How to send email in java using asynchronous API

In Spring MVC, we have a TaskExecutor which makes sending asynchronous emails easier.

<!-- Mail sender bean -->
 <bean class="org.springframework.mail.javamail.JavaMailSenderImpl" id="mailSender">
  <property name="host"><value>mail.test.com</value></property>
         <property name="port"><value>25</value></property>
         <property name="protocol"><value>smtp</value></property>
         <property name="username"><value>no-reply@test.com</value></property>
         <property name="password"><value>pass</value></property>
         <property name="javaMailProperties">
             <props>
                 <prop key="mail.smtp.auth">true</prop>
<!--                  <prop key="mail.smtp.starttls.enable">true</prop> -->
                 <prop key="mail.smtp.quitwait">false</prop>
             </props>
         </property>
     </bean> 

<bean class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor" id="taskExecutor">
     <property name="corePoolSize" value="5"></property>
     <property name="maxPoolSize" value="10"></property>
     <property name="queueCapacity" value="40"></property>
     <property name="waitForTasksToCompleteOnShutdown" value="true"></property>
    </bean>

Your java class should look like this:

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.core.io.FileSystemResource;
import org.springframework.core.task.TaskExecutor;
import org.springframework.mail.MailParseException;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessageHelper;
import org.springframework.stereotype.Service;

@Service("mailService")
public class MailService {
    @Autowired
    private JavaMailSender mailSender;

    @Autowired
    private TaskExecutor taskExecutor;

    private static Log log = LogFactory.getLog(MailService.class);

 /**
  * @param text - message
  * @param from - sender email
  * @param to - receiver email
  * @param subject - subject
  * @param filePath - file to attach, could be null if file not required
  * @throws Exception
  */
 public void sendMail(final String text,  final String from, final String to, final String subject, final File file) throws Exception {
   taskExecutor.execute( new Runnable() {
   public void run() {
    try {
      sendMailSimple(text, to, subject, file.getAbsolutePath());
    } catch (Exception e) {
     e.printStackTrace();
     log.error("Failed to send email to: " + to + " reason: "+e.getMessage());
    }
   }
  });
 }

  private void sendMailSimple(String text, String from, String to, String subject, String filePath) throws Exception { 
  MimeMessage message = mailSender.createMimeMessage();
  try {
   MimeMessageHelper helper = new MimeMessageHelper(message, true);
   helper.setFrom(from);
   helper.setTo(to);
   helper.setSubject(subject);
   helper.setText(text);
   if(filePath != null){
    FileSystemResource file = new FileSystemResource(filePath);
    helper.addAttachment(file.getFilename(), file);
   }
  } catch (MessagingException e) {
    throw new MailParseException(e);
  }
  mailSender.send(message);

  if(log.isDebugEnabled()){
   log.debug("Mail was sent successfully to: " + to + " with file: "+filePath);
  }
  }
}