System.out.println("USE A LOGGER!!!");

No matter if you are developing a small library, a complex framework or an application for end users - at some point you will come to the point that you want to log information. Here the Java community offers a whole wealth of solutions: Besides java.util.Logging there are libraries like commons-logging, Log4J or Logback. Where are the differences and unique selling points of the frameworks? In addition, actually everyone says that only the use of slf4J is "best practice". But why should I use an abstraction when developing a concrete application? Or does slf4j perhaps offer completely different advantages? And as if that weren't enough questions, with Java 9 a new logger, System.Logger, was quietly integrated into the OpenJDK.
This talk gives an understandable guide through the logging jungle and shows a few practices that help to get the logging of libraries and applications under control. If you're on the verge of going back to System.out out of frustration, this session is for you.

Transcript

1. View Slide

2. System.out.println(
   );
   "USE A LOGGER!!"
   

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3. This is a very very very long gag
   @hendrikEbbers
   Hendrik
   • Karakun Co-Founder
   • Founder of JUG Dortmund
   • JSR EG member
   • JavaOne Rockstar, Java Champion
   • AdoptOpenJDK TSC member
   

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4. This is a very very very long gag
   @hendrikEbbers
   Stephan
   • Karakun Co-Founder
   • SoCraTes CH community member
   • OpenWebStart committer
   • Conference speaker
   

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5. Content
   

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6. This is a very very very long gag
   @hendrikEbbers
   Content
   • Logging 101
   • Java Logging & Libraries
   • Integration & Architecture
   • Centralized Logging
   • Outlook - Future of Logging
   

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7. This is a very very very long gag
   @hendrikEbbers
   Content
   Go to www.menti.com and use the code 4490 2536
   

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8. Logging 101
   

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9. This is a very very very long gag
   @hendrikEbbers
   Definition of 'log'
   • a thick piece of wood cut from a
   tree
   • a written record of things that
   happen, especially an official record
   of a journey on a ship or in a plane
   • a logarithm
   * from the Macmillan Dictionary
   

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10. This is a very very very long gag
    @hendrikEbbers
    Why should you log?
    Log = Events which happened in the past
    • retrace what has happened
    • understand why an event occurred
    • gather information about how the software is used
    • learn from the past
    

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11. This is a very very very long gag
    @hendrikEbbers
    What should you log?
    • important events
    • input from outside the software / module
    • unexpected behavior
    

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12. This is a very very very long gag
    @hendrikEbbers
    What should you NOT log?
    • too many details
    • events in a loop
    • sensitive data
    08:34:23 INFO User 'Max' with birthday '01/01/1970' mutates password field with new value '1'
    08:34:23 INFO User 'Max' with birthday '01/01/1970' mutates password field with new value '1A'
    08:34:23 INFO User 'Max' with birthday '01/01/1970' mutates password field with new value '1A3'
    08:34:23 INFO User 'Max' with birthday '01/01/1970' mutates password field with new value '1A3.'
    

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13. This is a very very very long gag
    @hendrikEbbers
    How long should you keep a log?
    • forever
    • until you are certain you will never ever need the log
    any more
    Since you can never be certain:
    KEEP IT FOREVER
    

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14. This is a very very very long gag
    @hendrikEbbers
    • performance
    • code cluttering
    LOG.info("We start the transaction");
    manager.beginTransaction();
    LOG.info("DB query will be executed");
    LOG.debug("DB query: select * from users");
    long start = now();
    users = manager.query("select * from users");
    LOG.info("DB query executed");
    LOG.debug("DB query executed in " + (now() - start) + " ms");
    LOG.info("Found " + users.size() + " entities");
    manager.endTransaction();
    LOG.info("Transaction done");
    Has logging any downsides?
    

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15. This is a very very very long gag
    @hendrikEbbers
    Logging Concept
    • What's your motivation ?
    • who is reading / monitoring the log ?
    • what do you want to extract from the logs ?
    • what do you not want to extract ?
    • how is logging different in production/test/dev ?
    

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16. Logging in Java
    

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17. This is a very very very long gag
    @hendrikEbbers
    System.out
    System.out.print("Who needs a logger ??")
    

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18. This is a very very very long gag
    @hendrikEbbers
    Logger Architecture
    

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19. This is a very very very long gag
    @hendrikEbbers
    Architecture Detail
    

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20. This is a very very very long gag
    @hendrikEbbers
    Data from Application
    • Message
    • Exception (optional)
    • Marker (optional)
    

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21. This is a very very very long gag
    @hendrikEbbers
    Data from Logger
    • Logger Name
    • Log Level (Info, Warning, Debug ...)
    • Timestamp
    • Thread
    • Additional Context
    

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22. This is a very very very long gag
    @hendrikEbbers
    Data from Logger
    • Calling Class
    • Calling Method
    • Calling File
    • Calling Line Number
    • Calling Stack
    

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23. This is a very very very long gag
    @hendrikEbbers
    Additional Context
    • Context of the Logger
    • Properties/Attributes of the Logger
    • Context from the Application (MDC)
    In general this is based on
    the current thread
    

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24. This is a very very very long gag
    @hendrikEbbers
    Appender - Filter
    • Filter messages and only append
    the relevant to the log
    • By log level
    • By marker
    • By any other data provided
    by the logger
    

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25. This is a very very very long gag
    @hendrikEbbers
    Appender - Layout
    • Layout the message to fit the
    storage
    • Plain String / HTML
    • JSON / XML
    • GELF (Graylog Extended Log Format)
    • Optionally group messages to bulks
    

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26. This is a very very very long gag
    @hendrikEbbers
    Appender
    • Send the message to the storage
    • Console (stdout/stderr)
    • File (plain text, html, json, xml, etc)
    • DB
    • Remote
    

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27. This is a very very very long gag
    @hendrikEbbers
    Logging Frameworks
    2012 2013 2014 2016 2017 2019 2020
    2015 2018
    Log4j
    Logback
    Log4j2
    Commons Logging
    SLF4J
    Java 8 Java 9 Java 11
    TinyLog
    

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28. This is a very very very long gag
    @hendrikEbbers
    Logging Frameworks
    2012 2013 2014 2016 2017 2019 2020
    2015 2018
    Log4j
    Logback
    Log4j2
    TinyLog
    Commons Logging
    SLF4J
    Java 8 Java 9 Java 11
    

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29. Let's talk about
    PERFORMANCE
    

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30. This is a very very very long gag
    @hendrikEbbers
    Performance - Create Messages
    • Guard logging code
    • Delay string concatenation
    • Delay arguments calculation
    LOG.info("Hello " + username + "!");
    if (LOG.isInfo()) {LOG.info("Hello " + getUserNameFromServer() + "!");}
    LOG.info("Hello {}!", userName);
    LOG.info("Hello {}!", () -> getUserNameFromServer());
    

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31. This is a very very very long gag
    @hendrikEbbers
    Performance - Enhance Message
    • Avoid expensive meta data
    • Delay calculation of expensive meta data
    08:34:23 INFO [com.sample.MyClass] com.sample.MyClass.java:319 Hello World!
    LOgger name Source Information
    

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32. This is a very very very long gag
    @hendrikEbbers
    Performance - Enhance Message
    • Avoid expensive meta data
    • Delay calculation of expensive meta data
    08:34:23 INFO [com.sample.MyClass] com.sample.MyClass.java:319 Hello World!
    LOgger name Source Information
    Do we really need
    this?
    

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33. This is a very very very long gag
    @hendrikEbbers
    Performance - Persist Message
    • Asynchronous write to the storage
    • Bulk write to storage
    

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34. Logging Integration &
    Architecture
    

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35. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    • Let's have a look at some samples
    • As always we start with 'Hello World'
    

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36. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    HelloLogger.java
    Just a simple java class
    

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37. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    HelloLogger.java
    java.util.logging
    We use the 'Standard'
    Java logging
    

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38. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    package com.karakun;
    import java.util.logging.Logger;
    public class HelloLogging {
    private static final Logger LOG = Logger.getLogger("com.karakun.HelloLogging");
    public static void main(final String[] args) {
    LOG.info("Hello World");
    }
    }
    

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39. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    HelloLogger.java
    java.util.logging
    app-log.txt
    Level: INFO
    logging.properties
    We can configure
    the logger by using
    a properties file
    

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40. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    • Well that worked quite good
    • Let's have a look at a more complex
    application
    

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41. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    My Application
    database-access security-lib
    Our application has some
    dependencies
    

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42. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    My Application
    database-access security-lib
    jul Logging
    app-log.txt
    Level: INFO
    logging.properties
    We can still
    configure the
    logger by using a
    properties file
    

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43. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    My Application
    database-access
    Log4j
    security-lib
    jul Logging
    app-log.txt
    Level: INFO
    logging.properties
    The Dependency uses another
    logger to create log messages
    

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44. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    My Application
    database-access
    Log4j
    security-lib
    TinyLog
    jul Logging
    app-log.txt
    Level: INFO
    logging.properties
    ... and here we have
    another logger
    

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45. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    My Application
    database-access
    Log4j
    security-lib
    TinyLog
    jul Logging
    app-log.txt
    Level: INFO
    logging.properties
    

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46. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    My Application
    database-access
    Log4j
    security-lib
    TinyLog
    jul Logging
    ???????
    Level: ?
    app-log.txt
    Level: INFO
    ???????
    Level: ?
    logging.properties
    Where can we find
    that Logging?
    

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47. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    My Application
    database-access
    Log4j
    security-lib
    TinyLog
    jul Logging
    db-log.txt
    Level: INFO
    app-log.txt
    Level: INFO
    sec-log.txt
    Level: INFO
    logging.properties
    log4j.properties
    tinylog.properties
    

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48. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    My Application
    logging.properties
    log4j.properties
    tinylog.properties log4j2.properties
    db-log.txt app-log.txt sec-log.txt
    

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49. This is a very very very long gag
    @hendrikEbbers
    Application Architecture
    • Providing different configs for
    all possible logging libs can't
    be the solution
    • Let's get back to the table and
    sketch a good solution
    

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50. This is a very very very long gag
    @hendrikEbbers
    A Perfect LOG
    08:34:23 INFO Application starts
    08:34:24 DEBUG Connection to DB 'my-db'
    08:34:26 DEBUG Database connection created
    08:34:28 INFO Application started
    08:35:12 INFO User 'Hendrik' tries to log in to the system
    08:35:13 WARN Password for user 'Hendrik' is incorrect
    08:35:46 INFO User 'Hendrik' tries to log in to the system
    08:35:47 INFO User 'Hendrik' logged in
    08:36:22 DEBUG User 'Hendrik' opens search dialog
    08:36:34 INFO User 'Hendrik' starts search
    08:36:34 DEBUG User 'Hendrik' starts search with name='*java*'
    08:36:34 DEBUG Executing query on db
    08:36:47 DEBUG ResulSet contains 7 entries
    08:36:47 DEBUG User 'Hendrik' - Search result count: 7
    08:36:48 INFO User 'Hendrik' successfully executed search
    08:36:52 INFO User 'Hendrik' logged out
    

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51. This is a very very very long gag
    08:34:23 INFO Application starts
    08:34:24 DEBUG Connection to DB 'my-db'
    08:34:26 DEBUG Database connection created
    08:34:28 INFO Application started
    08:35:12 INFO User 'Hendrik' tries to log in to the system
    08:35:13 WARN Password for user 'Hendrik' is incorrect
    08:35:46 INFO User 'Hendrik' tries to log in to the system
    08:35:47 INFO User 'Hendrik' logged in
    08:36:22 DEBUG User 'Hendrik' opens search dialog
    08:36:34 INFO User 'Hendrik' starts search
    08:36:34 DEBUG User 'Hendrik' starts search with name='*java*'
    08:36:34 DEBUG Executing query on db
    08:36:47 DEBUG ResulSet contains 7 entries
    08:36:47 DEBUG User 'Hendrik' - Search result count: 7
    08:36:48 INFO User 'Hendrik' successfully executed search
    08:36:52 INFO User 'Hendrik' logged out
    @hendrikEbbers
    A Perfect LOG
    My Application
    jul Logging
    app-log.txt
    Level: ALL
    

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52. This is a very very very long gag
    08:34:23 INFO Application starts
    08:34:24 DEBUG Connection to DB 'my-db'
    08:34:26 DEBUG Database connection created
    08:34:28 INFO Application started
    08:35:12 INFO User 'Hendrik' tries to log in to the system
    08:35:13 WARN Password for user 'Hendrik' is incorrect
    08:35:46 INFO User 'Hendrik' tries to log in to the system
    08:35:47 INFO User 'Hendrik' logged in
    08:36:22 DEBUG User 'Hendrik' opens search dialog
    08:36:34 INFO User 'Hendrik' starts search
    08:36:34 DEBUG User 'Hendrik' starts search with name='*java*'
    08:36:34 DEBUG Executing query on db
    08:36:47 DEBUG ResulSet contains 7 entries
    08:36:47 DEBUG User 'Hendrik' - Search result count: 7
    08:36:48 INFO User 'Hendrik' successfully executed search
    08:36:52 INFO User 'Hendrik' logged out
    @hendrikEbbers
    A Perfect LOG
    My Application
    Log4j
    Logging
    db-log.txt
    Level: ALL
    DB Lib
    

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53. This is a very very very long gag
    @hendrikEbbers
    A Perfect LOG
    08:34:23 INFO Application starts
    08:34:24 DEBUG Connection to DB 'my-db'
    08:34:26 DEBUG Database connection created
    08:34:28 INFO Application started
    08:35:12 INFO User 'Hendrik' tries to log in to the system
    08:35:13 WARN Password for user 'Hendrik' is incorrect
    08:35:46 INFO User 'Hendrik' tries to log in to the system
    08:35:47 INFO User 'Hendrik' logged in
    08:36:22 DEBUG User 'Hendrik' opens search dialog
    08:36:34 INFO User 'Hendrik' starts search
    08:36:34 DEBUG User 'Hendrik' starts search with name='*java*'
    08:36:34 DEBUG Executing query on db
    08:36:47 DEBUG ResulSet contains 7 entries
    08:36:47 DEBUG User 'Hendrik' - Search result count: 7
    08:36:48 INFO User 'Hendrik' successfully executed search
    08:36:52 INFO User 'Hendrik' logged out
    How can we achieve
    this combination in
    one file?
    

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54. This is a very very very long gag
    @hendrikEbbers
    A stupid idea
    • Maybe we can just configure all logging libs to write in
    the same file...
    

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55. This is a very very very long gag
    @hendrikEbbers
    A stupid idea
    • Maybe we can just configure all logging libs to write in
    the same file...
    Bild: Freepik.com
    Concurrency
    issues
    File Locks
    Multiple
    Messages in
    one line
    Really a bad
    idea...
    Don't do this at
    home
    

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56. This is a very very very long gag
    @hendrikEbbers
    Logging issues
    • We have several loggers on the classpath
    • We want to have one central configuration
    • We want to have one central output
    • We do not want to miss logging messages from
    dependencies
    

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57. This is a very very very long gag
    @hendrikEbbers
    Let's sketch a solution
    My Application & Dependencies
    Logging
    Framework A
    Logging
    Framework B
    Logging
    Framework C
    Central
    Appender/Config
    Single Storage
    collect all messages
    

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58. This is a very very very long gag
    @hendrikEbbers
    SLF4J as Logging Facade
    • The SLF4J projects provide then needed
    functionalities
    • Logging facade
    • Logging bridges / adapters
    • Logging bindings
    Common API
    Forward messages to API/Facade
    Implementation of API/Facade
    

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59. This is a very very very long gag
    @hendrikEbbers
    Logging redirection
    My Application & Dependencies
    Commons
    logging API
    SLF4J API
    slf4j-api.jar
    Log4j API
    jcl-over-slf4j.jar log4j-over-slf4j.jar
    Underlying logging
    framework
    logback-classic.jar
    

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60. This is a very very very long gag
    @hendrikEbbers
    Logging redirection
    My Application & Dependencies
    Commons
    logging API
    SLF4J API
    slf4j-api.jar
    Log4j API
    jcl-over-slf4j.jar log4j-over-slf4j.jar
    Underlying logging
    framework
    logback-classic.jar
    Facade / API
    

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61. This is a very very very long gag
    @hendrikEbbers
    Logging redirection
    My Application & Dependencies
    Commons
    logging API
    SLF4J API
    slf4j-api.jar
    Log4j API
    jcl-over-slf4j.jar log4j-over-slf4j.jar
    Underlying logging
    framework
    logback-classic.jar
    Adapters
    

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62. This is a very very very long gag
    @hendrikEbbers
    Logging redirection
    My Application & Dependencies
    Commons
    logging API
    SLF4J API
    slf4j-api.jar
    Log4j API
    jcl-over-slf4j.jar log4j-over-slf4j.jar
    Underlying logging
    framework
    logback-classic.jar
    log4j-over-slf4j.jar
    replaces log4j.jar
    

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63. This is a very very very long gag
    @hendrikEbbers
    Logging redirection
    My Application & Dependencies
    Commons
    logging API
    SLF4J API
    slf4j-api.jar
    Log4j API
    jcl-over-slf4j.jar log4j-over-slf4j.jar
    Underlying logging
    framework
    logback-classic.jar
    log4j-over-slf4j.jar
    replaces log4j.jar
    log4j-over-slf4j.jar contains a custom
    org.apache.log4j.Logger class
    

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64. This is a very very very long gag
    @hendrikEbbers
    Logging redirection
    My Application & Dependencies
    Commons
    logging API
    SLF4J API
    slf4j-api.jar
    Log4j API
    jcl-over-slf4j.jar log4j-over-slf4j.jar
    Underlying logging
    framework
    logback-classic.jar
    Implementation of
    API &
    Binding to Logging
    Framework
    

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65. This is a very very very long gag
    @hendrikEbbers
    Logging redirection
    My Application & Dependencies
    Commons
    logging API
    SLF4J API
    slf4j-api.jar
    Log4j API
    jcl-over-slf4j.jar log4j-over-slf4j.jar
    Underlying logging
    framework
    logback-classic.jar
    No configuration!
    logger.properties
    Only configure The
    underlying Logger
    

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66. This is a very very very long gag
    @hendrikEbbers
    Solutions
    • There is no 'simple' solution that just fits for all
    scenarios and setups
    • Projects like SLF4J provides all that is needed to
    configure even complex use cases
    • Knowledge of the libs is needed
    

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67. This is a very very very long gag
    @hendrikEbbers
    Logging Facades
    2012 2013 2014 2016 2017 2019 2020
    2015 2018
    Log4j
    Logback
    Log4j2
    TinyLog
    Commons Logging
    SLF4J
    Java 8 Java 9 Java 11
    

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68. This is a very very very long gag
    @hendrikEbbers
    Java System.Logger
    • Part of OpenJDK (since 9)
    • See JEP 264 (https://openjdk.java.net/jeps/264)
    • Minimal Logging API / Facade
    • Used internally in the OpenJDK
    • Default adapter is java.util.logging
    

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69. This is a very very very long gag
    @hendrikEbbers
    Java System.Logger
    public class MainApp {
    private static System.Logger LOGGER = System.getLogger("MainApp");
    public static void main(String[] args) {
    LOGGER.log(Level.ERROR, "error test");
    LOGGER.log(Level.INFO, () -> "info test");
    }
    }
    Remember our
    performance discussion?
    

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70. This is a very very very long gag
    @hendrikEbbers
    Non-Goals of System.Logger
    • It is not a goal to define a general-purpose interface
    for logging. The service interface contains only the
    minimal set of methods that the JDK needs for its own
    usage.
    • It is not a goal to support programmatic logging
    configuration (setting levels, destination files, etc...)
    via the API.
    

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71. This is a very very very long gag
    @hendrikEbbers
    Best Practice for System.Logger
    • Do not use it as your application logger
    • Configure a bridge within the logger facade you are
    using (by using SPI)
    • Use it directly in small libraries to remove
    dependencies (no slf4j-api is needed anymore)
    

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72. Centralized Logging
    

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73. This is a very very very long gag
    @hendrikEbbers
    Application landscapes today
    • We now have a real good solutions to create and store
    the logging for one application
    • In a real world scenario this is not enough!
    • Let's take this a step further...
    

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74. This is a very very very long gag
    @hendrikEbbers
    Modern usecases
    • Will I have 1 log file for each node if my application is
    clustered?
    • Can I get my application log synchronised with the log
    of the database or the docker container?
    • How can I search in my logs and display all logs for 1
    specific request?
    

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75. What happens if we
    use Microservices?
    😱
    

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76. This is a very very very long gag
    @hendrikEbbers
    Modern usecases
    LOG
    LOG
    LOG
    LOG
    LOG
    LOG
    LOG
    LOG
    

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77. This is a very very very long gag
    @hendrikEbbers
    Let's sketch a solution
    • We need to find a way to centralise our logging
    • All log messages must be pushed / pulled to one
    central place
    • Based on the amount of logging this needs a special
    solution
    • The solutions needs good search functionality
    

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78. This is a very very very long gag
    @hendrikEbbers
    Centralized Log Management
    Logger
    Logentries
    json-file
    System Journal
    Syslog
    fluentd
    Windows Event Store
    Splunk
    GELF
    Amazon CloudWatch
    Google Cloud
    UDP / TCP
    TCP / HTTPS
    TCP / HTTPS
    TCP / HTTPS
    TCP / (HTTP & HTTPS)
    TCP
    UDP / TCP / TLS HTTP / HTTPS
    

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79. This is a very very very long gag
    @hendrikEbbers
    Graylog / GELF example
    Applications
    GELF
    Docker Containers
    GELF UDP / TCP
    UDP / TCP
    DB / System / Services
    GELF UDP / TCP
    JSON Format
    

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80. View Slide

81. View Slide

82. Remember
    Markers & MDC?
    

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83. Next steps
    

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84. This is a very very very long gag
    @hendrikEbbers
    Tracing
    • Tracing libraries provide important metadata in a
    distributed environment
    • Metadata is added to HTTP header
    • Follow a request over several services Use MDC & Metadata to see all
    log messages of this flow
    

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85. This is a very very very long gag
    @hendrikEbbers
    Analyze Logs using AI
    • Use 'log intelligence' to get better feedback
    • Detect issues automatically
    • Detect anomalies before they create issues
    • Understand and react to users and their behavior
    

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86. Stay safe & healthy
    

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87. • Use a Logging Facade
    • Use Centralized Logging (even of you
    have only 1 log file)
    • Use MDC and Markers
    

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