Byron Nevins: Byron's Pointless Ramblings

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This chapter can be downloaded here.

This zip file has the entire Chapter1 NetBeans project in it. I highly recommend using NetBeans 5.51 for this tutorial. And of course you are going to need GlassFish

The first thing that we need to get working is the automatic downloading of the Dean Edell mp3 files. We're going to make a simple stand-alone Java SE application to do the downloading. We will then create a simple script to run the java application. After testing it to make sure all is well we'll get the operating system to call it every Monday through Friday night at 11:30 PM PDT.

The Java Technology Portion

The source consists of two files:

• HTTPDownloader.javaA simple class that takes a URL string and a filename string. It fetches the file that the URL is pointing to and writes it to the filename. This is where Jaca Technology really pays off. It's ridiculously easy to do.
• DeanEdellDownloader.javaThis class is also pretty simple. The most difficult part is assembling a distinctive filename based on the date.

DeanEdellDownloader uses HTTPDownloader to fetch the current Dean Edell mp3 file. It refuses to run on weekends. The URL and the location to write the mp3 files is hard-coded here. That's OK in this scenario because we are going to build it once and forget about it.

You will need to change the value of one variable in DeanEdellDownloader. The last line of the file contains the target directory from my GlassFish installation. Replace it with your path:

private final static String DEFAULT_DIR_HTTP = "C:/as/domains/domain1/docroot/DeanEdellFiles";

The Script

NetBeans automatically put a manifest file pointing to the correct main in the jar file. On my Windows system I put a script in DeanEdell.bat in a scripts directory. The command in the script is:

java -jar path-of-jar-file

Run the script. A 10.5 MB mp3 file should appear in [domain]/docroot/DeanEdellFiles (unless it is the weekend!)

Calling the Script Automatically Forever

If you are on UNIX or Linux you are on your own here. You need to create a chron job that runs the script Monday through Friday around 11:30 PM PDT. It's OK to run it on weekends too -- it won't do anything.

On Windows this is super easy to do: Go to Control Panel and then run Scheduled Tasks. It will take you by the hand and guide you in making a chron job. Just have it call the batch file every Monday through Friday around 11:30 PM PDT. Make sure you enter your account password.

And that's all there is to Chapter 1. We now have DeanEdell mp3's appearing automatically in a folder under docroot inour domain.

Next Installment: Chapter 2 - Create a Web Application to serve up the files

This is the first chapter in a n-chapter tutorial on how to exploit Glassfish capabilities. I learned long ago that the only way I can really cement into my head a hunk of technology is to just do it. I came up with a useful application for web technology. In this series we will be building an application that will slowly but surely use these areas of javaee. They are in the approximate order that we will tackle in the project.

• HTTP File downloading (HyperText Transfer Protocol)
• Servlets
• JSPs (Java Server Pages)
• User Authentication - Basic, then File Realms, then JDBC Realms
• Derby Database
• JNI (Java Naming Interface)
• EJB 3.0 (Enterprise Java Beans)
• JPA (Java Persistence API)
• EJB Timer Service
• Struts
• JSP Tag Libraries
• MDB (Message Driven Beans)

Chapter 0: The Application Description

Dr. Dean Edell has an interesting radio talk show on KGO radio in San Francisco. His show is from 1 to 2 PM Monday through Friday. KGO posts an mp3 file for the show once a day. KGO takes it down, forever, after 24 hours. KGO does not maintain an archive of old shows. I like to burn the shows onto CDs and listen to them in my car. What this application will do is:

• Automatically download the mp3 at 11:38 PM every night, Monday through Friday and save them to a subdirectory of docroot on my Glassfish Application Server.
• Maintain user accounts for people that wish to download the files. New accounts will be accepted and added to the list on demand.
• The application will persist which files have been downloaded for each user. When a user is authenticated he will see his own custom list of programs he has yet to download.
• A list of all available programs will also be available in case of trouble (like the dog eating the Dean Edell CDs)

This sounds like a lot of overkill for such modest sounding requirements. But making it 100% automatic is a bit challenging. Besides, the whole point of this is to create an application - any application -- in order to learn how to do all this stuff. We will start simple but thorough and correct. We will constantly change and modify it to use the cutting edge Java EE technology as the tutorial progresses.

Stay Tuned for the next installment, Chapter 1:

Write a stand alone Java application that will download the mp3 file. The OS will be in charge of running this application via a chron/at job.

A little known fact: there are scripts for starting and stopping the 3 different kinds of Glassfish servers. The three kinds of servers are:

• Domain Administration Server (the only server available in a development profile)
• Node Agent Server
• Instance Server

These scripts have always been there but were never officially supported.  They were difficult to use.  E.g. you had to know to type in username, password and master password into the void at the command window for strtserv to work.  The scripts were used internally in pre-V2 versions.  They are not used at all in V2.  They are there for your use exclusively now.

Where Are These Scripts?

They are named: 

	Start Script	Stop Script
Windows	startserv.bat	stopserv.bat
Not Windows	startserv	stopserv

 

In my own personal default environment, they are here:

Domain Administration Server	c:/as/domains/domain1/bin
Node Agent Server	c:/as/nodeagents/na/agent/bin
Instance Server	c:/as/nodeagents/na/i1/bin

 

How Do I Use Them?

To start a server run the appropriate startserv script.  It will ask you for the administrator's username, pssword and the master password.  If you don't know what a master password is -- just enter changeit.  This is not really needed for the Domain Administration Server in a developer profile, but the script does not yet have the smarts to know whether or not the server is secure.  A future release may fix this problem. 

To stop a server simply run the stopserv script.  No authentiction information is needed or asked for.

 Features

•  The scripts are relocatable.  I.e., if you use asadmin backup-domain and asadmin restore-domain to clone a domain to a different location -- the scripts will still work.
• Shutdown is very fast and efficient.
• This is the only way you can start an instance with no running Domain Administration Server and no running Node Agent Server.
• You can take over the lifecycle management of one or more Instance Servers.  If you start the Instance Server with the script then the Node Agent Server will not automatically stop it when the Node Agent Server is stopped.
  

I'm a developer for Glassfish.  My area is Administration.  I am also a glassfish user.  I have a real-world web site that's been running continuously for 2 years

Now when I try to do something in a different area of the Appserver like Web Applications, I'm just as much of a helpless newbie as anyone else.

I developed a semi-cool way to publish lots and lots of pictures on my website with little manual intervention.  It works great.  One day I downloaded a ton of pictures  from my camera to the website.  I put the "magic URL" that causes a servlet to layout the pictures in a URL which worked fine.  When you click on any of these small pictures it displays  a large version of the picture.  But, wait!  I''d click and instead of seeing a picture, I'd get a download dialog from Firefox!  After looking around on the filesystem I located the problem.  The camera saves the pictures with an extension of JPG while all of my other pictures had an extension of jpg.

I posted a comment about it. Jan Luehe (super web-server guru) saw it, figured out the problem right away and filed a bug.  the bug was fixed in the very next build of glassfish.  Now that's service!

So -- Glassfish is fast, reliable, free, it has great clustering capability, it's open-source and there are very smart knowledgeable people listening in on all the posts and ready to jump into action to help you.  What else do you need?!?

This is why Glassfish gets my vote as World's Greatest Appserver.

 

There used to be a big problem in trying to attach a debugger to a clustered server instance in Glassfish.  As of today (build 45), it is a snap to do it!

The problem was that a cluster config could only specify one debugging port.  This would work if you started one and only one server instance.  As soon as you tried to start a second instance it would try to use the same jdwp port and it would fail to launch.  It was (almost) impossible to debug 2 instances on the same machine at the same time.

The solution is to defer the actual port number selection.  I.e. the instance needs to choose its own port.  Each instance specifies a different port and, voila, problem solved.

Here is how to do it:

We developers do this all the time:

• start DAS and/or NodeAgent
• tail -f on the 2 server.logs
  

There is an easier way!  Use the --verbose option.  This will start the server but it will not return control to asadmin.  Instead it will take over the command window and all logging output will go to the window as well as the server logfile.  As a bonus, you can press Ctrl-Break (on Windows) to trigger a thread dump. 

You can Ctrl-C out of the command window at any time without disturbing the server. 

asadmin start-domain --verbose
asadmin start-node-agent --verbose

We have totally changed the way that Thread Dumps are collected in Glassfish. Forget everything about how it used to be done.

• You need not run the servers in native mode. The same procedure works in native and non-native mode
• Thread dumps are available for all 3 kinds of servers -- Domain Administration Servers, Node Agents and Server Instances
• The new behavior is totally automatic, you don't need to do anything other than send a signal to the JVM to trigger it.

How to Trigger a Thread Dump in Windows

• Get the PID of the server with jps.
• Run sendsignal giving it the PID of the server.

How to Trigger a Thread Dump in UNIX and Linux

• Get the PID of the server with jps.
• Run kill -3 PID

Where did my Thread Dump Go?

The Thread Dump is appended to a file named jvm.log in the same directory as the normal server logfile. E.g. /gf/domains/domain1/logs/jvm.log

Important: the jvm.log file is deleted every time the server is restarted. If you want to keep the contents you will need to copy the file.