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Showing posts from 2006

How to force decimal separator char upon java region code?

Java application could be run on any compliant platform. And that's great. But, when you provide it to your customer, you don't know the region code of his server. For exemple, you don't know if is configured to work in english or french.

By the way, let's take the previous example. In franch, decimal separator char is ',' (comma). In english, it is '.' (dot). When prensenting data to end user, you probably want to ensure that the decimal separator char is the right. So, you can for it usiing DecimalFormat.

Let's see it in the following code :

public class AfficheurDecimal {

public AfficheurDecimal() {

private void testerReste(double reste) {
if (reste != 0) {
DecimalFormat formatEntier = new DecimalFormat("0.00");
DecimalFormatSymbols symbols = formatEntier.getDecimalFormatSymbols();
String msg = "Il…

Multibase application could be like in the song : it's just an illusion

Today, my friend and excellent architect Marc Godin told me something very interesting that sumarize an illusion that java introduced with its virtual machine. He said :

"L'adhérence a la base de donnée est à acter comme celle à la JVM"

Sorry, it's in french. BTW, the text tells that you had to choose your database as you chose you JVM.

Why primitive types are unprecises? the unacceptable explaination...

Another excellent article by Brian Goetz on numerical java data type storing. It's just a question of IEEE 754. So, don't expect to work with primitive types in Java for finacial applications. Such a pity! My old Casio FX-7000 is more powerfull than my computer.

Financial programs represents a major part of softwares all over the world. If you want my opinion, its unacceptable to have to work with wrapped types!!!

James Goslin, any solution? You're welcome if you have one.

Open ESB

Great news,

I just learnt that Sun launched an open source ESB project with a tool suite for NetBeans. This fact of having developped graphical tools to design processes and mappings is a very (VERY) important point in my point of view. Something tells me that, if the product is well done, the situation will be harder for webMethods in several months.

I will publish my Violet UML Editor as quickly as possible to investigate on it.

Searching files on unix

Want to find files and perform massives operations on them, here are tws sample commands for unix platforms :

find -name "[filename]"

find -name "[filename]" -exec [command] '{}' \;

where [filename] and [command] should be replaced by real values. [command] is another unix command to execute on each file found. The file found is represented by '{}' in the command to execute. \; indicates to end of the command.

Ex : find -name "*.tmp" -exec rm '{}' \; -> deletes all tmp files.

Hibernate 3 and Oracle 9i cursors : how does it work?

Here is a post I found on the hibernate forum. It explains why cursors opened are not released on session.close() :

OK. Here's the result of this thread:

For the environment, JDK1.4.2_01, Oracle 9i server, oracle 9i jdbc driver (ojdbc14.jar) and oci connection to the database (not thin driver);

There's no problem with hibernate's prep stmt cache nor with Oracle Jdbc driver with regard to cursors remaining open after Session.close().

Every Session.iterate() and Session.load() calls cause a prep stmt to be created on the server side. And after you close the session with Session.close(), hibernate explicitly calls appropriate driver methods to close the resultsets and prepared statements.

However, after you close the session, you won't see the cursors de-allocated (or closed) on the server side. While it seems to be a bug, it actually is not. The driver maintains a list of prep statements and open cursors in its memory and as soon as you re-use the same connection by opening …

Java primitive types

Just to remember... nothing more :

byteShort numerical from -128 to +1271 byteshortShort numerical from -32768 to +327672 bytesintNumerical from -2 147 483 648 to +2 147 483 6474 byteslongLong numerical from -263 to +263 -18 bytesfloatDecimal from -1.4 * 10-45 to +3.4 * 10384 bytesdoubleLong decimal from 4.9 * 10-324 to +1.7 * 103088 bytescharUnicode character (65536 possible characters)2 bytesbooleanBoolean (true or false)1 byte

Let's work in full screen mode

One of the greats features offered by Java is its capability to switch in full screen mode. The following article is a sun's tutorial on this subject :

To illustrate how it is benefit to use this mode, I want to opposite it to web based applications that impose the display of unusefull navigator toolbars (taking 25% of the screen workspace).

I will implement full screen mode in Violet UML Editor.

Inside the Sun's JVM memory

Yesterday, my manager asked me about a problem concerning the eden space memory. So, this is a summary of JVM's memory management.
Heap Size
The allocation of memory for the JVM is specified using -X options when starting ColdFusionJVM option Meaning
-Xms initial java heap size
-Xmx maximum java heap size
-Xmn the size of the heap for the young generation
(extended options)
-XX:MaxPermSize maximum permanent generation size (for creating object instances)
For efficient garbage collection, the -Xmn value should be lower than the -Xmx value.Heap size does not determine the amount of memory your process uses
If you monitor your java process with an OS tool like top or taskmanager, you may see the amount of memory you use exceed the amount you have specified for -Xmx. -Xmx limits the java heap size, java will allocate memory for other things, including a stack for each thread. It is not unusual for the total memory consumption of the VM to exceed the value of -Xmx.Garba…

Batch processing in Hibernate

I read this article that is very interesting (thank you very much Marco) :

Suppose you need to insert 200,000 records into a database in Hibernate. You'll need to adjust the following settings:
//set the JDBC batch size (it is fine somewhere between 20-50)
hibernate.jdbc.batch_size 30

//disable second-lavel cache
hibernate.cache.use_second_level_cache false

//and now do your job like this
Session S=SF.openSession(); //SF = SessionFactory object
Transaction T=S.beginTransaction();

for (int i=0;i<200000;i++)
record r=new record(...);;
if(i % 30==0)
{ //30, same as the JDBC batch size
//flush a batch and release memory

(Author : Anghel Leonard)

First Step

Humm... Well it's done! I don't want to spam Marco's blog (javacomptoir) anymore with dailly messages. On this blog, I will write about my readings, about articles I found on the web. In many cases, I will be about Java. But sometimes, It will be about related technologies such as databases, global software architecture and... my favorite activity during spare times : Violet, THE Very Intuitive Object modeling software that I develop behind Cay S. Horstmann.

Thus, this blog will be a sort of bookmark with some experience feedbacks