Fix: Null-check return value of log4j.Category.getAllAppenders()

[lttng-ust.git] / liblttng-ust-java-agent / java / lttng-ust-agent-log4j / org / lttng / ust / agent / log4j / LttngLog4jAgent.java

diff --git a/liblttng-ust-java-agent/java/lttng-ust-agent-log4j/org/lttng/ust/agent/log4j/LttngLog4jAgent.java b/liblttng-ust-java-agent/java/lttng-ust-agent-log4j/org/lttng/ust/agent/log4j/LttngLog4jAgent.java
index 5dd846872308eb2d46c1f1dc94175f7b9acf4eec..157ff3fe879395b88b1d0592805537201457a02c 100644 (file)
--- a/liblttng-ust-java-agent/java/lttng-ust-agent-log4j/org/lttng/ust/agent/log4j/LttngLog4jAgent.java
+++ b/liblttng-ust-java-agent/java/lttng-ust-agent-log4j/org/lttng/ust/agent/log4j/LttngLog4jAgent.java
@@ -17,6 +17,17 @@
 
 package org.lttng.ust.agent.log4j;
 
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.List;
+import java.util.Set;
+import java.util.TreeSet;
+
+import org.apache.log4j.Appender;
+import org.apache.log4j.Category;
+import org.apache.log4j.LogManager;
+import org.apache.log4j.Logger;
 import org.lttng.ust.agent.AbstractLttngAgent;
 
 /**
@@ -40,4 +51,55 @@ class LttngLog4jAgent extends AbstractLttngAgent<LttngLogAppender> {
                return instance;
        }
 
+       @Override
+       public Collection<String> listAvailableEvents() {
+               Set<String> ret = new TreeSet<String>();
+
+               @SuppressWarnings("unchecked")
+               List<Logger> loggers = Collections.list(LogManager.getCurrentLoggers());
+               for (Logger logger : loggers) {
+                       if (logger == null) {
+                               continue;
+                       }
+
+                       /*
+                        * Check if that logger has at least one LTTng log4j appender
+                        * attached.
+                        */
+                       if (hasLttngAppenderAttached(logger)) {
+                               ret.add(logger.getName());
+                       }
+               }
+
+               return ret;
+       }
+
+       private static boolean hasLttngAppenderAttached(Category logger) {
+               @SuppressWarnings("unchecked")
+               Enumeration<Appender> appenders = logger.getAllAppenders();
+               if (appenders != null) {
+                       for (Appender appender : Collections.list(appenders)) {
+                               if (appender instanceof LttngLogAppender) {
+                                       return true;
+                               }
+                       }
+               }
+
+               /*
+                * A parent logger, if any, may be connected to an LTTng handler. In
+                * this case, we will want to include this child logger in the output,
+                * since it will be accessible by LTTng.
+                */
+               Category parent = logger.getParent();
+               if (parent != null) {
+                       return hasLttngAppenderAttached(parent);
+               }
+
+               /*
+                * We have reached the root logger and have not found any LTTng handler,
+                * this event will not be accessible.
+                */
+               return false;
+       }
+
 }