I am trying to package my web application into war file using Ant.
When I build, I am getting the following error:
C:\Documents and Settings\Administrator\workspace\Assignment7\build.xml:67: 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 "C:\Program Files\Java\jre6"
The following is my build.xml
<?xml version="1.0" encoding="UTF-8"?>
<project name="Generate War" default="install" basedir=".">
<property name="build.dir" value="build"/>
<property name="dir.name" value="Assignment7"/>
<property name="package.name" value="${dir.name}.war"/>
<property name="content" value="webContent"/>
<property name="web-inf" value="${content}\WEB-INF"/>
<property name="meta-inf" value="${content}\META-INF"/>
<property name="jsp.dir.name" value="${content}"/>
<property name="lib" value="${web-inf}\lib"/>
<property name="src" value="src"/>
<property name="dest.dir" value="target"/>
<!-- Setting path to the server webapp folder -->
<property name="webapp.dir" value="C:\Program Files\Apache Software Foundation\Tomcat 6.0\webapps"/>
<!-- Using temp folder for convinence -->
<property name="temp.dir" value="temp"/>
<property name="temp.dir.web-inf" value="${temp.dir}\WEB-INF"/>
<property name="temp.dir.meta-inf" value="${temp.dir}\META-INF"/>
<property name="temp.dir.lib" value="${temp.dir.web-inf}\lib"/>
<property name="temp.dir.classes" value="${temp.dir.web-inf}\classes"/>
<!--<property name="temp.dir.classes.dir" value="${temp.dir.classes}\**"/>-->
<property name="package.file" value="${dest.dir}\${package.name}"/>
<path id="build.class.path">
<fileset dir="${lib}">
<include name="**/*.jar"/>
</fileset>
</path>
<path id="build.class.path1">
<fileset dir="C:\program files\java\jre6\lib">
<include name="**/*.jar"/>
</fileset>
</path>
<target name="clean">
<delete>
<fileset dir="${dest.dir}" includes="**/*"/>
</delete>
<delete dir="${temp.dir}"/>
<delete dir="${temp.dir.classes}"/>
<delete dir="${temp.dir.web-inf}"/>
<delete dir="${temp.dir.meta-inf}"/>
</target>
<target name="prepare" depends="clean">
<mkdir dir="${dest.dir}"/>
<mkdir dir="${temp.dir}"/>
<mkdir dir="${temp.dir.web-inf}"/>
<mkdir dir="${temp.dir.lib}"/>
<mkdir dir="${temp.dir.classes}"/>
<mkdir dir="${temp.dir.meta-inf}"/>
</target>
<target name="compile" depends="prepare">
<echo>==="complie"===</echo>
<javac srcdir="${src}" destdir="${temp.dir.classes}" debug="on">
<classpath refid="build.class.path"></classpath>
</javac>
<!--<copydir src="${build.dir}\classes" dest="${temp.dir.classes}"/>-->
</target>
<target name="package" depends="compile">
<echo>"PACKAGING THE FILES"</echo>
<copy file="${meta-inf}\MANIFEST.MF" tofile="${temp.dir.meta-inf}\MANIFEST.MF" overwrite="true"/>
<copy file="${web-inf}\web.xml" tofile="${temp.dir.web-inf}\web.xml" overwrite="true"/>
<copy file="${web-inf}\tiles.xml" tofile="${temp.dir.web-inf}\tiles.xml" overwrite="true"/>
<copy todir="${temp.dir.classes}">
<fileset dir="${src}">
<include name="**/*.xml"/>
</fileset>
</copy>
<war destfile="${package.file}" webxml="${temp.dir.web-inf}\web.xml" basedir="${temp.dir}">
<fileset dir="${jsp.dir.name}"/>
<lib dir="${lib}"></lib>
<classes dir="${temp.dir.classes}"></classes>
</war>
</target>
<target name="jsps">
<copy todir="${webapp.dir}\${dir.name}">
<fileset dir="${content}">
<include name="**/*.jsp"/>
<include name="**/*.html"/>
<include name="**/*.css"/>
<include name="**/*.gif"/>
<include name="**/*.jpg"/>
<include name="**/*.png"/>
<include name="**/*.js"/>
</fileset>
</copy>
</target>
<target name="install" depends="package">
<copy file="${package.file}" todir="${webapp.dir}" overwrite="true"/>
</target>
</project>
How can I compile a class file that does not have a main class?
How do I set the class path?
For reference, I am using Eclipse.
All your ant stuff will work fine except the javac task which needs the tools.jar, located in the /lib directory from the JDK, JRE is not sufficient in that case. Therefore the hint from ant : "Unable to find a javac compiler;..."
When working with Eclipse the default setting points to your JRE installation.
So, one of your first steps after starting Eclipse for the first time should be :Window > Preferences > Java > Installed JREs and change the settings from JRE to JDK.
Alternatively use :Window > Preferences > Ant > Runtime > Classpath > Global Entries
and add the tools.jar from your JDK/lib folder
I had the same problem. In my case, I fixed it by pointing JAVA_HOME to the JDK folder, rather than the JDK\bin folder.
Currently you have set JAVA_HOME to your installed jre instead of the jdk. Install the current JDK then set JAVA_HOME to your JDK Directory.
You'll find the current jdk here http://www.oracle.com/technetwork/java/javase/downloads/index.html
I had this problem and commented on https://stackoverflow.com/a/8406221/866333 saying the fix was no good. (Actually it was reporting that JAVA_HOME was something else so I suggested a script was changing it).
As their reply stated the compiler doesn't lie.
So true, I eventually spotted my old JAVA_HOME variable was something like JDK_v7.0.7 when I'd just removed that (from a 2012 restore DVD) and updated to like JDK_v7.7.1. Why it saw fit to fallback to the JRE, suppose it was a convenience.
eg
JAVA_HOME = c:\Java\JDK_v7.0.7
@runs script...@
Perhaps JAVA_HOME does not point to the JDK. It is currently set to "C:\Program Files\Java\jre7"
@check at cmd prompt@
set
JAVA_HOME = c:\Java\JDK_v7.0.7
so it is kinda lieing isn't it?
I made the mistake of installing the JDK and the JRE to the same location. Installing the JDK automatically installs a JRE and I inadvertently selected the same location as the JDK.
This caused considerable confusion in eclipse.
Install the JDK and the JRE to different locations.
This a is a common mistake by most of the beginners,
JRE is just for running java based code/applications.
If you want to compile java code, you must use JDK.
So open environment variables, and set JAVA_HOME path to JDK folder instead of JRE
I was getting this error while trying to install a java based tool, using ant.
My $JAVA_HOME environment variable, in ~/.bash_profile, was set to /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.141-1.b16.el7_3.x86_64/jre
By removing the jre, (going one directory level up), making $JAVA_HOME, /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.141-1.b16.el7_3.x86_64/, fixed the issue for me.
Don't forget to run, source ~/.bash_profile, after making the change ! HTH
来源：https://stackoverflow.com/questions/8400637/unable-to-find-a-javac-compiler