AEM::Writing outputstream to response object

Question

I am working on a requirement to display a PDF document on the page. This document is pulled from a back end service in the form of byte array. I convert this byte array to outputstream and then write it to the response in a Sling Servlet. The Servlet gets the byte array from an OSGi Service. I am wondering if is possible for me to use a Sling Model instead of a Sling Servlet. The Sling Model would call the OSGi Service to get the byte array but I am not sure about the next steps. I injected the response object in Sling Model using

@SlingObject
private SlingHttpServletResponse response;

But it won't do the trick. Any guidance would be helpful.

Thanks in advance

Just to clarify: You want to have a Sling Model that uses a OSGi service to get a PDF and then you want to write the PDF to the output stream of the response? Depending one the requirement you could do it with a Sling Model, but usually something like this is done by a Servlet. Can you please explain what the requirement is and why you think a Model would be better than a Servlet? — Jens
Thank you for your response @Jens. My requirement is on click of a URL a soap call gets called. The SOAP call returns PDF in the form of byte array. I have already written the OSGi service for SOAP call. — user972418
In that case I'd go for a servlet. The link points to the servlet and the servlet is going to do all the SOAP calls etc. I would not recommend using a Model for that. — Jens

Jens Jens · Accepted Answer · 2019-05-25T10:47:46

Disclaimer

Without knowing your specific requirements I would recommend using a servlet instead of using a Sling Model. A Sling Model is meant to be a representation of a JCR resource in the repository not be abused as servlet.

A Sling Model has a different "life cycle" than a servlet. While a servlet is instantiated as a OSGi service/component (which is a singleton in most cases) a Sling Model can be instantiated multiple times during a single request. So be aware of that difference and the consequences.

That said, you have two options to write the PDF to the response with a Sling Model:

During the initialisation of the Sling Model
When a specific method is called

Example for 1:

@Model(adaptables = SlingHttpServletRequest.class)
public class MyModel {

    @SlingObject
    private SlingHttpServletResponse response;

    @OSGiService
    private PDFService pdfService;

    @PostConstruct
    public void init() {
        response.setContentType("application/pdf");

        [... code to write PDF to response ...]
    }
}

The method annotated with @PostConstruct is called after all annotated fields are injected, so that you can run your initialisation code.

Example for 2:

@Model(adaptables = SlingHttpServletRequest.class)
public class MyModel {

    @SlingObject
    private SlingHttpServletResponse response;

    @OSGiService
    private PDFService pdfService;

    public void writePDFtoResponse() {
        response.setContentType("application/pdf");

        [... code to write PDF to response ...]
    }
}

Obviously, with the second example you would have to have some kind of code that instantiates the model and calls writePDFtoResponse().

AEM::Writing outputstream to response object

1 Answers