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Date: Mon, 21 Dec 2009 20:26:06 +0200
From: Juha Laiho <Juha.Laiho@iki.fi>
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Subject: Re: Java in JDK but ANT can't find it!
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I came across this oldish thread while trying to resolve the same
problem:

David Nemer wrote:
 > I am running ANT programmatically in JAVA. So, my task is to build the
 > BUILD.XML.
 > I'm able to do so, but it throws an exception saying:
 >
 > /scratch2/nemer/test/xfire/build.xml:5: The following error occurred 
while
 > executing this line:
 > /scratch2/nemer/test/xfire/build-common.xml:81: Unable to find a javac
 > compiler;
 > com.sun.tools.javac.Main is not on the classpath.
 > Perhaps JAVA_HOME does not point to the JDK.
 > It is currently set to "/opt/jdk1.6.0_06/jre"


I think I have found an explanation on what is going on, at least
for cases where ant is run using a shell script on the command line.


Environment:
Linux (Slackware)
Java is Sun JDK 1.6.0_17-b04, from Slackware packages

build.xml for the test:
<project>
   <echo message="JAVA_HOME: ${java.home}"/>
</project>

Environment variables, executable locations:
bash-3.1$ echo $JAVA_HOME
/usr/lib64/java
bash-3.1$ echo $PATH
/usr/lib64/java/bin:/usr/bin:/bin:/home/jlaiho/aa/apache-ant-1.7.1/bin
bash-3.1$ type -a ant
ant is /home/jlaiho/aa/apache-ant-1.7.1/bin/ant
bash-3.1$ type -a java
java is /usr/lib64/java/bin/java

The installation pointed to by JAVA_HOME is a JDK installation
(tools.jar does exist in $JAVA_HOME/lib). A JRE installation
also exists, at $JAVA_HOME/jre .

bash-3.1$ ls -l /usr/lib64/java/lib/tools.jar
-rw-r--r-- 1 root root 12590684 2009-11-05 23:08 
/usr/lib64/java/lib/tools.jar

Running the test:
bash-3.1$ ant
Buildfile: build.xml
      [echo] JAVA_HOME: /usr/lib64/java/jre

BUILD SUCCESSFUL
Total time: 0 seconds

What happened? Explanation can be found in the ant shell script,
starting at line 125 (at which point there hasn't been anything
that would set JAVACMD):

if [ -z "$JAVACMD" ] ; then
   if [ -n "$JAVA_HOME"  ] ; then
     # IBM's JDK on AIX uses strange locations for the executables
     if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
       JAVACMD="$JAVA_HOME/jre/sh/java"
     elif [ -x "$JAVA_HOME/jre/bin/java" ] ; then
       JAVACMD="$JAVA_HOME/jre/bin/java"
     else
       JAVACMD="$JAVA_HOME/bin/java"
     fi
   else
     JAVACMD=`which java 2> /dev/null `
     if [ -z "$JAVACMD" ] ; then
         JAVACMD=java
     fi
   fi
fi

... so, as JAVACMD was empty, and JAVA_HOME was set, AND
$JAVA_HOME/jre/bin/java did exist, then the JAVA_HOME was
forcible overridden with the JRE home directory. I don't
understand why, but that is what happens.

Is this a bug - perhaps? At least it's not what I would
expect.
-- 
..Juha


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