Seveur smtp en java

Bonjour,
je développe une application J2EE sur netbeans6.5 (jdk1.6) et je voudrais realiser une notification par mail en cas d'erreur.
J ai recupere ce code sur le web pour faire un essai
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import java.util.logging.Level;
import java.util.logging.Logger;
import javax.mail.*;
import javax.mail.internet.*;
import java.util.*;
/**
*
* @author skander.laabidi.stg
*/
public class postMail {

public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
{
boolean debug = false;

//Set the host smtp address
Properties props = new Properties();
props.put("mail.smtp.host", " smtp.gmail.com");

// create some properties and get the default Session
Session session = Session.getDefaultInstance(props, null);
session.setDebug(debug);

// create a message
Message msg = new MimeMessage(session);

// set the from and to address
InternetAddress addressFrom = new InternetAddress(from);
msg.setFrom(addressFrom);

InternetAddress[] addressTo = new InternetAddress[recipients.length];
for (int i = 0; i < recipients.length; i++)
{
addressTo[i] = new InternetAddress(recipients[i]);
}
msg.setRecipients(Message.RecipientType.TO, addressTo);


// Optional : You can also set your custom headers in the Email if you Want
msg.addHeader("MyHeaderName", "myHeaderValue");

// Setting the Subject and Content Type
msg.setSubject(subject);
msg.setContent(message, "text/plain");
Transport.send(msg);
}

public static void main(String[] args) {
// TODO code application logic here
postMail p =new postMail();
String add[] = new String[10];
for(int i=0;i<add.length;i++)
add[i]= new String("skander.lab@gmail.com");

try {
p.postMail(add, "salut", "bonjour", "skanblues@hotmail.fr");
} catch (MessagingException ex) {
Logger.getLogger(postMail.class.getName()).log(Level.SEVERE, null, ex);
}

}

}

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rq: j ai mis mes propres mail pour essayer

Alors j ai un probleme avev le serveur
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javax.mail.MessagingException: Unknown SMTP host: smtp.gmail.com;
nested exception is:
java.net.UnknownHostException: smtp.gmail.com
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1389)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:412)
at javax.mail.Service.connect(Service.java:288)
at javax.mail.Service.connect(Service.java:169)
at javax.mail.Service.connect(Service.java:118)
at javax.mail.Transport.send0(Transport.java:188)
at javax.mail.Transport.send(Transport.java:118)
at postMail.postMail(postMail.java:49)
at postMail.main(postMail.java:60)
Caused by: java.net.UnknownHostException: smtp.gmail.com
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:177)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
at java.net.Socket.connect(Socket.java:520)
at java.net.Socket.connect(Socket.java:470)
at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:233)
at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:189)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1359)
... 8 more

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pourrier vous m'aider C URGENT