HADOOP-8951. Merge 1400921 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1400926 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -110,6 +110,9 @@ Release 2.0.3-alpha - Unreleased
     HADOOP-8948. TestFileUtil.testGetDU fails on Windows due to incorrect
     assumption of line separator. (Chris Nauroth via suresh)
 
+    HADOOP-8951. RunJar to fail with user-comprehensible error 
+    message if jar missing. (stevel via suresh)
+
 Release 2.0.2-alpha - 2012-09-07 
 
   INCOMPATIBLE CHANGES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/RunJar.java

@@ -126,6 +126,10 @@ public class RunJar {
     int firstArg = 0;
     String fileName = args[firstArg++];
     File file = new File(fileName);
+    if (!file.exists() || !file.isFile()) {
+      System.err.println("Not a valid JAR: " + file.getCanonicalPath());
+      System.exit(-1);
+    }
     String mainClassName = null;
 
     JarFile jarFile;