Link Preview Service from SUSI Server

 SUSI Webchat, SUSI Android app, SUSI iOS app are various SUSI clients which depend on response from SUSI Server. The most common response of SUSI Server is in form of links. Clients usually need to show the preview of the links to the user. This preview may include featured image, description and the title of the link.  Clients show this information by using various 3rd party APIs and libraries. We planned to create an API endpoint for this on SUSI Server to give the preview of the link. This service is called LinkPreviewService.
String url = post.get("url", "");
        if(url==null || url.isEmpty()){
            jsonObject.put("message","URL Not given");
            return new ServiceResponse(jsonObject);

This API Endpoint accept only 1 get parameter which is the URL whose preview is to be shown.

Here we also check if no parameter or wrong URL parameter was sent. If that was the the case then we return an error message to the user.

 SourceContent sourceContent =     TextCrawler.scrape(url,3);
        if (sourceContent.getImages() != null) jsonObject.put("image", sourceContent.getImages().get(0));
        if (sourceContent.getDescription() != null) jsonObject.put("descriptionShort", sourceContent.getDescription());
        if(sourceContent.getTitle()!=null)jsonObject.put("title", sourceContent.getTitle());
        return new ServiceResponse(jsonObject);

The TextCrawler function accept two parameters. One is the url of the website which is to be scraped for the preview data and the other is depth. To get the images, description and title there are methods built in. Here we just call those methods and set them in our JSON Object.

 private String htmlDecode(String content) {
        return Jsoup.parse(content).text();

Text Crawler is based on Jsoup. Jsoup is a java library that is used to scrape HTML pages.

To get anything from Jsoup we need to decode the content of HTML to Text.

public List<String> getImages(Document document, int imageQuantity) {
        Elements media ="[src]");
        while(var5.hasNext()) {
            Element srcElement = (Element);
            if(srcElement.tagName().equals("img")) {

 The getImages method takes the HTML document from the JSoup and find the image tags in that. We have given the imageQuantity parameter in the function, so accordingly it returns the src attribute of the first n images it find.

This API Endpoint can be seen working on<ANY URL>

A real working example of this endpoint would be


Web Crawlers:


JSoup Api Docs:

Parsing HTML with JSoup:

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Deleting SUSI Skills from Server

SUSI Skill CMS is a web application to create and edit skills. In this blog post I will be covering how we made the skill deleting feature in Skill CMS from the SUSI Server.
The deletion of skill was to be made in such a way that user can click a button to delete the skill. As soon as they click the delete button the skill is deleted it is removed from the directory of SUSI Skills. But admins have an option to recover the deleted skill before completion of 30 days of deleting the skill.

First we will accept all the request parameters from the GET request.

        String model_name = call.get("model", "general");
        String group_name = call.get("group", "Knowledge");
        String language_name = call.get("language", "en");
        String skill_name = call.get("skill", "wikipedia");

In this we get the model name, category, language name, skill name and the commit ID. The above 4 parameters are used to make a file path that is used to find the location of the skill in the Susi Skill Data repository.


We need to move the skill to a directory called deleted_skills_dir. So we check if the directory exists or not. If it not exists then we create a directory for the deleted skills.

  if (skill.exists()) {
   File file = new File(DAO.deleted_skill_dir.getPath()+path);
   Boolean changed =  new File(DAO.deleted_skill_dir.getPath()+path).setLastModified(System.currentTimeMillis());

This is the part where the real deletion happens. We get the path of the skill and rename that to a new path which is in the directory of deleted skills.

Also here change the last modified time of the skill as the current time. This time is used to check if the skill deleted is older than 30 days or not.

    try (Git git = DAO.getGit()) {
                DAO.pushCommit(git, "Deleted " + skill_name, rights.getIdentity().isEmail() ? rights.getIdentity().getName() : "[email protected]");
                json.put("accepted", true);
                json.put("message", "Deleted " + skill_name);
            } catch (IOException | GitAPIException e) {

Finally we add the changes to Git. DAO.pushCommit pushes to commit to the Susi Skill Data repository. If the user is logged in we get the email of the user and set that email as the commit author. Else we set the username “[email protected]”.

Then in the caretaker class there is a method deleteOldFiles that checks for all the files whose last modified time was older than 30 days. If there is any file whose last modified time was older than 30 days then it quietly delete the files.

public void deleteOldFiles() {
     Collection<File> filesToDelete = FileUtils.listFiles(new         File(DAO.deleted_skill_dir.getPath()),
            TrueFileFilter.TRUE);    // include sub dirs
        for (File file : filesToDelete) {
               boolean success = FileUtils.deleteQuietly(file);
            if (!success) {
                System.out.print("Deleted skill older than 30 days.");

To test this API endpoint, we need to call http://localhost:4000/cms/deleteSkill.txt?model=general&group=Knowledge&language=en&skill=<skill_name>


JGit Documentation:

Commons IO:

Age Filter:

JGit User Guide:

JGit Repository access:

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Getting SUSI Skill at a Commit ID

Susi Skill CMS is a web app to edit and create new skills. We use Git for storing different versions of Susi Skills. So what if we want to roll back to a previous version of the skill? To implement this feature in Susi Skill CMS, we needed an API endpoint which accepts the name of the skill and the commit ID and returns the file at that commit ID.

In this blog post I will tell about making an API endpoint which works similar to git show.

First we will accept all the request parameters from the GET request.

        String model_name = call.get("model", "general");
        String group_name = call.get("group", "Knowledge");
        String language_name = call.get("language", "en");
        String skill_name = call.get("skill", "wikipedia");
        String commitID  = call.get("commitID", null);

In this we get the model name, category, language name, skill name and the commit ID. The above 4 parameters are used to make a file path that is used to find the location of the skill in the Susi Skill Data repository.

This servlet need CommitID to work and if commit ID is not given in the request parameters then we send an error message saying that the commit id is null and stop the servlet execution.

    Repository repository = DAO.getRepository();
    ObjectId CommitIdObject = repository.resolve(commitID);

Then we get the git repository of the skill from the DAO and initialize the repository object.

From the commitID that we got in the request parameters we create a CommitIdObject.

   (RevWalk revWalk = new RevWalk(repository)) {
   RevCommit commit = revWalk.parseCommit(CommitIdObject);
   RevTree tree = commit.getTree();

Now using commit’s tree, we will find the find the path and get the tree of the commit.

From the TreeWalk in the repository we will set a filter to find a file. This searches recursively for the files inside all the folders.

                revWalk = new RevWalk(repository)) {
                try (TreeWalk treeWalk = new TreeWalk(repository)) {
                    if (! {
                        throw new IllegalStateException("Did not find expected file");

If the TreeWalk reaches to an end and does not find the specified skill path then it returns anIllegal State Exception with an message saying did not found the file on that commit ID.

       ObjectId objectId = treeWalk.getObjectId(0);
       ObjectLoader loader =;
       OutputStream output = new OutputStream();

And then one can the loader to read the file. From the treeWalk we get the object and create an output stream to copy the file content in it. After that we create the JSON and put the OutputStream object as as String in it.


This Servlet can be seen working


JGit Documentation:

JGit User Guide:

JGit Repository access:

JGit Github:

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Adding Servlet for SUSI Service

Whenever we ask anything to SUSI, we get a intelligent reply. The API endpoints which clients uses to give the reply to users is, and this API endpoint is defined in In this blog post I will explain how any query is processed by SUSI Server and the output is sent to clients.

public class SusiService extends AbstractAPIHandler implements APIHandler

This is a public class and just like every other servlet in SUSI Server, this extends AbstractAPIHandler class, which provides us many options including AAA related features.

    public String getAPIPath() {
           return "/susi/chat.json";

The function above defines the endpoint of the servlet. In this case it is  “/susi/chat.json”. The final API Endpoint will be API

This endpoint accepts 6 parameters in GET request . “q” is the query “parameter”, “timezoneOffset” and “language” parameters are for giving user a reply according to his local time and local language, “latitude” and “longitude” are used for getting user’s location.

      String q = post.get("q", "").trim();
        int count = post.get("count", 1);
        int timezoneOffset = post.get("timezoneOffset", 0); // minutes, i.e. -60
        double latitude = post.get("latitude", Double.NaN); // i.e. 8.68
        double longitude = post.get("longitude", Double.NaN); // i.e. 50.11
        String language = post.get("language", "en"); // ISO 639-1

After getting all the parameters we do a database update of the skill data. This is done using DAO.susi.observe() function.

Then SUSI checks that whether the reply was to be given from a etherpad dream, so we check if we are dreaming something.

if (etherpad_dream != null && etherpad_dream.length() != 0) {
    String padurl = etherpadUrlstub + "/api/1/getText?apikey=" + etherpadApikey + "&padID=$query$";

If SUSI is dreaming something then we call the etherpad API with the API key and padID.

After we get the response from the etherpad API we parse the JSON and store the text from the skill in a local variable.

JSONObject json = new JSONObject(serviceResponse);
String text = json.getJSONObject("data").getString("text");

After that, we fill an empty SUSI mind with the dream. SUSI susi_memory_dir is a folder named as “susi” in the data folder, present at the server itself.

SusiMind dream = new SusiMind(DAO.susi_memory_dir); 

We need the memory directory here to get a share on the memory of previous dialogues, otherwise, we cannot test call-back questions.

JSONObject rules = SusiSkill.readEzDSkill(new BufferedReader(new InputStreamReader(new ByteArrayInputStream(text.getBytes(StandardCharsets.UTF_8)), StandardCharsets.UTF_8)));
dream.learn(rules, new File("file://" + etherpad_dream));

When we call dream.learn function, Susi starts dreaming. Now we will try to find an answer out of the dream.

The SusiCognition takes all the parameters including the dream name, query and user’s identity and then try to find the answer to that query based on the skill it just learnt.

    SusiCognition cognition = new SusiCognition(dream, q, timezoneOffset, latitude, longitude, language, count, user.getIdentity());

If SUSI finds an answer then it replies back with that answers else it tries to answer with built-in intents. These intents are both existing SUSI Skills and internal console services.

if (cognition.getAnswers().size() > 0) {          DAO.susi.getMemories().addCognition(user.getIdentity().getClient(), cognition);
    return new ServiceResponse(cognition.getJSON());

This is how any query is processed by SUSI Server and the output is sent to clients.

Currently people use Etherpad ( to make their own skills, but we are also working on SUSI CMS where we can edit and test the skills on the same web application.


Java Servlet Docs:

Embedding Jetty:

Server-Side Java:

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Skill Editor in SUSI Skill CMS

SUSI Skill CMS is a web application built on ReactJS framework for creating and editing SUSI skills easily. It follows an API centric approach where the SUSI Server acts as an API server. In this blogpost we will see how to add a component which can be used to create a new skill SUSI Skill CMS.

For creating any skill in SUSI we need four parameters i.e model, group, language, skill name. So we need to ask these 4 parameters from the user. For input purposes we have a common card component which has dropdowns for selecting models, groups and languages, and a text field for skill name input.

    floatingLabelText="Enter Skill name"
    hintText="My SUSI Skill"
<RaisedButton label="Save" backgroundColor="#4285f4" labelColor="#fff" style={{marginLeft:10}} onTouchTap={this.saveClick} />

This is the card component where we get the user input. We have API endpoints on SUSI Server for getting the list of models, groups and languages. Using those APIs we inflate the dropdowns.
Then the user needs to edit the skill. For editing of skills we have used Ace Editor. Ace is an code
editor written in pure javascript. It matches the features native editors like Sublime and TextMate.

To use Ace we need to install the component.

npm install react-ace --save                        

This command will install the dependency and update the package.json file in our project with this dependency.

To use this editor we need to import AceEditor and place it in the render function of our react class.

    mode=" markup"
    height= "400px"
    editorProps={{$blockScrolling: true}}

Now we have a page that looks something like this

Now we need to handle the click event when a user clicks on the save button.

First we check if the user is logged in or not. For this we check if we have the required cookies and the access token of the user.

 if(!cookies.get('loggedIn')) {
                message: 'Not logged In',
                description: 'Please login and then try to create/edit a skill',
                icon: <Icon type="close-circle" style={{ color: '#f44336' }} />,
            return 0;

If the user is not logged in then we show him a error notification and asks him to login.

Then we check if he has filled all the required fields like name of the skill etc. and after that we call an API Endpoint on SUSI Server that will finally store the skill in the skill_data_repo.

let url= “”
    dataType: 'jsonp',
    jsonp: 'callback',
    crossDomain: true,
    success: function (data) {
                message: 'Accepted',
                description: 'Your Skill has been uploaded to the server',
                icon: <Icon type="check-circle" style={{ color: '#00C853' }} />,

In the success function of ajax call we check if accepted parameter is true from the server or not. If accepted is true then we show user a notification with a message that “Your Skill has been uploaded to the server”.

To see this component running please visit



Ace Editor:


Universal Cookies:

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Uploading Images to SUSI Server

SUSI Skill CMS is a web app to create and modify SUSI Skills. It needs API Endpoints to function and SUSI Server makes it possible. In this blogpost, we will see how to add a servlet to SUSI Server to upload images and files.

The file is the servlet which handles the process of creating new Skills. It requires different user roles to be implemented and hence it extends the AbstractAPIHandler.

Image upload is only possible via a POST request so we will first override the doPost method in this servlet.

  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  resp.setHeader("Access-Control-Allow-Origin", "*"); // enable CORS

resp.setHeader enables the CORS for the servlet. This is required as POST requests must have CORS enables from the server. This is an important security feature that is provided by the browser.

        Part file = req.getPart("image");
        if (file == null) {
            json.put("accepted", false);
            json.put("message", "Image not given");

Image upload to servers is usually a Multipart Request. So we get the part which is named as “image” in the form data.

When we receive the image file, then we check if the image with the same name exists on the server or not.

Path p = Paths.get(language + File.separator + “images/” + image_name);

        if (image_name == null || Files.exists(p)) {
                json.put("accepted", false);
                json.put("message", "The Image name not given or Image with same name is already present ");

If the same file is present on the server then we return an error to the user requesting to give a unique filename to upload.

Image image =;
BufferedImage bi = this.createResizedCopy(image, 512, 512, true);
if(!Files.exists(Paths.get(language.getPath() + File.separator + "images"))){
   new File(language.getPath() + File.separator + "images").mkdirs();
ImageIO.write(bi, "jpg", new File(language.getPath() + File.separator + "images/" + image_name));

Then we read the content for the image in an Image object. Then we check if images directory exists or not. If there is no image directory in the skill path specified then create a folder named “images”.

We usually prefer square images at the Skill CMS. So we create a resized copy of the image of 512×512 dimensions and save that copy to the directory we created above.

BufferedImage createResizedCopy(Image originalImage, int scaledWidth, int scaledHeight, boolean preserveAlpha) {
        int imageType = preserveAlpha ? BufferedImage.TYPE_INT_RGB : BufferedImage.TYPE_INT_ARGB;
        BufferedImage scaledBI = new BufferedImage(scaledWidth, scaledHeight, imageType);
        Graphics2D g = scaledBI.createGraphics();
        if (preserveAlpha) {
        g.drawImage(originalImage, 0, 0, scaledWidth, scaledHeight, null);
        return scaledBI;

The function above is used to create a  resized copy of the image of specified dimensions. If the image was a PNG then it also preserves the transparency of the image while creating a copy.

Since the SUSI server follows an API centric approach, all servlets respond in JSON.


At last, we set the character encoding and the character set of the output. This helps the clients to parse the data easily.

To see this endpoint in live send a POST request at


Apache Docs:

Multipart POST Request Tutorial:

Java File Upload tutorial:

Jetty Project:

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Integrating Swagger with SUSI Server

The goal of Swagger is to define a standard interface for REST APIs which allows humans to understand the capabilities of the APIs without access to source code or documentation.

SUSI Server is now completely API centric. As more and more people make their own bots using SUSI Server they will be needing documentation for the APIs. We can use swagger so that without looking at the javadocs or documentation people can consume the REST APIs.

In this I post will walk you through the steps to integrate Swagger with SUSI Server which is running on Jetty.

Add the following dependencies to build.gradle file. These add Swagger Annotations, Swagger Models, Swagger UI and Glassfish containers.

  compile group: 'io.swagger', name: 'swagger-annotations',version: swaggerVersion
  compile group: 'io.swagger', name: 'swagger-core', version: swaggerVersion
  compile group: 'io.swagger', name: 'swagger-jersey2-jaxrs', version: swaggerVersion
  compile group: 'io.swagger', name: 'swagger-models', version: swaggerVersion
  compile group: 'org.glassfish.jersey.core', name: 'jersey-server', version: versionJersey
  compile group: 'org.glassfish.jersey.containers', name: 'jersey-container-servlet-core', version: versionJersey
  compile group: 'org.webjars', name: 'swagger-ui', version: '2.1.4'

Now SusiServer.class is the main file which initializes all the servlets and server handlers.

Here, we need to tell the SusiServer to look for the swagger annotations and use them to build the documentation.

In the main function, before starting the server we set the serverHandlers from setServerHandler function.

public static void main(String[] args) throws Exception {
  // init the http server
        try {
            setupHttpServer(httpPort, httpsPort);
        } catch (Exception e) {
        SusiServer.caretaker = new Caretaker();

Now, we will modify the setServetHandler function for registering the Swagger Handler.

There are already 2 handlers so I used a handerCollection object, so that we can give multiple handlers to handerCollection and set the serverHandler as handerCollection.

private static void setServerHandler(File dataFile){
         ServletContextHandler servletHandler = new ServletContextHandler();
        ContextHandlerCollection contexts = new ContextHandlerCollection();
        ServletContainer sc = new ServletContainer(resourceConfig);
        ServletHolder holder = new ServletHolder(sc);

        servletHandler.addServlet(holder, "/docs/*");


servletHandler.addServlet(holder, “/docs/*”), this line in the setServerHandler method sets the default swagger.json path to

This is all the basic setup to initialize swagger and now we need to modify our API endpoints and set annotations for the base URL and parameters.

Now I will discuss how to add swagger annotations to our Servlets.

For the demo, I will use GetAllUsers.class file, which returns the list of all users to Admins.

@Api(value = "/AAA")
public class GetAllUsers extends AbstractAPIHandler implements APIHandler {

Just before the class starts we will add the Path of the API endpoint and the result it produces. In this case, GetAllUsers returns JSON and is a part of aaa group.

@ApiOperation(value = "Get All Users Registered on SUSI.AI",
        notes = "This API Endpoint returns the list of all users registered on SUSI Server",
        responseContainer = "Object")
@ApiResponses(value = { @ApiResponse(code = 200, message = "Success"),
@ApiResponse(code = 401, message = "Base user role not sufficient") })

Inside the class, we will declare the path of the API endpoint. A description of this endpoint and the sample response code.

In this file, there are only two possible responses.
1. Response code 200 – when everything goes well.

2. Response code 401 – when base user role is not sufficient, i.e when user is not Admin

When we save the file and browse to
We get a response something like –

The Swagger UI is used to parse this JSON and create a UI for the documentation, where we can see the sample responses of the API endpoints, error codes and other things.

Swagger UI presents us the API documentation something like this image below.


Susi Server:


Swagger and Jetty Tutorial:

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Pie Chart Responses from SUSI Server

Giving out responses in charts and graphs is a very common reply of various assistants. We also have it in SUSI. We can show users the output of stocks, market covers and various percentages output in Pie Charts.  

A pie chart is a circular chart/graph which is divided in some segments like a pie. The segments in a pie chart shows the share of each object or category.

The PieChartServlet  in SUSI Server is a servlet that takes the JSON data of a the pie chart components as input parameters and returns an Image of the rendered Pie Chart..

public class PieChartServlet extends HttpServlet {

This is a simple HttpServlet. It does not require any authentication or base user role. So we extend the HttpServlet here.

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws  IOException {

doGet is a method which is triggered whenever the PieChartServlet receives a GET Query. This will contain all the code that we will need to render the final output.


This is the sample JSON that we send to the PieChartServlet. This contains the names of the pie chart components and their respective percentages. After we receive these parameters we parse them and store them in our local variables.
These variables are then further used to plot the pie chart.

To plot these values in pie chart we have used a library JFreeChart.

This is a free and well documented Java chart library. This library supports PNGs and JPEGs as well as vector graphics file formats

JFreeChart chart = getChart(json, legendBit, tooltipBit);

From here we call a function getChart This function accept 3 parameters. The json which we sent as the GET parameter, legendBit and tooltilBit. These are also sent as GET parameters. In this example I will use legendBit as true and tooltipBit as false.

        JFreeChart chart = ChartFactory.createPieChart("SUSI Visualizes -   PieChart", dataset, legend, tooltips, urls);

        chart.setBorderStroke(new BasicStroke(5.0f));

        return chart;

 This is the function getChart. It creates a chart using the ChartFactory method and set sets the SUSI branding on it as “SUSI Visualizes – PieChart”. It accepts the datasets, legends and tool tips. The variable, dataset is nothing but the json keys and their values.

After the ChartFactory returns the chart we set the border of the chart and returns a pie chart back the function where it was called.

ChartUtilities.writeChartAsPNG(outputStream, chart, width, height);

Finally we write the chart as a PNG image and send it to the user.


This can be tested at{%22ford%22:%2217.272992%22,%22toyota%22:%2227.272992%22,%22renault%22:%2247.272992%22}&width=1000&height=1000&legend=true&tooltip=false


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Markdown responses from SUSI Server

Most of the times SUSI sends a plain text reply. But for some replies we can set the type of the query as markdown and format the output in computer or bot typed images. In this blog I will explain how to get images with markdown instead of large texts.

This servlet is a simple HttpServlet and do not require any types of user authentication or base user roles. So, instead of extending it from AbstractAPIHandler we extend a HttpServlet.

public class MarkdownServlet extends HttpServlet {

This method is fired when we send a GET request to the server. It accepts those parameters and send it to the “process(…)” method.

One major precaution in open source is to ensure no one takes advantages out of it. In the first steps, we ensure that a user is not trying to access the server very frequently. If the server find the request frequency high, it returns a 503 error to the user.

if (post.isDoS_blackout()) {response.sendError(503, "your request frequency is too high"); return;} // DoS protection
process(request, response, post);

 The process function is where all the processing is done. Here the text is extracted from the URL. All the parameters are sent in GET request and the “process(…)” functions parses the query. After we check all the parameters like color, padding, uppercase, text color and get them in our local variables.

Here we calculate the optimum image size. A perfect size has the format 2:1, that fits into the preview window. We should not allow that the left or right border is cut away. We also resize the image here if necessary. Different clients can request different sizes of images and we can process the optimum image size here.

int lineheight = 7;
int yoffset = 0;
int height = width / 2;
while (lineheight <= 12) {
height = linecount * lineheight + 2 * padding - 1;
if (width <= 2 * height) break;
yoffset = (width / 2 - height) / 2;
height = width / 2;

Then we print our text to the image. This is also done using the RasterPlotter. Using all the parameters that we parsed above we create a new image and set the colors, linewidth, padding etc. Here we are making a matrix with and set all the parameters that we calculated above to our image.

RasterPlotter matrix = new RasterPlotter(width, height, drawmode, color_background);
if (c == '\n' || (c == ' ' && column + nextspace - pos >= 80)) {
x = padding - 1;
y += lineheight;
column = 0;
hashcount = 0;
if (!isFormatted) {
isBold = false;
isItalic = false;

After we have our image we print the SUSI branding. Susi branding is put at the bottom right of the image. It prints “MADE WITH HTTP://SUSI.AI” at the bottom right of the image.

PrintTool.print(matrix, matrix.getWidth() - 6, matrix.getHeight() - 6, 0, "MADE WITH HTTP://SUSI.AI", 1, false, 50);

At the end we write  the image and set the cross origin access headers. This header is very important when we are using different domains on different clients. If this is not provided, the query may give the error of “Cross Origin Access blocked”.

response.addHeader("Access-Control-Allow-Origin", "*");
RemoteAccess.writeImage(fileType, response, post, matrix);

This servlet can be locally tested at:


Or at API Server



Oracle ImageIO Docs:

Markdown Tutorial:

Java 2D Graphics:

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Sending Emails for Email-Verification from SUSI Server

In this blog post, I will explain how emails are sent from the SUSI server to validate Email IDs.

Whenever a user creates an account on SUSI.AI Client we are required to check the email and verify that email in order to activate it. By doing so we can reduce the number of spam and fake accounts.

//After all the imports 
public class EmailHandler {

This is a regex expression for validating the user input on the server side. This expression checks that the email address entered must match something similar to “[email protected]”.

    public static final String EMAIL_PATTERN = "^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@"
            + "[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";

This function below sends an email to the parameter addressTo. “subject” is the email subject and text the content of the Mail. The content of the mail could be plain text or HTML. Using HTML in emails helps to make clickable links and more formatted emails.

    public static void sendEmail(@Nonnull String addressTo, @Nonnull String subject, @Nonnull String text) throws Exception {
        String senderEmail = DAO.getConfig("", null);
        String displayname = DAO.getConfig("smtp.sender.displayname", null);
        sendEmail(senderEmail, displayname, addressTo, subject, text);

This function below is an example of Function overloading. This is used when a displayName parameter is passed and then a mail is sent with the name of the user.

For applications using SSL/TLS endpoints whose certificates are not signed by a public CA, it is required to tell applications to trust self-signed certs.

 public static void sendEmail(String senderEmail, String displayname, @Nonnull String addressTo, @Nonnull String subject, @Nonnull String text) throws Exception {
        if (!"true".equals(DAO.getConfig("smtp.mails.enabled", "false"))) {
            throw new Exception("Mail sending disabled");

        String username = DAO.getConfig("smtp.sender.username", null);
        String password = DAO.getConfig("smtp.sender.password", null);
        String hostname = DAO.getConfig("", null);
        String encryption = DAO.getConfig("", null);
        boolean disableCertChecking = DAO.getConfig("smtp.trustselfsignedcerts", false);

Here are some null checks so that server should not crash unexpectedly. Here we are checking for Sender Email, password and the hostname. These are used to generate the SMTP configuration for sending emails.

if(senderEmail == null || password == null || hostname == null){
            throw new Exception("Invalid SMTP configuration");

Now we check the regex of the previously declared regex expression for validating the email addresses. This is done using the pattern that we defined at the very beginning of this file.

Pattern pattern = Pattern.compile(EMAIL_PATTERN);
        if (!new TimeoutMatcher(pattern.matcher(addressTo)).matches()) {
            throw new Exception("Invalid email ID");
        if (!new TimeoutMatcher(pattern.matcher(senderEmail)).matches()) {
            throw new Exception("Invalid sender ID");

Finally, the email is composed here with all the headers, subject and text. The Mime Message and Transport are a part of javax.mail library.

You can install that by adding the below line in you build.gradle file.

compile group: 'com.sun.mail', name: 'javax.mail', version: '1.+'
    MimeMessage message = new MimeMessage(session);
        message.addHeader("Content-type", "text/HTML; charset=UTF-8");
        message.addHeader("format", "flowed");
        message.addHeader("Content-Transfer-Encoding", "8bit");
        message.setSentDate(new Date());
        message.setReplyTo(new Address[]{new InternetAddress(senderEmail, displayname)});
        message.setFrom(new InternetAddress(senderEmail, displayname));
        message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(addressTo, false));
        message.setSubject(subject, "UTF-8");
        message.setText(text, "UTF-8");

Then we call the send method to finally send an email to the user. This sends the “message” that we composed above with all out headers, encodings, dates etc.

        Log.getLog().info("Successfully send mail to " + addressTo);

This is a pretty old technique to validate email addresses. Mail addresses cannot be created and doctored too quickly. Also, email address verification is not the only way to verify users. This can be totally replaced by using social logins.


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