I want to implement a logger at a functionality level in my application. so when and where log needed for debugging I can turn on and start logged activities. For example, i want to enable logging for registration functionality only.
I am not sure that this is possible or not but my requirement is like that. If possible please give a solution or any insight on that is appreciatable.
If you use the slf4j/log4j API, this is a feature you get pretty much "for free". If you follow the standard practice of creating a logger for each of your classes, via a line like:
static Logger log = LoggerFactory.getLogger(UserRegistration.class);
and use that logger for all logging in that class. You also choose the appropriate log level for each of your logging calls (WARN, INFO, DEBUG, etc.). Then you can turn the log level up/down in your logging configuration file for just one class with a line like this:
<logger name="com.mycompany.util.registration.UserRegistration"><level value="DEBUG"/></logger>
You can also turn the logging level up/down for the whole module that this class comes from with a line like:
<logger name="com.mycompany.util.registration"><level value="DEBUG"/></logger>
You use config lines like these to turn on certain log calls by raising them above the default log level you've set. You set the default log level with something like this:
<root><level value="WARN" /></root>
So with just these lines, you would only get WARN level logging for most of your code, but for that one module or class file, you'd also get INFO and DEBUG level logging.
You can do more complicated things, like send logging for certain parts of your code to a special log file. Maybe that's what you're talking about when you say you only want to log "registration functionality". You could set up your logging config so that only classes involved in "registration" are sent to a special file.
The main point of this is that you don't need to think about this too much in advance. You just attach the name of each class to all the logging calls made in that class, and choose the appropriate log level (WARN, INFO, DEBUG) for each of your logging calls, and you can decide later via your logging config file what you want to see or not see, and where you want logging information to go.
You can use API calls to configure logging more dynamically when your program first starts, or even while it is running. The main point, again, is that you don't think ahead about which parts of your code you want to see detailed logging for. You just put logging calls everywhere, and then decide which ones you actually see the output from later on.
Related
I'd like messages logged from a testing library to be auto-prefixed with "TEST" so they are easier to highlight or filter from the primary output.
Libraries: SLF4J / Logback
I'd prefer this as a feature of the logging rather than making every test class have to implement something special it although I wouldn't be against making them all apply a consistent Marker if that helps.
How can certain loggers be intercepted and prefixed?
Is there a way that doesn't involve a test-only log config file?
I have an existing application that logs messages using the java.util.logging API. As far as I can see, there are no configuration files for it in the framework, though there is some code to create a file appender. When I run the application, I get log messages to the console and to a file.
Now, I need to incorporate a library that uses Log4j 2. When I do so, I lose the console logging from the main application (though log messages still get written to the file appender that is created programmatically).
I imagine that, since the file appender is working in the original application, that I can solve my problem by also programmatically creating a console appender in the main application. However, I don't know if that's right or a kludge.
So, my question: is there anything general that I need to know about making java.util.logging and Log4j 2 interoperate? If the original application is not coded properly or according to best practices, I can change it.
Now, I need to incorporate a library that uses Log4j 2. When I do so, I lose the console logging from the main application (though log messages still get written to the file appender that is created programmatically).
The
Log4jBridgeHandler will remove handlers if the install method is called from code. You can always print the log tree to see what handlers are attached or attach a tool like JConsole to inspect the logger tree with and without the 3rd party lib.
I imagine that, since the file appender is working in the original application, that I can solve my problem by also programmatically creating a console appender in the main application. However, I don't know if that's right or a kludge.
Programmatic configuration of the logger tree should be done with the LogManager config option:
A property "config". This property is intended to allow arbitrary configuration code to be run. The property defines a whitespace or comma separated list of class names. A new instance will be created for each named class. The default constructor of each class may execute arbitrary code to update the logging configuration, such as setting logger levels, adding handlers, adding filters, etc.
Create a stand alone named class that just installs the handlers in the constructor.
Set the java.util.logging.config.class system parameter to the name of your class.
Otherwise if you have a logging.properties you set config to your class name.
So, my question: is there anything general that I need to know about making java.util.logging and Log4j 2 interoperate? If the original application is not coded properly or according to best practices, I can change it.
The java.util.logging.LogManager can only see classes on the system class loader. In that case log configuration in code is required to gain access to the correct classloader.
It might be easier to remove all JUL configuration and bridge to Log4j2. You can then leverage the configuration needed through that framework.
I understand that I can use
Logger.setLevel(<level here>);
To set the level of logging (turn it off, turn it on, etc). However, I'm not sure how I can conditionally log based on the log level the user specifies.
In essence, I have a class that uses the logging API. I wish to give the user of the class the power to configure the log level how they please. I've seen this done with log4j but not with the logging API.
Is there a best practice for this? Should I just have some function
setLogLevel()
that the user can pass a Level.INFO or whatever to? Or is there a better way?
Thank you!
I'm not sure, if understand this question correctly, but you shouldn't set the logging level from the code, which calls the logger. The idea behind logging is, that the developer logs all messages at the appropriate level. For example "Started to compute xyz" at DEBUG level, "New user have been set into DB" at INFO level and "Caught exception from..." at ERROR level. The logger will print the message only if it has the same or higher logging level. The logging level should be set according to environment, for example DEBUG for development and INFO for production, from outside the application.
Conditional logging is useful if the creation of the message is time consuming and you don't want to create the log message unless it will be really logged (check out this link). If you want to check, that the logger from the java.util.logging will actually log at given level, you can use this method.
However, I'm not sure how I can conditionally log based on the log level the user specifies.
Your question is unclear, but I think you are asking how log stuff depending on the log level that the user sets. The answer to that is that you just write your log statements normally; e.g.
logger.warning("Danger Will Robinson");
...
anotherLogger.info("It's good to be alive");
... and let the user specify what logging to capture using the logging configuration. Generally speaking the logging configuration is specified by a config file that is loaded at runtime, and can be altered by the user. It is also possible to create or alter the logging configuration programmatically, though presenting this functionality to the user via some kind of user-friendly UI is going to be something of a challenge.
In theory, it is also possible to a given log events at different levels depending on some condition. However, you are probably taking control away from the user by doing that.
I am using slf4j+log4J in Spring.
I want to store logs in different files based on log levels and also in one common file,so that I will first check this common log file and later review individual level logs files.
In short all level logs in one log file and then individual level logs in individual files.
Please guide me how to do this?
Also ,suggest suitable purpose of the levels keeping live projects in view.like where to use info,debug etc.
It should be straight forward. I am not giving the config directly but I think it should be easy for you to figure out the real config.
First, in the root logger (or the parent logger you want), point to several appenders, e.g. FILE_ALL, FILE_ERROR, FILE_WARN etc
Then declare FILE_ALL as normal file appender, which accept log event of all levels.
For other "level-specific" appender, it is still a normal file appender, PLUS a filter config. You may make use of LevelMatchFilter and declare the "level to match" as the corresponding level of the file.
I'm using log4j for the first time in a project. A fellow programmer told me that using System.out.println is considered a bad style and that log4j is something like standard for logging matters nowadays.
We do lots of JUnit testing - System.out stuff turns out to be harder to test.
Therefore I began utilizing log4j for a Console controller class, that's just handling command-line parameters.
// log4j logger config
org.apache.log4j.BasicConfigurator.configure();
Logger logger = LoggerFactory.getLogger(Console.class);
Category cat = Category.getRoot();
Seems to work:
logger.debug("String");
Produces:
1 [main] DEBUG project.prototype.controller.Console - String
I got two questions regarding this:
From my basic understanding using this logger should provide me comfortable options to write a logfile with timestamps - instead of spamming the console - if debug mode is enabled at the logger?
Why is System.out.println harder to test? I searched stackoverflow and found a testing recipe. So I wonder what kind of advantage I really get by using log4j.
The logger gives to ability to define different levels of importance of the logged messages and the ability to use different sink for the output - the console, a file, etc.
Also it's easy to enable or disable only some type of message when using a logger - for example you don't want to see every debug message in production.
I don't think that using loggers offers any significant advantages in unit tests, but I'd prefer it even there anyways. In unit tests asserts are usually my primary concern.
Btw you should really consider using something like Commons Logging or SLF4J as a log framework facade - it's bad style to tie your code to a specific logging framework. Common Logging and SLF4J make it easy to switch logging frameworks if you choose to.
Anything that you print to System.out will go to "standard out", and while you can redirect standard out to a file and compare it, what have you, that is very inflexible. Additionally, you cannot filter what goes to standard out if you use System.out... everything will be printed. With log4j, you can set different logging levels, so that logging messages that are below a certain severity/importance threshold are not printed (e.g. if you change the logging level to WARN, then DEBUG and INFO messages will not be displayed anymore).
Additionally, log4j allows logging to be controlled on a class-by-class basis, whereas System.out can only be controlled at the granularity of the entire application (if you redirect System.out, you redirect it for the entire program). By contrast, each logger in log4j can be given a different appender. In addition, you can give a log4j logger multiple appenders (so that it goes the system logger, and over the network, for example). You can even have a log4j logger append to a StringBuilder, so that you can easily read what was written. And while System.out can be redirected, this redirection tends to be fairly limited; System.out can be redirected to a file or to a pipe (to another program), but you wouldn't be able to redirect it to a URL, for example; by contrast, it would be very easy to create an appender that transmits logging messages using HTTP POST.
Use e.g.
org.apache.log4j.BasicConfigurator.configure(new FileAppender(
new PatternLayout("%d{ISO8601} %-5p %t: %m%n"), // see e.g. http://en.wikipedia.org/wiki/Log4j#TTCC
"log/mainWhatever.log"));
Using logger.setLevel(...) you can easily choose whether to display logger.debug(..) messages, e.g. set it to level warn and any trace, debug and info statements will not be printed. This saves you the time of having to comment out only occasionally needed debug statements.
Also have a look at Wikipedia.
Using logger.setLevel(...) you can easily choose whether to display logger.debug(..) messages, e.g. set it to level warn and any trace, debug and info statements will not be printed. This saves you the time of having to comment out only occasionally needed debug statements
In the case of log4j,It provide a middle ware service where you can manage logging levels like DEBUG,INFO,ERROR etc. And you can enable and disable logging.But in the case of System.out.println() you have to manage every thing.