Posts Tagged: development

Debugging Ant tasks in Eclipse

Today I came  an issue that required me to debug a custom Ant task that we have. While the Eclipse integrated debugger allows you to step through the targets and tasks in the build.xml file using the action Debug As -> Ant Script, it doesn’t actually let you step into the java class that implements the task. This is a major drawback, as most of the complexity (and issues :-)) tend to be in the task implementation code.

After searching around for a bit, I came across the Eclipse Remote Debugger debug configuration. This configuration allows you to remotely debug applications, by establishing a JDWP (Java Debug Wire Protocol, part of JPDA – Java Platform Debug Architecture) connection between the running application and the debugger. After learning about this, setting up the environment to debugg Ant tasks from within Eclipse was pretty straightforward.

The first step is to setup the Ant script launcher to run in debug mode and attach to the debug server. The following should be used as JRE arguments for the Ant configuration:

-Xdebug -agentlib:jdwp=transport=dt_socket,server=y,address=8000

You can setup your Ant configuration by going to Run -> External Tools -> External Tools Configurations and creating a new Ant Build configuration. Inser the location of the build file in the main tab and setup the arguments in the JRE tab:


After the Ant configuration is setup, we need to take care of the remote debugger configuration. Go to Run -> Debug Configurations… and create a new configuration for Remote Java Application. Make sure you set the same port number that you used in the Ant configuration, and you are good to go.

Now, place the breakpoints in your build.xml and java classes. In order to debug, you need to first launch the Ant script and then attach the debugger to it. Do right click in the build.xml file and select Debug As -> Ant Script. Then go to Run -> Debug Configurations… select the Remote Ant Debugger and click Debug. The debugger will now attach to the running proccess and let you step through both the xml file and the java classes:

Have fun!

Mylyn task manager

When I migrated my development environment to Eclipse 3.4 Ganymede, one of the things that caught my attention on Eclipse’s update website was a plugin called Mylyn. A visit to the website, a look over the webcast and it sounded something promising.

It definitely is! Mylyn is a task manager that changes your IDE context based on tasks. You create a task, add resources to its context and when you activate the task, it hides all the other (unneeded) resources from your views (project/package explorer, outlines, editors, etc…). It provides integration with several task repositories, like Bugzilla and Trac. Unfortunately, it doesn’t provide a connector to Clearcase, but I’m still able to use it in an automated way.

I find the tool really awesome when I do something basic like switching tasks: it just closes all the editor windows and projects in the explorer for the task I’m leaving and opens all the files I was working on for the task I’m switching to. This would take me several minutes to do by myself, so having a tool that does that in 1 second is pretty neat!

Here are some more things I like about Mylyn:

  • ability to customize CVS/SVN checkin comments based on templates. Most, if not all, of my commit comments are in the form of “Bug#xxxxx: 1 line description of the bug and fix”. With Mylyn, I can get the comment populated automatically with information from the associated task.
  • when I (re)activate a task, it positions the cursor in the file and method (if java file) I was working on.
  • I can use the URL feature to link to the Clearcase defect page for each one of my defects
  • dynamically adds resources as we follow method references
  • Mylyn filters unrelated content from all views, but I especially like the end result for the package explorer and outline view. When working with classes that have tens of methods, showing just a handful of them in the outline simplifies things a lot!

And the things I don’t like that much:

  • no connector to Rational ClearCase. I have to copy some notes and Defect info from Clearcase to my task manually.
  • the option to show filtered content only shows content at the same level. I would like to have a “show all” option for when I need to look for some resource.
  • It slows down the system a bit. Not too bad, but I do notice it when I have several eclipse instances running.

Overal, I think Mylyn is a great tool and very useful! Even more if you are working with Bugzilla/Trac projects.

If you want to give it a try, this is Mylyn’s homepage and this is a Mylyn tutorial.

 

JDBC performance tips

If you are into java and database development, you will find this article to be a gold mine: http://www.javaperformancetuning.com/tips/jdbc.shtml

It contains links and summary to tens of other performance articles related with java database application development.

SQLJ and JDBC

As a follow up on my last post comparing Static SQL with Dynamic SQL, I will now post an example of how to run the same code using static and dynamic SQL.

One of my visitors left a comment saying that the scope of static and dynamic SQL in Oracle is different than the one I mentioned. I am not familiar at all with Oracle, but was able to find some information on their documentation where they compare JDBC and SQLJ. Since their concept of static vs dynamic SQL is different from the concept in DB2, so my examples may not make sense for Oracle users. I also found out that although Oracle has had plans to desupport SQLJ in its data server, that support has been reinstated in their 10g release.

The two code samples I will show next are shipped with DB2 (get your free copy of DB2 Express-C) and can be found in the file %DB2FOLDER%/samples/java/sqlj/TbRead.java. I’ll just use one of the several examples in that file, that executes a sub-select statement in the employee table.

Sample code in SQLJ:

#sql cur7 = {SELECT job, edlevel, SUM(comm)
	FROM employeeWHERE job IN('DESIGNER', 'FIELDREP')GROUP BY ROLLUP(job, edlevel)};
while (true){
	#sql {FETCH :cur7 INTO :job, :edlevel, :commSum};
	if (cur7.endFetch()){
		break;
	}
	System.out.print("Job: " + job + " Ed Level: " + edlevel + " Tot Comm: " +commSum);
}

Sample code in JDBC:

Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT job, edlevel, SUM(comm) "
	+"  FROM employee "
	+"  WHERE job IN('DESIGNER','FIELDREP') "
	+"  GROUP BY ROLLUP(job, edlevel)");
	while (rs.next())
	{
	if (rs.getString(1) != null)
		{
		job = rs.getString(1);
		edlevel = rs.getString(1);
		commSum = rs.getString(1);
		System.out.print("Job: " + job + " Ed Level: " + edlevel + " Tot Comm: " +commSum);
		}
	}

Although both styles present different syntax, from a developer’s perspective, the only main difference is than when using JDBC one needs to explicitly fetch the row values into Java variables one by one. A common comment from Java developers is that SQLJ is not really Java (one needs to use annotations instead of java method calls), so they prefer to stick with JDBC.

Like I explained in my previous post, the biggest difference between these two styles (static SQL using SQLJ and dynamic SQL using JDBC) is that the SQL statements in the SQLJ files need to be compiled and bound to the database ahead of runtime. The following diagram illustrates this process:

staticSQL.jpg

After the deployment process, SQLJ execution is simpler than JDBC. While JDBC statements need to be prepared at execution time, SQLJ statements are already compiled and ready to use. The two following diagrams illustrate these differences:

jdbcstatement.jpgsqljstatement.jpg

As you can see, static SQL execution process is much simpler, but it requires a complex deployment process. This is an aspect of database development where there is a clash between DBAs and Developers. While ones – the DBAs – prefer the much more refined security and execution control provided by SQLJ and static SQL, others – the Developers – prefer the easier development process of dynamic SQL in the form of JDBC.

Soon, I will talk here about a new Java Data Access platform that supports the usage of both static and dynamic SQL at runtime (through a JVM property), allowing DBAs and Developers to use dynamic SQL on development and test environments and going with static SQL on the production environment. This way, the development community will get the best of both worlds: ease of deployment during development and testing phase and greater performance and control on the production environment.

If you are looking for a data management and application development tool, you should take a look at the new IBM Data Studio. It is an eclipse-based development environment, free to download and to use and with support to all major RDBMS. Download IBM Data Studio.