I'd like to put the logger.debug(...) call into a helper method, and call that helper method from anywhere that needs to write the log. While this mostly works fine, the log entry itself shows the helper method as the source of the call, which is understandable since log4j isn't aware of me using a helper method for logging.
Is there any way to tell it to skip the helper method when figuring out the source of the logger.debug(...) call and instead use its caller?
By source, I mean %F:%L of org.apache.log4j.PatternLayout: https://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/PatternLayout.html
To illustrate what I mean, here's an example stack trace:
1. logger.debug(msg, throwable)
2. logHelper(logger, msg, throwable) <-- currently shows as the source of the call, since it calls logger.debug directly
3. someFunction <-- where the real logable event occurs, so I'd want this to be logged as the source
The reason I'm doing this is because I'd like an exception logged only by name (e.toString) if the log level is INFO, or with a full stack trace if the level is DEBUG. I'm open to suggestions for alternatives.
Thanks! :)
You can't instruct Log4J to "skip" a level in its source detection.
What you can do, though, is subclass PatternLayout and override the format(LoggingEvent) method to your liking (i.e. only produce the exception's toString() when in INFO mode, etc).
One way to do this is to have the helper class call:
logger.log(LogHelper.class.getName(), Level.DEBUG, message, t);
... instead of:
logger.debug(message, t);
So when log4j tries to determine the source of the event, it will stop when it reaches the parent of LogHelper instead of the parent of Logger.
Verified working as expected.
For Log4j2 the answer is provided completely by the use of logger wrappers as described in the Log4j2 manual under Example Usage of a Generated Logger Wrapper. One can simply generate (using the org.apache.logging.log4j.core.tools.Generate$ExtendedLogger tools illustrated there) a logger wrapper with a single STUB level, and then adapt that to create custom logging methods mimicking the use of the logIfEnabled(FQCN, LEVEL, Marker, message, Throwable) - possibly ignoring the STUB level and using the regular ones - then if desired, deleting or commenting out the STUB level and its methods). For this purpose the FormattedMessage can be helpful.
The method and source line, while expensive, can then be easily shown as part of the full location information by using the %l location conversion pattern element in the PatternLayout given in the configuration, or more specifically using the %L line number and/or the %M method conversion.
Now with complete example at: Java Logging: Log4j Version2.x: show the method of an end-client caller (not an intermediate logging helper method)
For log4j2, you can write a simple wrapper class or generate one as Webel suggests. See my answer for log4j2:
https://stackoverflow.com/a/39045963/116810
Related
I am trying to upgrade log4j to log4j2. The particular line of code I am trying to upgrade is:
log(targetClass, Priority.DEBUG_INT, message, null);
The static field Priority.DEBUG_INT is no longer available in the new Priority. Instead it looks like the getPriority(Facility facility, org.apache.logging.log4j.Level level) static method is used to access priority int value, to which DEBUG can be specified as the Level.
However, this method also requires a Facility to be specified. How do I know which Facility to specify when calling getPriority?
old Priority: https://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Priority.html
new Priority: https://logging.apache.org/log4j/2.x/log4j-core/apidocs/org/apache/logging/log4j/core/net/Priority.html
new Facility: https://logging.apache.org/log4j/log4j-2.8/log4j-core/apidocs/org/apache/logging/log4j/core/net/Facility.html
Assuming you are talking about Log4j 1's Category.log(String, Priority, Object, Throwable), it appears these Priority classes are pretty (if not completely) unrelated. Log4j 1's Priority is actually the level (indeed it has a subclass Level).
So you would have to look at Log4j 2's Logger class to see if any method with Level parameter matches, but there appears to be no identical alternative (except logMessage maybe, but that appears to be pretty low level).
However, you should check whether that targetClass argument for parameter callerFQCN is actually needed. It looks like it is intended to find the caller of the logger method and might mainly be intended for usage by logging libraries extending Log4j 1. Unless you are indeed upgrading such library, I would assume that the method is misused and a regular Log4j 2 logger.debug(message) would do equally well. Though it would help nonetheless if you could provide more context.
Although in some tutorials, for example here (Parametrized logging section), said that Logback message {} parametrization help us to avoid unnecessary calculation in logging data (if logging level is not DEBUG):
logger.debug("The bonus for employee {} is {}",
employee.getName(), employeeService.calculateBonus(employee));
I tested (on logback version 1.2.3) that this optimization works only for unnecessary toString() of parameter object - as this works for log4j.
Logback documentation doesn't cover this detail.
So, we have to use isDebugEnabled() for all 'expensive' logging, do we?
Take a look at the example here
Since 2.4, methods have been added to the Logger interface to support lambda expressions. The new methods allow client code to lazily log messages without explicitly checking if the requested log level is enabled. For example, previously one would write:
// pre-Java 8 style optimization: explicitly check the log level
// to make sure the expensiveOperation() method is only called if necessary
if (logger.isTraceEnabled()) {
logger.trace("Some long-running operation returned {}", expensiveOperation());
}
With Java 8, the same effect can be achieved with a lambda expression:
// Java-8 style optimization: no need to explicitly check the log level:
// the lambda expression is not evaluated if the TRACE level is not enabled
logger.trace("Some long-running operation returned {}", () -> expensiveOperation());
When you make a method call, e.g. employeeService.calculateBonus(employee), you're calling that method. Simple as that. So you are calculating the employee bonus every time this line is hit. There is no lazy evaluation here.
Whether or not to use log.isDebugEnabled() depends on the situation. In this situation, if that method call is expensive, you should wrap that in a debug enabled check.
In the case of getters, this isn't usually necessary. So, for instance, I would not wrap this in an isDebugEnabled check:
log.debug("Calculating bonus for employee {} {}", employee.firstName(), employee.lastName());
These are simple getters that return a String, so no expensive calculations are done.
I'm frequently annoyed by having
System.out.println(someObject);
and, when changing it to using whatever logger is required
LOG.info(someObject);
and having to add the .toString() to make it compile
LOG.info(someObject.toString());
I cannot recall having used a logger that does not simply take in an Object and tries do to .toString() on it, making me wonder if there is a specific reason for this. Surely I cannot be the only one annoyed by having to add .toString() to everything?
The key point is to understand the purpose of logging. Loggers are there to print human readable english messages regarding any event that occurs within an application. And the logging API's are built following this basic principle
LOG.info(someObject.toString());
The problem with the above line is that the basic concept of logging is somewhat different from what you are trying to achieve. You want to log an object which is already not a human readable entity and then to make it work by casting it either to a string or you could implement the toString() method or lastly you can take a look at one of the overloaded function
public void info(String format, Object... arguments)
Logging an object directly is mostly done by developers when they want to debug to lets say the contents of the object or something like that, so the best way to achieve that would be to correctly implement the toString() method.
I would also advise to take a look into the Project Lombok, it provides ready to use implementations of common hashCode() and toString() functions of your beans so you don't have to go through your code and implement the method one by one.
I am trying to implement logger using apache commonn logging and log4j.xml file as configuration file .
So in the actual java code i am writing log as
I am using appache common logging
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
and i am logging information such as in . I am creating a instance of log for each class
private static Log logger = LogFactory.getLog( MyClass.class );
private static final String name ="SAM";
logger.info("name= "+name);
So now my question is does implementing logger like this create a performanace issue?
Is it necessary to check log like
if ( log.isInfoEnabled( ) )
{
log.info( "Info message" );
}
The confusion is mainly because in Apache common logging they have mentioned to do this and in log4j they have mentioned it is unnecessary.
Each time when we write log in the files?
-Sam
yes and no, logging always reduces your performance, but some functions are more expensive then others, e.g. getting the calling class/method-Name uses reflection and is very slow. But a normal logfuntion is not that expensive if you do not have an expensive statement in the calling logging function (this will be evaluated every time before the log-Level is checked. In this case you can use the .isLevelEnabledcheck to prevent the evaluation). Also logging to the console takes longer for the output than logging to a file. You will find more information about this by googling and in the FAQ/manual of log4j.
You do not have to check the Log-Level before logging. This is done within the log-function itself. Therefore are the different methods for every Level or the Level-Argument in the generic log-Method.
A big potential performance problem with logging is usually if you have something passed into the log method that is very expensive to convert to a string. That's why you have methods like isInfoEnabled(), so that the code can avoid creating the message string from the parameter (otherwise the check within the info() method is too late, the conversion is already done). If your objects passed into the log methods are strings or are not very involved then the is*Enabled() methods won't be that useful.
SLF4J is worth checking out. It doesn't depend on classloader tricks (which is a big part of why commons-logging is reviled), and it has a different way of creating log messages which delays when the message string gets created so that the enabled check can take place within the logging method.
There's a better way to do all of this. You can get really great performance without having to add the clutter of ifDebugEnabled, etc methods. Check out something like Logback (or SLF4J). Here's the great documentation about what kind of an API you want. Note that Log4J and Commons-Logging doesn't have an API like this. Use Parameterized Logging.
On my team we have a logging standard, and for the most part the
Logger.log(Level, String, [Throwable])
methods works fine (it gives us automatic timestamp, class name, method name, message, and throwable information in the log). However, we have an additional identifier we log, and it's part of our standard (we use it to help monitor the logs).
My problem is that I want to be able to easily enforce this standard in a fairly painless way. At first we created a wrapper logger class, but the problem is you lose the benefit of Logger knowing which method you are in.
void myLoggerMethod(Level level, String msg, String identifier) {
logger.log(level, identifier + " " + msg);
}
will log things mostly correct, but then it logs the wrong method name. You can use logp to get around this, but then you have to send in the method name as a String and it becomes pretty gross.
Is there a good way to allow people to enter an additional piece of data to log? Is there any extension mechanism that allows this, or something in the API i'm missing?
I don't fully understand your usecase, but you can try to implement a custom Formatter (or Handler) Or you can extend an existing one, like SimpleFormatter / FileHandler.
You could look at it another way and set up code templates in your IDE.
For instance I have my IDE set up to change logdebug, logerror, loginfo to code snippets for my logging.
In my IDE, I type logdebug, hit ctrl+space and it converts it to
if(logger.isDebugEnabled()){
logger.debug("xxx");}
I can then just fill in the message I want.