log4j(day 11)

log4j:

• Using the log4j as a standard approach to logging .
• Logging defined as "A record,as of the performance of a machine or the progress of an undertaking.

Topics in log4j:

• The value of logging
• Approaches to logging-tracing
• Java Specification Request 47
• Log4J Background
• Log4J Configuration
• Using Log47

The value of logging:

Do programmers use debuggers or Loggers?

• Logging is often faster than using a debugger.
• Logging can be used to diagnose problems in the field.
• Debugging is difficult in a distributed computing environment.

Note:The key to using a logger for debugging is to have lots of events recorded.

Logging Activities:

• Tracing
• Debugging
• Error Handling
• Logging

What is Logged?:
Types of information logged:

• Program flow
• Detailed information about what occurs in a method at a granular level
• Information about a specific error that occurred in the system
• Document historical business events that have occurred

Approaches to logging: 

System.out.println

• poor performance
• All or none
• example below

some people use a class like 
class foo{
public staticfinal boolean debug=true;
public void test(){
if(debug)
System.out.println("i exist only in a test environment");
}
}

Custom log api

• More code to maintain
• Classic build vs buy (or use) decision

Open source (like Log4j)

Java Specification Request 47:

• Enable/disable logging at run time.
• control logging at a fairly fine granularity.

                    -Disable logging for specific functionality.

• Bridge services that connect the logging APIs to existing logging services(Operating System Logs,Third party logs).

 

Basic usage example:
class Foo{
category log=null;
public Foo(){
log=Category.getinstance(getclass());
log.info("Constructing foo");
}
public String doStuff(Long x){
log.debug("debug stuff");
}
}