Using MailGun on AppEngine Java

Question

I'm trying to get the libraries needed to send mail on AppEngine.

The docs (https://cloud.google.com/appengine/docs/standard/java/mail/mailgun) state that these need to be added if using Maven:

jersey-core 1.19.4

jersey-client 1.19.4

jersey-multipart 1.19.4

Adding them however, results in an error message in Eclipse.

The type javax.ws.rs.ext.RuntimeDelegate$HeaderDelegate cannot be resolved. It is indirectly referenced from required .class files

That can be resolved by adding javax.ws.rs-api-2.0.1, but using that jar seems problematic.

Appengine is throwing an error:

Caused by: java.lang.ExceptionInInitializerError

    ... 44 more
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException: org.glassfish.jersey.internal.RuntimeDelegateImpl

    at com.sun.jersey.core.header.MediaTypes.<clinit>(MediaTypes.java:65)
    ... 62 more
Caused by: java.lang.ClassNotFoundException: org.glassfish.jersey.internal.RuntimeDelegateImpl
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at com.google.apphosting.runtime.ApplicationClassLoader.findClass(ApplicationClassLoader.java:45)

In a thread here though that error org.glassfish.jersey.internal.RuntimeDelegateImpl NOT FOUND is said to be solvable by removing javax.ws.rs-api-2.0

Other suggestions include using jersey2, but that requires additional configuration I believe and the AppEngine docs don't show how to do that.

How can I send mail on Appengine using Mailgun???

You'll have to provide more details about what you're trying to do as using the sample code works for me. Have you tried using the sample project at https://github.com/GoogleCloudPlatform/java-docs-samples/tree/master/appengine-java8/mailgun? Are you trying to use a non-Maven project? — Brian de Alwis, Mar 26 '18 at 16:45

user1258245 · Accepted Answer · 2018-06-07T09:19:53.480

I solved it by using Jersey 2.27 (JAX-RS 2.1 / Jersey 2.26+) available as a download from https://jersey.github.io/download.html

I needed the following jars:

        hk2-api-2.5.0-b32.jar
        hk2-locator-2.5.0-b42.jar
        hk2-utils-2.5.0-b32.jar
        javax.inject-1.jar
        javax.inject-2.5.0-b42.jar
        jersey-client.jar
        jersey-common.jar
        jersey-guava-2.26-b03.jar (from Jersey 2.25.1)
        jersey-media-jaxb.jar
        javax.ws.rs-api-2.1.jar

And modified the AppEngine sample to use Jersey 2.26+ as below:

import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Entity;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.Form;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import org.glassfish.jersey.client.authentication.HttpAuthenticationFeature;

public static void sendSimpleMessage(String recipient) {
        Client clientMail = ClientBuilder.newBuilder().build();
              clientMail.register(HttpAuthenticationFeature.basic("api", MAILGUN_API_KEY));

        WebTarget targetMail = clientMail.target("https://api.mailgun.net/v3/" + MAILGUN_DOMAIN_NAME + "/messages");

        Form formData = new Form();
              formData.param("from", "Mailgun Sandbox <"+DOMAIN_MAIL_ADDRESS+">");
              formData.param("to", recipient);
              formData.param("subject", "Simple Mailgun Example");
              formData.param("text", "Plaintext content");

        Response response = targetMail.request().post(Entity.entity(formData, MediaType.APPLICATION_FORM_URLENCODED_TYPE));
        System.out.println("Mail sent : " + response);

    }

The MAILGUN_API_KEY is available from MailGun. MAILGUN_DOMAIN_NAME is my custom domain and DOMAIN_MAIL_ADDRESS is the address I wish to send from.

Note: I have guava-gwt and gauva on my classpath too, so perhaps it was the addition of jersey-guava that did the trick. Actually, jersey-gauva was only in jaxrs-ri-2.25.1 and not in jaxrs-ri-2.27 (JAX-RS 2.1 / Jersey 2.26+). It was definitely needed though.

Using MailGun on AppEngine Java

1 Answers1