code: protected boolean openJARs() {
          if (started && (jarFiles.length > 0)) {
              lastJarAccessed = System.currentTimeMillis();
              if (jarFiles[0] == null) {
                  for (int i = 0; i < jarFiles.length; i++) {
                      try {
                          jarFiles[i] = new JarFile(jarRealFiles[i]);
                      } catch (IOException e) {
                          if (log.isDebugEnabled()) {
                              log.debug("Failed to open JAR", e);
                          }
                          return false;
                      }
                  }
              }
          }
          return true;
      }
docs: Used to periodically signal to the classloader to release JAR resources.