Fix: log4j example: set logger level to prevent unexpected level inheritance

[lttng-ust.git] / doc / examples / java-log4j / Hello.java

diff --git a/doc/examples/java-log4j/Hello.java b/doc/examples/java-log4j/Hello.java
index c51d4d4013b1d7d7979de3ec65ea6487cf1dcc14..2f1119c05e346d85d9da45f5650d1d355bf5cf24 100644 (file)
--- a/doc/examples/java-log4j/Hello.java
+++ b/doc/examples/java-log4j/Hello.java
@@ -26,10 +26,26 @@ import java.io.IOException;
 import org.apache.log4j.Appender;
 import org.apache.log4j.BasicConfigurator;
 import org.apache.log4j.Logger;
+import org.apache.log4j.Level;
 import org.lttng.ust.agent.log4j.LttngLogAppender;
 
 /**
- * Example application using the LTTng-UST Java JUL agent.
+ * Example application using the LTTng-UST Java log4j agent.
+ *
+ * <p>
+ * To obtain LTTng trace events, you should run the following sequence of
+ * commands:
+ * </p>
+ *
+ * <ul>
+ * <li>$ lttng create</li>
+ * <li>$ lttng enable-event -l -a</li>
+ * <li>$ lttng start</li>
+ * <li>(run this program)</li>
+ * <li>$ lttng stop</li>
+ * <li>$ lttng view</li>
+ * <li>$ lttng destroy</li>
+ * </ul>
  *
  * @author Alexandre Montplaisir
  * @author Christian Babeux
@@ -44,15 +60,28 @@ public class Hello {
         * @param args
         *            Command-line arguments
         * @throws IOException
-        * @throws InterruptedException
+        *             If the required native libraries cannot be found. You may
+        *             have to specify "-Djava.library.path=..." on the "java"
+        *             command line.
         */
-       public static void main(String args[]) throws IOException, InterruptedException {
+       public static void main(String args[]) throws IOException {
+
+               /*
+                * Set lowest level to make sure all event levels are logged.
+                * Any jar can override the default log4j rootLogger level
+                * and a logger with no explicit level defaults to the non-null
+                * parent level. Events could be ignored if the inherited value
+                * is to low.
+                * e.g BSF  -> https://issues.apache.org/jira/browse/BSF-24
+                */
+               HELLO_LOG.setLevel(Level.ALL);
+
                /* Start with the default Log4j configuration, which logs to console */
                BasicConfigurator.configure();
 
                /*
-                * Add a LTTng log appender to the logger, which will also send the
-                * logged events to UST.
+                * Instantiate a LTTng log appender and attach it to the logger, which
+                * will now send the logged events to UST.
                 */
                Appender lttngAppender = new LttngLogAppender();
                HELLO_LOG.addAppender(lttngAppender);
@@ -63,18 +92,13 @@ public class Hello {
                 */
                // PropertyConfigurator.configure(fileName);
 
-               /*
-                * Gives you time to do some lttng commands before any event is hit.
-                */
-               Thread.sleep(5000);
-
-               /* Trigger a tracing event using the Log4j Logger created before. */
+               /* Trigger some tracing events using the Log4j Logger created before. */
                HELLO_LOG.info("Hello World, the answer is " + 42);
+               HELLO_LOG.info("Another info event");
+               HELLO_LOG.error("An error event");
 
-               System.out.println("Firing second event in 5 seconds...");
-               Thread.sleep(5000);
-               HELLO_LOG.info("Hello World delayed...");
-
+               /* Cleanup */
+               HELLO_LOG.removeAppender(lttngAppender);
                lttngAppender.close();
        }
 }