无法从php页面运行java

I'm using Ubuntu with PHP installed on it. I create a php page with content below:

<?php
    $cmd='/var/www/selenium/projects/QA\ Automation/grid/./SimplePolicytest';
    exec($cmd);
?>

What's in SimplePolicytest is two very simple command as shown below:

cd /var/www/selenium/projects/QA\ Automation/grid/bin
echo Test Start
../jdk1.7.0/bin/java -classpath .:../jar:..//jar/selenium-server.jar:../jar/junit-4.10.jar org.junit.runner.JUnitCore simple.SimplePolicy

echo Test Complete

But when I load the page, this command didn't do anything.