7/31/2019 Logging v.2

1/84

S

Loggingor System.out.println() 2.0author: Alex Maskovyak

date: 2012-04-27

7/31/2019 Logging v.2

2/84

S

Loggingor System.out.println() 2.0author: Alex Maskovyak

date: 2012-04-27

7/31/2019 Logging v.2

3/84

S

Metadata

7/31/2019 Logging v.2

4/84

Agenda

S Objectives

S Overview

S Principles

S Next Steps

7/31/2019 Logging v.2

5/84

S

Objectives

7/31/2019 Logging v.2

6/84

Objectives

S Define what logging is.

S Understand the benefits of logging.

S Identify logging best practices.

S Understand how to use the new logging framework.

7/31/2019 Logging v.2

7/84

Motivation

S Make the life of you, the developer, easier

S Make the life of the developer after you easier

7/31/2019 Logging v.2

8/84

S

Overview

7/31/2019 Logging v.2

9/84

Definition

S process of recording events, with an automated

computer program, in a certain scope in order toprovide an audit trail that can be used tounderstand the activity of the system and todiagnose problems

7/31/2019 Logging v.2

10/84

Definition

S process of recording events, with an automated

computer program, in a certain scope in order toprovide an audit trail that can be used tounderstand the activity of the system and todiagnose problems

7/31/2019 Logging v.2

11/84

What it is

S Provides insight into the state and operation of the

system.

S Provides application-level information in anaudience-appropriate manner.

S Necessary operation of software during themaintenance phase of an applications life.

S Part of the Definition of Done

7/31/2019 Logging v.2

12/84

Purposes

S Expose application state

S Trace execution

S Document configuration state

S Monitor for errors/warnings

S Debug code

S Provide system performance/timing

7/31/2019 Logging v.2

13/84

What it isnt

S Calls to System.out.println()

S Necessary only during development

S Magic that occurs without developer support

S Complete substitute for documentation, comments,and testing.

7/31/2019 Logging v.2

14/84

Java Logging

S Libraries

S JDK 1.4+ java.util.logging (JUL)

S log4j

S nlog4j

S log5j

S LogBack

S Common frameworks

S Jakarta/Apache Commons Logging

S Slf4j

S Log Viewers Analyzers

S Chainsaw

S Lilith

7/31/2019 Logging v.2

15/84

slf4j

S Simple Logging Facade for Java

S Designed by log4j creator

S Binds to logging frameworks

S Bridges to legacy logging APIs

S Provides a migrator

S Supports parameterized logging

S slf4j-access provides servlet support

S JBoss provides slf4j-jboss-logmanager.jar

7/31/2019 Logging v.2

16/84

LogBack

S Successor to log4j

S Fast message generation

S Automatic configuration file reloading

S Conditional configuration files

S Filters

S Logback Console Plugin

7/31/2019 Logging v.2

17/84

Java Logging ExampleJUL

7/31/2019 Logging v.2

18/84

public class AwesomeObject {private static Logger logger =

Logger.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.log(Level.INFO, Starting app, explicit Level ex.);

logger.finer(Got arg0=+args[0]+ arg1+args[1]);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

19/84

public class AwesomeObject {private static Logger logger =

Logger.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.log(Level.INFO, Starting app, explicit Level ex.);

logger.finer(Got arg0=+args[0]+ arg1+args[1]);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

20/84

public class AwesomeObject {private static Logger logger =

Logger.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.log(Level.INFO, Starting app, explicit Level ex.);

logger.finer(Got arg0=+args[0]+ arg1+args[1]);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

21/84

public class AwesomeObject {private static Logger logger =

Logger.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.log(Level.INFO, Starting app, explicit Level ex.);

logger.finer(Got arg0=+args[0]+ arg1+args[1]);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

22/84

public class AwesomeObject {private static Logger logger =

Logger.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.log(Level.INFO, Starting app, explicit Level ex.);

logger.finer(Got arg0=+args[0]+ arg1+args[1]);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

23/84

public class AwesomeObject {private static Logger logger =

Logger.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.log(Level.INFO, Starting app, explicit Level ex.);

logger.finer(Got arg0=+args[0]+ arg1+args[1]);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

24/84

public static void main(String args) {logger.entering(AwesomeObject.class.getName(),main,args);

try { crash(); }

catch( Exception e ) {logger.logp(Level.SEVERE,AwesomeObject.class.getName(),main,Encountered a problem! See exc, e);

}

logger.exiting(AwesomeObject.class.getName(),main,Exiting application.,0);

}

7/31/2019 Logging v.2

25/84

public static void main(String args) {logger.entering(AwesomeObject.class.getName(),main,args);

try { crash(); }

catch( Exception e ) {logger.logp(Level.SEVERE,AwesomeObject.class.getName(),main,Encountered a problem! See exc, e);

}

logger.exiting(AwesomeObject.class.getName(),main,Exiting application.,0);

}

7/31/2019 Logging v.2

26/84

public static void main(String args) {logger.entering(AwesomeObject.class.getName(),main,args);

try { crash(); }

catch( Exception e ) {logger.logp(Level.SEVERE,AwesomeObject.class.getName(),main,Encountered a problem! See exc, e);

}

logger.exiting(AwesomeObject.class.getName(),main,Exiting application.,0);

}

7/31/2019 Logging v.2

27/84

Java Logging Exampleslf4j & LogBack

7/31/2019 Logging v.2

28/84

public class AwesomeObject {private static Logger logger =

Logger.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.info(Starting application.);

logger.finer(Got arg0=+args[0]+ arg1+args[1]);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

29/84

public class AwesomeObject {private static Logger logger =

LoggerFactory.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.info(Starting application.);

logger.finer(Got arg0=+args[0]+ arg1+args[1]);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

30/84

public class AwesomeObject {private static Logger logger =

LoggerFactory.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.info(Starting application.);

logger.finer(Got arg0=+args[0]+ arg1+args[1]);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

31/84

public class AwesomeObject {private static Logger logger =

LoggerFactory.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.info(Starting application.);

logger.debug(Got args: {}, args);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

32/84

public class AwesomeObject {private static Logger logger =

LoggerFactory.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.info(Starting application.);

logger.debug(Got args: {}, args);

try { crash(); }catch( Exception e ) {

logger.severe(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

33/84

public class AwesomeObject {private static Logger logger =

LoggerFactory.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.info(Starting application.);

logger.debug(Got args: {}, args);

try { crash(); }catch( Exception e ) {

logger.error(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

34/84

public class AwesomeObject {private static Logger logger =

LoggerFactory.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.info(Starting application.);

logger.debug(Got args: {}, args);

try { crash(); }catch( Exception e ) {

logger.error(Encountered a problem! See exc, e);}

logger.log(Level.FINER, Exiting application.);}

}

7/31/2019 Logging v.2

35/84

public class AwesomeObject {private static Logger logger =

LoggerFactory.getLogger(AwesomeObject.class.getName());

public static void main(String args) {logger.info(Starting application.);

logger.debug(Got args: {}, args);

try { crash(); }catch( Exception e ) {

logger.error(Encountered a problem! See exc, e);}

logger.log(new myExitMarker(), Exiting application.);}

}

7/31/2019 Logging v.2

36/84

Know Your Audience

S System administrators/operators

S Installing application.

S Starting application.

S Shutting down application.

7/31/2019 Logging v.2

37/84

Know Your Audience

S Support Personnel

S Monitors of application.

7/31/2019 Logging v.2

38/84

Know Your Audience

S Developers

S Debugging applications.

S Measuring performance.

S Using your class/API.

7/31/2019 Logging v.2

39/84

Know Your Audience

S Machines

S Scripts

S Automation tools

S Operation tools

7/31/2019 Logging v.2

40/84

Severity Levels

S Partition log space

S Digestible pieces

S Triage-able levels.

7/31/2019 Logging v.2

41/84

Not Triage-able

S DEBUG: Began session

S DEBUG: DB access pass for user_id=154314, measure_id=14.

S DEBUG: DB access fail for user_id=41234113, measure_id=15.

S DEBUG: DB access pass for user_id=1341234, measure_id=14.

S DEBUG: DB access pass for user_id=8224122, measure_id=14.

S DEBUG: DB access pass for user_id=1143456, measure_id=14.

S DEBUG: DB access pass for user_id=17111341, measure_id=14.

S DEBUG: DB access fail for user_id=17521344113, measure_id=14.

S DEBUG: DB access pass for user_id=17, measure_id=131422.

S DEBUG: Ended session

7/31/2019 Logging v.2

42/84

via audit tool...or even a grep

S DEBUG: Began session

S DEBUG: DB access pass for user_id=154314, measure_id=14.

S ERROR: DB access fail for user_id=41234113, measure_id=15.

S DEBUG: DB access pass for user_id=1341234, measure_id=14.

S DEBUG: DB access pass for user_id=8224122, measure_id=14.

S DEBUG: DB access pass for user_id=1143456, measure_id=14.

S DEBUG: DB access pass for user_id=17111341, measure_id=14.

S ERROR: DB access fail for user_id=17521344113, measure_id=14.

S DEBUG: DB access pass for user_id=17, measure_id=131422.

S DEBUG: Ended session

7/31/2019 Logging v.2

43/84

Severity Levels

S FATAL

S Application down.

S Application inaccessible.

S High-level features are inaccessible.

S Application aborted.

7/31/2019 Logging v.2

44/84

Severity Levels

S ERROR (SEVERE)

S Application was unable to recover from a problem.

S Application was able to recover but was unable tofulfill a request or contract.

7/31/2019 Logging v.2

45/84

Severity Levels

S WARN

S Potentially harmful problem has occurred that warrantsfurther investigation.

S No fault occurred.

7/31/2019 Logging v.2

46/84

Severity Levels

S INFO

S Broad-brush

S High-level

S Coarse-grain

S System progress or state.

7/31/2019 Logging v.2

47/84

Severity Levels

S DEBUG (FINE)

S Low-level

S Fine-grain

S Information for debugging

S Generally turned off on production systems unless a

problem is detected where high-level information isinsufficient.

7/31/2019 Logging v.2

48/84

Hierarchies

S Further separation of concerns

7/31/2019 Logging v.2

49/84

Hierarchies

S NONE: All technical details

S TIMING: Performance info

7/31/2019 Logging v.2

50/84

Hierarchies

S SECURITY: Security relevant information

S Failed logins

S Creation of users

S Access to invalid URLs

S Potentially unsafe user-input

S Spikey user requests

7/31/2019 Logging v.2

51/84

Hierarchies

S AUDIT

S Completed / Failed business transactions.

S DB access.

S Service access.

7/31/2019 Logging v.2

52/84

Hierarchies

S USER: user behavior

S Invalid data entered

S Actions used

7/31/2019 Logging v.2

53/84

Persistence

S Multiple files.

S Per application.

S Per date.

S Per hierarchy/concerns.

7/31/2019 Logging v.2

54/84

Persistence

S File-system first, HBase later.

S /usr/local/explorys/[application-name]/

S [application-name]-[date].log

7/31/2019 Logging v.2

55/84

S

PrinciplesWhat, Where, When, & How

7/31/2019 Logging v.2

56/84

Principle #1

System.out is not adequate logging

7/31/2019 Logging v.2

57/84

Principle #2

Logging should occur during development

7/31/2019 Logging v.2

58/84

Principle #3

Logging must be descriptive and useful to others

Principle #3

7/31/2019 Logging v.2

59/84

Principle #3Ex.1

S NO (does not contain valuable information):

S log.debug(Here);

S log.debug(+++DEBUG+++);

S log.debug(randomVariableWithoutLogComment);

Principle #3

7/31/2019 Logging v.2

60/84

Principle #3Ex.2

S NO:

S log.debug(Array values: {}, myArray);S Will print out a reference identity: Array@4dc911a5

S Does not have an overloaded toString();

S YESS log.debug(Array values: {}, Arrays.toString(myArray));

S Prints out a human-readable string value.

Principle #3

7/31/2019 Logging v.2

61/84

Principle #3Recipe for a Good Message

S What is your reason for logging

/ Why are you logging.S Root cause.

Principle #3

7/31/2019 Logging v.2

62/84

Principle #3Recipe for a Good Message

S What needed to happen

/ Affected use-case.S User creation?

S Measure execution?

S Measure deletion?

Principle #3

7/31/2019 Logging v.2

63/84

Principle #3Recipe for a Good Message

S What instance was effected?

S User id.

S Measure id.

S Measure group id.

Principle #3

7/31/2019 Logging v.2

64/84

Principle #3Recipe for a Good Message

S What did and what didnt happen

/ Effect on Use-caseS User needs to repeat action, or did it succeed?

S Did entire batch fail, or did just a single step?

Principle #3

7/31/2019 Logging v.2

65/84

Principle #3Where & When

S Application state changes

S Startup

S Shut-down

Principle #3

7/31/2019 Logging v.2

66/84

Principle #3Where & When

S Configuration

S Source of configurationS Files used

S Environment

S VM arguments

S

Values of parametersS Packages/Libraries

Principle #3

7/31/2019 Logging v.2

67/84

Principle #3Where & When

S Method Invocation

S StartS Method name

S Parameter names/values

S Time entered

S End

S Method return valueS Exit statement

S Time returned

Principle #3

7/31/2019 Logging v.2

68/84

Principle #3Ex.3

public Measures[] getMeasures(User user, String type) {log.debug(

BEGIN getMeasures(user={}, type={}),user, type);

Measures[] res = ;log.debug(END getMeasures() => {}, res.length);return res;

}

Principle #3

7/31/2019 Logging v.2

69/84

Principle #3Where & When

S Exceptions

S Where the exception is actually handled/caught.S Top-most level.

S Not where it is transformed.

S Not when it is first thrown.

S

When all information is availableS Avoid repetition

Principle #3

7/31/2019 Logging v.2

70/84

Principle #3Ex.4

S NO:try {}catch(Exception e) {

log.error(Caught exception, did nothing, e);throw e;

}

S NO:

Exception e = ;log.error(Created exc and printed it redundantly here, e);

throw e;

Principle #3

7/31/2019 Logging v.2

71/84

Principle #3Where & When

S Long-lived Calls

S e.g.S IO

S File

S DB

S Services

S SOAS REST

S Log before & after call

7/31/2019 Logging v.2

72/84

Principle #4

Logging should be DRY and concise.

7/31/2019 Logging v.2

73/84

Principle #5

Log with an audience in mind.

Principle #5

7/31/2019 Logging v.2

74/84

Principle #5Ex.1

S ADMIN:

S log.error(PDV failed to start because the datasource {} couldnot be accessed, please ensure that {} is accessibleby);

S DEV:

S log.error(PDV attempted to do {} but was unable to becauseof exception {});

7/31/2019 Logging v.2

75/84

Principle #6

Be mindful of performance

Principle #6

7/31/2019 Logging v.2

76/84

Principle #6Ex.1

S Acquire a single logger instance.

S private Logger logger =LoggerFactory.getLogger(classname);

S @Inject Logger logger;

S Avoid processing large collections of objects.

S No: log.info(Returning measures {}, measures);

S Yes: log.info(Returning measured ids {}, );

S Yes: log.info(Returning total measure id count {}, );

Principle #6

7/31/2019 Logging v.2

77/84

Principle #6Ex.2

S Logging info quantity/size can/should be altered

based upon status.

If (log.isDebugEnabled()) {log.debug(Measures requested {});

} else {

log.info(Measure ids requested {});}

7/31/2019 Logging v.2

78/84

Principle #7

Use performance values appropriately.

Principle #7 Ex 1

7/31/2019 Logging v.2

79/84

S Yes:

StopWatch watch = new LoggingStopWatch( dbio );longlivedIO();watch.stop();

S Yes:

log.info(Finished {} measure results in {} secs.);log.info(Average calculation {} secs / result);

S No:

public String getName() {}

Principle #7 Ex.1

7/31/2019 Logging v.2

80/84

Principle #8

S Be safe

S Avoid causing problems

S Avoid side effects

Principle #8

7/31/2019 Logging v.2

81/84

Principle #8Ex.1

S log.debug(Obtained {}, user.getId());S are you sure user isnt null?

S log.debug(Obtained {}, collection.get(1));S are you sure there there are enough elements?

S log.debug(Connection closed: {}, conn.close());S are you sure debug level statements are enabled?

S are you sure theyll be enabled in production?

7/31/2019 Logging v.2

82/84

S

Next Steps

7/31/2019 Logging v.2

83/84

Action Items

S Alex

S Test slf4j and LogBack integration in current environment.S Test slf4j migrator.

S Test LogBack Eclipse tool.

S Team

S Study logger use.

S Begin using standard jdk logging in the areas identified.

S Be mindful of best-practices and principles.

7/31/2019 Logging v.2

84/84