liblttng-ust-java-agent/java/lttng-ust-agent-log4j/org/lttng/ust/agent/log4j/LttngLog4jAgent.java

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2015 EfficiOS Inc.
   5  * Copyright (C) 2015 Alexandre Montplaisir <alexmonthy@efficios.com>
   6  */
   7
   8 package org.lttng.ust.agent.log4j;
   9
  10 import java.util.Collection;
  11 import java.util.Collections;
  12 import java.util.Enumeration;
  13 import java.util.List;
  14 import java.util.Set;
  15 import java.util.TreeSet;
  16
  17 import org.apache.log4j.Appender;
  18 import org.apache.log4j.Category;
  19 import org.apache.log4j.LogManager;
  20 import org.apache.log4j.Logger;
  21 import org.lttng.ust.agent.AbstractLttngAgent;
  22
  23 /**
  24  * Agent implementation for using the Log4j logger, connecting to a root session
  25  * daemon.
  26  *
  27  * @author Alexandre Montplaisir
  28  */
  29 class LttngLog4jAgent extends AbstractLttngAgent<LttngLogAppender> {
  30
  31         private static LttngLog4jAgent instance = null;
  32
  33         private LttngLog4jAgent() {
  34                 super(Domain.LOG4J);
  35         }
  36
  37         public static synchronized LttngLog4jAgent getInstance() {
  38                 if (instance == null) {
  39                         instance = new LttngLog4jAgent();
  40                 }
  41                 return instance;
  42         }
  43
  44         @Override
  45         public Collection<String> listAvailableEvents() {
  46                 Set<String> ret = new TreeSet<String>();
  47
  48                 @SuppressWarnings("unchecked")
  49                 List<Logger> loggers = Collections.list(LogManager.getCurrentLoggers());
  50                 for (Logger logger : loggers) {
  51                         if (logger == null) {
  52                                 continue;
  53                         }
  54
  55                         /*
  56                          * Check if that logger has at least one LTTng log4j appender
  57                          * attached.
  58                          */
  59                         if (hasLttngAppenderAttached(logger)) {
  60                                 ret.add(logger.getName());
  61                         }
  62                 }
  63
  64                 return ret;
  65         }
  66
  67         private static boolean hasLttngAppenderAttached(Category logger) {
  68                 @SuppressWarnings("unchecked")
  69                 Enumeration<Appender> appenders = logger.getAllAppenders();
  70                 if (appenders != null) {
  71                         for (Appender appender : Collections.list(appenders)) {
  72                                 if (appender instanceof LttngLogAppender) {
  73                                         return true;
  74                                 }
  75                         }
  76                 }
  77
  78                 /*
  79                  * A parent logger, if any, may be connected to an LTTng handler. In
  80                  * this case, we will want to include this child logger in the output,
  81                  * since it will be accessible by LTTng.
  82                  */
  83                 Category parent = logger.getParent();
  84                 if (parent != null) {
  85                         return hasLttngAppenderAttached(parent);
  86                 }
  87
  88                 /*
  89                  * We have reached the root logger and have not found any LTTng handler,
  90                  * this event will not be accessible.
  91                  */
  92                 return false;
  93         }
  94
  95 }