private static File findToolsJar() {
        if (JavaVersionUtils.isGreaterThanJava8()) {
            return null;
        }

        String javaHome = findJavaHome();
        File toolsJar = new File(javaHome, "lib/tools.jar");
        if (!toolsJar.exists()) {
            toolsJar = new File(javaHome, "../lib/tools.jar");
        }
        if (!toolsJar.exists()) {
            // maybe jre
            toolsJar = new File(javaHome, "../../lib/tools.jar");
        }

        if (!toolsJar.exists()) {
            throw new IllegalArgumentException("Can not find tools.jar under java home: " + javaHome);
        }

        AnsiLog.debug("Found tools.jar: " + toolsJar.getAbsolutePath());
        return toolsJar;
    }
<pre>
1. Try to find java home from System Property java.home
2. If jdk > 8, FOUND_JAVA_HOME set to java.home
3. If jdk <= 8, try to find tools.jar under java.home
4. If tools.jar do not exists under java.home, try to find System env JAVA_HOME
5. If jdk <= 8 and tools.jar do not exists under JAVA_HOME, throw IllegalArgumentException
</pre>

@return
cop/src/main/java/code/landgrey/copagent/utils/ProcessUtils.java