Question

I am using Log4j in a java web app.

Now, when I run a servlet of that web app, this is the error message that I get–

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet execution threw an exception

root cause

java.lang.NoClassDefFoundError: org/apache/log4j/Logger
com.test.ConfigHelper.<clinit>(ConfigHelper.java:45)
com.test.runsinglecrawljob.doGet(runsinglecrawljob.java:126)
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

root cause


java.lang.ClassNotFoundException: org.apache.log4j.Logger
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1688)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1533)
com.test.ConfigHelper.<clinit>(ConfigHelper.java:45)
com.test.runsinglecrawljob.doGet(runsinglecrawljob.java:126)
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

Now the line of code in ConfigHelper.java (line 45) is given below—

protected static final Logger log = Logger.getLogger(ConfigHelper.class);

I checked Java Build Path– the JAR file for log4j has been added to build path.

What am I doing wrong here? How do I make log4j work without any problems?

Answer 1

I checked Java Build Path– the JAR file for log4j has been added to build path.

Being part of the build path isn’t enough – you need to make sure it’s available at execution time, for example by putting it in the WEB-INF/lib directory in your web application, or potentially in the library path of your servlet container.