BASIC LOGGING

BEST PRACTICES

THINK TWICE ABOUT THE LOGGING LEVEL

AVOID SYSTEM.OUT.PRINTLN

Logging frameworks are:

Faster
Configurable
Flexible

The shell is your friend (blame command):

workspace$ grep -irl -C3 --include '*.java' 'out.println' *

DON'T HIDE STACK TRACES

Avoid these forms:

The correct way is:

 logger.error("Exception message", ex);

 logger.error("Exception: " + ex); logger.error("Exception: " + ex.getMessage());

YOU CAN LOG EXCEPTIONS TO AN SPECIAL LOG FILE

 try {   ... } catch (Exception ex) {   logger.error("Message");   stackTracesLogger.error("Message", ex); }

AVOID TO BUILD HEAVY MESSAGES IF LOGGING IS DISABLED

 if (logger.isDebugEnabled()) {     logger.debug(buildVeryHeeeeeeavyMessage()); }

DON'T ADD INFO LOG4J GIVES YOU FOR FREE

Instead add configuration (log4j.xml):

<appender ...>  <layout class="org.apache.log4j.PatternLayout">    <param name="ConversionPattern"       value="%d{yyyy-MM-dd HH:mm:ss,SSS} %5p [%t] %c{1} - %m%n"/>  </layout></appender>

 logger.error("[TheClassName.theMethodName] The message");

DON'T CLUTTER REQUEST WITH DIAGNOSTIC ATTRIBUTES, INSTEAD USE THREAD LOCAL

Use the MDC/NDC API (E.g. from Servlet Filter):

Then log MDC attributes through ConversionPattern:

 %X{'httpId'} ... MDC attribute %x           ... NDC

 MDC.put('httpId', UUID.randomUUID.toString());