Sling Servlet in AEM

Writing a Sling Servlet in AEM is one of the basic building block to start working with AEM. Sling servlet are basically used when front end developers need to make ajax call and want to get response in form of json. There are two ways in which a developer can register a servlet using path or selector.

In this tutorial i will tell you which approach is better and what are the best practices to create sling servlet in AEM.

After completing this tutorial , you will have a clear understanding about:-

How to write Sling Servlet using path in AEM.
How to write Sling Servlet using a resource type and selector.
Advantages of registering servlet using selector over path.
Sling Servlet Best Practices

Pre-requisite:-

You have setup you eclipse and code base. If not go through this tutorial to Set up AEM Project in Eclipse.

Write Sling Servlet using path in AEM

Lets write a sling servlet that returns json data by registering using path. When you create a project using AEM plugin, it will create a sample servlet file for you under core–> servlet

Open SimpleServlet.java file and paste below code, i will explain the code line by line.

/*
 *  Copyright 2015 Adobe Systems Incorporated
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.training.aemcq5tutorials.core.servlets;

import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.sling.SlingServlet;
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.SlingAllMethodsServlet;
import org.apache.sling.api.servlets.SlingSafeMethodsServlet;
import org.apache.sling.commons.json.JSONException;
import org.apache.sling.commons.json.JSONObject;

import javax.jcr.Repository;
import javax.servlet.ServletException;
import java.io.IOException;

/**
 * Servlet that writes some sample content into the response. It is mounted for
 * all resources of a specific Sling resource type. The
 * {@link SlingSafeMethodsServlet} shall be used for HTTP methods that are
 * idempotent. For write operations use the {@link SlingAllMethodsServlet}.
 */
@SuppressWarnings("serial")
@SlingServlet(paths = "/bin/custom/path")
public class SimpleServlet extends SlingSafeMethodsServlet {
	@Reference
	private Repository repository;
    @Override
    protected void doGet(final SlingHttpServletRequest req,
            final SlingHttpServletResponse resp) throws ServletException, IOException {
    	resp.setContentType("application/json");
    	String keys[] = repository.getDescriptorKeys();
    	JSONObject jsonobject = new JSONObject();
    	for(int i=0;i&amp;lt;keys.length;i++){
    		try {
				jsonobject.put(keys[i], repository.getDescriptor(keys[i]));
			} catch (JSONException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
    	}
    	resp.getWriter().println(jsonobject.toString());

    }
}

 Here i am registering our simple servlet at path /bin/custom/path.
 Then i am setting the content type as json.
 Finally i am returning the response.
Ajax call that you can use to call this servlet using Rest API:-
		$.ajax({
			type : "GET",
			url : '/bin/custom/path',
			/*data : {
				pass your request parameter here, currently we are not passing any data
			},*/
			success : function(data, textStatus, jqXHR) {
				//write your logic that you need to perform on sucess
                        },
			error : function(XMLHttpRequest, textStatus, errorThrown) {
				//write your logic that you need to perform on error
			}
		});
Now go to your browser type http://localhost:4502/bin/custom/path and you can see you json, This url can be used by front end developers to get the json response and process it accordingly.
Write Sling Servlet using a resource type and selector
Lets write a sling servlet that returns json data by registering using resource type and selector.
 Again Open SimpleServlet.java file and paste below code, i will explain the code line by line.
/*
 *  Copyright 2015 Adobe Systems Incorporated
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.training.aemcq5tutorials.core.servlets;

import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.sling.SlingServlet;
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.SlingAllMethodsServlet;
import org.apache.sling.api.servlets.SlingSafeMethodsServlet;
import org.apache.sling.commons.json.JSONException;
import org.apache.sling.commons.json.JSONObject;

import javax.jcr.Repository;
import javax.servlet.ServletException;
import java.io.IOException;

/**
 * Servlet that writes some sample content into the response. It is mounted for
 * all resources of a specific Sling resource type. The
 * {@link SlingSafeMethodsServlet} shall be used for HTTP methods that are
 * idempotent. For write operations use the {@link SlingAllMethodsServlet}.
 */
@SuppressWarnings("serial")
@SlingServlet(resourceTypes = "geometrixx/components/homepage",
selectors = "data",
extensions = "html",
methods = "GET",
metatype =true)
public class SimpleServlet extends SlingSafeMethodsServlet {
	@Reference
	private Repository repository;
    @Override
    protected void doGet(final SlingHttpServletRequest req,
            final SlingHttpServletResponse resp) throws ServletException, IOException {
    	resp.setContentType("application/json");
    	String keys[] = repository.getDescriptorKeys();
    	JSONObject jsonobject = new JSONObject();
    	for(int i=0;i&amp;lt;keys.length;i++){
    		try {
				jsonobject.put(keys[i], repository.getDescriptor(keys[i]));
			} catch (JSONException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
    	}
    	resp.getWriter().println(jsonobject.toString());

    }
}

 Here i am registering our simple servlet at resourceType geometrixx/components/homepage and selector data.
     
Ajax call that you can use to call this servlet using Rest API:-
		$.ajax({
			type : "GET",
			url : '/content/geometrixx/en.data.html,
			/*data : {
				pass your request parameter here, currently we are not passing any data
			},*/
			success : function(data, textStatus, jqXHR) {
				//write your logic that you need to perform on sucess
                        },
			error : function(XMLHttpRequest, textStatus, errorThrown) {
				//write your logic that you need to perform on error
			}
		});
Now go to your browser type http://localhost:4502/content/geometrixx/en.data.html and you can see you json, This url can be used by front end developers to get the json response and process it accordingly.
Advantages of registering servlet using selector over path:-

 Adobe recommends using resourceType instead of using path because of following reasons:-
 When we register a servlet using path , we must be specific what all paths are allowed as If we define something randomly, our servlet might not be function properly. Only a limited set of paths are allowed and the rest are blocked. We can add more path using Apache Sling Servlet / Script Resolver and Error Handler. Allowing more paths to execute servlet make you application vulnerable. That’s why you should not open more doors for servlets to run until and unless it is required.
 You might also need to tell specific paths to your consumers , who are consuming servlet response using ajax and any change in that path could have a serious affect. This might not be the case when you use resourceType.
 Sling Engine will take care of permissions if you register servlet using Resource Type. Users who cannot access a particular resource will not be able to invoke the servlet.
Sling Servlet Best Practices:-
DO’S
@SlingServlet(
resourceTypes = "sling/servlet/default",
selectors = "selector",
extensions = "tab",
methods = HttpConstants.METHOD_GET
)
DONT
@Component
@Service(value = javax.servlet.Servlet.class)
@Properties({ @Property(name = "sling.servlet.resourceTypes", value = { "sling/servlet/default" }),
@Property(name = "sling.servlet.selectors", value = { "selector" }),
@Property(name = "sling.servlet.extensions", value = { "tab" }),
@Property(name = "sling.servlet.methods", value = { HttpConstants.METHOD_GET }) })
DO’S
@SlingServlet(
resourceTypes = "sling/servlet/default", selectors = "selector",
extensions = "tab", methods = HttpConstants.METHOD_GET
)
@Properties({
@Property(name = Constants.SERVICE_VENDOR, value = "Cognifide"),
@Property(name = Constants.SERVICE_DESCRIPTION, value = "Some description")
})
DONT
@SlingServlet(methods = "GET")
@Properties({
@Property(name = Constants.SERVICE_VENDOR, value = "Cognifide"),
@Property(name = Constants.SERVICE_DESCRIPTION, value = "Some description"),
@Property(name = "sling.servlet.selectors", value = "selector"),
@Property(name = "sling.servlet.extensions", value = "tab"),
@Property(name = "sling.servlet.resourceTypes", value = { "sling/servlet/default" })
})
DO’S
@SlingServlet(
resourceTypes = "sling/servlet/default", selectors = "selector",
extensions = "tab", methods = HttpConstants.METHOD_GET
)
DONT
@Service
@Component
@SlingServlet(
resourceTypes = "sling/servlet/default", selectors = "selector",
extensions = "tab", methods = HttpConstants.METHOD_GET
)
That’s all about working with Sling Servlet in AEM.
     
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14 Responses to "Sling Servlet in AEM"

rish says:
March 20, 2017 at 11:22 am
Write Sling Servlet using path in AEM : Can you share some more example in which front end developers to get the json response when rest api get method request is made.
json response data will be the input given by author by using classic dialog and which gets stores in oak repository (jcr:content).
Reply
1. rish says:
  May 5, 2017 at 4:46 pm
  still waiting for input from you on this.
  Reply
Cronos says:
July 11, 2017 at 2:13 pm
You say is a best practice to use:
@SlingServlet
than
@Component(label = ”Text…”)
@Service(value = Servlet.class)
@Properties({
@Property(name = “sling.servlet.methods” , value = “GET”, propertyPrivate = true),
@Property(name = “sling.servlet.paths” , value = {“/bin/servletTest1”}, propertyPrivate = true)
})
But, in : https://sling.apache.org/documentation/the-sling-engine/servlets.html
They say the recommended is OSGi DS annotations (recommended).
So? what so you think about it?
Reply
Shivani says:
December 21, 2017 at 5:47 pm
Hi Ankur,
I think in ajax call path must be http://localhost:4502/content/geometrixx/en/jcr:content.data.html.
because this path /content/geometrixx/en doesn’t have the resourceType in it. Please correct me if i am wrong.
Reply
1. Asutosh says:
  March 17, 2018 at 5:09 pm
  Shivani, you are correct.
  It should be page/jcr:content as it has the resourceType property.
  Reply
kumar says:
June 12, 2018 at 5:10 pm
Hi Ankur,
As I’m new to AEM. Could please help me when should i use sling servlet instead of OSGI service.
Please help me.
Reply
1. Prashant says:
  October 5, 2018 at 10:07 am
  You cannot call OSGi service from front-end (AJAX). OSGI services can be injected into a component as well as servlets. OSGi services and servlets serve a completely different purpose. Infact it’s always a good practice to use OSGi service inside a servlet. Any interactions with JCR, or complex business logic are best segregated to an OSGI service. Servlets should be created if you need the JCR content to be exposed to external REST based clients.
  Reply
satish says:
July 23, 2019 at 8:40 pm
Hi,
I am trying to implement the post servlet in similar manner.
– created a servlet with resourceType = “/bin/customPath”
– created a page with ‘sling:resourceType = /bin/customPath”
– when I tried to hit the page URL as post method with proper payload, request is not hitting my servlet.
– the same thing worked for GET though.
Am I missing any config changes here?
Any suggestion would be helpful.
Thank you!
Reply
1. Ankur Ahlawat says:
  August 10, 2019 at 4:26 am
  2 things for post check that you are passing methods = “POST” and instead of SlingSafeMethodsServlet you are extending SlingAllMethodsServlet
  Reply
Ritu says:
September 3, 2019 at 1:03 pm
@Satish – is POST call to sling servlet with resource type resolved? I am also facing the same issue. Already check:
1. Passing method is “POST”
2. extended SlingAllMethodsServlet
@Ankur – Can you please help here?
AEM version is 6.2
Reply
SV says:
January 24, 2020 at 6:08 am
Hi, Will implementing the resource type servlet I am getting additional this HTML code in the response. If I call a servlet through the ajax then it will give an error due to this. So how can I stop this additional code. Is there any other way in which we can provide the path of the node instead of /app/demo/component/page, the node is present in the /content/ and we can add selector also.
Reply
Satish says:
February 26, 2020 at 3:20 pm
Hi Ankur,
I am little bit confused.
You created servlet with resource type and same resource type you mentioned in page level jcr:content property. Now you are accessing servlet by using below URL.
http://localhost:4502/content/geometrixx/en/jcr:content.data.html.
The above URL is looks like page URL.
Now I have a component there in that I am making ajax call using above URL and I added this component in same page. Now my question is can I use same component in different page(Ajax call will work). I will not add any resource type in that page.
Could you please help me.
Thanks,
Satish
Reply
Giuliano Peretti says:
March 22, 2021 at 11:25 pm
This article is a mess…
You declare a Servlet with GET method and call it with POST, using resourceType implies that you have to use “jcr:content” to invoke it
Reply
1. Ankur Ahlawat says:
  April 1, 2021 at 11:49 am
  Hello Giuliano,
  Ajax POST call is jus a sample, that if you have to make a POST ajax call, you can use mentioned syntax. doGet example i am showing using browser hit directly. I am sorry , if i failed to explain. I will take out some time this weekend and restructure it for your better clarity.
  Reply