No appenders could be found for logger(log4j)?

Question

I have put log4j to my buildpath, but I get the following message when I run my application:

log4j:WARN No appenders could be found for logger (dao.hsqlmanager).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

What do these warnings mean? Whats the appender here?

Answer 1

First import:

 import org.apache.log4j.PropertyConfigurator;

Then add below code to main method:

String log4jConfPath ="path to/log4j.properties";
PropertyConfigurator.configure(log4jConfPath);

Create a file at path to and add the below code to that file.

log4j.rootLogger=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yy/MM/dd HH:mm:ss} %p %c{2}: %m%n

Answer 2

This is just a warning.

Fixing

This occurs when the default configuration files log4j.properties and log4j.xml can not be found and the application performs no explicit configuration.

To fix that, simply create/copy log4j.properties or log4j.xml into your a location on the classpath (usually the same as the jar files).

Optionally set java option: -Dlog4j.configuration=file:///path/to/log4j.properties.

log4j uses Thread.getContextClassLoader().getResource() to locate the default configuration files and does not directly check the file system. Knowing the appropriate location to place log4j.properties or log4j.xml requires understanding the search strategy of the class loader in use. log4j does not provide a default configuration since output to the console or to the file system may be prohibited in some environments.

Debugging

For debugging, you may try to use -Dlog4j.debug=true parameter.

Configuration of log4j.properties

Sample configuration of log4j.properties:

# Set root logger level to DEBUG and its only appender to A1.
log4j.rootLogger=DEBUG, A1

# A1 is set to be a ConsoleAppender.
log4j.appender.A1=org.apache.log4j.ConsoleAppender

# A1 uses PatternLayout.
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

# Print only messages of level WARN or above in the package com.foo.
log4j.logger.com.foo=WARN

Here is another configuration file that uses multiple appenders:

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=%5p [%t] (%F:%L) - %m%n

log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=example.log

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=%p %t %c - %m%n

Apache Solr

If using Solr, copy <solr>/example/resources/log4j.properties into a location on the classpath.

Sample configuration of log4j.properties from Solr goes like:

#  Logging level
solr.log=logs/
log4j.rootLogger=INFO, file, CONSOLE

log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender

log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%-4r [%t] %-5p %c %x \u2013 %m%n

#- size rotation with log cleanup.
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.MaxFileSize=4MB
log4j.appender.file.MaxBackupIndex=9

#- File to log to and log format
log4j.appender.file.File=${solr.log}/solr.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%-5p - %d{yyyy-MM-dd HH:mm:ss.SSS}; %C; %m\n

log4j.logger.org.apache.zookeeper=WARN
log4j.logger.org.apache.hadoop=WARN

# set to INFO to enable infostream log messages
log4j.logger.org.apache.solr.update.LoggingInfoStream=OFF

---

See also:

• Short introduction to log4j: Default Initialization Procedure
• Why can't log4j find my properties in a J2EE or WAR application?

Answer 3

I ran into this issue when trying to build an executable jar with maven in intellij 12. It turned out that because the java manifest file didn't include a class path the log4j properties file couldn't be found at the root level (where the jar file was executed from.)

FYI I was getting the logger like this:

Logger log = LogManager.getLogger(MyClassIWantedToLogFrom.class);

And I was able to get it to work with a pom file that included this:

         <plugin>
            <artifactId>maven-assembly-plugin</artifactId>
            <version>2.2-beta-5</version>
            <configuration>
                <archive>
                    <manifest>
                        <addClasspath>true</addClasspath> 
                        <mainClass>com.mycompany.mainPackage.mainClass</mainClass>
                    </manifest>
                    <manifestEntries>
                        <Class-Path>.</Class-Path> <!-- need to add current directory to classpath properties files can be found -->
                    </manifestEntries>
                </archive>
                <descriptorRefs>
                    <descriptorRef>jar-with-dependencies</descriptorRef>
                </descriptorRefs>
            </configuration>
            <executions>
                <execution>
                    <id>make-assembly</id>
                    <phase>package</phase>
                    <goals>
                        <goal>single</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>

Answer 4

If log4j.properties is indeed on the classpath, you are using Spring Boot to make a WAR file for deployment to an app server, you are omitting a web.xml file in favour of Spring Boot's autoconfigure, and you are not getting any log messages whatsoever, you need to explicitly configure Log4j. Assuming you are using Log4j 1.2.x:

public class AppConfig extends SpringBootServletInitializer {

    public static void main( String[] args ) {
        // Launch the application
        ConfigurableApplicationContext context = SpringApplication.run( AppConfig.class, args );
    }

    @Override
    protected SpringApplicationBuilder configure( SpringApplicationBuilder application ) {
        InputStream log4j = this.getClass().getClassLoader().getResourceAsStream("log4j.properties");
        PropertyConfigurator.configure(log4j);
        return application;
    }

// Other beans as required...
}

Answer 5

Log4J display this warning message when Log4j Java code is searching to create a first log line in your program.

At this moment, Log4j make 2 things

1. it search to find log4j.properties file
2. it search to instantiate the appender define in log4j.properties

If log4J doesn't find log4j.properties file or if appender declared in log4j.rootlogger are not defined elsewhere in log4j.properties file the warning message is displayed.

CAUTION: the content of Properties file must be correct.

The following content is NOT correct

log4j.rootLogger=file

log4j.appender.FILE=org.apache.log4j.FileAppender
log4j.appender.FILE.File=c:/Trace/MsgStackLogging.log
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.ConversionPattern=%m%n
log4j.appender.FILE.ImmediateFlush=true
log4j.appender.FILE.Threshold=debug
log4j.appender.FILE.Append=false

because file appender is declared in LOWER-CASE in log4j.rootlogger statement and defined in log4j.appender statement using UPPER-CASE !

A correct file would be

log4j.rootLogger=FILE

log4j.appender.FILE=org.apache.log4j.FileAppender
log4j.appender.FILE.File=c:/Trace/MsgStackLogging.log
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.ConversionPattern=%m%n
log4j.appender.FILE.ImmediateFlush=true
log4j.appender.FILE.Threshold=debug
log4j.appender.FILE.Append=false

If MAVEN is used, you must put log4j.properties files in src/main/resources AND start a MAVEN build.

Log4j.properties file is then copied in target/classes folder.

Log4J use the log4j.properties file that it found in target/classes !

Answer 6

The reason can be lack of the word static in some:

final static Logger logging = Logger.getLogger(ProcessorTest.class);

If I make logger the instance field, I am getting exactly this very warning:

No appenders could be found for logger (org.apache.kafka.producer.Sender)

What is worse, the warning points not to ProcessorTest, where the mistake lives, but to an absolutely different class (Sender) as a source of problems. That class has correct set logger and need not any changes! We could look for the problem for ages!