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log4J2 Store and use variables / lookup-values

In my java program I want to use several log files.
So according to the log4j documentation I would assume that lookup values are use to do that.
The Lookups page describe how to build the configuration files. But has only little information about how to store the values so that the configuration file is retrieving the values.
So I want to have logfilename dynamically filled.
Test with envrimonment works:
<File name="MyFile" fileName="${env:USERERNAME}" immediateFlush="false" append="false">
<PatternLayout pattern="%d{yyy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
</File>
I would assume that System.getProperty("USER") would match the java lookup ${java:USER} but it does not work.
I tested both variables using:
System.out.println("USER: " + System.getProperty("USER"));
System.out.println("USERNAME: " + System.getenv("USERNAME"));
So how to fill the variables for
Context Map Lookup
Java lookup
Which are the differences?

There are various ways of lookup in log4j2. Let me add some details to them -
Context Map Lookup - For putting value using context map, use below code -
org.apache.logging.log4j.ThreadContext.put("logFileName", "app.log");
Variable can be accessed in configuration file using ${ctx:logFileName} or %X{logFileName}.
Context map lookup is generally used in web application where you want some value for each user request i.e. for each thread.
Environment Lookup - Environment lookup is used for looking up system environment variables like USERNAME, PLATFORM. You can print all environment variables in Java using below -
System.out.println(System.getenv());
OR any specific environment variable -
System.out.println(System.getenv("NUMBER_OF_PROCESSORS"));
However, from Java program, you can not set environment variables.
As you mentioned in your code, environment variables can be accessed using ${env:NUMBER_OF_PROCESSORS} syntax.
Java Lookup - Java lookup is for Java environment information like java version, hardware etc. Variables are fixed and can not be set in java program.
Such variables can be accessed using ${java:vm} syntax where vm is java environment related variable name.
System Properties Lookup - It is easy to get and set such properties using below code -
System.setProperty("logFileName", "app.log");
System.getProperty("logFileName");
Variables can be accessed in log4j2 configuration file using ${sys:logFileName} syntax.
Good thing about these system properties is you can pass these properties as VM Arguments to your program like -DlogFileName=app3.log.
There are other lookup mechanism also like Date Lookup, Map Lookup etc which are mostly used. Rest details can be checked here
Since you want to set file name dynamically in your application and if you want to set file name only once, I would suggest to you System property. But ensure that, you set System Property before initializing log4j

Log4j2 Rolling appender - fileName "sliding" according to pattern

I am looking for rollover strategy where current log (active output target in manual's terminology) file name is not fixed but specified by a pattern, or - more precisely - same pattern as in filePattern attribute.
I want to achieve daily rollover where today's log is, say, log-2015-05-05.log and on midnight framework just stops writing it and starts writing into log-2015-05-06.log. However, AFAIK, current configuration allows only
<RollingFile name="ROLFILE"
fileName="log.log"
filePattern="log-%d{yyyy-MM-dd}.log"
>
Specifying same value into fileName attribute doesn't work (leads to file with sensitive characters literally interpreted). I noticed no example or SO question with such a dynamic value of fileName. Note the fileName="log-${date:yyyy-MM-dd}.log" doesn't solve problem since expression is evaluated only at startup and events are still sent into file even if their timestamp doesn't match the expression.
I am migrating from Log4j 1.2 to Log4j 2.2. In old version, required behavior was possible using
<appender name="ROLFILE" class="org.apache.log4j.rolling.RollingFileAppender">
<rollingPolicy class="org.apache.log4j.rolling.TimeBasedRollingPolicy">
<param name="FileNamePattern" value="log-%d{yyyy-MM-dd}.log" />
</rollingPolicy>
...
I prefer to preserve current way since some log analyzing tools rely on it.
Is it possible in Log4j2?
Thanks.

Note sure if this works, but you can try using a double $$ in the date lookup. This allows the variable to be resolved at runtime.
<RollingFile name="ROLFILE"
fileName="log-$${date:yyyy-MM-dd}.log"
filePattern="oldlog-%d{yyyy-MM-dd}.log"
>
You may need to be careful to ensure that the active output target file name is different from the after-rollover file name. (I used 'oldlog' in the snippet above.)

Finally, I wrote my own rollover strategy which generates different set of rollover actions. Instead renaming active file the active file name is simply replaced inside RollingFileManager. Yes, it's ugly reflection hack and also appender must be initialized with fileName constant corresponding with current date and having same pattern, e.g.
<RollingFile name="ROLFILE"
fileName="log-${date:yyyy-MM-dd}.log"
filePattern="log-%d{yyyy-MM-dd}.log"
>
<SlidingFilenameRolloverStrategy />
...
yet for me this solution is worth doing it despite these small drawbacks.
(Initial fileName stays forever as a key in AbstractManager registry MAP even if in manager itself it has been changed - seems it doesn't mind, I also tried replacing manager in registry for new one but it's impossible to collect all parameters necessary for its construction.)
I hope this hack shouldn't have been so ugly if RollingFileManager API made it possible normal way. I got some hope seeing this javadoc but framework AFAIK never utilizes this field, let alone for mutating RollingFileAppender.

I think it would work just fine using:
fileName="log-${date:yyyy-MM-dd}.log"
filePattern="log-%d{yyyy-MM-dd}.log"
I use it with log4j2 version 2.5

This has been implemented in Log4j 2.8 (see issue LOG4J2-1101).
Currently it only works with a RollingFile appender by omitting the filename parameter and using a DirectWriteRolloverStrategy.
Also, this feature seems to have some issues with the TimeBasedTriggeringPolicy (the first rollover doesn't happen so every logfile is offset by one interval); CronTriggeringPolicy works properly.
Example config:
<RollingRandomAccessFile name="MyLogger"
filePattern="logs/application.%d{yyyy-MM-dd}.log">
<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
<Policies>
<CronTriggeringPolicy schedule="0 * * * * ?" evaluateOnStartup="true"/>
</Policies>
<DirectWriteRolloverStrategy/>
</RollingRandomAccessFile>
Support for RollingRandomAccessFile appender is requested in issue LOG4J2-1878.
Edit: Changed to CronTriggeringPolicy policy after finding TimeBasedTriggeringPolicy had issues.

Console output of Eclipse with timestamp

I am using Eclipse for my selenium webdriver scripts.Is there any settings/tools/plugins/process so that i can see console output with timestamps.
I am using application log using log4j framework.But there is a requirement from my client that they need console output with timestamps.I have thought of using printing of time before every command,but its not an effective way of doing so.
Thanks,
Manash

Use:
log4j.appender.ConsoleAppender.layout.ConversionPattern=[%-5p] %d %c - %m%n
You have info on the ConversionPattern's printing performance here: http://www.codejava.net/coding/common-conversion-patterns-for-log4js-patternlayout

Not sure if this answer will be valid, unfamiliar with selenium and I dislike log4j (so I will give an answer that works without it).
The documentation for System can be useful, particularly setErr and setOut. You can change the output streams to streams that attach the timestamp before directing the given string to the console. Or instead of doing System.setOut & System.setErr you write a class ABC with public static printstreams like System. When you call the ABC.out.print or ABC.err.print methods, the class adds the timestamp then directs it to System.out & System.err respectively.

Can you please try the below code. The below code is working fine for me.
log4j.rootLogger=debug, stdout, R
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
# Pattern to output the caller's file name and line number.
log4j.appender.stdout.layout.ConversionPattern=%d{dd/MM/yyyy HH:mm:ss}:
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=applicationlog path
log4j.appender.R.MaxFileSize=100KB
# Keep one backup file
log4j.appender.R.MaxBackupIndex=1
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d{dd/MM/yyyy HH:mm:ss}:
Thanks,
Sudhansu, Mindfiresolutions
http://www.mindfiresolutions.com/

Best technique to print text to console

I am writing a command line tool that performs a number of tests to our servers and reports an output to screen.
I am currently using log4j to print to screen and to a log file.
However, I was wondering if there was a better technique to manage all the printing from one class instead of having the "print" commands scattered all over my code.
e.g.
logger.info("Connecting to environment: " + envName);
if (cmd.hasOption(OPTION_CHECK_PRIMARY)) {
//print primary leg
String primaryLegName = env.getPrimaryLeg().getLegName();
String message = "is primary";
logger.info(String.format("%s : %-4s %s", envName, primaryLegName, message));
}
This is an example of the output that is now scattered across all my code.
Would it be best to have a Formatter class that handles all the printing?
What is the best approach to create it?
What do you think about something like:
Formatter pf = new PlainFormatter();
...
pf.printEnvironment(envName);
if (cmd.hasOption(OPTION_CHECK_PRIMARY)) {
//print primary leg
String primaryLegName = env.getPrimaryLeg().getLegName();
pf.printPrimary(envName, primaryLegName);
}

Have you tried using log4j.properties to format the text. I think if you are trying to format uniquely for each class, then this is still possible using log4j.properties.
Here is a simple example of log4j.properties
log4j.rootLogger=INFO, A1
log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
You can use Pattern in properties like so:
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n

log4j has appenders to redirect log messages to different locations. quote" Multiple appenders exist for the console, files, GUI components, remote socket servers, JMS, NT Event Loggers, and remote UNIX Syslog daemons "unquote

A beginner's log4J question

i configured log4j for basic purpose usin the conversion pattern :-
log4j.appender.rollingFile.layout.ConversionPattern=%p %t %c - %m%n
But now i want to log the class name from which the error came as well as the username(available in session object) as well as the date and time when that event occurs. How do i do this? What changes do i need to make in format string?
Thanks in advance :)

Take a look at the PatternLayout docs for most of what you want.
The headache you face is getting the user name from the session (Log4j can't do this automatically). I would perhaps investigate NDCs or MDCs, and populate these from the session (perhaps in a servlet filter?). They are per-thread, so assuming your user has the same scope then this may help.

To get the class name out you can use %l, but you'll take a bit of performance hit.
To get the username out, you'll need to use a mapped or nested diagnostic context and then specificy %X or %x respectively in the pattern string.
Check the PatternLayout javdocs.