Java Logging API

1
Java Logging API

• An alternative to Debug by println
• Christopher J Coakley

2
Overview

• Debug by println Server Example
• Adding granularity
• DIY Logging API
• Logging API
• Changing Logging Levels and Handlers
• Apache log4j
• Conclusion

3
Debug by println

• Use System.out.println when in doubt
• PROS
• Easy to Implement
• Effective
• CONS
• Annoying to remove (readd)
• All or Nothing Approach
• Example Server1.java

4
Adding Granularity

• Create local level variable and constants
• Preface println statements with if braces
• if (level lt SERIOUS) System.out.println(Crash)
  
• CONS more code to look at
• Example Server2.java

5
DIY Logging API

• Encapsulate the level
• Allow alternative output
• Example MyLogger.java
• PROS Does everything we wanted
• CONS What if we want more

6
Logging API

• Encapsulates (almost) everything
• java.util.logging.Logger
• Create with Logger.getLogger() factory method
• Logger log Logger.getLogger( this.class.getName(
  ) )
• log.warning(bad news)
• log.severe(fatal program error)
• log.info(boring stuff)
• Example Server3.java

7
Changing Logging Levels and Handlers

• A handler is responsible for the level
• Delegation allows multiple handlers
• Output everything to file, critical to System.err
• Supports inheritance
• Logger pre-filters messages
• Warning Suns info is wrong (incomplete)!

8
Handlers Continued

• StreamHandler can wrap System.err
• SocketHandler can write over TCP
• FileHandler supports log file rotation
• FileHandler defaults to XMLFormatter
• FileHandler(pattern, limit, count, append)
• Example Server4.java

9
Apache log4j

• Replacement for Java logging
• Cool Features
• System Logger
• GUI log file viewer
• Universal and Generic Logging Interface
• http//logging.apache.org/log4j/docs/

10
Conclusion

• Logging is not Testing
• Logging is a Debug by println replacement
• Useful for long running server applications

11
Questions?
12
Factory Pattern - Encapsulate new

• public class myclass
• private static HashMap h_ new HashMap()
• public static MyClass getMyClass(String name)
• MyClass ret (MyClass)h_.get(name)
• if (ret null)
• ret new MyClass(name)
• h.put(name,ret)
• return ret

13
Java Properties

• java.util.Properties
• Just a hash table
• System.getProperties()
• Used by a variety of APIs and Extensions
• Can be used by logging to change preferences.
• Example PropLog.java