How to Call Api in AEM Servlet

This article will discuss the process of creating a servlet in AEM and then demonstrate how to execute this servlet from external locations such as Postman or React components.

Request Flow

first of all we need to understand the request flow.

React will to AEM for Data
AEM Request to MicroServices
MicroServices will Response to AEM
AEM will Response to React.

Create Servlet File

Goto yourProject > core > src > main > java > sa > com > stc > core > servlet
Start by creating a new servlet file, such as "ExternalApiServlet.java."
In this servlet, we'll implement our business logic to make API calls.
The servlet code is provided below, with important sections explained in comments.

ExternalApiServlet.java

/*

* Import Important NameSpaces

*/

    package sa.com.stc.core.servlets;

    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 com.google.gson.Gson;

    import javax.servlet.Servlet;

    import java.io.IOException;

    import org.slf4j.Logger;

    import org.slf4j.LoggerFactory;

    import sa.com.stc.core.utilities.RequestHandler;

    import sa.com.stc.core.utilities.ApisUrlConstant;

/*

* We establish the servlet path, which will be used to execute the servlet in Postman. * We define the servlet method, and we will use the same method to execute it from external sources.

*/

    @Component(service = { Servlet.class }, property = {

            "sling.servlet.paths=/bin/external-api",

            "sling.servlet.methods=GET"

})

    public class ExternalApiServlet extends SlingSafeMethodsServlet {

/*

* I have created a separate RequestHandler class and instantiated an object for it.

*/

        RequestHandler requestHandler = new RequestHandler();

/*

          * Create object of logger class for logs

*/

        private static final Logger LOGGER = 

        LoggerFactory.getLogger(ExternalApiServlet.class);

/*

          * doGet Method used to call get type Api

*/

        @Override

        protected void doGet(SlingHttpServletRequest request, 

        SlingHttpServletResponse response) throws IOException {

            LOGGER.info("ServletCalled");

            try {

                Gson gson = new Gson();

/*

          * getServletCallRequestBody function is managing some Constant and Query Parms

*/

                String resuestBody=requestHandler.getServletCallRequestBody(request);

/*

          * fetchRequestResponse function is calling api 

*/

                String jsonResponse = gson.toJson(requestHandler.fetchRequestResponse

                (request, ApisUrlConstant.FETCH_EBU_TICKET_TYPES));

/*

          * returning API Response 

*/

                response.getWriter().write(resuestBody == null ? jsonResponse : resuestBody);

            } catch (Exception e) {

                Gson gson = new Gson();

                String jsonResponse = gson.toJson(e);

                response.getWriter().write(jsonResponse);

}

}

}

Custom Class RequestHandler.java

This class have some custom functions for managing planeString or Hashing

package sa.com.stc.core.utilities;

import java.util.Date;
import java.text.SimpleDateFormat;

// Hasing
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

import java.nio.charset.StandardCharsets;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import org.apache.sling.api.SlingHttpServletRequest;

public class RequestHandler {

    String agent = null;
    String appVersion = null;
    String client = null;
    String secretKey = null;
    String lang = null;
    String version = null;
    String url = null;
    String resourcePath = null;
    String basePath = GlobalConstant.BASE_PATH;

    // MANAGE CONSTATNS FOR SLING MODEL CALL
    public void setSlingModelConstant(String AGENT, String APP_VERSION, 
    String CLIENT, String SECRET_KEY, String LANG,
            String VERSION, String RESOUCE_PATH) {

        agent = AGENT;
        appVersion = APP_VERSION;
        client = CLIENT;
        secretKey = SECRET_KEY;
        lang = LANG;
        version = VERSION;
        resourcePath = RESOUCE_PATH;
    }

    // SERVLET CALL REQUEST BODY RESOLVED;
    public String getServletCallRequestBody(SlingHttpServletRequest request) {
        try {
             

            agent = GlobalConstant.AGENT;
            appVersion = GlobalConstant.APP_VERSION;
            client = GlobalConstant.CLIENT;
            secretKey = GlobalConstant.SECRET_KEY;
            resourcePath = request.getParameter("resourcePath");
            lang = request.getParameter("lang");
            version = request.getParameter("version");
            return (resourcePath == null || resourcePath.isEmpty() || lang == null || 
            lang.isEmpty() || version == null
            || version.isEmpty()) ? "lang,version and resourcePath is required" : null;

        } catch (Exception e) {

            return "Error";
        }

    }

    // GET CURRENT TIME
    public String currentTimeString() {
        Date currentTime = new Date();
        SimpleDateFormat dateFormat = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz");
        dateFormat.setTimeZone(java.util.TimeZone.getTimeZone("GMT"));
        String currentTimeString = dateFormat.format(currentTime);
        return currentTimeString;
    }

    // Resolve Request
    public void resolvedRequest(String fullPath) {
        String[] resolvedRequest = fullPath.split("/resources/");
         url = "/" + resolvedRequest[1];

    }

    // PLAN STRING GENRATOR
    public String PlainStringToHash(String httpMethod, String fullPath) {
        resolvedRequest(fullPath);
        String plainStringToHash = httpMethod + url + lang + currentTimeString() +
         agent + version + appVersion + client + httpMethod;
        return plainStringToHash;
    }

    // HASH GERNRATOR FOR HEADER
    public String hashGenrator(String httpMethod, String fullPath) {

        String plainStringToHash = PlainStringToHash(httpMethod, fullPath);
        String hash = null;
        String secretKeys = secretKey; // Secret key
        try {

            Mac hmacSha256 = Mac.getInstance("HmacSHA256");
            SecretKeySpec secretKeySpec = new SecretKeySpec(secretKeys.getBytes
            (StandardCharsets.UTF_8), "HmacSHA256");
            try {
                hmacSha256.init(secretKeySpec);
                byte[] hashBytes = hmacSha256.doFinal(plainStringToHash.getBytes
                (StandardCharsets.UTF_8));
                String hashBase64 = Base64.getEncoder().encodeToString(hashBytes);
                hash = hashBase64 + "~" + agent + "~" + appVersion;

            } catch (InvalidKeyException e) {
                e.printStackTrace();
            }

        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        return hash;
    }

    // Call Api
    public String fetchRequestResponse(SlingHttpServletRequest request, String costantApisUrl) {
        String httpMethod = request.getMethod(); // GET REQUEST METHOD

        String fullPath = basePath + resourcePath + "/" + version + "/" + lang
                + costantApisUrl;


        // CALLING API WITH HEADERS
        try {
            HttpClient httpClient = HttpClients.createDefault();
            HttpGet httpGet = new HttpGet(fullPath);
            httpGet.setHeader("Cookie",
             "2ac066e4fab68d5d7fe73dc2d44aac44=66152fdf70ae6129e08e3884a9ac4d81");
            httpGet.setHeader("X-STC-API-Key", GlobalConstant.CLIENT);
            httpGet.setHeader("EDA-CLIENT", hashGenrator(httpMethod, fullPath));
            httpGet.setHeader("EDA-DATE", currentTimeString());

            HttpResponse responsed = httpClient.execute(httpGet);
            if (responsed.getStatusLine().getStatusCode() == 200) {
                String responseData = EntityUtils.toString(responsed.getEntity());
                return responseData;
            } else {
             String errorMessage = "Error: " + responsed.getStatusLine().getStatusCode() + " "
                        + responsed.getStatusLine().getReasonPhrase();
                return errorMessage;
            }
        } catch (Exception e) {
            return "catch error";
        }

    };
}

Custom class GlobalConstant.java

This class manages all the global constants that we use in both our RequestHandler class and the servlet.

package sa.com.stc.core.utilities;

public class GlobalConstant {
   
    public static final String BASE_PATH = "https://sandbox.api.stc.com.sa:9503";
    public static final String AGENT = "web";
    public static final String APP_VERSION = "1.0";
    public static final String CLIENT = "PjQZWFkfNDDfBg6FqBYDDfSJG5qXGyK0GHMCVSO";
    public static final String SECRET_KEY = "uHf5LxGmzZtYzJXHmnad95ftD8u6Amh8CAMpV";
    public static final String LANG_EN = "en";
    public static final String LANG_AR = "ar";
    public static final String VERSION_1 = "v1";
    public static final String VERSION_2 = "v2";
    public static final String VERSION_3 = "v3";
   

    
}

Custom Class ApisUrlConstant.java

This class will contain all the API constants that we will use in our servlet.

package sa.com.stc.core.utilities;

public class ApisUrlConstant {
    public static final String FETCH_PUBLIC_PRODUCTS = "/public/content/products";
    public static final String FETCH_EBU_TICKET_TYPES = 
                                        "/public/content/strings/key/EBUTicketTypes";
    
}