The goal of the Apache Jakarta Commons Project is the development of reusable Java components, such as validation classes, command line option parsers, etc. Once of the components in this project is the Commons Logging component, which allows us to easily produce a log from our Java class.

The Commons Logging component has 6 levels of logging. This means that we are not limited to just one type of log message, but 6 types of messages with varying degree of 'severity'. This allows us to filter the types of messages, so we have a log with only the information we want. For example, at one point we might be interested in producing a log with all the debugging information, but later on we will probably only want a log with errors and warnings produced by our program.

The six levels of log messages are:

What messages go into each category is entirely up to the programmer, as we'll see in the next page.