Creating a unified logging schema for the JVM was introduced in Java 9. Here is a comprehensive list of the goals of that effort:

• To create a JVM-wide set of command line options for all logging operations
• To use categorized tags for logging
• To permit messages to have multiple tags, also referred to as tag sets
• To provide six levels of logging:
• Error
• Warning
• Information
• Debug
• Trace
• Develop

• To select which messages are logged based on levels
• To optionally direct logging to the console or a file:
• Print one line at a time and do not support interleaving within the same line
• To permit the output of multiple line logs (non-interleaved)
• To format all logging messages so that they are easily human-read
• To add decorations such as uptime, level, and tags
• Like levels, to select which messages are logged based on decorations
• To convert pre-Java 9 tty>print logging to use unified logging as the output
• To permit dynamic message configuration using jcmd and MBeans
• To permit the ability to enable and disable individual log messages
• To add the ability to determine the order in which decorations are printed

The unified logging changes to the JVM can be grouped into the following five categories:

• Command-line options
• Decorations
• Levels
• Output
• Tags

Let's briefly look at each of these categories.