From 6016d7d4da2a414390294b5539a2c8f2a437b340 Mon Sep 17 00:00:00 2001
From: Todd Lipcon <todd@apache.org>
Date: Mon, 27 Jan 2014 22:15:01 +0000
Subject: [PATCH] HADOOP-10288. Explicit reference to Log4JLogger breaks
 non-log4j users. Contributed by Todd Lipcon.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1561882 13f79535-47bb-0310-9956-ffa450edef68
---
 hadoop-common-project/hadoop-common/CHANGES.txt      |  3 +++
 .../java/org/apache/hadoop/http/HttpRequestLog.java  | 12 +++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index 5c39282e9af..bb1be6d0aea 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -542,6 +542,9 @@ Release 2.4.0 - UNRELEASED
     HADOOP-10250. VersionUtil returns wrong value when comparing two versions.
     (Yongjun Zhang via atm)
 
+    HADOOP-10288. Explicit reference to Log4JLogger breaks non-log4j users
+    (todd)
+
 Release 2.3.0 - UNRELEASED
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/http/HttpRequestLog.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/http/HttpRequestLog.java
index eb8968bcc49..52d985042ad 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/http/HttpRequestLog.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/http/HttpRequestLog.java
@@ -53,7 +53,17 @@ public class HttpRequestLog {
     String appenderName = name + "requestlog";
     Log logger = LogFactory.getLog(loggerName);
 
-    if (logger instanceof Log4JLogger) {
+    boolean isLog4JLogger;;
+    try {
+      isLog4JLogger = logger instanceof Log4JLogger;
+    } catch (NoClassDefFoundError err) {
+      // In some dependent projects, log4j may not even be on the classpath at
+      // runtime, in which case the above instanceof check will throw
+      // NoClassDefFoundError.
+      LOG.debug("Could not load Log4JLogger class", err);
+      isLog4JLogger = false;
+    }
+    if (isLog4JLogger) {
       Log4JLogger httpLog4JLog = (Log4JLogger)logger;
       Logger httpLogger = httpLog4JLog.getLogger();
       Appender appender = null;