Mike`s Blog - Java

Consolas

info@mhaller.de (Mike Haller) — Sat, 23 Jan 2010 15:27:12 +0100

Dan writes about it, Sven & Vitaly are writing about it, Jeff, Scott and Steve found it years ago and are probably using it ever since. Many StackOverflow users do it as well. So why don't I?

Well, now I did and so far, it's promosing.
I switched from Courier New to Consolas.

Besides gaining some more space, it really looks much nicer.

But compare for yourself:

Consolas is a commercial font and if you're on Windows and have any of the Microsoft products installed, chances are that you already have Consolas installed on your system. If you don't, check out the other programming fonts features on Smashing Magazines articles.

Tracing with JDK Logging

info@mhaller.de (Mike Haller) — Sat, 16 Jan 2010 16:02:01 +0100

Imagine you're writing a small test case to check out some new library or version or cool new technology.

You're eager to try out that stuff, learn how it works and how to use it.
But, unfortunately, something goes wrong and you see the following:

Exactly, you see nothing.

You didn't quite read the quick start tutorial carefully and you must have missed something at the configuration file or at the code. You're not sure - all you get is a mysterious exception or the code just doesn't do anything visible, as it does here. At this point, you just want it to print out what's going on, anything - you would like to have some fine-grained logging output on your console.

You know it's a pain to set up all that logging facility stuff correctly and your loved pre-configured log4j.xml with all the handy shortcuts is on the other machine. Okay, all you needed was just the whole debug output of that library to get it to know better and see what's going wrong.

The project already has commons-logging on it's classpath, but gladly no implementation, so it's using JDK Logging as a backend. Commons-logging should die anyway. Really. I mean it.. You can see that it's using JDK Logging since the console output is two-line formatted like the following snippet. The name of the logger is the adapter used to bridge between Commons-Logging and JDK Logging, and in this case it's iBatis 3 JakartaCommonsLoggingImpl.
16.01.2010 16:20:27 org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl debug
FEIN: PooledDataSource forcefully closed/removed all connections.
16.01.2010 16:20:27 org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl debug
FEIN: PooledDataSource forcefully closed/removed all connections.

Now, back to the example which is currently not printing out anything. To get decent logging output to your console with standard JDK logging, you either have to create a logging.properties and fill it with some obscure properties like .handlers and anyway you don't know how to configure that correctly. Isn't there anywhere a good and quick to find example for that?

I started using this code, which seems to be the simplest possible way of getting something to the console quickly.

Logger rootLogger = LogManager.getLogManager().getLogger("");
Handler handler = new ConsoleHandler();
handler.setLevel(Level.ALL);
rootLogger.addHandler(handler);
rootLogger.setLevel(Level.ALL);

As you can see, there's some output now.
But it's red (System.err stream) and there are too many newlines for my taste.

It uses the root logger, identified by the empty string (""), adds a Handler, which is responsible for printing the log messages to the console. Other Handlers write the log messages to the file system or send it over the wire. The Level is the log level, which determines which log messages are being sent to the Handler and which are ignored. For example, you can set it to INFO, so only Info, Warning, Error-level log messages are being printed. Log messages of level Debug and Trace are being ignored.

Since I don't like the output being spread over two lines (it makes it reading much harder, especially if your output is tabular like like the iBatis output for java.sql statements. So I ended up with something like this, to format the lines into a single line and get it to print out on System output console instead of System error:

Logger logger = LogManager.getLogManager().getLogger("");
class RedirectingConsoleHandler extends ConsoleHandler {
	public RedirectingConsoleHandler(OutputStream target) {
		super();
		setOutputStream(target);
	}
}
;
Handler handler = new RedirectingConsoleHandler(System.out);
handler.setLevel(Level.ALL);
// handler.setFormatter(new XMLFormatter());
Formatter newFormatter = new Formatter() {

	@Override
	public String format(LogRecord record) {
		return String.format("%tT %-40.40s %-8.8s %s\n", new Date(),
				record.getLoggerName(), record.getLevel().getLocalizedName(),
				formatMessage(record));
	}
};
handler.setFormatter(newFormatter);
logger.addHandler(handler);
logger.setLevel(Level.ALL);

This code will redirect the output of the Logging facility to a configure stream, in this case the System.out stream. That's the RedirectingConsoleHandler class is for. The anonymous Formatter class will format the log message, e.g. add a timestamp, the name of the logger, on which level it was logged and the actual log message of the log record and only use one single line. The output looks much more how I like it:

(Yeah, i know the SQL statements are truncated at the example screenshot. But in modern times, with larger screens, it's no problem since the consoles are much broader than the space available on my blog)

Note: this is only used for testing, not for production, not for performance measurements, not for audit logging. This kind of logging is only meant for technical debug tracing. Logging is among the Top10 unknown performance killers in enterprise applications.

Memory leaks et alii

info@mhaller.de (Mike Haller) — Wed, 30 Dec 2009 14:30:15 +0100

Leaky web application

One of the most common problems in building enterprise web applications are leaks. A leak is consumption of a resource by a program where the program is unable to release the resource. Leaks come in various types, such as

Memory leaks

Thread and ThreadLocal leaks

ClassLoader leaks

System resource leaks

Connection leaks

Continue reading "Memory leaks et alii"

Per-unit-test profiling

info@mhaller.de (Mike Haller) — Mon, 16 Nov 2009 23:01:55 +0100

As a preparation for long-term performance measurements, (sometimes called Continuous Performance Management or CPM), I tried to automate the creation of JProfiler profiling snapshots and, along the way, came up with the following side product: Automated per-test method profiling.

Basically, the idea is to go from here:

to here

"What's so great about this?", you wonder?

Read the full article for fancy screenshots and code snippets.

(Btw, the test cases are due to this question. Usually, i don't do String performance tests

Continue reading "Per-unit-test profiling"

Top10 programming controversial

info@mhaller.de (Mike Haller) — Wed, 04 Nov 2009 11:02:37 +0100

There's a Stackoverflow question about controversial programming opinions:
The top ten as voted by the SO community:

1. The only "best practice" you should be using all the time is Use Your Brain
2. Most comments in code are in fact a pernicious form of code duplication
3. Programmers who don't code in their spare time for fun, will never become as good as those that do
4. Not all programmers are created equal
5. XML is highly overrated
6. "Googling it" is okay!
7. I fail to understand why people think that Java is absolutely the best "first" programming language to be taught in universities
8. If you only know *one language*, no matter how well you know it, you're not a great programmer
9. Performance does matter
10. The Business Apps farce (You have to read it to understand)

Where have all the threads gone?

info@mhaller.de (Mike Haller) — Mon, 06 Jul 2009 15:37:04 +0200

Recently, we got a nasty error in the log file:

java.lang.OutOfMemoryError: unable to create new native thread

Although we had specified -XX:HeapDumpOnOutOfMemoryError, this does not include dumping the heap to disk when the heap is not involved in an OutOfMemoryError. In this case, the JVM was unable to create new threads as the limit of threads was reached.

So, the question is: How many threads can be created?
The answer is, as usual: It depends!

Continue reading "Where have all the threads gone?"

My Own Twitter Client

info@mhaller.de (Mike Haller) — Sun, 17 May 2009 22:01:31 +0200

Using twitter4j, it's pretty easy to hack together a new Twitter desktop client. What I wanted to do is to have search capabilities and have all the tweets in a local database, so I could have a look and work with the messages people write even when i'm offline (which never happens anyway, but just in case).

So, taking Eclipse RCP, munching it with twitter4j, adding a bit of Apache Derby and other stuff, I ended up with the following prototype in a couple of hours:

It has a virtual table, so it loads tweets on-demand from the local database when you scroll down. It only reloads the latest 20 tweets from Twitter.com in online mode. There is an offline-mode to decrease the amount of network bandwidth and service utilization. Twitter is already pretty slow. The client caches all the profile images for faster loading. It displays the time of the tweet and highlights URLs. I had a feature in it which resolves shortened URLs and displays the real ones on hover, but i disabled it as I've got problems displaying a nice hover. Hover's in Eclipse RCP/SWT/JFace just don't look very nice, compared to all the new Web 2.0 or Mac designs found in modern apps today.

What other features could be put into yet-another-twitter-client? Tag clouds? URL clouds? Charts? Google Maps? Automatic translations like Babelfish?

In-Memory Databases

info@mhaller.de (Mike Haller) — Tue, 05 May 2009 21:58:48 +0200

For testing and demo installation purposes, or for in-memory data aggregation operations, it may be suitable to use a "nearly full-blown" database. They're called in-memory databases and there are some implementation for the Java platform which are used since years:

hsqldb
One of the first 100% Java implementations of a SQL relational database management system. Like all the others, it can be run from a persistent file system or run in-memory. It's fast, it has a very low footprint and it can be embedded in any Java application. Hsqldb was my favourite for years to use in unit tests and integration tests. It can also read and write CSV files.

H2Database
The successor of hsqldb is H2. It's better documented, performs even better and has more options. There's even a web console where you can work with the data in the in-memory database like you can do with phpMyAdmin. Great thing. I'm currently using H2 at home and at work.

Derby
Derby, the Java database, now also supports the in-memory protocol. That's great to hear and an additional argument for switching to Derby as the default implementation for databases in embedded versions or for demo installations.

Monitoring code quality

info@mhaller.de (Mike Haller) — Sun, 26 Apr 2009 13:35:02 +0200

I've been looking for tools to measure and visualize code quality for some time now. Every once in a while, there's some tool which aggregates results from quality measurements and monitoring tools like PMD, Findbugs, Checkstyle etc. but I haven't yet found something which attracted my interest.

Read on to find out about Codehaus' Sonar.

Codehaus Sonar for code quality

Continue reading "Monitoring code quality"

Java Class Popularity

info@mhaller.de (Mike Haller) — Fri, 17 Apr 2009 08:00:00 +0200

Taken from a heap dump of a JBoss Application Server with some applications deployed, i've look at the number of objects in the heap and compiled a 'popularity list' accordingly:

java.util
1. ArrayList
2. HashMap
3. TreeMap
4. Vector
5. Hashtable
6. LinkedList
7. HashSet
8. WeakHashMap
9. TreeSet

Read on to see the full list. I've marked some classes which I find interesting enough to have a second look on them. Know your library.

Continue reading "Java Class Popularity"

Date ranges in Lucene

info@mhaller.de (Mike Haller) — Sat, 04 Apr 2009 13:23:59 +0200

Lucene is a very efficient and fast Java search engine. Once indexed, any object can be found by looking for attribute matches. An object in Lucene is called Document and its attributes are called Fields. Lucene uses Query and Filter objects to narrow down the search to what the user wants to find. A Query makes the amount of data to be searched smaller while a Filter is used for more fine-grained control over what a search result shall include. Queries are more memory-hungry than filters, but for the usual use cases, both are very good.

In this post, I'd like to show how you can search for Date and Time ranges, for example modification dates of files. I'd like to find all files on my local file system which were modified in April 2009.

Continue reading "Date ranges in Lucene"

Extending SQuirreL with plugins

info@mhaller.de (Mike Haller) — Sat, 07 Mar 2009 16:33:16 +0100

SQuirreL is a 100% pure-Java implementation of a generic SQL client. You can browse and analyse any database which provides a JDBC driver. You can execute any kind of SQL statements. SQuirreL provides a plugin mechanism to hook in additional features. The default installation comes with a lot of plugins, for example MySQL-specific plugins, code completion, data import plugins and more.

In this article, I'd like to show you how to write your own plugin for SQuirreL and what you need to do to set up your development environment. I'll implement two features for indexing tables and their content into an Apache Lucene index and to make it searchable using full-text search.

Continue reading "Extending SQuirreL with plugins"

XML Schema Validation done right

info@mhaller.de (Mike Haller) — Wed, 04 Mar 2009 13:06:49 +0100

To validate an XML document against an XSD Schema, Java 5 offers standard functionality with the built-in JAXP API. To do that, first create the Schema object as follows:

URL resource = getClass().getResource( SCHEMA_FILE );
SchemaFactory factory = SchemaFactory.newInstance( XMLConstants.W3C_XML_SCHEMA_NS_URI );
Schema schema = factory.newSchema( resource );

Continue reading "XML Schema Validation done right"

Dynamic Applications

info@mhaller.de (Mike Haller) — Mon, 16 Feb 2009 00:15:00 +0100

What are Dynamic Applications?

It's the software-way of putting the business people back in charge. Today, changes to enterprise business software takes ages to get into production. Endless analyze-redesign-implement-test-deploy cycles affecting multiple stakeholders: IT, QA, vendors and of course the sponsor.

How would it feel if the first three stakeholders could be removed from the process, once the application has been finalized in its initial state? How about giving the sponsor or business department the ability to adapt and change applications on their own? How about giving them the ability to change complex business logic, fine-tune parameters and model work flow to reflect the reality when and as soon as it changes?

Continue reading "Dynamic Applications"

Dumb Annotations

info@mhaller.de (Mike Haller) — Thu, 22 Jan 2009 10:57:02 +0100

I just read the article about the new Java Servlet 3.0 Specification over at dZone when it once again struck me: Annotations!

Continue reading "Dumb Annotations"