Using log4j on Google App Engine

Question

I need to use log4j in my application, but I don't know how I can get properties loaded. Deafult properties files says that I should put log4j.properties to /WEB-INF/classes/ folder, but in eclipse I cannot see that folder and I cannot create it, because it already exists. And I cannot add any files to that folder either.

Here is error that I get:

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

So how can I get web application to load log4j properties?

Answer 1

Put the log4j.properties file into a source directory of your project, e.g. /src. Eclipse will copy it into your target build directory.

I recomend using SLF4J with Log4J, and the SpringSource Tool Suite (STS) for your project.

Answer 2

Here is how to get log4j working using Eclipse with the Google plugin.

Modify appengine-web.xml as follows:

<system-properties> 
  <property name="java.util.logging.config.file" value="WEB-INF/classes/log4j.properties"/> 
</system-properties> 

You can add the following code to your servlet:

import org.apache.log4j.Logger; 
... 
Logger logger = Logger.getLogger("com.foo"); 
logger.debug("Yay2!"); 

Put the log4j.properties file in the src/ directory with the following content:

log4j.rootLogger=DEBUG, 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{ABSOLUTE} %5p %t %c{1}:%M:%L - %m%n 

You can do a Project > Clean then allow it to automatically build, The build copies the log4j.properties file to /war/WEB-INF/classes/. You'll see the log displayed when you Run As > Web Application and request a URL.

I know that you're not using Maven but I will add instructions below in case anyone else needs them. These instructions will work with com.google.appengine.archetypes:guestbook-archetype.

Add the following to pom.xml:

<dependency> 
<groupId>log4j</groupId> 
<artifactId>log4j</artifactId> 
<version>1.2.16</version> 
</dependency> 

Add the following code to guestbook.jsp:

<%@ page import="org.apache.log4j.Logger" %> 
... 
<% 
Logger logger = Logger.getLogger("com.foo"); 
logger.debug("Yay2!"); 
%> 

Create src/main/webapp/WEB-INF/classes/log4j.properties with the same content as above.

Then run:

mvn clean 
mvn verify 
mvn appengine:devserver 

You will see log output in our console after calling http://localhost:8080/.