code: public B withContextRootDirectory(File webappRootDirectory) {
          assertNotNull(webappRootDirectory, "webapp root directory could not be null.");
          if (!webappRootDirectory.exists()) {
              throw new IllegalArgumentException("webapp root directory ["
                      + webappRootDirectory.getAbsolutePath() + "] must exist.");
          }
          if (!webappRootDirectory.isDirectory()) {
              throw new IllegalArgumentException("the specified value ["
                      + webappRootDirectory.getAbsolutePath() + "] is not a directory!");
          }
          getConfig().setContextRootDirectory(webappRootDirectory);
          return self();
      }
docs: Specifies the context root directory to use for the web application. The specified
  <tt>webappRootDirectory</tt> must exist and must be a directory.
  <p/>
  Any static resources under that directory will be available for the deployed web application.
  
  @param webappRootDirectory the root directory of the deployed web application
  @return this