contents/using-lttng/instrumenting/java-application/log4j.md

   1 ---
   2 id: log4j
   3 since: 2.6
   4 ---
   5
   6 LTTng features an Apache log4j 1.2 agent, which means your existing
   7 Java applications using log4j 1.2 for logging can record events to
   8 LTTng traces with just a minor source code modification.
   9
  10 <div class="tip">
  11 <p>
  12     <span class="t">Note:</span>This version of LTTng does not
  13     support Log4j 2.
  14 </p>
  15 </div>
  16
  17 Here's an example:
  18
  19 ~~~ java
  20 import org.apache.log4j.Logger;
  21 import org.apache.log4j.BasicConfigurator;
  22 import org.lttng.ust.agent.LTTngAgent;
  23
  24 public class Test
  25 {
  26     private static final int answer = 42;
  27
  28     public static void main(String[] argv) throws Exception
  29     {
  30         // create and configure a logger
  31         Logger logger = Logger.getLogger(Test.class);
  32         BasicConfigurator.configure();
  33
  34         // call this as soon as possible (before logging)
  35         LTTngAgent lttngAgent = LTTngAgent.getLTTngAgent();
  36
  37         // log at will!
  38         logger.info("some info");
  39         logger.warn("some warning");
  40         Thread.sleep(500);
  41         logger.debug("debug information; the answer is " + answer);
  42         Thread.sleep(123);
  43         logger.error("error!");
  44         logger.fatal("fatal error!");
  45
  46         // not mandatory, but cleaner
  47         lttngAgent.dispose();
  48     }
  49 }
  50 ~~~
  51
  52 To compile the snippet above, do:
  53
  54 <pre class="term">
  55 javac -cp /usr/lib/lttng/java/liblttng-ust-agent.jar:$LOG4JCP Test.java
  56 </pre>
  57
  58 where `$LOG4JCP` is the log4j 1.2 JAR file path.
  59
  60 You can run the resulting compiled class like this:
  61
  62 <pre class="term">
  63 java -cp /usr/lib/lttng/java/liblttng-ust-agent.jar:$LOG4JCP:. Test
  64 </pre>