Skip to main content

classpath*: making your Modular Spring Resources

Spring gives multiple options to load XML resources for building contexts. the reference documentation does explain this feature quite well. However, I am taking my shot at explaining the different practical scenarios ( by order of growing modularisation)

For Example, A simplest Spring based web Context Loader can be configured with resources like this
<context-param> 
  <param-name>contextConfigLocation</param-name>
  <param-value>applicationContext.xml</param-value>
</context-param>

<listener>
   <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

You just need to put applicationContext.xml in WEB-INF/ folder of your webapp.

However, Typically an application is n-tiered. You can also have multiple files setup and in relative paths.
like
<param-value>
  context-files/applicationContext.xml
  context-files/dao.xml
  context-files/service.xml 
</param-value>

put them in WEB-INF/context-files folder.

But as Spring Conventions suggest, generally, applicationContext is generally the file that is defined in context loading, and the others are "imported" into the context
<param-value>
  context-files/applicationContext.xml
</param-value>
and in applicationContext.xml
<import  resource="dao.xml"/>
note that the resource is relative (no context-files/dao.xml)

Again, as projects grow, each tier (service, dao .. ) are modularised into separate jars, so the respective config file(s) also move to those jars. so, referencing those xml files relatively will not work, because they are may be loaded by a different class loader. So to reference across class loaders
<!-- applicationContext.xml is same, dao.xml is jar-ed in dao-module.jar under context-file/ --> <import  resource="classpath:context-files/dao.xml"/>

Further down, daos, themselves might be separated by components in applications
 <import  resource="classpath:com/company/common/dao.xml"/>
 <import  resource="classpath:com/company/order/dao.xml"/>
 <import  resource="classpath:com/company/account/dao.xml"/>
 <import  resource="classpath:com/company/account/legacy/dao.xml"/>
 <import  resource="classpath:com/company/cs/dao.xml"/>

The above can be achieved using ant wild card like in
<!-- notice, the all directories and sub directories (account/legacy/ too) --> 
<import  resource="classpath:com/company/**/dao.xml"/> 

Getting the drift? Best is yet to come. You know you could actually have these context files loaded by different class loaders but in same application. Ex: EAR loading contexts in war and META-INF jars in separate class loaders. As Long as these are in the same VM, You can do a multi classloader resource look up like this:
<!-- notice, the asterisk --> 
<import  resource="classpath*:com/company/**/dao.xml"/> 

There are other less used schemes like file: and http:. There are to be avoided in JEE for apparent reasons. Albeit, they are extremely useful in some scenarios, like, TestCases and WebServices.

Popular posts from this blog

Javascript: Convert Strings to Binary (and representing in a nerdy way!)

I follow those GoogleDevelopers Videos . Sometime back, in one of the presentations on GoogleIO, there was this interesting string of dots at the bottom of each page of the presentation . They looked like random big and small dots. A similar bunch of dots were also on the T-shirt of a presenter was wearing in another presentation . While it seemed something in the pattern, I could not find what it was. Finally, another presenter cleared the matter that those dots are just binary representation of "GOOGLEIO" (So much for advertizing Google IO, Impressive!). So I wanna do it. Takes me back to days of those DSP classes at school. Nerdy me had to churn some old brain cells. I remember those first programming language classes in Pascal and C when you were asked to do fibonacci series and converting a binary string to ascii codes. That *experience* came handy here: Check it out! Text to Binarize: For those who came to copy the javascript code to convert string to binary,

MySql Copying Table Structures.

Some times you need to copy only table structures across databases. This article describes two ways of doing it. If the whole database schema need to be exported, mysqldump is very effective. A --nodata flag will dump all tables' schema. Like this. mysqldump --nodata -p -u username databaseName But if you want to copy a specific table, individually, you could use "create table like" feature. You could create it even from a different database. However it must be on the same mysqld instance. Like this. create table newtable like oldtable; --Or from a table in other database create table mytable like otherdatabase.tablename;

javascript maxlength for textarea with \r\n breaks in java (esp Firefox)

Textareas allow new lines to enter. These are represented by \n (1) or \r\n (2) characters. But when you save to DB you have a limit to certain length of chars. There is no maxlength attribute in HTML that will stop you from entering data. This is generally acomplished by Javascript. You do a onkeyup hook and stop event or trim after textarea.value.length > maxlength. There are many other solutions out there.. But.. Here is the problem that most of those solutions overlook, How do you deal with the count on \n and \r\n representations. Lets first see how it matters. If the text entered has new lines, the length is calculated differently in Firefox and IE. When you enter a Text like 01234 567890 You expect the textarea.value.length to be 11. (10 chars + new line).On the backend, however, java would recieve it as 12 chars (10 chars + \r\n) (this is irrespective of FF or IE). So you are effectively saving 12 chars to DB. Worse yet, IE seems to figure textarea.value.length as 12 (