AEM Servlet – Best Practices

Problem Statement:

What is the best way to write a Sling servlet?

Requirement:

What is recommended way to register a sling servlet?

Introduction:

Servlets and scripts are themselves resources in Sling and thus have a resource path: this is either the location in the resource repository, the resource type in a servlet component configuration or the “virtual” bundle resource path (if a script is provided inside a bundle without being installed into the JCR repository).

OSGi DS – SlingServletResourceTypes

OSGi DS 1.4 (R7) component property type annotations for Sling Servlets (recommended)

  • Component as servlet based on OSGi R7/8
  • Provide resourcetype, method and extensions
  • ServiceDescription for the servlet
package com.mysite.core.servlets;

import com.day.cq.commons.jcr.JcrConstants;
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.HttpConstants;
import org.apache.sling.api.servlets.SlingAllMethodsServlet;
import org.apache.sling.api.servlets.SlingSafeMethodsServlet;
import org.apache.sling.servlets.annotations.SlingServletResourceTypes;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.propertytypes.ServiceDescription;
import javax.servlet.Servlet;
import javax.servlet.ServletException;
import java.io.IOException;

@Component(service = { Servlet.class })
@SlingServletResourceTypes(resourceTypes = "mysite/components/page", methods = HttpConstants.METHOD_GET, extensions = "txt")
@ServiceDescription("Simple Demo Servlet")
public class SimpleServlet extends SlingSafeMethodsServlet {

	private static final long serialVersionUID = 1L;

	@Override
	protected void doGet(final SlingHttpServletRequest req, final SlingHttpServletResponse resp)
			throws ServletException, IOException {
		final Resource resource = req.getResource();
		resp.setContentType("text/plain");
		resp.getWriter().write("Title = " + resource.getValueMap().get(JcrConstants.JCR_TITLE));
	}
}

Simple OSGi DS 1.2 annotations

Registering Servlet by path

  • Component as servlet based on OSGi R7/8
  • Servlet paths, metod and other details
package com.mysite.core.servlets;

import com.drew.lang.annotations.NotNull;
import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.servlets.SlingSafeMethodsServlet;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.ConfigurationPolicy;
import javax.servlet.Servlet;
import javax.servlet.ServletException;
import java.io.IOException;

@Component(service = { Servlet.class }, configurationPolicy = ConfigurationPolicy.REQUIRE, property = {
        "sling.servlet.paths=" + PathBased.RESOURCE_PATH, "sling.servlet.methods=GET" })
public class PathBased extends SlingSafeMethodsServlet {
    static final String RESOURCE_PATH = "/bin/resourcepath";

    @Override
    protected void doGet(@NotNull SlingHttpServletRequest request, @NotNull SlingHttpServletResponse response)
            throws ServletException, IOException {
    }
}
@SlingServlet(
    resourceTypes = "/apps/my/type",
    selectors = "hello",
    extensions = "html",
    methods = "GET")
public class MyServlet extends SlingSafeMethodsServlet {

    @Override
    protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response) throws ServletException, IOException {
        ...
    }
}

Configuration Policy – Required

  • configurationPolicy is mandatory to avoid calling any servlet or services outside particular environment
  • Its always recommended to run certain services like datasource to work only in authors
File Name - com.mysite.core.servlets.PathBased
<?xml version="1.0" encoding="UTF-8"?>
<jcr:root xmlns:sling="http://sling.apache.org/jcr/sling/1.0" xmlns:jcr="http://www.jcp.org/jcr/1.0"
          jcr:primaryType="sling:OsgiConfig"/>

Project Structure

References:

https://sling.apache.org/documentation/the-sling-engine/servlets.html

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s