How a Java developer code is logging part of the application by examples and questions.

1. Proper Application
Logging
Vidula Hasaranga

2. What is Logging?

3. Why Logging is important?

4. Logging Antipatterns
1.No Logging at All
2.Wrong Log Level
3.Catch Log Throw
4.Logging to stderr or stdout
5.Complex Logging Statements

5. What framework to use
1.Log4J
2.SLF4J with Logback
3.????

6. Know your Log Level
1.ERROR
2.WARN
3.INFO
4.DEBUG
5.TRACE

7. Correct or Incorrect
log.debug("Remote Service XYZ is not available");
or
log.info("Remote Service XYZ is not available");
or
log.warn("Remote Service XYZ is not available");

8. Correct or Incorrect
log.debug("Processing request " + request);
or
log.isDebugEnabled() {
log.debug("Processing request " + request);
}

9. Correct or Incorrect
log.debug("Processing request with id: {}", request.getId());

10. Correct or Incorrect
try {
log.trace("Id=" + request.getUser().getId() + " accesses "
+ manager.getPage().getUrl().toString())
} catch(NullPointerException e) {}

11. Correct or Incorrect
log.debug("Message processed");
log.debug(message.getJMSMessageID());
log.debug("Message with id '{}' processed",
message.getJMSMessageID());

12. Correct or Incorrect
log.info(“Authentication successful. Username [“ +
username + “], password [“ + password + “]”);

13. Correct or Incorrect
try {
//----
} catch (IOException e) {
}

14. Correct or Incorrect
try {
//----
} catch (IOException e) {
e.printStacktrace();
}

15. Correct or Incorrect
try {
//----
} catch (IOException e) {
log.error("IO exception", e);
throw new MyCustomException(e);
}

16. Correct or Incorrect
try {
Integer x = null;
++x;
} catch (Exception e) {
log.error(e); //A
log.error(e, e); //B
log.error("" + e); //C
log.error(e.toString()); //D
log.error(e.getMessage()); //E
log.error(null, e); //F
log.error("", e); //G
log.error("{}", e); //H
log.error("{}", e.getMessage()); //I
log.error("Error reading configuration file: " + e); //J
log.error("Error reading configuration file: " + e.getMessage()); //K
log.error("Error reading configuration file", e); //L
}

17. Questions...