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dynamically set the level based on the application is run on the server

I want to change the log level dynamically based on TEST/PROD server accessing the application.
Our web app has a lot of DEBUG and INFO,error log statements. Once we deploy the .war file to the test / production servers,
the log4j.xml also gets deployed which results in a lot of DEBUG and INFO statements in the log files.
How to show only error logs in PROD server and debug and error logs in DEV/TEST server. Apache Tomcat is the server we are using to deploy the application.
log4j.xml:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration>
<!-- This appender logs to the console -->
<appender name="consoleAppender" class="org.apache.log4j.ConsoleAppender">
<param name="Target" value="System.out"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="[%-5p] [%c{1}] [%M:%L] - %m%n"/>
</layout>
</appender>
<appender name="fileAppender" class="org.apache.log4j.RollingFileAppender">
<param name="file" value="${catalina.home}/logs/myProject.log"/>
<param name="append" value="true" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L %m %n" />
</layout>
</appender>
<!-- Set "debug" log level for project code -->
<logger name="com.choonchernlim.myproject">
<level value="info"/>
</logger>
<!-- Set "info" log level for Spring framework -->
<logger name="org.springframework">
<level value="info"/>
</logger>
<!-- Set "debug" log level for Hibernate framework -->
<logger name="org.hibernate">
<level value="debug"/>
</logger>
<root>
<!-- The default log level is "warn" -->
<priority value="warn"/>
<appender-ref ref="consoleAppender"/>
</root>
</log4j:configuration>
Included below tags in web.xml:
<context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>/WEB-INF/log4j.xml</param-value>
</context-param>
One approach i could think of is to edit setenv.bat from apachetomcatserver\bin and add loglevel. But how to set loglevels dynamically in the log4j.xml file???
in tomcatserver : catalinahome\bin\setenv.bat
set loglevel=error
How to dynamically set the loglevel so that when application is deployed in TEST all logs are shown and when deployed in PROD only error log messages are shown in the log file.
I am using log4j1.2,spring,java.

You would have to create different log4j.xml-files for the corresponding environments. And then during startUp, you can simply provide the path to the log4j.xml configuration it should use.
Application parameter:
-Dlog4j.configuration=path/to/env/folder/log4j.xml

If you are using spring framework, you can use logback for logging configuration and then you can control log level based on your active spring profile.
You can get some help form following examples-
http://www.baeldung.com/spring-profiles
https://springframework.guru/using-logback-spring-boot/

How to separate web application logging in Tomcat

I have my webapp some-app.war running under Tomcat 8.5. I use Slf4j and Logback for logging within the webapp. When I log using log.info() or similar, the output gets written to catalina.out, the same log file as Tomcat uses for its internal logging. I want the logs from my application to be written to a separate log file. But I do NOT want to use logback's FileAppender to do it. I'd prefer to leave Logback using ConsoleAppender as I may deliver the WAR to others who won't have the same logging needs. I see the location of the log file as an aspect of the deployment environment, not the code.
Is there a way that I can manage per-application log files from the configuration of the Tomcat server itself -- while still using Slf4j and Logback in my code?

You can't know about others' logging needs, so there's not a silver bullet solution for this. However I'm sure the best option is not "I'm gonna leave it configured really badly because someone might log differently".
You can configure it how you wish for yourself, using FileAppenders and document the necessary steps to reconfigure it (e.g. edit the war).
You can also use more advanced configurations such as making use of syslog. Now other users have a standardized configuration option, just as long as they use syslog.
There are other options as well, but the common thread here is that you can't know what others may want, so don't waste time trying to guess it. Just do what works well for you at least.

If you placed logging.properties at [CATALINA_HOME/conf/logging.properties] then it should use it as your root logging properties file. Put you logging.properties or log.xml file in your application at [MyApp/WEB_INF/classes/logging.properties] and configure it like blow.
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration debug="true"
xmlns:log4j='http://jakarta.apache.org/log4j/'>
<appender name="stderr" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="Target" value="System.err"/>
<param name="ConversionPattern"
value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n" />
</layout>
</appender>
<appender name="stdout" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="Target" value="System.out"/>
<param name="ConversionPattern"
value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n" />
</layout>
</appender>
<appender name="file" class="org.apache.log4j.RollingFileAppender">
<param name="append" value="true" />
<param name="maxFileSize" value="2MB" />
<param name="maxBackupIndex" value="100" />
<param name="file" value="${catalina.base}/logs/MyApp/MyApp.log" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern"
value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n" />
</layout>
</appender>
<root>
<level value="DEBUG" />
<appender-ref ref="stdout" />
<appender-ref ref="stderr" />
<appender-ref ref="file" />
</root>
</log4j:configuration>

Log4j stops to write to console after tomcat context reload

I have a problem with log4j under tomcat.
When Eclipse deploys new version of application to tomcat, it reloads application context. After reloading context is completed, web application level logger stops to write to console.
Only tomcat logger still works.
My configuration in log4j.xml in web appplication is following:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/xml/doc-files/log4j.dtd">
<log4j:configuration xmlns:log4j='http://jakarta.apache.org/log4j/'>
<appender name="stdout" class="org.apache.log4j.ConsoleAppender">
<param name="Target" value="System.out" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"/>
</layout>
</appender>
<root>
<level value="INFO" />
<appender-ref ref="stdout"/>
</root>
</log4j:configuration>
I've put log4j-1.2.16.jar to /WEB-INF/lib directory of my application. Besides that I've put another copy of log4j-1.2.16.jar to tomcat's /lib directory, according to tutorial presented on official tomcat site.

Use the follow option of org.apache.log4j.ConsoleAppender. This options determines if the appender honors reassignments of System.out or System.err made after configuration. By default, false.
<appender name="stdout" class="org.apache.log4j.ConsoleAppender">
<param name="Target" value="System.out" />
<param name="Follow" value="true" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern"
value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"/>
</layout>
</appender>

Thanks to Paul's answer I've discovered the real reason why logger didn't log after reloading context. The problem was that on application initialization I was invoking the following code:
System.setErr( new PrintStream( new LoggingOutputStream( Logger.getLogger("outLog"), Level.ERROR ), true));
System.setOut( new PrintStream( new LoggingOutputStream( Logger.getLogger("outLog"), Level.INFO ), true));
This code is supposed to write all output written to console (like System.out.println) to xml log on production server, but during devlopment I'm using console so it has to be turned off.
When I added <param name="Follow" value="true" /> to my configuration, there was no output at all in any case, so thanks to this option I managed to discover the real problem.

Problem with loading custom appender using log4j property file

Merged with Log4j not finding custom appender using a property file.
I'm working on an Eclipse RCP project comprised from multiple plugin projects, and having trouble load a custom appender using the following property file in log4j:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="eclipseErrorView" class="com.mypackage.EclipseLoggingAppender">
</appender>
<appender name="console" class="org.apache.log4j.ConsoleAppender">
<param name="Target" value="System.out"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %c{1} - %m%n"/>
</layout>
</appender>
<root>
<priority value ="warn" />
<appender-ref ref="eclipseErrorView" />
</root>
<root>
<priority value ="debug" />
<appender-ref ref="console" />
</root>
</log4j:configuration>
But when coming to load this property file I get the following error:
log4j:ERROR Could not create an Appender. Reported error follows.
java.lang.ClassNotFoundException: com.mypackage.EclipseLoggingAppender
Where should I include this package in order for log4j to recoginze it? Note that I'm working on multiple plugin projects, all of them use log4j for logging purposes...
Thanks

How to Write Java server logs to separate log file

Right now we are using a customized logger method for our application but now we have a stand alone code for which we need to write to a separate log file. We have little idea about log4j. I just want to know where to change properties if any so that i don't disturb the existing logger application as well as we write our logs into new log file.

First define a file appender:
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=/mylogfile.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d [%t] %-5p %c %x - %m%n
Then point your package to use this appender:
log4j.logger.mypackage=LOGFILE
log4j.additivity.mypackage=false
The last line is important if you do not want your package to inherit the global appender. Doing so will result in the log messages from mypackage also printed at the default appender.

in log4j you can direct log entries to separate files based upon pacakge name.
log4j.logger.your.package1= LOG,STDOUT
log4j.additivity.your.package1=false
log4j.logger.your.package2= DEBUG, STDOUT
log4j.additivity.your.package2=false

I use XML configuration.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="logfile" class="org.apache.log4j.FileAppender">
<param name="file" value="app.log"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d-%5p(%F:%L)-%m%n"/>
</layout>
</appender>
<appender name="myLogfile" class="org.apache.log4j.FileAppender">
<param name="file" value="myFile.log"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d-%5p(%F:%L)-%m%n"/>
</layout>
</appender>
<logger name="org.myApp">
<level value="INFO"/>
<appender-ref ref="myLogfile" />
</logger>
<root>
<level value="ERROR" />
<appender-ref ref="logfile" />
</root>
</log4j:configuration>

Just use FileAppender and specify a new filename in the constructor.