我的Web应用程序如何识别Tomcat库中的JAR

Question

I'm currently developing a java webapp that sends emails. Since I'm deploying it on Tomcat 7 I configured the Resource mail/Session on my context.xml file and copied the latest version of mail.jar to Tomcat's lib folder.

When I deploy my web app and run it I get the following exception:

java.lang.ClassCastException: javax.mail.Session cannot be cast to javax.mail.Session

This is the code I'm using to send the email on my class:

Context initCtx = new InitialContext();
Context envCtx = (Context) initCtx.lookup("java:comp/env");
Session session = (Session) envCtx.lookup("mail/Session");

Message message = new MimeMessage(session);
message.setFrom(new InternetAddress(from));
InternetAddress toIA[] = new InternetAddress[1];
toIA[0] = new InternetAddress(to);
message.setRecipients(Message.RecipientType.TO, toIA);
message.setSubject(subject);
message.setContent(mensagem, "text/plain");
Transport.send(message);

I understand that this is probably being thrown because I have the mail.jar both in Tomcat lib folder and in my web app lib folder, the problem is that I can't simply remove the dependency from Maven's pom.xml , because if I do so, Eclipse says that it can't find certain classes (such as Session ).

How can I use the classes responsible for sending an email if I can't have the corresponding JAR in my webapp?

Answer 1

Mark scope of the specific dependency as provided in pom.xml :

<scope>provided</scope>

provided

This is much like compile, but indicates you expect the JDK or a container to provide the dependency at runtime . For example, when building a web application for the Java Enterprise Edition, you would set the dependency on the Servlet API and related Java EE APIs to scope provided because the web container provides those classes. This scope is only available on the compilation and test classpath, and is not transitive.

Such a dependency won't be packaged along with your application on export because it is assumed that the container where the app will be deployed provides it. There is more information in the official documentation .