AEM custom renderer

CustomPDFRendererServlet.java

package com.wemblog.cq.core.servlet;

import com.day.cq.dam.api.Asset;
import com.day.cq.dam.commons.util.DamUtil;
import com.wemblog.utility.RunModeUtil;
import java.io.IOException;
import java.util.Dictionary;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import org.apache.commons.lang3.StringUtils;
import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Properties;
import org.apache.felix.scr.annotations.Property;
import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.Service;
import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.resource.Resource;
import org.apache.sling.api.servlets.OptingServlet;
import org.apache.sling.api.servlets.SlingSafeMethodsServlet;
import org.apache.sling.commons.osgi.PropertiesUtil;
import org.osgi.service.component.ComponentContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * Servlet to add extra header to PDF file request based on authored property
 * @author Yogesh Upadhyay
 *
 */

@Component(metatype = true)
@Service
@Properties({ @Property(name = "sling.servlet.resourceTypes", value = "nt:file", propertyPrivate = true), @Property(
    name = "sling.servlet.methods", value = { "GET" }, propertyPrivate = true) })
public class CustomPDFRendererServlet extends SlingSafeMethodsServlet implements OptingServlet {

  private static final long serialVersionUID = 1L;
  private static final Logger LOGGER = LoggerFactory.getLogger(CustomPDFRendererServlet.class);

  //This is custom RunMode util. You might have write this. Should be simple
  //Let me know if you need any help. Here is one example http://wemcode.wemblog.com/check-run-mode
  //Or http://programtalk.com/vs/acs-aem-commons/bundle/src/main/java/com/adobe/acs/commons/util/ModeUtil.java/
  @Reference
  RunModeUtil runModeUtil;

  @Property(label = "disable.customPDFRenderor", description = "Disable Custom PDF Renderor", boolValue = false)
  private static final String DISABLE_PDF_RENDEROR = "disable.customPDFRenderor";
  private boolean _disableCustomPdfRenderor;

  private static final String PROPERTY_REL_CANONICAL_URL = "pdf:canonicalUrl";
  private static final String PROPERTY_NO_INDEX = "pdf:noIndex";
  private static final String HEADER_DISPATCHER_NAME = "Dispatcher";
  private static final String HEADER_DISPATCHER_VALUE = "no-cache";
  private static final String PDF_CUSTOM_REQUEST_ATTRIBUTE = "PDF_CUSTOM_HEADER_SET";
  private static final String HEADER_NO_INDEX_NAME = "X-Robots-Tag";
  private static final String HEADER_NO_INDEX_VALUE = "noindex";
  private static final String HEADER_REL_CANONICAL = "Link";

  @Override
  protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response) throws ServletException,
      IOException {
    final Resource resource = request.getResource();
    final RequestDispatcher crd = request.getRequestDispatcher(resource);
    //request attribute is required to avoid infinite redirect
    request.setAttribute(PDF_CUSTOM_REQUEST_ATTRIBUTE, "true");
    if (resource != null) {
      LOGGER.debug("Resource Path is {}", resource.getPath());
      //Get Asset path based on internal asset path
      final Asset asset = DamUtil.resolveToAsset(resource);
      if (asset != null) {
        LOGGER.debug("This is PDF Asset path is {}", asset.getPath());
        boolean isDispatcherCache = true;
        if (getNoIndexHeaderString(asset) != null) {
          response.setHeader(HEADER_NO_INDEX_NAME, HEADER_NO_INDEX_VALUE);
          isDispatcherCache = false;
        }
        if (getRelCanonicalHeaderString(asset) != null) {
          response.setHeader(HEADER_REL_CANONICAL, getRelCanonicalHeaderString(asset));
          isDispatcherCache = false;
        }
        //If custom property is set do not cache this document in dispatcher
        if (!isDispatcherCache) {
          response.setHeader(HEADER_DISPATCHER_NAME, HEADER_DISPATCHER_VALUE);
          crd.include(request, response);
          return;
        }
      }
    }
    //For all other PDF request just forward to next handler
    crd.forward(request, response);

  }

  /**
   * Check if No index is enabled for this document
   * @param asset
   * @return
   */
  private boolean isNoIndexEnabled(Asset asset) {
    if (StringUtils.isNotBlank(asset.getMetadataValue(PROPERTY_NO_INDEX))) {
      LOGGER.debug("No index is set for document {}", asset.getPath());
      return Boolean.parseBoolean(asset.getMetadataValue(PROPERTY_NO_INDEX));
    }
    return false;
  }

  /**
   * Get rel canonical property from document
   * @param asset
   * @return
   */
  private String getRelCanonicalProperty(Asset asset) {
    if (StringUtils.isNotBlank(asset.getMetadataValue(PROPERTY_REL_CANONICAL_URL))) {
      LOGGER.debug("Custom rel Canonical set for document {}", asset.getPath());
      return asset.getMetadataValue(PROPERTY_REL_CANONICAL_URL);
    }
    return null;
  }

  /**
   * Get Header String based on property
   * Example: https://developers.google.com/webmasters/control-crawl-index/docs/robots_meta_tag
   * @param asset
   * @return
   */
  private String getNoIndexHeaderString(Asset asset) {
    if (isNoIndexEnabled(asset)) {
      return HEADER_NO_INDEX_VALUE;
    }
    return null;
  }

  /**
   * Get custom rel canonical string
   * Example: http://moz.com/blog/how-to-advanced-relcanonical-http-headers
   * @param asset
   * @return
   */
  private String getRelCanonicalHeaderString(Asset asset) {
    if (null != getRelCanonicalProperty(asset)) {
      StringBuilder builder = new StringBuilder();
      builder.append("<");
      builder.append(getRelCanonicalProperty(asset));
      builder.append(">; ");
      builder.append("rel=\"canonical\"");
      return builder.toString();

    }
    return null;
  }

  /**
   * Check if this is PDF request
   * @param request
   * @return
   */
  private boolean isPDFRequest(SlingHttpServletRequest request) {
    return request != null && request.getRequestURI() != null ? request.getRequestURI().endsWith("pdf") : false;
  }

  /**
   * Check if this servlet is already called
   * @param request
   * @return
   */
  private boolean isCustomPDFHeaderSet(SlingHttpServletRequest request) {
    return request.getAttribute(PDF_CUSTOM_REQUEST_ATTRIBUTE) != null;
  }

  /**
   * Method to decide whether given request will be handled by this servlet
   */
  @Override
  public boolean accepts(SlingHttpServletRequest request) {
    return runModeUtil.isPublish() && isPDFRequest(request) && !isCustomPDFHeaderSet(request)
        && !this._disableCustomPdfRenderor;
  }

  @Activate
  protected final void activate(final ComponentContext componentContext) {
    final Dictionary<?, ?> config = componentContext.getProperties();
    this._disableCustomPdfRenderor = PropertiesUtil.toBoolean(config.get(DISABLE_PDF_RENDEROR), false);
  }

}