how do you go about structuring logging in your java projects?
I have used log4j2, logback etc, however this is not a question about libraries but about setup and best practices.
I have tried:
in filter
but it does not have enough detail. For example i cannot log method calls, input/output values in methods etc. Also it does not feel good when i need detailed logs of user activities.
in each class
In each class, a static field for the logger, then in methods where needed i log what i need to. This way i have all the detail i want, but it's a lot pf work and it feels like the code is littered with log stuff.
What do you use in your projects?
Thanks
I generally go with a similar approach to that of using static loggers in Class, but with a twist. Generally, I use only one static logger and a collection of Aspects. When a method requires to be logged, and usually it's input/output that needs to be logged, I simply use an #Around aspect. This keeps your code clean and separates the concerns of business logic with the concerns of the programmer (logging).
Here's a great place to start: http://docs.spring.io/spring/docs/current/spring-framework-reference/html/aop.html
Related
I have been working on a project that logs using what are essentially just println statements with a prefixed string tag. I have been looking into implementing support for an actual logging library such as Logback the past few days and had some questions relating to best-practices about logging in general. I know a lot of what I'm doing is probably stupid, but I want to change :)
When I'm extending the code and adding new features, such as testing a new codec, I have been using liberal logging to ensure the code behaves as expected (instead of actual unit tests), and then using constant booleans at the top to disable that logging when the codec is finished (in case it's needed again or a bug is found, I can flip the boolean while testing). I don't know if the granularity that debug level provides would be enough and would prefer some way to define levels differently for different features. Leaving these enabled by default would really bloat the console and probably effect performance -- is this what filters are usually used for?
I've also found myself in more than one case prepending spaces to my messages so that I can better follow the flow of the code. I've found this to be really helpful. In a way, the tabbed messages are like a debug-debug level.
Doing something
Reading a file
header of file: ...
body of file: ...
Back at main
What are good practices for logging? Can someone refer me a good resource that I can dig into or explain if what I'm doing is stupid and why it's stupid? What are some alternatives? An open source project as an example would be extremely helpful. Thanks, I appreciate any guidance.
Some advice:
Never substitute unit tests for logging only.
Regarding logging you should log whatever makes you find bugs quicker.
Log libraries support async logging which will not affect the performance of your application (log4j2 async logging). Logback supports async too.
Do not use booleans inside your code to decide to log or not to log. Use the logging levels (TRACE, DEBUG, INFO, WARN, ERROR) and set them accordingly. Usually in PROD environment you will use a WARN level and in DEV you can set it on debug.
Logging on different levels depending on the package is quite useful (you can use appenders to customize this and other stuff).
In resume, the important is to read the documentation of whatever library you are using
I am aware that MDC is provided by Log4j and is used for the purpose of grouping the related log messages together aiming easier debugging.
But, should MDC only used for that purpose? Is it considered to be a bad practice if I use MDC for keeping small business information in the executing thread. ?
I don't know your scenario. It sounds like you're using MDC for something it is not made for. Except you want to use those business information for log purposes.
There are many ways to keep data in you application. Making a custom ThreadLocal / custom context.
Take a look at Baeldung - ThreadLocal.
I am having a fairly large legacy (swing) application and currently brainstorming and evaluating the strategies to add logging in it.
Key point is that it's fairly large (like I said above) and thinking what could be the strategy to do it quickly and completely (100% coverage for argument sake) (let's say logging is no customer facing core business functionality, so let's say not getting paid for it)
So the two strategies as such are -
Do use log4j2 add the debug statements, add appenders, file rolling rules, add dynamic on/off and change of log levels etc and thus do it the way it ideally should be done.
Use AOP to define endpoints and advices declaratively/programmaticly. Device such elaborate rules, add in the rest of the part (appenders, rolling rules etc.) and thus wont be touching each and every file and adding a revision just for that.
The second strategy is what I want to explore if someone has experience with, if somebody has gone that route.
The cons I can think of -
No standard / convention in apps, would be 99% impossible to define endpoints completely
Sphagetti and unmaintainable code in AOP module above, largely a result of the above problem
Adding same and matching set to logging to future classes.
Can you guys suggest me wither ways
While I am a big proponent of refactoring and clean code, I suggest you use AspectJ to add logging and see how far you get. Probably you will be surprised by how much logging you get with a little aspect.
IMHO logging is a cross-cutting concern and not core functionality. I would try to avoid logging in my core code. My expecience with AspectJ is only positive, I warmly recommend it. You should take some time to get acquainted with its power, though.
If you need something like a call trace (maybe neatly indented) or just plain method call logging with parameters and maybe return values, you will get quick results with AspectJ without cluttering your application code. The aspect can always be improved and maintained in a single spot, which is very clean. No need to be afraid of spaghetti aspect code. It will not happen if you don't totally abuse AspectJ.
You will only run into problems if your core code is already spaghetti code and you have very long methods which need log statements inside those methods and not around them. Then you might need to refactor and break down monster methods into smaller ones. But that is a problem no matter which logging approach you choose. My own experience with ugly legacy code and AspectJ-based logging tells me that it helps a lot because even spaghetti code calls other methods and that can be nicely traced in AspectJ.
i am currently working on a java application for some network monitoring tool. In my code i am supposed to use logging a lot. Since its a network management software, the information in logs is quite useful to the user hence its compulsory to use them. But now I am bit confused with what kind of logger method i should prefer. Right now i am using Logger.lop(...//...) since with its help we are also logging the class name and method so its becoming very easy for me (developers) to debug the code and find the error. But finally I am confused should i deliver it to the end user with the same logging mechanism??? Is it any harm to let your user know what kind of class is executing currently , in which method error has occured. I have seen many times in many product in exception handling stacktrace is used so normally we get class name as well. So is there is no problem to let enduser know what your class name and method is??
Before considering the security implications of it, consider the performance. In most logging systems, getting the actual classname and method name dynamically by the logging facility requires reflection and dramatically slows down the logging - usually a synchronous operation. My guess is that in a network monitoring application, you really don't want that.
If you're hard-coding the method name into the log message (either by making it part of the message or by the category), that's a different story. As a security person, I don't consider it to be that big of a deal - if your code is in Java, it can be reversed anyhow, so your code should operate in such a way that it would be secure even if the code was given away.
All that being said, you could either use a different logging configuration for development and production, or those fine-grained messages could go in debug, trace, etc. If you're using log4j, it's generally advisable to use isDebugEnabled to wrap any logging statements which include anything dynamically-calculated as those get calculated before the logging statement determines whether it's enabled.
log4j/logback/slf4j allow you to have different formats for different appenders. For development you can enable a console appender where you include the class name in the format, while for the end-users you can omit it (for a file appender)
It's worth mentioning that such logging is performance costly in Java, contrary to C++ where it is usually implemented with preprocessor. Fortunately, with log4j/logback you can switch it on and off — follow Bozho's advice.
I've got a method in my class only for testing purpose :
private void printOut(String msg, Object value)
{
System.out.println(msg + value);
}
It is a wrapper method for System.out.println();
So I hope, with the use of Annotation, I can choose not to run this method during productive environment while still keep those diagnostic output ready if I am to switch back to debugging environment.
Which Annotation shall I put on top of the method name?
As I stated above you should use logging.
Here are some of the benefits of using logging in an application:
Logging can generate detailed information about the operation of an application.
Once added to an application, logging requires no human intervention.
Application logs can be saved and studied at a later time.
If sufficiently detailed and properly formatted, application logs can provide audit trails.
By capturing errors that may not be reported to users, logging can help support staff with troubleshooting.
By capturing very detailed and programmer-specified messages, logging can help programmers with debugging.
Logging can be a debugging tool where debuggers are not available, which is often the case with multi-threaded or distributed applications.
Logging stays with the application and can be used anytime the application is run.
Read more about logging here
There are a lot of logging frameworks in java:
Log4j
java.util.logging
Logback.
And several facades, which provides abstraction for various logging frameworks:
slf4j
commons-logging
One solution is to use AspectJ to do this, as you can control the behavior based on annotations.
Here is a tutorial on how to use annotations as join points:
http://www.eclipse.org/aspectj//doc/next/adk15notebook/annotations-pointcuts-and-advice.html
What you could do is to have:
#DebugMessage
private void printOut(String msg, Object value)
{ }
Then, in your aspect you could have the aspect do the println call.
This way, in production, the aspect isn't included, but, should you ever need to have this active, then just add the aspect, even to production code, to get some debugging.
You should really follow uthark's advice and use a logging framework.
Those have been specifically designed for this situation.
Doing something "funky" will probably cause problems later on.