MimeMessage.saveChanges is really slow

问题

The following test is taking around 5 seconds to execute due to the inclusion of m.saveChanges().

import org.junit.Before;
import org.junit.Test;    
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.internet.MimeMessage;
import java.io.IOException;
import java.util.Properties;
import static org.junit.Assert.assertEquals;   
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

@Test
public void test1() throws MessagingException, IOException {
    Session s = Session.getDefaultInstance(new Properties());
    MimeMessage m = new MimeMessage(s);
    m.setContent("<b>Hello</b>", "text/html; charset=utf-8");
    m.saveChanges();
    assertEquals(m.getContent(), "<b>Hello</b>");
    assertEquals(m.getContentType(), "text/html; charset=utf-8");
}

I have also mocked the Session with mockito but it doesn't help:

Session s = mock(Session.class);
when(s.getProperties()).thenReturn(new Properties());

What is the problem here? What can I mock to speed things up?

回答1:

Fix the most common mistakes people make when using JavaMail in your code first.

DNS lookup can hurt performance on some machines. For the JDK you can change the security properties for caching DNS lookup networkaddress.cache.ttl and networkaddress.cache.negative.ttl or set the system properties sun.net.inetaddr.ttl and sun.net.inetaddr.negative.ttl. The default behavior in JDK 7 and later does a good job of caching.

Preferably, you can use the session properties to avoid some these lookups.

Set the session property for mail.smtp.localhost to prevent name lookup on the HELO command.
Set session property for mail.from or mail.host (not the protocol versions) as that will prevent the name lookup on InternetAddress.getLocalAddress(Session). Calling MimeMessage.saveChanges(), MimeMessage.updateHeaders(), MimeMessage.updateMessageID(), or MimeMessage.setFrom()will trigger this method.
Set session property for mail.smtp.from to prevent lookup on EHLO command.
Alternatively, you can set the system property mail.mime.address.usecanonicalhostname to falseif your code is relying on the setFrom() but this should be handled by point #2.
For IMAP, you can try to set mail.imap.sasl.usecanonicalhostname to false which is the default value.

Since your are not transporting a message, apply rule #2 by changing your code to:

@Test
public void test1() throws MessagingException, IOException {
    Properties props = new Properties();
    props.put("mail.host", "localhost"); //Or use IP.
    Session s = Session.getInstance(props);
    MimeMessage m = new MimeMessage(s);
    m.setContent("<b>Hello</b>", "text/html; charset=utf-8");
    m.saveChanges();
    assertEquals(m.getContent(), "<b>Hello</b>");
    assertEquals(m.getContentType(), "text/html; charset=utf-8");
}

If you are transporting a message then combine the rules #1, #2, and #3 which will prevent accessing the host system for a name lookup. If you want to prevent all DNS lookups during a transport then you have to use IP addresses.

来源：https://stackoverflow.com/questions/44435457/mimemessage-savechanges-is-really-slow

标签

java

junit

javamail

mime-message