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org.slf4j.Logger logs to console, how do I log to file?

I am using the org.slf4j.Logger to log output. Output is going to console. How do I get logging logged to a log file?
private static final Logger LOG = LoggerFactory.getLogger(ClassName.class );
LOG.info("Logging output to console");
I am not using a log4j.properties file. I am assuming I will need one.
I added the following log4j.properties file and placed it in different parts of my eclipse project.
# Define the file appender
log4j.appender.FileAppender=org.apache.log4j.RollingFileAppender
log4j.appender.FileAppender.File=logger.log
log4j.appender.FileAppender.layout = org.apache.log4j.PatternLayout
log4j.appender.FileAppender.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n
# Direct all messages there
log4j.rootLogger = INFO, FileAppender
I even used
PropertyConfigurator.configure("log4j.properties");
But no logging file appears. log4j.properties doesn't seem to have an effect.

The simplest way, I think, is to define a FileAppender in a log4j.properties file:
# Define the file appender
log4j.appender.FileAppender=org.apache.log4j.RollingFileAppender
log4j.appender.FileAppender.File=[log filename].log
log4j.appender.FileAppender.layout = org.apache.log4j.PatternLayout
log4j.appender.FileAppender.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n
# Direct all messages there
log4j.rootLogger = INFO, FileAppender
Just replace [log filename] with some relevant filename. I think Log4j is able to automatically locate the file when you run the project from Eclipse if the file is in your project directory, but I'm not 100% sure. You can use PropertyConfigurator at the start of your application to tell Log4j where to find the properties file, e.g.:
PropertyConfigurator.configure("log4j.properties");

You can create a log4j.xml in the resource folder.
Import log4j package in the class.
Inside the class, instantiate a logger object using Logger.getLogger( ) static method.
Instantiate layouts (readymade or user-defined) to be assigned to appenders.
Instantiate appenders and assign desired layout to them by passing the layout object as parameter to their constructors.
Assign the instatiated appenders to the Logger object by invoking its addAppender( ) method with desired appender as parameter.
Invoke appropriate printing methods on Logger object to perform logging.
.
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="CONSOLE" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%p [%t] %c{1}.%M(%L) | %m%n" />
</layout>
</appender>
<appender name="FILE" class="org.apache.log4j.rolling.RollingFileAppender">
<rollingPolicy class="org.apache.log4j.rolling.TimeBasedRollingPolicy">
<param name="fileNamePattern" value="/yourfolder/debug_%d{dd-MM-yy}.log" />
</rollingPolicy>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%p [%t] %c{1}.%M(%L) | %m%n" />
</layout>
</appender>
<root>
<level value="WARN" />
<appender-ref ref="CONSOLE" />
<appender-ref ref="FILE" />
</root>
</log4j:configuration>

log4j: archived files removing policy

I'm using TimeBasedRollingPolicy and RollingFileAppender to have a my logs rolling over and be archived as myLogFileName..log.gz:
<appender class="org.apache.log4j.rolling.RollingFileAppender" name="myLogFile">
<param value="/var/log/my/myLogFileName.log" name="File"/>
<rollingPolicy class="org.apache.log4j.rolling.TimeBasedRollingPolicy">
<param name="FileNamePattern" value="/var/log/my/myLogFileName.%d.log.gz" />
</rollingPolicy>
<layout class="org.apache.log4j.PatternLayout">
<param value="%d [%t] %-5p - %m%n" name="ConversionPattern"/>
</layout>
</appender>
What I don't understand - is where it is defined when and how really old archived files will be totally removed from the filesystem?
And, if I want to keep always only no older than one month old files - where I can set it up (using log4j (extras))?

TimeBasedRollingPolicy is defined by apache-log4j-extras. This dependency will need to be on the classpath in order to use that policy.
RollingFileAppender includes a maxBackupIndex property, which specifies the maximum number of rolled over backup files to retain. However, I don't believe this property is supported when using a TimeBasedRollingPolicy. This means that, when using RollingFileAppender with the TimeBasedRollingPolicy, old backup files will not be removed by the appender.
If you were using Logback as the logging implementation (perhaps in conjunction wiht SLF4J), then you could achieve the desired outcome using the
Logback RollingPolicy. I acknowledge that the question is seeking a log4j solution, but I'm not aware one.

Use system properties OR variables in log4j

I want to to do like this:
<appender name="ErrorLog" class="org.apache.log4j.FileAppender">
<param name="File" value="${error.log.path}"/>
<param name="Append" value="true" />
<param name="Threshold" value="ERROR"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%C{1} %L [%t] %d{dd MMM,yyyy HH:mm:ss.SSS} %-5p - %m%n" />
</layout>
</appender>
Notice this line: <param name="File" value="${error.log.path}"/>
I tried to set the values like this:
public static void main(String[] args) {
System.setProperty("error.log.path", "/test/crm/log/error.log");
ApplicationContext context = new ClassPathXmlApplicationContext("blah.xml");
..........
..........
}
But I don't see any effect.
Is log4j gets configured before calling the main method?
Is there any other way to do this?

Look at this thread
It looks like you did everything right. I don't think there is any difference between setting the property inside your main class with System.setProperty() and specifying it via the command line as long as it happens befor actual log4j initialization.
I think your issue is that your logging framework gets loaded before you specify the property.
I can say that the logging framework (log4j) will get configured when you call the configurator. Stuff like BasicConfigurator.configure() (in your case its xml configurator).
Otherwise the first attempt to use the logging will cause message like "log4j is not configured properly".
The real question is whether your code snippet with 'main' is not oversimplified.
With this in mind, another question that I have to ask - whether you're running inside some container or you're running a real vanilla method main and configure everything by yourself? I'm asking because if you're running in container, the chances are that container will by itself somehow configure its logging, for example JBoss will do so. In this case more investigation is required.
Hope this helps

You can do it by configure appender pragmatically
FileAppender fa = new FileAppender();
fa.setFile("/test/crm/log/error.log");
fa.setLayout(new
PatternLayout("%C{1} %L [%t] %d{dd MMM,yyyy HH:mm:ss.SSS} %-5p - %m%n"));
fa.setThreshold(Level.ERROR);
fa.setAppend(true);
fa.activateOptions();
Logger.getRootLogger().addAppender(fa);
// similarly you can add all appenders.
// or just append file name alone
Logger log = Logger.getLogger(YourClass.class);
FileAppender appender = (FileAppender) log.getAppender("ErrorLog");
appender.setFile("appender");

System Properties can be used as ${user.home}, pick required from here http://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html
example :
<appender name="errorLog" class="com.qait.logger.IOPFileAppender">
<param name="Threshold" value="ERROR" />
<param name="File"
value="${user.home}/Harvestors/IOP Error Logs/error.log" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d%-5p [%c{1}] %m %n" />
</layout>
<filter class="org.apache.log4j.varia.LevelMatchFilter">
<param name="LevelToMatch" value="ERROR" />
<param name="AcceptOnMatch" value="true" />
</filter>
<filter class="org.apache.log4j.varia.DenyAllFilter" />
</appender>

Access to your property via "sys:" prefix.
Example:
<param name="File" value="${sys:error.log.path}"/>
For more information follow this link: https://logging.apache.org/log4j/2.x/manual/lookups.html

maven document:
System properties. The formats are ${sys:some.property} and ${sys:some.property:-default_value}.
from Maven Property Substitution

Setting the system property does not come into affect here. You'll need to pass it as a argument to java while executing. Try
java -Derror_log_path=/test/crm/log/error.log
Note: I am not sure if dot . works in there so replaced it with underscore _.

log4j. Unique log-file name

How I can create a uniquely named log file using log4j?. When I used Logback, I can do it like this:
<!-- current time formatted as "yyyyMMdd'T'HHmmss". This value will be available to all
subsequent configuration elements. -->
<timestamp key="bySecond" datePattern="yyyyMMdd'T'HHmmss" />
and inside logger appender define file name pattern:
<file>${bySecond}.log</file>

I believe there's no support for this feature in log4j 1.7 out of the box. But you can extend RollingFileAppender's setFile method by altering fileName parameter to support the time-based feature.

the DailyRollingFileAppender appends the current date afer rolling over to the next file, so you get a unique name ending with the date of the log for every file.
Cite JavaDoc:
For example, if the File option is set to /foo/bar.log and the
DatePattern set to '.'yyyy-MM-dd, on 2001-02-16 at midnight, the
logging file /foo/bar.log will be copied to /foo/bar.log.2001-02-16
and logging for 2001-02-17 will continue in /foo/bar.log until it
rolls over the next day.
add something like this to your properties XML file:
<appender name="roll" class="org.apache.log4j.DailyRollingFileAppender">
<param name="File" value="application.log" />
<param name="DatePattern" value=".yyyy-MM-dd" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern"
value="%d{yyyy-MMM-dd HH:mm:ss,SSS} [%t] %c %x%n %-5p %m%n"/>
</layout>
</appender>

Log4j: How to configure simplest possible file logging?

My story:
I want to make a thing which is as simple as a simplest possible log4j logger that logs rows to a file. I have found several examples with some functionality, but not a basic, general one that really works, and not one with an explanation how the each row work.
Question:
Could anybody provide one?
Prerequisites:
I already know where to put the file and I have the log4j configured and working for console logging.
Now I want to log to a file and also find the file from file system once the program has run.
Rows needed to be added to the existing log4j.properties file are the desired output.

I have one generic log4j.xml file for you:
<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd" >
<log4j:configuration debug="false">
<appender name="default.console" class="org.apache.log4j.ConsoleAppender">
<param name="target" value="System.out" />
<param name="threshold" value="debug" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{ISO8601} %-5p [%c{1}] - %m%n" />
</layout>
</appender>
<appender name="default.file" class="org.apache.log4j.FileAppender">
<param name="file" value="/log/mylogfile.log" />
<param name="append" value="false" />
<param name="threshold" value="debug" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{ISO8601} %-5p [%c{1}] - %m%n" />
</layout>
</appender>
<appender name="another.file" class="org.apache.log4j.FileAppender">
<param name="file" value="/log/anotherlogfile.log" />
<param name="append" value="false" />
<param name="threshold" value="debug" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{ISO8601} %-5p [%c{1}] - %m%n" />
</layout>
</appender>
<logger name="com.yourcompany.SomeClass" additivity="false">
<level value="debug" />
<appender-ref ref="another.file" />
</logger>
<root>
<priority value="info" />
<appender-ref ref="default.console" />
<appender-ref ref="default.file" />
</root>
</log4j:configuration>
with one console, two file appender and one logger poiting to the second file appender instead of the first.
EDIT
In one of the older projects I have found a simple log4j.properties file:
# For the general syntax of property based configuration files see
# the documentation of org.apache.log4j.PropertyConfigurator.
# The root category uses two appenders: default.out and default.file.
# The first one gathers all log output, the latter only starting with
# the priority INFO.
# The root priority is DEBUG, so that all classes can be logged unless
# defined otherwise in more specific properties.
log4j.rootLogger=DEBUG, default.out, default.file
# System.out.println appender for all classes
log4j.appender.default.out=org.apache.log4j.ConsoleAppender
log4j.appender.default.out.threshold=DEBUG
log4j.appender.default.out.layout=org.apache.log4j.PatternLayout
log4j.appender.default.out.layout.ConversionPattern=%-5p %c: %m%n
log4j.appender.default.file=org.apache.log4j.FileAppender
log4j.appender.default.file.append=true
log4j.appender.default.file.file=/log/mylogfile.log
log4j.appender.default.file.threshold=INFO
log4j.appender.default.file.layout=org.apache.log4j.PatternLayout
log4j.appender.default.file.layout.ConversionPattern=%-5p %c: %m%n
For the description of all the layout arguments look here: log4j PatternLayout arguments

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/" debug="false">
<appender name="fileAppender" class="org.apache.log4j.RollingFileAppender">
<param name="Threshold" value="INFO" />
<param name="File" value="sample.log"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d %-5p [%c{1}] %m %n" />
</layout>
</appender>
<root>
<priority value ="debug" />
<appender-ref ref="fileAppender" />
</root>
</log4j:configuration>
Log4j can be a bit confusing. So lets try to understand what is going on in this file:
In log4j you have two basic constructs appenders and loggers.
Appenders define how and where things are appended. Will it be logged to a file, to the console, to a database, etc.? In this case you are specifying that log statements directed to fileAppender will be put in the file sample.log using the pattern specified in the layout tags. You could just as easily create a appender for the console or the database. Where the console appender would specify things like the layout on the screen and the database appender would have connection details and table names.
Loggers respond to logging events as they bubble up. If an event catches the interest of a specific logger it will invoke its attached appenders. In the example below you have only one logger the root logger - which responds to all logging events by default. In addition to the root logger you can specify more specific loggers that respond to events from specific packages. These loggers can have their own appenders specified using the appender-ref tags or will otherwise inherit the appenders from the root logger. Using more specific loggers allows you to fine tune the logging level on specific packages or to direct certain packages to other appenders.
So what this file is saying is:
Create a fileAppender that logs to
file sample.log
Attach that appender to the root
logger.
The root logger will respond to any
events at least as detailed as
'debug' level
The appender is configured to only
log events that are at least as
detailed as 'info'
The net out is that if you have a logger.debug("blah blah") in your code it will get ignored. A logger.info("Blah blah"); will output to sample.log.
The snippet below could be added to the file above with the log4j tags. This logger would inherit the appenders from <root> but would limit the all logging events from the package org.springframework to those logged at level info or above.
<!-- Example Package level Logger -->
<logger name="org.springframework">
<level value="info"/>
</logger>

Here's a simple one that I often use:
# Set up logging to include a file record of the output
# Note: the file is always created, even if there is
# no actual output.
log4j.rootLogger=error, stdout, R
# Log format to standard out
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern= %5p\t[%d] [%t] (%F:%L)\n \t%m%n\n
# File based log output
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=owls_conditions.log
log4j.appender.R.MaxFileSize=10000KB
# Keep one backup file
log4j.appender.R.MaxBackupIndex=1
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern= %5p\t[%d] [%t] (%F:%L)\n \t%m%n\n
The format of the log is as follows:
ERROR [2009-09-13 09:56:01,760] [main] (RDFDefaultErrorHandler.java:44)
http://www.xfront.com/owl/ontologies/camera/#(line 1 column 1): Content is not allowed in prolog.
Such a format is defined by the string %5p\t[%d] [%t] (%F:%L)\n \t%m%n\n. You can read the meaning of conversion characters in log4j javadoc for PatternLayout.
Included comments should help in understanding what it does. Further notes:
it logs both to console and to file; in this case the file is named owls_conditions.log: change it according to your needs;
files are rotated when they reach 10000KB, and one back-up file is kept

Here is a log4j.properties file that I've used with great success.
logDir=/var/log/myapp
log4j.rootLogger=INFO, stdout
#log4j.rootLogger=DEBUG, stdout
log4j.appender.stdout=org.apache.log4j.DailyRollingFileAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{MM/dd/yyyy hh:mm:ss a}|%-5p|%-30c{1}| %m%n
log4j.appender.stdout.DatePattern='.'yyyy-MM-dd
log4j.appender.stdout.File=${logDir}/myapp.log
log4j.appender.stdout.append=true
The DailyRollingFileAppender will create new files each day with file names that look like this:
myapp.log.2017-01-27
myapp.log.2017-01-28
myapp.log.2017-01-29
myapp.log <-- today's log
Each entry in the log file will will have this format:
01/30/2017 12:59:47 AM|INFO |Component1 | calling foobar(): userId=123, returning totalSent=1
01/30/2017 12:59:47 AM|INFO |Component2 | count=1 > 0, calling fooBar()
Set the location of the above file by using -Dlog4j.configuration, as mentioned in this posting:
java -Dlog4j.configuration=file:/home/myapp/config/log4j.properties com.foobar.myapp
In your Java code, be sure to set the name of each software component when you instantiate your logger object. I also like to log to both the log file and standard output, so I wrote this small function.
private static final Logger LOGGER = Logger.getLogger("Component1");
public static void log(org.apache.log4j.Logger logger, String message) {
logger.info(message);
System.out.printf("%s\n", message);
}
public static String stackTraceToString(Exception ex) {
StringWriter sw = new StringWriter();
PrintWriter pw = new PrintWriter(sw);
ex.printStackTrace(pw);
return sw.toString();
}
And then call it like so:
LOGGER.info(String.format("Exception occurred: %s", stackTraceToString(ex)));