You can easily do this via ant. Here is a build.xml file for doing this
<project name="genTestReport" default="gen" basedir=".">
<description>
Generate the HTML report from JUnit XML files
</description>
<target name="gen">
<property name="genReportDir" location="${basedir}/unitTestReports"/>
<delete dir="${genReportDir}"/>
<mkdir dir="${genReportDir}"/>
<junitreport todir="${basedir}/unitTestReports">
<fileset dir="${basedir}">
<include name="**/TEST-*.xml"/>
</fileset>
<report format="frames" todir="${genReportDir}/html"/>
</junitreport>
</target>
</project>
This will find files with the format TEST-*.xml and generate reports into a folder named unitTestReports.
To run this (assuming the above file is called buildTestReports.xml) run the following command in the terminal:
ant -buildfile buildTestReports.xml