Skip to main content

Generating log statements from your application

In most software applications, control passes through complex code while users use the system. For large applications it is very important to keep track of where control is passing through in the application, if any exceptions are being thrown and what actions are being invoked by the user. Keepingtrack of these things help in maintaining an audit log and also in debugging the system if it fails at any point.

In this section we will understand why we should not use System.out.println() and we will also understand how to use a very good open source alternative called Log4J.


When you write small programs and run them, how do you keep track of where your program is passing control? How do you debug your program if it does'nt work properly? Most likely the answer is:

System.out.println("some message");

This is the most common way to debug and track a small program, but it is also a flawed approach.

  • It is cumbersome to print the source of the message.
  • It is cumbersome to print a timestamp with the message.
  • We cannot associate different levels with message.
  • We cannot direct the message to different locations.
  • We cannot selectively turn of logging based on source or level.

These factors are not very important for small assignments, but they gain a lot of importance for industrial code, which may send out thousands of log statements that are used not only for debugging, but also for auditing.

Traditionally most companies used to create their own logging libraries, which they used in their software. But this is such a waste. All companies end up making almost the same kind of library, and all of them maintain it for the same reasons.

Log4J, is an open source logging library, that helps us achieve all the above points and more. In the next few posts I will write about how to use Log4J to incorporate logging in your applications.



Even though I speak about Log4J, Java has a standards compliant logging library bundled with the JDK, and the Jakarta Commons Logging framework can call into both Log4J as well as Java Logging API's.



Discuss this post in the learning forum.



Note: This text was originally posted on my earlier blog at http://www.adaptivelearningonline.net
Here are the comments from the original post


 


 



Commercial Links


Labels:

Comments

Post a Comment

Popular posts from this blog

My HSQLDB schema inspection story

This is a simple story of my need to inspect the schema of an HSQLDB database for a participar FOREIGN KEY, and the interesting things I had to do to actually inspect it. I am using an HSQLDB 1.8 database in one of my web applications. The application has been developed using the Play framework , which by default uses JPA and Hibernate . A few days back, I wanted to inspect the schema which Hibernate had created for one of my model objects. I started the HSQLDB database on my local machine, and then started the database manager with the following command java -cp ./hsqldb-1.8.0.7.jar org.hsqldb.util.DatabaseManagerSwing When I tried the view the schema of my table, it showed me the columns and column types on that table, but it did not show me columns were FOREIGN KEYs. Image 1: Table schema as shown by HSQLDB's database manager I decided to search on StackOverflow and find out how I could view the full schema of the table in question. I got a few hints, and they all pointed to ...
Post a Comment
Read more

Commenting your code

Comments are an integral part of any program, even though they do not contribute to the logic. Appropriate comments add to the maintainability of a software. I have heard developers complain about not remembering the logic of some code they wrote a few months back. Can you imagine how difficult it can be to understand programs written by others, when we sometimes find it hard to understand our own code. It is a nightmare to maintain programs that are not appropriately commented. Java classes should contain comments at various levels. There are two types of comments; implementation comments and documentation comments. Implementation comments usually explain design desicisions, or a particularly intricate peice of code. If you find the need to make a lot of implementation comments, then it may signal overly complex code. Documentation comments usually describe the API of a program, they are meant for developers who are going to use your classes. All classes, methods and variables ...
Post a Comment
Read more

Inheritance vs. composition depending on how much is same and how much differs

I am reading the excellent Django book right now. In the 4th chapter on Django templates , there is an example of includes and inheritance in Django templates. Without going into details about Django templates, the include is very similar to composition where we can include the text of another template for evaluation. Inheritance in Django templates works in a way similar to object inheritance. Django templates can specify certain blocks which can be redefined in subtemplates. The subtemplates use the rest of the parent template as is. Now we have all learned that inheritance is used when we have a is-a relationship between classes, and composition is used when we have a contains-a relationship. This is absolutely right, but while reading about Django templates, I just realized another pattern in these relationships. This is really simple and perhaps many of you may have already have had this insight... We use inheritance when we want to allow reuse of the bulk of one object in other ...
3 comments
Read more