Email and Java

Email templates

https://mailo.app/

Mailtrap

Mailtrap allows up to 1,000 emails to be sent per month for free.

Please sign up for an account or sign in if you already have an account.
Navigate to your inbox list and click the inbox labeled "My Inbox".
Click the Integration tab.
Click the API tab.
Click the Java tab.
Study and copy the code.

OkHttpClient client = new OkHttpClient().newBuilder()
    .build();
MediaType mediaType = MediaType.parse("application/json");
RequestBody body = RequestBody.create(mediaType, "{\"from\":{\"email\":\"mailtrap@example.com\",\"name\":\"Mailtrap Test\"},\"to\":[{\"email\":\"your-email@example.com\"}],\"subject\":\"You are awesome!\",\"text\":\"Congrats for sending test email with Mailtrap!\",\"category\":\"Integration Test\"}");
Request request = new Request.Builder()
    .url("https://sandbox.api.mailtrap.io/api/send/YOUR-INBOX-ID")
    .method("POST", body)
    .addHeader("Authorization", "Bearer YOUR-TEST-API-CODE")
    .addHeader("Content-Type", "application/json")
    .build();
Response response = client.newCall(request).execute();

OkHttp Dependency

Add the OkHttp dependency to the pom.xml file.
- This package will allow us to make HTTP requests to third-party APIs.
Paste the sample code to the project's main method.
Wrap the execute() method inside a try-catch statement.

try {
    Response response = client.newCall(request).execute();
    System.out.println("Email sent");
} catch (IOException e) {
    System.out.println("Email not sent");
}

The RequestBody.create() method has a warning message saying 'create(okhttp3.MediaType, java.lang.String)' is deprecated.
- According to Stack Overflow, the solution is to flip the arguments so the String is first and the MediaType is second.
Run the program. View your Mailtrap inbox.
Note that a real email does not send.

JSON

Use a JSON formatter to study how the JSON object is formatted.
JavaScript Object Notation (JSON) is made up of "key" : "value" pairs.
- The keys (from, to, subject, text, category) must be Strings.
- The values can be objects, arrays, or Strings.
  - Curly brackets indicate an object.
  - Square brackets indicate an array.
  - Quotation marks indicate a String.

{
  "from": {
    "email": "mailtrap@example.com",
    "name": "Mailtrap Test"
  },
  "to": [
    {
      "email": "your-email@example.com"
    }
  ],
  "subject": "You are awesome!",
  "text": "Congrats for sending test email with Mailtrap!",
  "category": "Integration Test"
}

MailtrapPerson class

Note that "from" is an object that contains two Strings: email and name.
Note that "to" is an array of objects that contains one String: email.
- The name String is optional.
Create a class called MailtrapPerson that represents an individual sender or recipient. Include constructors and getter methods.

public class MailtrapPerson {
    private String email;
    private String name;

    public MailtrapPerson(String email) {
        this.email = email;
        this.name = "";
    }

    public MailtrapPerson(String email, String name) {
        this.email = email;
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public String getName() {
        return name;
    }
 }

MailtrapEmail class

Create a class called MailtrapEmail that represents the entire JSON object. Include a constructor and getter methods.
Remember that "from" is an object, "to" is a List of objects, and "subject", "text", and "category" are Strings.

public class MailtrapEmail {
    private MailtrapPerson from;
    private List<MailtrapPerson> to;
    private String subject;
    private String text;
    private String category;

    public MailtrapEmail(MailtrapPerson from, List<MailtrapPerson> to, String subject, String text, String category) {
        this.from = from;
        this.to = to;
        this.subject = subject;
        this.text = text;
        this.category = category;
    }

    public MailtrapPerson getFrom() {
        return from;
    }

    public List<MailtrapPerson> getTo() {
        return to;
    }

    public String getSubject() {
        return subject;
    }

    public String getText() {
        return text;
    }

    public String getCategory() {
        return category;
    }
}

Google Gson, Serialization

Add the Google Gson dependency to the pom.xml file.
- This dependency will be used to convert Java objects to JSON (called serialization) or convert JSON to Java objects (called deserialization).
Modify the code to instantiate our custom objects, serialize them, and send the email.

OkHttpClient client = new OkHttpClient().newBuilder()
        .build();
MediaType mediaType = MediaType.parse("application/json");
MailtrapPerson from = new MailtrapPerson("mailtrap@example.com", "Mailtrap Test");
List<MailtrapPerson> to = new ArrayList<>();
to.add(new MailtrapPerson("your-email@example.com"));
String subject = "You are awesome!";
String text = "Congrats for sending test email with Mailtrap!";
String category = "Integration Test";
MailtrapEmail mailtrapEmail = new MailtrapEmail(from, to, subject, text, category);
String serializedMailtrapEmail = new Gson().toJson(mailtrapEmail);
RequestBody body = RequestBody.create(serializedMailtrapEmail, mediaType);
Request request = new Request.Builder()
        .url("https://sandbox.api.mailtrap.io/api/send/2541140")
        .method("POST", body)
        .addHeader("Authorization", "Bearer 9a7fa0723b331f4eec4d5d5e5a9ba0ea")
        .addHeader("Content-Type", "application/json")
        .build();
try {
    Response response = client.newCall(request).execute();
    System.out.println("Email sent");
} catch (IOException e) {
    System.out.println("Email not sent");
}

This code is an example of how Gson can deserialize an object.

String json = "{\"from\":{\"email\":\"mailtrap@example.com\",\"name\":\"Mailtrap Test\"},\"to\":[{\"email\":\"your-email@example.com\"}],\"subject\":\"You are awesome!\",\"text\":\"Congrats for sending test email with Mailtrap!\",\"category\":\"Integration Test\"}";
MailtrapEmail mailtrapEmail = new Gson().fromJson(json, MailtrapEmail.class);
System.out.println(mailtrapEmail.toString());

Google Gson, Deserialization

This code is an example of how Gson can deserialize an object.
Generate toString methods in the MailtrapEmail and MailtrapPerson classes before running it.

String json = "{\"from\":{\"email\":\"mailtrap@example.com\",\"name\":\"Mailtrap Test\"},\"to\":[{\"email\":\"your-email@example.com\"}],\"subject\":\"You are awesome!\",\"text\":\"Congrats for sending test email with Mailtrap!\",\"category\":\"Integration Test\"}";
try {
    MailtrapEmail mailtrapEmail = new Gson().fromJson(json, MailtrapEmail.class);
    System.out.println(mailtrapEmail.toString());
} catch(JsonSyntaxException e) {
    System.out.println("Invalid JSON");
}

public class MailtrapEmail {
    // Code omitted

    @Override
    public String toString() {
        return "MailtrapEmail{" +
                "from=" + from +
                ", to=" + to +
                ", subject='" + subject + '\'' +
                ", text='" + text + '\'' +
                ", category='" + category + '\'' +
                '}';
    }
}

public class MailtrapPerson {
    // Code omitted

    @Override
    public String toString() {
        return "MailtrapPerson{" +
                "email='" + email + '\'' +
                ", name='" + name + '\'' +
                '}';
    }
}

Keys that are misspelled or have incorrect capitalization will be assigned null values.
An invalid JSON String will cause a JsonSyntaxException.

Dotenv

Add .env to the .gitignore file so Git does not track our environment variables.

.env

Add the Dotenv dependency to the pom.xml file.
- This package will allow us to get environment variables from the .env file.
Upgrade the Kotlin Stdlib dependency to remove the warning.

Create a .env file in the /src/main/resources folder.
The EMAIL_SERVICE variable defines which email service to use.
The ADMIN_EMAIL and ADMIN_EMAIL_NAME define the email account I will send emails from.
Change the values of MAILTRAP_INBOX and MAILTRAP_KEY to define your personal account info.

EMAIL_SERVICE=mailtrap
ADMIN_EMAIL=YOUR-EMAIL
ADMIN_EMAIL_NAME=YOUR-NAME
MAILTRAP_HOST_URL=YOUR-MAILTRAP-HOST-URL
MAILTRAP_API_TOKEN=YOUR-MAILTRAP-API-TOKEN

MailtrapEmail.send()

Create a method called send() in the MailtrapEmail class.
Call helper methods to get the environment variables.
This method includes code specific to Mailtrap.

public class MailtrapEmail {
    // Code omitted

    public static boolean send(String sendFromEmail, String sendFromName, String sendToEmail, String sendToName, String subject, String message, String category) {
        String hostURL = getURL();
        String apiToken = getToken();
        MailtrapPerson from = new MailtrapPerson(sendFromEmail, sendFromName);
        List<MailtrapPerson> to = new ArrayList<>();
        to.add(new MailtrapPerson(sendToEmail, sendToName));
        MailtrapEmail mailtrapEmail = new MailtrapEmail(from, to, subject, message, category);
        String serializedMailtrapEmail = new Gson().toJson(mailtrapEmail);
        OkHttpClient client = new OkHttpClient().newBuilder()
                .build();
        MediaType mediaType = MediaType.parse("application/json");
        RequestBody body = RequestBody.create(serializedMailtrapEmail, mediaType);
        Request request = new Request.Builder()
                .url(hostURL)
                .method("POST", body)
                .addHeader("Authorization", "Bearer " + apiToken)
                .addHeader("Content-Type", "application/json")
                .build();
        try(Response response = client.newCall(request).execute()) {
            return response.isSuccessful();
        } catch (IOException e) {
            return false;
        }
    }

    private static String getURL() {
        Dotenv dotenv = Dotenv.load();
        String url = dotenv.get("MAILTRAP_HOST_URL");
        if(url == null) {
            throw new RuntimeException("MAILTRAP_HOST_URL environment variable not set");
        }
        return url;
    }

    private static String getToken() {
        Dotenv dotenv = Dotenv.load();
        String url = dotenv.get("MAILTRAP_API_TOKEN");
        if(url == null) {
            throw new RuntimeException("MAILTRAP_API_TOKEN environment variable not set");
        }
        return url;
    }
}

EmailService.sendTestEmail()

Create a new class called EmailService. This class will contain methods to send various emails (examples: user registration, login, password reset, account security, marketing, etc.)
Create a method to send a test email. This method should contain generic content that can be used with any email service.
Call helper methods to get the environment variables.

public class EmailService {
    public static boolean sendTestEmail(String sendToEmail, String sendToName) {
        boolean sent = false;
        String subject = "You are awesome!";
        String message = "Congrats for sending test email!";
        String emailService = getEmailService();
        String[] sendFrom = getSendFrom("admin");
        if(emailService.equals("mailtrap")) {
            String category = "Integration test";
            sent = MailtrapEmail.send(sendFrom[0], sendFrom[1], sendToEmail, sendToName, subject, message, category);
        }
        return sent;
    }

    private static String getEmailService() {
        Dotenv dotenv = Dotenv.load();
        String emailService = dotenv.get("EMAIL_SERVICE");
        if(emailService == null) {
            throw new RuntimeException("EMAIL_SERVICE environment variable not set");
        }
        return emailService;
    }

    private static String[] getSendFrom(String type) {
        Dotenv dotenv = Dotenv.load();
        String[] sendFrom = new String[2];
        String sendFromEmail = "";
        String sendFromName = "";
        if(type.equals("admin")) {
            sendFromEmail = dotenv.get("ADMIN_EMAIL");
            sendFromName = dotenv.get("ADMIN_EMAIL_NAME");
            if(sendFromEmail == null) {
                throw new RuntimeException("ADMIN_EMAIL environment variable not set");
            }
            if(sendFromName == null) {
                throw new RuntimeException("ADMIN_EMAIL_NAME environment variable not set");
            }
        }
        sendFrom[0] = sendFromEmail;
        sendFrom[1] = sendFromName;
        return sendFrom;
    }
}

public class Main {
    public static void main(String[] args)  {
        boolean sent = EmailService.sendTestEmail("YOUR-EMAIL-ADDRESS", "YOUR-NAME");
        System.out.println(sent ? "Email sent" : "Email not sent");
    }
}

Call the sendTestEmail() method from the main method to test it.

Email Domains

You must own a domain in order to send real emails. Mailtrap allows one domain for free.
These domain registration services offer free domains for students enrolled as a GitHub Student Developer.
- name.com, namecheap.com, get.tech
Go to Mailtrap’s "Sending Domains" section to add your domain.
- Mailtrap verification with Namecheap
I used Siteground hosting to setup my domain, javability.com

Email Domains

From Mailtrap’s "Sending Domains" section, click the Integration tab. Click the blue Integrate button in the Transactional Stream section.
Click the API tab, then the Java tab.
Notice the code is the same, but the URL and API key are different.
Update the .env file with the new URL and API key.

EMAIL_SERVICE=mailtrap
ADMIN_EMAIL=YOUR-DOMAIN-SPECIFIC-EMAIL
ADMIN_EMAIL_NAME=YOUR-NAME
MAILTRAP_HOST_URL=YOUR-MAILTRAP-PRODUCTION-HOST-URL
#YOUR-MAILTRAP-TEST-HOST-URL
MAILTRAP_API_TOKEN=YOUR-MAILTRAP-PRODUCTION-API-TOKEN
#YOUR-MAILTRAP-TEST-API-TOKEN

When I tested this, it delivered 24 minutes later to my school email account, and it delivered immediately to my gmail account.
From Mailtrap’s "Email API/SMTP" section, visit the subsections to see data about the emails you sent.

More GSON

Compare the Google GSON dependency with the Jackson Databind Dependency.
- https://www.baeldung.com/jackson-vs-gson
Save Data to JSON File with GSON
- https://www.baeldung.com/gson-save-file

Java Send Email

By Marc Hauschildt

Java Send Email

Marc Hauschildt

Web Technologies and Computer Software Development Instructor at Kirkwood Community College in Cedar Rapids, IA.

kirkwood.edu/businessit

Email and Java

Email templates

Mailtrap

OkHttp Dependency

JSON

MailtrapPerson class

MailtrapEmail class

Google Gson, Serialization

Google Gson, Deserialization

Dotenv

MailtrapEmail.send()

EmailService.sendTestEmail()

Email Domains

Email Domains

More GSON

Java Send Email

More from Marc Hauschildt