Creating an asynchronous publish/subscription web application that translates messages using the AWS SDK for Java
| Heading | Description |
|---|---|
| Description | Discusses how to develop a dynamic web MVC application that has subscription and publish functionality by using the AWS SDK for Java (v2). This example uses the asynchronous client. |
| Audience | Developer (beginner / intermediate) |
| Required skills | Java, Maven |
You can create a web application that has subscription and publish functionality by using the Amazon Simple Notification Service (Amazon SNS). The application created in this AWS tutorial is a Spring Boot web application that lets a user subscribe to an Amazon SNS topic by entering a valid email address. A user can enter many emails and all of them are subscribed to the given SNS topic (once the email recipients confirm the subscription). The user can publish a message that results in all subscribed emails receiving the message.
Note: Amazon SNS is a managed service that provides message delivery from publishers to subscribers (also known as producers and consumers). For more information, see What is Amazon SNS?
Note: This example application uses the Asynchronous client that belongs to the AWS SDK for Java V2 for the Amazon SNS and Amazon Translate services. For more information, see Asynchronous programming in the AWS SDK for Java 2.x.
- Prerequisites
- Understand the Publish/Subscription application
- Create an IntelliJ project
- Add the POM dependencies to your project
- Create the Java classes
- Create the HTML files
- Run the application.
To complete the tutorial, you need the following:
- An AWS account
- A Java IDE (this tutorial uses the IntelliJ IDE)
- Java JDK 17
- Maven 3.6 or later
- The AWS services included in this document are included in the AWS Free Tier.
- This code has not been tested in all AWS Regions. Some AWS services are available only in specific regions. For more information, see AWS Regional Services.
- Running this code might result in charges to your AWS account.
- Be sure to terminate all of the resources you create while going through this tutorial to ensure that you’re not charged.
Create an Amazon SNS queue that is used in the Java code. For information, see Creating an Amazon SNS topic.
To subscribe to an Amazon SNS topic, the user enters a valid email address into the web application.
The specified email address recieves an email message that lets the recipient confirm the subscription.
Once the email recipient accepts the confirmation, that email is subscribed to the specific SNS topic and recieves published messages. To publish a message, a user enters the message into the web applicaiton and then chooses the Publish button.
This application lets a user specify the language of the message that is sent. For example, the user can select French from the dropdown field and then the message appears in that language to all subscribed users.
Note: The Amazon Translate Service is used to translate the body of the message. The code is shown later in this document.
This example application lets you view all of the subscribed email recipients by choosing the List Subscriptions button, as shown in the following illustration.
Create an IntelliJ project that is used to create the web application.
-
In the IntelliJ IDE, choose File, New, Project.
-
In the New Project dialog box, choose Maven.
-
Choose Next.
-
In GroupId, enter spring-aws.
-
In ArtifactId, enter SpringSubscribeApp.
-
Choose Next.
-
Choose Finish.
Make sure that your project's pom.xml file looks like the POM file in this Github repository.
Create a Java package in the main/java folder named com.spring.sns. The Java classes go into this package.
Create these Java classes:
- SubApplication - Used as the base class for the Spring Boot application.
- SubController - Used as the Spring Boot controller that handles HTTP requests.
- SnsService - Used to invoke Amazon SNS operations by using the Amazon SNS SnsAsyncClient.
The following Java code represents the SubApplication class.
package com.spring.sns;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class SubApplication {
public static void main(String[] args) {
SpringApplication.run(SubApplication.class, args);
}
}The following Java code represents the SubController class.
package com.spring.sns;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@Controller
public class SubController {
private final SnsService sns;
@Autowired
SubController(
SnsService sns
) {
this.sns = sns;
}
@GetMapping("/")
public String root() {
return "index";
}
@GetMapping("/subscribe")
public String add() {
return "sub";
}
@RequestMapping(value = "/addEmail", method = RequestMethod.POST)
@ResponseBody
String addItems(HttpServletRequest request, HttpServletResponse response) {
String email = request.getParameter("email");
return sns.subEmail(email);
}
@RequestMapping(value = "/delSub", method = RequestMethod.POST)
@ResponseBody
String delSub(HttpServletRequest request, HttpServletResponse response) {
String email = request.getParameter("email");
sns.unSubEmail(email);
return email +" was successfully deleted!";
}
@RequestMapping(value = "/addMessage", method = RequestMethod.POST)
@ResponseBody
String addMessage(HttpServletRequest request, HttpServletResponse response) {
String body = request.getParameter("body");
String lang = request.getParameter("lang");
return sns.pubTopic(body,lang);
}
@RequestMapping(value = "/getSubs", method = RequestMethod.GET)
@ResponseBody
String getSubs(HttpServletRequest request, HttpServletResponse response) {
return sns.getAllSubscriptions();
}
}The following Java code represents the SnsService class. This class uses the Java V2 SnsAsyncClient object to interact with Amazon SNS. For example, the subEmail method uses the email address to subscribe to the Amazon SNS topic. Likewise, the unSubEmail method unsubscibes from the Amazon SNS topic. The pubTopic publishes a message.
When working with the SnsAsyncClient, you use a CompletableFuture object that allows you to access the response when it’s ready. You can access the resp object by calling the futureGet.whenComplete method. Then you can get service data by invoking the applicable method that belongs to the resp object. For example, you can get the subscription Arn value by invoking the resp.subscriptionArn() method.
To return data that you read from the resp object (for example, a subscription Arn value), you must use an AtomicReference object. You cannot return data from within the futureGet.whenComplete method. If you attempt to perform this task, you get a compile error. You can set the data by using the AtomicReference object's set method. You can then access the AtomicReference object from outside the futureGet.whenComplete method to get the data by using the AtomicReference object's get method. Then you can return the data from a Java method, as shown in the following Java code example.
package com.spring.sns;
import org.springframework.stereotype.Component;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import software.amazon.awssdk.auth.credentials.EnvironmentVariableCredentialsProvider;
import software.amazon.awssdk.services.sns.model.ListSubscriptionsByTopicRequest;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.sns.SnsAsyncClient;
import software.amazon.awssdk.services.sns.model.ListSubscriptionsByTopicResponse;
import software.amazon.awssdk.services.sns.model.PublishRequest;
import software.amazon.awssdk.services.sns.model.PublishResponse;
import software.amazon.awssdk.services.sns.model.SnsException;
import software.amazon.awssdk.services.sns.model.SubscribeRequest;
import software.amazon.awssdk.services.sns.model.SubscribeResponse;
import software.amazon.awssdk.services.sns.model.Subscription;
import software.amazon.awssdk.services.sns.model.UnsubscribeRequest;
import software.amazon.awssdk.services.translate.TranslateAsyncClient;
import software.amazon.awssdk.services.translate.model.TranslateTextRequest;
import software.amazon.awssdk.services.translate.model.TranslateTextResponse;
import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.atomic.AtomicReference;
@Component
public class SnsService {
String topicArn = "<Enter your Amazon SNS Topic ARN>";
private SnsAsyncClient getSnsClient() {
return SnsAsyncClient.builder()
.credentialsProvider(EnvironmentVariableCredentialsProvider.create())
.region(Region.US_WEST_2)
.build();
}
public void unSubEmail(String emailEndpoint) {
try {
String subscriptionArn = getTopicArnValue(emailEndpoint);
SnsAsyncClient snsAsyncClient = getSnsClient();
UnsubscribeRequest request = UnsubscribeRequest.builder()
.subscriptionArn(subscriptionArn)
.build();
snsAsyncClient.unsubscribe(request);
} catch (SnsException e) {
System.err.println(e.awsErrorDetails().errorMessage());
System.exit(1);
}
}
// Returns the Sub ARN based on the given endpoint.
private String getTopicArnValue(String endpoint){
final AtomicReference<String> reference = new AtomicReference<>();
SnsAsyncClient snsAsyncClient = getSnsClient();
try {
ListSubscriptionsByTopicRequest request = ListSubscriptionsByTopicRequest.builder()
.topicArn(topicArn)
.build();
CompletableFuture<ListSubscriptionsByTopicResponse> futureGet = snsAsyncClient.listSubscriptionsByTopic(request);
futureGet.whenComplete((resp, err) -> {
List<Subscription> allSubs = resp.subscriptions();
for (Subscription sub: allSubs) {
if (sub.endpoint().compareTo(endpoint)==0)
reference.set(sub.subscriptionArn());
}
});
futureGet.join();
return reference.get();
} catch (SnsException e) {
System.err.println(e.awsErrorDetails().errorMessage());
System.exit(1);
}
return "";
}
// Create a Subscription.
public String subEmail(String email) {
final AtomicReference<String> reference = new AtomicReference<>();
try {
SnsAsyncClient snsAsyncClient = getSnsClient();
SubscribeRequest request = SubscribeRequest.builder()
.protocol("email")
.endpoint(email)
.returnSubscriptionArn(true)
.topicArn(topicArn)
.build();
CompletableFuture<SubscribeResponse> futureGet = snsAsyncClient.subscribe(request);
futureGet.whenComplete((resp, err) -> {
String subscriptionArn = resp.subscriptionArn();
reference.set(subscriptionArn);
});
futureGet.join();
return reference.get();
} catch (SnsException e) {
System.err.println(e.awsErrorDetails().errorMessage());
System.exit(1);
}
return "";
}
public String getAllSubscriptions() {
final AtomicReference<List<String>> reference = new AtomicReference<>();
List<String> subList = new ArrayList<>() ;
try {
SnsAsyncClient snsAsyncClient = getSnsClient();
ListSubscriptionsByTopicRequest request = ListSubscriptionsByTopicRequest.builder()
.topicArn(topicArn)
.build();
CompletableFuture<ListSubscriptionsByTopicResponse> futureGet = snsAsyncClient.listSubscriptionsByTopic(request);
futureGet.whenComplete((resp, err) -> {
List<Subscription> allSubs = resp.subscriptions();
for (Subscription sub: allSubs) {
subList.add(sub.endpoint());
}
reference.set(subList);
});
futureGet.join();
} catch (SnsException e) {
System.err.println(e.awsErrorDetails().errorMessage());
System.exit(1);
}
return convertToString(toXml(reference.get()));
}
public String pubTopic(String message, String lang) {
final AtomicReference<Integer> reference = new AtomicReference<>();
String body;
if (lang.compareTo("English")==0)
body = message;
else if(lang.compareTo("French")==0)
body = translateBody(message, "fr");
else
body = translateBody(message, "es");
try {
SnsAsyncClient snsAsyncClient = getSnsClient();
PublishRequest request = PublishRequest.builder()
.message(body)
.topicArn(topicArn)
.build();
CompletableFuture<PublishResponse> futureGet = snsAsyncClient.publish(request);
futureGet.whenComplete((resp, err) -> {
reference.set(resp.sdkHttpResponse().statusCode());
});
futureGet.join();
return " Message sent in " +lang +". Status was " + reference.get();
} catch (SnsException e) {
System.err.println(e.awsErrorDetails().errorMessage());
System.exit(1);
}
return "Error - msg not sent";
}
private String translateBody(String message, String lan) {
final AtomicReference<String> reference = new AtomicReference<>();
Region region = Region.US_WEST_2;
TranslateAsyncClient translateClient = TranslateAsyncClient.builder()
.credentialsProvider(EnvironmentVariableCredentialsProvider.create())
.region(region)
.build();
TranslateTextRequest textRequest = TranslateTextRequest.builder()
.sourceLanguageCode("en")
.targetLanguageCode(lan)
.text(message)
.build();
CompletableFuture<TranslateTextResponse> futureGet = translateClient.translateText(textRequest);;
futureGet.whenComplete((resp, err) -> {
reference.set(resp.translatedText());
});
futureGet.join();
return reference.get();
}
// Convert the list to XML to pass back to the view.
private Document toXml(List<String> subsList) {
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.newDocument();
// Start building the XML.
Element root = doc.createElement("Subs");
doc.appendChild(root);
// Iterate through the collection.
for (String sub : subsList) {
Element item = doc.createElement("Sub");
root.appendChild(item);
// Set email
Element email = doc.createElement("email");
email.appendChild(doc.createTextNode(sub));
item.appendChild(email);
}
return doc;
}catch(ParserConfigurationException e){
e.printStackTrace();
}
return null;
}
private String convertToString(Document xml) {
try {
TransformerFactory transformerFactory = getSecureTransformerFactory();
Transformer transformer = transformerFactory.newTransformer();
StreamResult result = new StreamResult(new StringWriter());
DOMSource source = new DOMSource(xml);
transformer.transform(source, result);
return result.getWriter().toString();
} catch(TransformerException ex) {
ex.printStackTrace();
}
return null;
}
private static TransformerFactory getSecureTransformerFactory() {
TransformerFactory transformerFactory = TransformerFactory.newInstance();
try {
transformerFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
} catch (TransformerConfigurationException e) {
e.printStackTrace();
}
return transformerFactory;
}
}Note: Make sure that you assign the SNS topic ARN to the topicArn data member. Otherwise, your code does not work.
At this point, you have created all of the Java files required for this example application. Now create HTML files that are required for the application's view. Under the resource folder, create a templates folder, and then create the following HTML files:
- index.html
- layout.html
- sub.html
The index.html file is the application's home view.
<!DOCTYPE html>
<html xmlns:th="https://www.thymeleaf.org">
<head>
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<script th:src="|https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js|"></script>
<link rel="stylesheet" th:href="|https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css|"/>
<link rel="stylesheet" href="../public/css/styles.css" th:href="@{/css/styles.css}" />
<link rel="icon" href="../public/img/favicon.ico" th:href="@{/img/favicon.ico}" />
<title>AWS Job Posting Example</title>
</head>
<body>
<header th:replace="layout :: site-header"/>
<div class="container">
<h3>Welcome to the Amazon Simple Notification Service example app</h3>
<p>Now is: <b th:text="${execInfo.now.time}"></b></p>
<p>The Amazon Simple Notification Service example uses multiple AWS Services and the Java V2 API. Perform these steps:<p>
<ol>
<li>You can subscribe to a SNS topic by choosing the <i>Manage Subscriptions</i> menu item.</li>
<li>Enter a valid email address and then choose <i>Subscribe</i>.</li>
<li>The sample application subscribes to the endpoint by using the SNS Java API V2.</li>
<li>You can view all the email addresses that have subscribed by choosing the <i>List Subscriptions</i> menu item.</li>
<li>You can unSubscribe by entering the email address and choosing <i>UnSubscribe</i>. </li>
<li>You can publish a message by entering a message and choosing <i>Publish</i>.
<li>All subscribed email recipients will receive the published message.</li>
</ol>
<div>
</body>
</html>The following code represents the layout.html file that represents the application's menu.
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head th:fragment="site-head">
<meta charset="UTF-8" />
<link rel="icon" href="../public/img/favicon.ico" th:href="@{/img/favicon.ico}" />
<script th:src="|https://code.jquery.com/jquery-1.12.4.min.js|"></script>
<meta th:include="this :: head" th:remove="tag"/>
</head>
<header th:fragment="site-header">
<a href="#" style="color: white" th:href="@{/}">Home</a>
<a href="#" style="color: white" th:href="@{/subscribe}">Manage Subscriptions</a>
</header>
</html>The sub.html file is the application's view that manages Amazon SNS Subscriptions.
<!DOCTYPE html>
<html xmlns:th="https://www.thymeleaf.org" lang="">
<head>
<meta charset="UTF-8" />
<title>Subscription</title>
<script th:src="|https://code.jquery.com/jquery-1.12.4.min.js|"></script>
<script th:src="|https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js|"></script>
<link rel="stylesheet" th:href="|https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css|"/>
<script src="../public/js/contact_me.js" th:src="@{/js/contact_me.js}"></script>
<link rel="stylesheet" href="../public/css/styles.css" th:href="@{/css/styles.css}" />
</head>
<body>
<header th:replace="layout :: site-header"/>
<div class="container">
<p>Now is: <b th:text="${execInfo.now.time}"></b></p>
<div class="row">
<div class="col">
<h4>Enter an email address<h3>
<input type="email" class="form-control" id="inputEmail1" aria-describedby="emailHelp" placeholder="Enter email">
<div class="clearfix mt-40">
<!-- Button trigger modal -->
<button type="button" onclick="subEmail() "class="btn btn-primary" >
Subscribe
</button>
<button type="button" class="btn btn-primary" onclick="getSubs()">
List Subscriptions
</button>
<button type="button" onclick="delSub()" class="btn btn-primary" >
UnSubscribe
</button>
<!-- Modal -->
<div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLongTitle" aria-hidden="true">
<div class="modal-dialog" role="document">
<div class="modal-content">
<div class="modal-header">
<h5 class="modal-title" id="exampleModalLongTitle">SNS Email Subscriptions</h5>
<button type="button" class="close" data-dismiss="modal" aria-label="Close">
<span aria-hidden="true">×</span>
</button>
</div>
<div class="modal-body">
</div>
<div class="modal-footer">
<button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<hr style="width:50%;text-align:left;margin-left:0">
<h4>Enter a message to publish</h4>
<div class="col-lg-12 mx-auto">
<div class="control-group">
<div class="form-group floating-label-form-group controls mb-0 pb-2">
<textarea class="form-control" id="body" rows="5" placeholder="Body" required="required" data-validation-required-message="Please enter a description."></textarea>
<p class="help-block text-danger"></p>
</div>
</div>
<br>
<div>
<label for="lang">Select a Language:</label>
<select name="lang" id="lang">
<option>English</option>
<option>French</option>
<option>Spanish</option>
</select>
</div>
<button type="submit" class="btn btn-primary btn-xl" id="SendButton">Publish</button>
</div>
</div>
</body>
</html>This application has a contact_me.js file that is used to send requests to the Spring Controller. Place this file in the resources\public\js folder.
$(function() {
$("#SendButton" ).click(function($e) {
var body = $('#body').val();
var lang = $('#lang option:selected').text();
if (body == '' ){
alert("Please enter text");
return;
}
$.ajax('/addMessage', {
type: 'POST',
data: 'lang=' + lang+'&body=' + body,
success: function (data, status, xhr) {
alert(data)
$('#body').val("");
},
error: function (jqXhr, textStatus, errorMessage) {
$('p').append('Error' + errorMessage);
}
});
} );
} );
function subEmail(){
var mail = $('#inputEmail1').val();
var result = validate(mail)
if (result == false) {
alert (mail + " is not valid. Please specify a valid email.");
return;
}
$.ajax('/addEmail', {
type: 'POST',
data: 'email=' + mail,
success: function (data, status, xhr) {
alert("Subscription validation is "+data)
},
error: function (jqXhr, textStatus, errorMessage) {
$('p').append('Error' + errorMessage);
}
});
}
function getSubs() {
$.ajax('/getSubs', {
type: 'GET',
success: function (data, status, xhr) {
$('.modal-body').empty();
var xml = data;
$(xml).find('Sub').each(function () {
var $field = $(this);
var email = $field.find('email').text();
// Append this data to the main list.
$('.modal-body').append("<p><b>"+email+"</b></p>");
});
$("#myModal").modal();
},
error: function (jqXhr, textStatus, errorMessage) {
$('p').append('Error' + errorMessage);
}
});
}
function delSub(event) {
var mail = $('#inputEmail1').val();
var result = validate(mail)
if (result == false) {
alert (mail + " is not valid. Please specify a valid email");
return;
}
$.ajax('/delSub', {
type: 'POST', // http GET method
data: 'email=' + mail,
success: function (data, status, xhr) {
alert("Subscription validation is "+data);
},
error: function (jqXhr, textStatus, errorMessage) {
$('p').append('Error' + errorMessage);
}
});
}
function validateEmail(email) {
const re = /^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
return re.test(email);
}
function validate(email) {
const $result = $("#result");
if (validateEmail(email)) {
return true ;
} else {
return false ;
}
}Using IntelliJ, you can run your application. After it starts, you will see the HOME page, as shown in this illustration.
Congratulations! You have created a Spring Boot application that contains subscription and publish functionality. As stated at the beginning of this tutorial, be sure to terminate all of the resources you create while going through this tutorial to ensure that you’re not charged.
For more AWS multiservice examples, see usecases.