@Override
                public int compare(File file1, File file2) {
                    try {
                        return file1.getCanonicalPath().length() - file2.getCanonicalPath().length();
                    } catch (IOException e) {
                        // ignore
                    }
                    return -1;
                }
<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