OkHttp + Mailgun

MailgunEmail.java

import java.util.LinkedList;
import java.util.List;
import okhttp3.MultipartBody;
import okhttp3.RequestBody;
import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

public class MailgunEmail {
  private static final DateTimeFormatter DATETIME_FORMATTER
      = DateTimeFormat.forPattern("EEE, dd MMM yyyy HH:mm:ss Z");

  public final Contact from;
  public final List<Contact> to;
  public final List<Contact> cc;
  public final List<Contact> bcc;
  public final String subject;
  public final String text;
  public final String html;
  public final List<Attachment> attachments;
  public final List<Attachment> inlines;
  public final List<String> tags;
  public final String campaignId;
  public final Boolean dkimEnabled;
  public final DateTime deliveryTime;
  public final boolean testMode;
  public final Boolean tracking;
  public final String trackingClicks;
  public final Boolean trackingOpens;
  public final boolean requireTls;
  public final boolean skipVerification;
  public final List<Header> extraHeaders;
  public final List<Variable> variables;

  private MailgunEmail(Contact from, List<Contact> to, List<Contact> cc, List<Contact> bcc,
      String subject, String text, String html, List<Attachment> attachments,
      List<Attachment> inlines, List<String> tags, String campaignId, Boolean dkimEnabled,
      DateTime deliveryTime, boolean testMode, Boolean tracking, String trackingClicks,
      Boolean trackingOpens, boolean requireTls, boolean skipVerification,
      List<Header> extraHeaders, List<Variable> variables) {
    this.from = from;
    this.to = to;
    this.cc = cc;
    this.bcc = bcc;
    this.subject = subject;
    this.text = text;
    this.html = html;
    this.attachments = attachments;
    this.inlines = inlines;
    this.tags = tags;
    this.campaignId = campaignId;
    this.dkimEnabled = dkimEnabled;
    this.deliveryTime = deliveryTime;
    this.testMode = testMode;
    this.tracking = tracking;
    this.trackingClicks = trackingClicks;
    this.trackingOpens = trackingOpens;
    this.requireTls = requireTls;
    this.skipVerification = skipVerification;
    this.extraHeaders = extraHeaders;
    this.variables = variables;
  }

  public MultipartBody toMultipartBody() {
    MultipartBody.Builder bodyBuilder = new MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("from", from.toString())
        .addFormDataPart("subject", subject);

    if (text != null) bodyBuilder.addFormDataPart("text", text);
    if (html != null) bodyBuilder.addFormDataPart("html", html);
    if (campaignId != null) bodyBuilder.addFormDataPart("o:campaign", campaignId);
    if (dkimEnabled != null) bodyBuilder.addFormDataPart("o:dkim", dkimEnabled ? "yes" : "no");
    if (deliveryTime != null) {
      bodyBuilder.addFormDataPart("o:deliverytime", deliveryTime.toString(DATETIME_FORMATTER));
    }
    if (testMode) bodyBuilder.addFormDataPart("o:testmode", "yes");
    if (tracking != null) bodyBuilder.addFormDataPart("o:tracking", tracking ? "yes" : "no");
    if (trackingClicks != null) bodyBuilder.addFormDataPart("o:tracking-clicks", trackingClicks);
    if (trackingOpens != null) {
      bodyBuilder.addFormDataPart("o:tracking-opens", trackingOpens ? "yes" : "no");
    }
    if (requireTls) bodyBuilder.addFormDataPart("o:require-tls", "yes");
    if (skipVerification) bodyBuilder.addFormDataPart("o:skip-verification", "yes");

    for (Contact contact : to) {
      bodyBuilder.addFormDataPart("to", contact.toString());
    }
    for (Contact contact : cc) {
      bodyBuilder.addFormDataPart("cc", contact.toString());
    }
    for (Contact contact : bcc) {
      bodyBuilder.addFormDataPart("bcc", contact.toString());
    }
    for (Attachment attachment : attachments) {
      bodyBuilder.addFormDataPart("attachment", attachment.name, attachment.file);
    }
    for (Attachment inline : inlines) {
      bodyBuilder.addFormDataPart("inline", inline.name, inline.file);
    }
    for (String tag : tags) {
      bodyBuilder.addFormDataPart("o:tag", tag);
    }
    for (Header extraHeader : extraHeaders) {
      bodyBuilder.addFormDataPart("h:" + extraHeader.name, extraHeader.value);
    }
    for (Variable variable : variables) {
      bodyBuilder.addFormDataPart("v:" + variable.name, variable.json);
    }

    return bodyBuilder.build();
  }

  public static class Contact {
    public final String name;
    public final String email;

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

    @Override public String toString() {
      return String.format("%s <%s>", name, email);
    }
  }

  public static class Attachment {
    public final String name;
    public final RequestBody file;

    public Attachment(String name, RequestBody file) {
      this.name = name;
      this.file = file;
    }
  }

  public static class Header {
    public final String name;
    public final String value;

    public Header(String name, String value) {
      this.name = name;
      this.value = value;
    }
  }

  public static class Variable {
    public final String name;
    public final String json;

    public Variable(String name, String json) {
      this.name = name;
      this.json = json;
    }
  }

  public static class Builder {
    private Contact from;
    private List<Contact> to = new LinkedList<>();
    private List<Contact> cc = new LinkedList<>();
    private List<Contact> bcc = new LinkedList<>();
    private String subject;
    private String text;
    private String html;
    private List<Attachment> attachments = new LinkedList<>();
    private List<Attachment> inlines = new LinkedList<>();
    private List<String> tags = new LinkedList<>();
    private String campaignId;
    private Boolean dkimEnabled;
    private DateTime deliveryTime;
    private boolean testMode;
    private Boolean tracking;
    private String trackingClicks;
    private Boolean trackingOpens;
    private boolean requireTls;
    private boolean skipVerification;
    private List<Header> extraHeaders = new LinkedList<>();
    private List<Variable> variables = new LinkedList<>();

    public Builder from(Contact from) {
      this.from = from;
      return this;
    }

    public Builder addTo(Contact contact) {
      this.to.add(contact);
      return this;
    }

    public Builder addCc(Contact contact) {
      this.cc.add(contact);
      return this;
    }

    public Builder addBcc(Contact contact) {
      this.bcc.add(contact);
      return this;
    }

    public Builder subject(String subject) {
      this.subject = subject;
      return this;
    }

    public Builder text(String text) {
      this.text = text;
      return this;
    }

    public Builder html(String html) {
      this.html = html;
      return this;
    }

    public Builder addAttachment(Attachment attachment) {
      this.attachments.add(attachment);
      return this;
    }

    public Builder addInline(Attachment inline) {
      this.inlines.add(inline);
      return this;
    }

    public Builder addTag(String tag) {
      this.tags.add(tag);
      return this;
    }

    public Builder campaignId(String campaignId) {
      this.campaignId = campaignId;
      return this;
    }

    public Builder dkimEnabled(Boolean dkimEnabled) {
      this.dkimEnabled = dkimEnabled;
      return this;
    }

    public Builder deliveryTime(DateTime deliveryTime) {
      this.deliveryTime = deliveryTime;
      return this;
    }

    public Builder testMode(Boolean testMode) {
      this.testMode = testMode;
      return this;
    }

    public Builder tracking(Boolean tracking) {
      this.tracking = tracking;
      return this;
    }

    public Builder trackingClicks(String trackingClicks) {
      this.trackingClicks = trackingClicks;
      return this;
    }

    public Builder trackingOpens(Boolean trackingOpens) {
      this.trackingOpens = trackingOpens;
      return this;
    }

    public Builder requireTls(Boolean requireTls) {
      this.requireTls = requireTls;
      return this;
    }

    public Builder skipVerification(Boolean skipVerification) {
      this.skipVerification = skipVerification;
      return this;
    }

    public Builder addExtraHeader(Header header) {
      this.extraHeaders.add(header);
      return this;
    }

    public Builder addVariable(Variable variable) {
      this.variables.add(variable);
      return this;
    }

    public MailgunEmail build() {
      checkNotNull(from, "Missing from contact");
      checkState(!to.isEmpty() || !cc.isEmpty() || !bcc.isEmpty(), "Need at least one recipient");
      checkState(text != null || html != null, "Missing a text or html body");
      checkState(tags.size() < 4, "Mailgun allows at most 3 tags");
      checkState(trackingClicks == null
          || trackingClicks.equals("yes")
          || trackingClicks.equals("no")
          || trackingClicks.equals("htmlonly"),
          "Invalid tracking clicks option");

      return new MailgunEmail(from, to, cc, bcc, subject, text, html, attachments, inlines, tags,
          campaignId, dkimEnabled, deliveryTime, testMode, tracking, trackingClicks, trackingOpens,
          requireTls, skipVerification, extraHeaders, variables);
    }
  }
}

MailgunService.java

import java.io.File;
import java.io.IOException;
import javax.inject.Inject;
import javax.inject.Named;
import javax.inject.Singleton;
import okhttp3.HttpUrl;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;
import okio.ByteString;

public class MailgunService {
  public final static String MAILGUN_API_USERNAME = "api";

  private final HttpUrl mailgunApiUrl;
  private final String authHeaderValue;

  public MailgunService(HttpUrl mailgunbaseUrl, String mailgunDomain, String mailgunApiKey) {
    this.mailgunApiUrl = HttpUrl.parse(mailgunbaseUrl.toString() + "/" + mailgunDomain);
    this.authHeaderValue = buildAuthHeader(mailgunApiKey);
  }

  public boolean sendMail(MailgunEmail email) throws IOException {
    Request request = new Request.Builder()
        .url(mailgunApiUrl.toString() + "/messages")
        .post(email.toMultipartBody())
        .addHeader("Authentication", authHeaderValue)
        .build();

    OkHttpClient okHttpClient = new OkHttpClient();
    Response response = okHttpClient.newCall(request).execute();
    return response.isSuccessful();
  }

  private static String buildAuthHeader(String mailgunApiKey) {
    String authString = String.format("%s:%s", MAILGUN_API_USERNAME, mailgunApiKey);
    ByteString authData = ByteString.encodeUtf8(authString);
    return "Basic " + authData.base64();
  }

  public static void main(String[] args) throws IOException {
    MailgunService mailgunService = new MailgunService(
        HttpUrl.parse("https://api.mailgun.net/v3"),
        "<YOUR MAILGUN DOMAIN>",
        "<YOUR MAILGUN API KEY>");

    MailgunEmail email = new MailgunEmail.Builder()
        .from(new MailgunEmail.Contact("Marcelo Cortes", "marcelo@example.com"))
        .addTo(new MailgunEmail.Contact("Marcelo +1", "marcelo+1@example.com"))
        .addCc(new MailgunEmail.Contact("Marcelo Cortes + 3", "marcelo+3@example.com"))
        .addBcc(new MailgunEmail.Contact("Marcelo +2", "marcelo+2@example.com"))
        .subject("Hi here!")
        .html("<html>Inline image here: <img src=\"cid:profile.jpg\"></html>")
        .addInline(new MailgunEmail.Attachment("profile.jpg",
            RequestBody.create(
                MediaType.parse("image/jpg"),
                new File("/Users/marcelo/Documents/profile.jpg"))))
        .build();

    boolean success = mailgunService.sendMail(email);
    System.out.println(success ? "MESSAGE SENT" : "FAILED TO SEND");
  }
}