalina.home}/www/deploy, and ${catalina.home}/conf/Catalina/www.myhostname.com

1. add a host entry in the server.xml file

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  <Host appBase="www/appBase" name="www.myhostname.com"/>

2. Create the the following file under conf/Catalina/www.myhostname.com/ROOT.xml

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<?xml version="1.0" encoding="UTF-8"?>
<Context
    path="/"
    docBase="www/deploy/mywebapp.war"
    reloadable="true" antiJARLocking="true">
</Context>

Add any parameters specific to this hosts webapp to this context file

3. put your war file in ${catalina.home}/www/deploy

When tomcat starts, it finds the host entry, then looks for any context files and will start any apps with a context

To add more sites just repeat and rinse, all webapps can share the same war file location and appbase

How will you load properties file?

* Use a ResourceBundle. See the Java docs for the specifics of how the ResourceBundle class works. Using this method, the properties file must go into the WEB-INF/classes directory or in a jar file contained in the WEB-INF/lib directory.

* Another way is to use the method getResourceAsStream() from the ServletContext class. This allows you update the file without having to reload the webapp as required by the first method. Here is an example code snippet, without any error trapping:

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// Assuming you are in a Servlet extending HttpServlet
                    // This will look for a file called "/more/cowbell.properties" relative
                    // to your servlet Root Context
                   InputStream is = getServletContext().getResourceAsStream("/more/cowbell.properties");
                   Properties  p  = new Properties();
                   p.load(is);
                 is.close();

Can I set Java system properties differently for each webapp?

No. If you can edit Tomcat’s startup scripts, you can add “-D” options to Java. But there is no way to add such properties in web.xml or the webapp’s context.

How do I configure Tomcat to work with IIS and NTLM?

Follow the standard instructions for when the isapi_redirector.dll Configure IIS to use “integrated windows security”

In server.xml, make sure you disable tomcat authentication:

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

How can I access members of a custom Realm or Principal?

When you create a custom subclass of RealmBase or GenericPrincipal and attempt to use those classes in your webapp code, you’ll probably have problems with ClassCastException. This is because the instance returned by request.getUserPrincipal() is of a class loaded by the server’s classloader, and you are trying to access it through you webapp’s classloader. While the classes maybe otherwise exactly the same, different (sibling) classloaders makes them different classes.

This assumes you created a My“Principal class, and put in Tomcat’s server/classes (or lib) directory, as well as in your webapp’s webinf/classes (or lib) directory. Normally, you would put custom realm and principal classes in the server directory because they depend on other classes there.

Here’s what you would like to do, but it throws ClassCastException:

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MyPrincipal p = request.getUserPrincipal();
String emailAddress = p.getEmailAddress();

Here are 4 ways you might get around the classloader boundary:

1) Reflection

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Principal p = request.getUserPrincipal();
String emailAddress = p.getClass().getMethod("getEmailAddress", null).invoke(p, null);

2) Move classes to a common classloader

You could put your custom classes in a classloader that is common to both the server and your webapp – e.g., either the “common” or bootstrap classloaders. To do this, however, you would also need to move the classes that your custom classes depend on up to the common classloader, and that seems like a bad idea, because there a many of them and they a core server classes.

3) Common Interfaces

Rather than move the implementing custom classes up, you could define interfaces for your customs classes, and put the interfaces in the common directory. You’re code would look like this:

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public interface MyPrincipalInterface extends java.security.Principal {
  public String getEmailAddress();
}
 
public class MyPrincipal implements MyPrincipalInterface {
...
  public String getEmailAddress() {
    return emailAddress;
  }
}
 
public class MyServlet implements Servlet {
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    MyPrincipalInterface p = (MyPrincipalInterface)request.getUserPrincipal();
    String emailAddress = p.getEmailAddress();
...
}

Notice that this method gives you pretty much the webapp code you wanted in the first place

4) Serializing / Deserializing

You might want to try serializing the response of ‘request.getUserPrincipal()’ and deserialize it to an instance of [webapp]MyPrincipal.

How do I override the default home page loaded by Tomcat?

After successfully installing Tomcat, you usually test it by loading http://localhost:8080 . The contents of that page are compiled into the index_jsp servlet. The page even warns against modifying the index.jsp files for this reason. Luckily, it is quite easy to override that page. Inside $TOMCAT_HOME/conf/web.xml there is a section called <welcome-file-list> and it looks like this:

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<welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>

The default servlet attempts to load the index.* files in the order listed. You may easily override the index.jsp file by creating an index.html file at $TOMCAT_HOME/webapps/ROOT. It’s somewhat common for that file to contain a new static home page or a redirect to a servlet’s main page. A redirect would look
like:

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<html>
 
<head>
<meta http-equiv="refresh" content="0;URL=http://mydomain.com/some/path/to/servlet/homepage/">
</head>
 
<body>
</body>
 
</html>

This change takes effect immediately and does not require a restart of Tomcat.

How do I enable Server Side Includes (SSI)?

Two things have to be done for tomcat to aknowledge SSI scripts:

1. Rename $CATALINA_BASE/server/lib/servlets-ssi.renametojar to $CATALINA_BASE/server/lib/servlets-ssi.jar.

2. Uncomment the section of web.xml found in $CATALINA_BASE/conf/web.xml that deals with SSI. it looks like this when it is uncommented:

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<servlet>
        <servlet-name>ssi</servlet-name>
        <servlet-class>
          org.apache.catalina.ssi.SSIServlet
        </servlet-class>
        <init-param>
          <param-name>buffered</param-name>
          <param-value>1</param-value>
        </init-param>
        <init-param>
          <param-name>debug</param-name>
          <param-value>0</param-value>
        </init-param>
        <init-param>
          <param-name>expires</param-name>
          <param-value>666</param-value>
        </init-param>
        <init-param>
          <param-name>isVirtualWebappRelative</param-name>
          <param-value>0</param-value>
        </init-param>
        <load-on-startup>4</load-on-startup>
    </servlet>

How do I use DataSources with Tomcat?

When developing J2EE web applications, the task of database connection management can be daunting. Best practice involves using a J2EE DataSource to provide connection pooling, but configuring DataSources in web application servers and connecting your application to them is often a cumbersome process and poorly documented.

The usual procedure requires the application developer to set up a DataSource in the web application server, specifying the driver class, JDBC URL (connect string), username, password, and various pooling options. Then, the developer must reference the DataSource in his application’s web.xml configuration file, and then access it properly in his servlet or JSP. Particularly during
development, setting all of this up is tedious and error-prone.

With Tomcat 5.5, the process is vastly simplified. Tomcat allows you to configure DataSources for your J2EE web application in a context.xml file that is stored in your web application project. You don’t have to mess with configuring the DataSource separately in the Tomcat server.xml, or referencing it in your application’s web.xml file. Here’s how:

Install the JDBC Driver

Install the .jar file(s) containing the JDBC driver in Tomcat’s common/lib folder. You do not need to put them in your application’s WEB-INF/lib folder. When working with J2EE DataSources, the web application server manages connections for your application.

Create META-INF/context.xml

In the root of your web app directory structure, create a folder named META-INF (all caps). Inside that folder, create a file named context.xml that contains a Resource like this:

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<?xml version="1.0" encoding="UTF-8"?>
 
<Context>
 
  <Resource name="jdbc/WallyDB" auth="Container"
            type="javax.sql.DataSource" username="wally" password="wally"
            driverClassName="com.microsoft.sqlserver.jdbc.SQLServerDriver"
            url="jdbc:sqlserver://localhost;DatabaseName=mytest;SelectMethod=cursor;"
            maxActive="8"
            />
 
</Context>

This example shows how to configure a DataSource for a SQL Server database named mytest located on the development machine. Simply edit the Resource name, driverClassName, username, password, and url to provide values appropriate for your JDBC driver.

Access the DataSource in Your Application

From a Servlet

Here’s how you might access the data in a servlet:

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InitialContext ic = new InitialContext();
  DataSource ds = (DataSource) ic.lookup("java:comp/env/jdbc/WallyDB");
  Connection c = ds.getConnection();
  ...
  c.close();

Notice that, when doing the DataSource lookup, you must prefix the JNDI name of the resource with java:comp/env/

Apache Ant Interview Questions – 1 1)What is ant? Ant is a small animal who can build magnificent buildings. Ant builds! ANT is a Java based building tool, which is similar to make, and so much better than make. ANT, what a smart name for a building tool, even the original author of ANT, James [...]

Apache Ant Interview Questions – 1

1)What is ant?

Ant is a small animal who can build magnificent buildings. Ant builds! ANT is a Java based building tool, which is similar to make, and so much better than make. ANT, what a smart name for a building tool, even the original author of ANT, James Duncan Davidson, meant “Another Neat Tool”. A win-win ant learning method

There is a shortcut.

If you download a small jakarta project, such as Log4J, which is built by ant. It is a good and simple example for you to learn ant. Actually, you hit two birds with one stone.
Ant is easy!
The hard part is how to make a very complicated diversified system work very simple and elegant. Knowledge about ant is not enough, you need an elegant and simple design, you need great naming convention, you need to optimize the code reusability and flexibility, you need a least maintenance system…
Then it is not easy now ..

2)How do I get started to use ant? Can you give me a “Hello World” ant script?

Simple.

• Download the most recent version of ant from Apache; unzip it some where on your machine.
• Install j2sdk 1.4 or above.
• Set JAVA_HOME and ANT_HOME to the directory your installed them respectively.
• Put %JAVA_HOME%/bin;%ANT_HOME%/bin on your Path. Use ${JAVA_HOME}/bin:${ANT_HOME}/bin on UNIX. Yes, you can use forward slash on windows.
• Write a “Hello world” build.xml

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<project name="hello" default="say.hello" basedir="." >
                    <property name="hello.msg" value="Hello, World!" />
                    <target name="say.hello" >
                      <echo>${hello.msg}</echo>
                    </target>
                  </project>

* Type ant in the directory your build.xml located.

* You are ready to go!!!!

3)How to delete files from a directory if it exists?

The following code fails when directory does not exist!

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<delete>
    <fileset dir="${upperdir.which.exists}">
      <include name="${classes.dir}/*.class" />
    </fileset>
  </delete>

Your code has many problems.

1. You should not use implicit fileset, which is deprecated. You should use nested fileset.

2. If dir does not exist, the build will fail, period!

3. If you are not sure, use a upper level dir, which exists for sure. See the following fileset.

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<path id="build.classpath">
    <fileset dir="${build.lib}" includes="**/*.jar"/>
    <fileset dir="${build.classes}" />
  </path>
 
  <target....>
    <javac ....>
      <classpath refid="build.classpath" />
    </java>
  </target>
 
  <target....>
    <java ....>
      <classpath refid="build.classpath" />
    </java>
  </target>

5)How does ant read properties? How to set my property system?

Ant sets properties by order, when something is set, the later same properties cannot overwrite the previous ones. This is opposite to your Java setters. This give us a good leverage of preset all properties in one place, and overwrite only the needed. Give you an example here. You need password for a task, but don’t want to share it with your team members, or not the developers outside your team.

Store your password in your ${user.home}/prj.properties

pswd=yourrealpassword

In your include directory master prj.properties

pswd=password

In your build-common.xml read properties files in this order

1. The commandline will prevail, if you use it: ant
-Dpswd=newpassword

2. ${user.home}/prj.properties (personal)

3. yourprojectdir/prj.properties (project team wise)

4. your_master_include_directory/prj.properties (universal)

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<cvsnttask password="${pswd} ... />

Problem solved!

6)How to modify properties in ant?

No, you can’t!

Properties in Ant are immutable. There is a good reason behind this, see this FAQ item for more details.

7)How to use ant-contrib tasks?

A: Simple, just copy ant-contrib.jar to your ant*/lib directory

And add this line into your ant script, all ant-contrib tasks are now available to you!

<taskdef
resource=”net/sf/antcontrib/antcontrib.properties” />

8)How to loop on a list or fileset?

Use ant-contrib <for> <foreach> tasks

General to say, use <for> is better than use <foreach> since for each is actually open another ant property space, use more memory too.

9)Why do I get en exception when I use location=”D:\\Code\\include” as
attribute of includepath?

See here.

You need to escape the string to “D:\\\\Code\\\\include” or use “D:/Code/include” instead!

Believe me or not? Forward slash works on windows in all ant or java code. It also works in windows environment variables. It does not work in cmd (dos) window before XP. It also works in XP dos window now!

10)Can I put the contents of a classpath or fileset into a property?

Yes, you can.

This is very similar to the call of Java class toString() method and actually it is calling the toString() method inside ant. For example

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<fileset id="fs1" dir="t1" includes="**/*.java"/>
<property name="f1.contents" refid="fs1"/>
<echo>f1.contents=${f1.contents}</echo>

What is Quartz? Quartz is a job scheduling system that can be integrated with, or used along side virtually any other software system. The term “job scheduler” seems to conjure different ideas for different people. As you read this tutorial, you should be able to get a firm idea of what we mean when we [...]

What is Quartz?

Quartz is a job scheduling system that can be integrated with, or used along side virtually any other software system. The term “job scheduler” seems to conjure different ideas for different people. As you read this tutorial, you should be able to get a firm idea of what we mean when we use this term, but in short, a job scheduler is a system that is responsible for executing (or notifying) other software components when a pre-determined (scheduled) time arrives.

Quartz is quite flexible, and contains multiple usage paradigms that can be used separately or together, in order to achieve your desired behavior, and enable you to write your code in the manner that seems most ‘natural’ to your project.

Quartz is very light-weight, and requires very little setup/configuration – it can actually be used ‘out-of-the-box’ if your needs are relatively basic.

Quartz is fault-tolerant, and can persist (‘remember’) your scheduled jobs between system restarts.

Although Quartz is extremely useful for simply running certain system processes on given schedules, the full potential of Quartz can be realized when you learn how to use it to drive the flow of your application’s business processes.
What is Quartz – From a Software Component View?

Quartz is distributed as a small java library (.jar file) that contains all of the core Quartz functionality. The main interface (API) to this functionality is the Scheduler interface. It provides simple operations such as scheduling/unscheduling jobs, starting/stopping/pausing the scheduler.

If you wish to schedule your own software components for execution they must implement the simple Job interface, which contains the method execute(). If you wish to have components notified when a scheduled fire-time arrives, then the components should implement either the TriggerListener or JobListener interface.

The main Quartz ‘process’ can be started and ran within your own application, as a stand-alone application (with an RMI interface), or within a J2EE app. server to be used as a resource by your J2EE components.

Why not just use java.util.Timer?

Since JDK 1.3, Java has “built-in” timer capabilities, through the java.util.Timer and java.util.TimerTask classes – why would someone use Quartz rather than these standard features?

There are many reasons! Here are a few:

1. Timers have no persistence mechanism.

2. Timers have inflexible scheduling (only able to set start-time & repeat interval, nothing based on dates, time of day, etc.)

3. Timers don’t utilize a thread-pool (one thread per timer)

4. Timers have no real management schemes – you’d have to write your own mechanism for being able to remember, organize and retreive your tasks by name, etc.

…of course to some simple applications these features may not be important, in which case it may then be the right decision not to use Quartz.

How can I control the instantiation of Jobs?

See org.quartz.spi.JobFactory and the org.quartz.Scheduler.setJobFactory(..) method.

How do I keep a Job from being removed after it completes?

Set the property JobDetail.setDurability(true) – which instructs Quartz not to delete the Job when it becomes an “orphan” (when the Job not longer has a Trigger referencing it).

How do I keep a Job from firing concurrently?

Make the job class implement StatefulJob rather than Job. Read the JavaDOC for StatefulJob for more information.

How do I stop a Job that is currently executing?

See the org.quartz.InterruptableJob interface, and the Scheduler.interrupt(String, String) method.

How do I chain Job execution? Or, how do I create a workflow?

There currently is no “direct” or “free” way to chain triggers with Quartz. However there are several ways you can accomplish it without much effort. Below is an outline of a couple approaches:

One way is to use a listener (i.e. a TriggerListener, JobListener or SchedulerListener) that can notice the completion of a job/trigger and then immediately schedule a new trigger to fire. This approach can get a bit involved, since you’ll have to inform the listener which job follows which – and you may need to worry about persistence of this information.

Another way is to build a Job that contains within its JobDataMap the name of the next job to fire, and as the job completes (the last step in its execute() method) have the job schedule the next job. Several people are doing this and have had good luck. Most have made a base (abstract) class that is a Job that knows how to get the job name and group out of the JobDataMap using special keys (constants) and contains code to schedule the identified job. Then they simply make extensions of this class that included the additional work the job should do.

In the future, Quartz will provide a much cleaner way to do this, but until then, you’ll have to use one of the above approaches, or think of yet another that works better for you.

Why isn’t my trigger firing?

The most common reason for this is not having called Scheduler.start(), which tells the scheduler to start firing triggers.

The second most common reason is that the trigger or trigger group has been paused.

Daylight Saving Time and Triggers

CronTrigger and SimpleTrigger each handle daylight savings time in their own way – each in the way that is intuitive to the trigger type.

First, as a review of what daylight savings time is, please read this resource: http://webexhibits.org/daylightsaving/g.html . Some readers may be unaware that the rules are different for different nations/contents. For example, the 2005 daylight savings time starts in the United States on April 3, but in Egypt on April 29. It is also important to know that not only the dates are different for different locals, but the time of the shift is different as well. Many places shift at 2:00 am, but others shift time at 1:00 am, others at 3:00 am, and still others right at midnight.

SimpleTrigger allows you to schedule jobs to fire every N milliseconds. As such, it has to do nothing in particular with respect to daylight savings time in order to “stay on schedule” – it simply keeps firing every N milliseconds. Regardless your SimpleTrigger is firing every 10 seconds, or every 15 minutes, or every hour or every 24 hours it will continue to do so. However the implication of this which confuses some users is that if your SimpleTrigger is firing say every 12 hours, before daylight savings switches it may be firing at what appears to be 3:00 am and 3:00 pm, but after daylight savings 4:00 am and 4:00 pm. This is not a bug – the trigger has kept firing exacly every N milliseconds, it just that the “name” of that time that humans impose on that moment has changed.

CronTrigger allows you to schedule jobs to fire at certain moments with respect to a “gregorian calendar”. Hence, if you create a trigger to fire every day at 10:00 am, before and after daylight savings time switches it will continue to do so. However, depending on whether it was the Spring or Autumn daylight savings event, for that particular Sunday, the actual time interval between the firing of the trigger on Sundary morning at 10:00 am since its firing on Saturday morning at 10:00 am will not be 24 hours, but will instead be 23 or 25 hours respectively.

There is one additional point users must understand about CronTrigger with respect to daylight savings. This is that you should take careful thought about creating schedules that fire between midnight and 3:00 am (the critical window of time depends on your trigger’s locale, as explained above). The reason is that depending on your trigger’s schedule, and the particular daylight event, the trigger may be skipped or may appear to not fire for an hour or two. As examples, say you are in the United States, where daylight savings events occur at 2:00 am. If you have a CronTrrigger that fires every day at 2:15 am, then on the day of the beginning of daylight savings time the trigger will be skipped, since, 2:15 am never occurs that day. If you have a CronTrigger that fires every 15 minutes of every hour of every day, then on the day daylight savings time ends you will have an hour of time for which no triggerings occur, because when 2:00 am arrives, it will become 1:00 am again, however all of the firings during the one o’clock hour have already occurred, and the trigger’s next fire time was set to 2:00 am – hence for the next hour no triggerings will occur.

How do I improve the performance of JDBC-JobStore?

There are a few known ways to speed up JDBC-JobStore, only one of which is very practical.

First, the obvious, but not-so-practical:
* Buy a better (faster) network between the machine that runs Quartz, and the machine that runs your RDBMS.

* Buy a better (more powerful) machine to run your database on.

* Buy a better RDBMS.

Now for something simple, but effective: Build indexes on the Quartz tables.

Most database systems will automatically put indexes on the primary-key fields, many will also automatically do it for the foreign-key field. Make sure yours does this, or make the indexes on all key fields of every table manually.

Next, manually add some additional indexes: most important to index are the TRIGGER table’s “next_fire_time” and “state” fields. Last (but not as important), add indexes to every column on the FIRED_TRIGGERS table.

Create Table Indexes

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create index idx_qrtz_t_next_fire_time on qrtz_triggers(NEXT_FIRE_TIME);
create index idx_qrtz_t_state on qrtz_triggers(TRIGGER_STATE);
create index idx_qrtz_t_nf_st on qrtz_triggers(TRIGGER_STATE,NEXT_FIRE_TIME);
create index idx_qrtz_ft_trig_name on qrtz_fired_triggers(TRIGGER_NAME);
create index idx_qrtz_ft_trig_group on qrtz_fired_triggers(TRIGGER_GROUP);
create index idx_qrtz_ft_trig_name on qrtz_fired_triggers(TRIGGER_NAME);
create index idx_qrtz_ft_trig_n_g on qrtz_fired_triggers(TRIGGER_NAME,TRIGGER_GROUP);
create index idx_qrtz_ft_trig_inst_name on qrtz_fired_triggers(INSTANCE_NAME);
create index idx_qrtz_ft_job_name on qrtz_fired_triggers(JOB_NAME);
create index idx_qrtz_ft_job_group on qrtz_fired_triggers(JOB_GROUP);

My DB Connections don’t recover properly if the database server is restarted.

If you’re having Quartz create the connection data source (by specifying the connection parameters in the quartz properties file) make sure you have a connection validation query specified, such as:
Connection Validation Query

org.quartz.dataSource.myDS.validationQuery=select 0 from dual

This particular query is extremly efficient for Oracle. For other databases, you’ll need to think of an efficient query that always works as long as the connection is good.

If you’re datasource is managed by your application server, make sure the datasource is configured in such a way that it can detect failed connections.

I’m using JobStoreCMT and I’m seeing deadlocks, what can I do?

JobStoreCMT is in heavy use, under heavy load by many people. It is believed to be free of bugs that can cause deadlock. However, every now and then we get complaints about deadlocks. In all cases thus far, the problem has turned out to be “user error”, thus the list below is some things for you to check if you are experiencing deadlocks.

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* Some databases falsely detect deadlocks when a tx takes a long time. Make sure you have put indexes on your tables (see improving performance of JDBCJobStore).
* Make sure you have at least number-of-threads-in-thread-pool + 2 connections in your datasources.
* Make sure you have both a managed and non-managed datasource configured for Quartz to use.
* Make sure that all work you do with the Scheduler interface is done from within a transaction. Accomplish this by using the Scheduler within a SessionBean that has its tx settings "Required" and "Container". Or within a MessageDrivenBean with similar settings. Finally, start a UserTransaction yourself, and commit the work when done.
* If your Jobs' execute() methods use the Scheduler, make sure a transaction is in progress by using a UserTransaction or by setting the Quartz config propery "org.quartz.scheduler.wrapJobExecutionInUserTransaction=true".