code: protected void buildJsonActiveItem(String itemUrl) {
  
          if (itemUrl.startsWith(OpenCms.getSiteManager().getWorkplaceServer())) {
              // remove workplace server prefix
              itemUrl = itemUrl.substring(OpenCms.getSiteManager().getWorkplaceServer().length());
          }
          // remove context prefix to read resource from VFS
          itemUrl = CmsLinkManager.removeOpenCmsContext(itemUrl);
          try {
              JspWriter out = getJsp().getJspContext().getOut();
              if (getCms().existsResource(itemUrl)) {
                  try {
                      out.print(buildJsonItemObject(getCms().readResource(itemUrl)));
                  } catch (CmsException e) {
                      // can not happen in theory, because we used existsResource() before...
                  }
              } else {
                  out.print(RETURNVALUE_NONE);
              }
          } catch (IOException e) {
              if (LOG.isErrorEnabled()) {
                  LOG.error(e.getLocalizedMessage(), e);
              }
          }
      }
docs: Builds the Javascript to set the currently active item object.<p>
  
  @param itemUrl the URL of the currently selected item