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 083ec12ab32953dd0618bff46a69bbfec067a4c3..2f1119c05e346d85d9da45f5650d1d355bf5cf24 100644 (file)
--- a/doc/examples/java-log4j/Hello.java
+++ b/doc/examples/java-log4j/Hello.java
@@ -1,4 +1,5 @@
 /*
+ * Copyright (C) 2015 - EfficiOS Inc., Alexandre Montplaisir <alexmonthy@efficios.com>
  * Copyright (C) 2014 - Christian Babeux <christian.babeux@efficios.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
@@ -19,37 +20,85 @@
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  * IN THE SOFTWARE.
  */
+
 import java.io.IOException;
 
-import org.apache.log4j.Logger;
+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;
 
-import org.lttng.ust.agent.LTTngAgent;
+/**
+ * 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
+ */
+public class Hello {
 
-public class Hello
-{
-       /* Of course :) */
-       private static final int answer = 42;
+       private static final Logger HELLO_LOG = Logger.getLogger(Hello.class);
 
-       static Logger helloLog = Logger.getLogger(Hello.class);
+       /**
+        * Application start
+        *
+        * @param args
+        *            Command-line arguments
+        * @throws IOException
+        *             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 {
 
-       private static LTTngAgent lttngAgent;
+               /*
+                * 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);
 
-       public static void main(String args[]) throws Exception
-       {
+               /* Start with the default Log4j configuration, which logs to console */
                BasicConfigurator.configure();
-               lttngAgent = LTTngAgent.getLTTngAgent();
 
                /*
-                * Gives you time to do some lttng commands before any event is hit.
+                * 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);
+
+               /*
+                * Here we've set up the appender programmatically, but it could also be
+                * defined at runtime, by reading a configuration file for example:
                 */
-               Thread.sleep(5000);
+               // PropertyConfigurator.configure(fileName);
 
-               /* Trigger a tracing event using the JUL Logger created before. */
-               helloLog.info("Hello World, the answer is " + answer);
+               /* 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 hello delay in 5 seconds...");
-               Thread.sleep(5000);
-               helloLog.info("Hello World delayed...");
+               /* Cleanup */
+               HELLO_LOG.removeAppender(lttngAppender);
+               lttngAppender.close();
        }
 }