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Mahesh_Gunaje
Level 7
February 18, 2024
Solved

Different way of calling the custom servlet in AEM

  • February 18, 2024
  • 3 replies
  • 2176 views

Hello Team,

 

In my application, customServlet has these details:  

 

@Component(service = Servlet.class, property = { "sling.servlet.resourceTypes=" + "/apps/abc/mycustomName",
"sling.servlet.methods=GET" }, immediate = true)
public class customServletName extends SlingSafeMethodsServlet { ....
}

 

In a javascript method, below code is written to call the custom Servlet.

$.ajax({
url: "/content/data/abc/servlet/mynode",
type: "GET",
// other necessary details
});

 

/content/data/abc/servlet/mynode   This is the jcr node, which has sling:resourceType as  /apps/abc/mycustomName

 

Instead of this, in the js method, I can call directly url: "/apps/abc/mycustomName"  Why above approach is used? is it known as Proxy servlet?  I am bit confused. Could you please give me some clarity?

cc @aanchal-sikka  @joerghoh  @briankasingli 

-Thanks

 

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Best answer by Mahesh_Gunaje

Hi @estebanbustamante  @raja_reddy 

Please ignore my query. I got the solution. Writing here, so that others can be aware of.

 

@Component(service = Servlet.class, property = { "sling.servlet.resourceTypes=" + "/apps/abc/mycustomName",
"sling.servlet.methods=GET" }, immediate = true)
public class customServletName extends SlingSafeMethodsServlet { ....
}

 

In a javascript method, below code is written to call the custom Servlet.

$.ajax({
url: "/content/data/abc/servlet/mynode",
type: "GET",
// other necessary details
});

 

/content/data/abc/servlet/mynode This is the jcr node, which has sling:resourceType as /apps/abc/mycustomName

 

In above case, servlet is called just because, js calls /content/data/abc/servlet/mynode. This node has sling:resourceType: /apps/abc/mycustomName  Thats why servlet call is happening. Instead, in the JS method, if I write url: "/apps/abc/mycustomName", this JS is not aware of the servlet.

 

3 replies

Raja_Reddy
Community Advisor
Raja_ReddyCommunity Advisor
Community Advisor
February 18, 2024

Hi @mahesh_gunaje 

The approach used in your code is known as a "resource type-based servlet resolution". In this approach, the servlet is registered with a specific `sling.servlet.resourceTypes` property, which specifies the resource type that the servlet is intended to handle. When a request is made to a resource with that resource type, the servlet is automatically selected to handle the request.

In your case, the custom servlet is registered to handle requests for resources with the resource type `/apps/abc/mycustomName`. When a request is made to `/content/data/abc/servlet/mynode`, which has the same resource type, the servlet is selected to handle the request.

This approach is useful when you want to associate a specific servlet with a specific resource type, and have the servlet automatically selected when a request is made to a resource with that type.

On the other hand, calling the servlet directly using its registered path (`/apps/abc/mycustomName`) is also a valid approach. This approach is known as a "path-based servlet resolution". In this approach, the servlet is registered with a specific path, and is selected to handle requests made to that path.

Both approaches have their own advantages and disadvantages, and the choice between them depends on the specific requirements of your application.

Regarding your question about proxy servlets, a proxy servlet is a servlet that acts as an intermediary between a client and a server. It is used to forward requests from the client to the server, and to forward responses from the server back to the client. Proxy servlets are commonly used in web applications to provide access to remote resources, or to implement load balancing and failover mechanisms. 

    M
    Mahesh_GunajeAuthor
    Level 7
    February 19, 2024

    Hi @raja_reddy 

     

    Thanks for your reply.

    As you have mentioned:  "On the other hand, calling the servlet directly using its registered path (`/apps/abc/mycustomName`) is also a valid approach. This approach is known as a "path-based servlet resolution". In this approach, the servlet is registered with a specific path, and is selected to handle requests made to that path."

    But in my case, Servlet is registered with "sling.servlet.resourceTypes=" + "/apps/abc/mycustomName",.  Servlet is not registered with path based servlet.

    So, my question is with resourceType only. From javascript, calling the node: /content/data/abc/servlet/mynode  this node has sling:resourceType as /apps/abc/mycustomName. why this is required?

      Raja_Reddy
      Community Advisor
      Raja_ReddyCommunity Advisor
      Community Advisor
      February 19, 2024

      Hi @mahesh_gunaje 

      please refer
      http://www.sgaemsolutions.com/2017/12/apache-sling-servlets-and-scripts.html 

      When we register a servlet using path, we must be specify what all paths are allowed as if we define something randomly, our servlet might not be functioning 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 servlets makes our application vulnerable. That’s why we should not open more doors for servlets to run until and unless it is required and cannot be achieved using resource type.

      We 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.

        EstebanBustamante
        Community Advisor and Adobe Champion
        EstebanBustamanteCommunity Advisor and Adobe Champion
        Community Advisor and Adobe Champion
        February 19, 2024

        Hi,

         

        I don't fully understand your question. Are you asking why calling "/apps/abc/mycustomName" via JS is invoking your servlet registered with a different resourceType? If so, the simple answer is, I don't know. There might be additional code in your application that is redirecting, proxying, or performing other processes that you haven't discovered yet. The easiest way to check what's happening is to use the Sling Servlet Resolver[1] to determine which servlet is handling that request.


        [1]. https://experienceleague.adobe.com/docs/experience-manager-learn/forms/creating-your-first-osgi-bundle/create-servlet.html?lang=en#test-the-servlet-resolver

         

        Hope this helps

        Esteban Bustamante
          M
          Mahesh_GunajeAuthorAccepted solution
          Level 7
          February 26, 2024

          Hi @estebanbustamante  @raja_reddy 

          Please ignore my query. I got the solution. Writing here, so that others can be aware of.

           

          @Component(service = Servlet.class, property = { "sling.servlet.resourceTypes=" + "/apps/abc/mycustomName",
          "sling.servlet.methods=GET" }, immediate = true)
          public class customServletName extends SlingSafeMethodsServlet { ....
          }

           

          In a javascript method, below code is written to call the custom Servlet.

          $.ajax({
          url: "/content/data/abc/servlet/mynode",
          type: "GET",
          // other necessary details
          });

           

          /content/data/abc/servlet/mynode This is the jcr node, which has sling:resourceType as /apps/abc/mycustomName

           

          In above case, servlet is called just because, js calls /content/data/abc/servlet/mynode. This node has sling:resourceType: /apps/abc/mycustomName  Thats why servlet call is happening. Instead, in the JS method, if I write url: "/apps/abc/mycustomName", this JS is not aware of the servlet.

           

            kautuk_sahni
            Community Manager
            kautuk_sahniCommunity Manager
            Community Manager
            February 21, 2024

            @mahesh_gunaje Did you find the suggestions from users helpful? Please let us know if more information is required. Otherwise, please mark the answer as correct for posterity. If you have found out solution yourself, please share it with the community.

            Kautuk Sahni
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