Monday, November 21, 2005

File Organisation in Web Applications

In Web Applications, you may have different kind of files like Servlet files ( .java files which define all the servlet methods), JSP Pages ( used for presentation purpose i.e., displaying information. It can be used in place of HTML to provide dynamic content unlike HTML's static content by embedding java commands in the JSP page), .properties file which contain the configuration details as (key,value) pair and also other .java files (which contains the business logic implemented in them).

To make the file organisation to be clean, we can follow seperate out presentation files and the business logic files and make them to be independent of each other. We should not include any business logic like reading from a database, writing to database or any other action in JSP files. Though it is always possible to accomodate any kind of java command and operation in jsp file, it is not advisable to do so. In Industry practice, the JSP Page and the .java file which has the business logic may be developed by two different person. JSP professional needs no knowledge of java. So it is better to avoid embedding complex business logic in jsp files. Minimal amount of java commands in jsp page for the purpose of presentation is acceptable.

So we can have all the business operations in .java file as a separate package and call them in the servlet files as and when needed. All the constants used in the application can be added in a .java file and could be declared as interface. We can make all the files that needs to use these constants to implement that interface for efficient space management. Moreover it is better to handle all the exceptions in any one particular level. Best practice is to handle the exceptions in the .java files which includes the business logic, instead of handling them in the servlet files. This method provides a greater amount of independence between the servlet files and the .java files.

All the configuration information could be stored in the .properties file and could be read from that file. It is easy to change any configuration in this method. Only the key,value pair in the .properties file needs to be changed to implement any change in the configuration.


Problem Description :
You are asked to create a simple web application which fetches the data from the Backend database and display all the entries on the Jsp page.

Possible file organisation:

Now, your file organisation can be like,

rootdir/src/"package1"/"any servlet/portlet file".java
rootdir/src/"package2"/"any business logic implementation file".java

Here you "jsps" directory holds all your jsp files. You can have
rootdir/web/jsps/help/ directory to hold your help.jsp files.

Then you can organise all your servlet/portlet files under one package.

And all your business logic implementation files i.e., here it could be the .java file that implements the jdbc connectivity methods to connect to the database, retrieve the data and all other database operations, could be placed in another package.

This organisation makes the package2 to be used independently in any other application when needed. You can import this package where ever needed.

Moreover, all the constants used in the web application can be added to an interface, may be, called "applicationname" and this file can be implemented by which ever file, which needs to use these constants.

If you want to create a package out of this application, you can add the following files and directories.

Using "ant" command, you can "build" the application using the build.xml file. Then snippet file contains all the files that has to be added into the package and also the file access permission for each of them. You can write script to read the snippet file and create package accordingly!

This is one possible method, but in Industry practice this method is widely used. If you feel this orientation is wrong, please correct me!

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