SMTPClient encapsulates all the functionality necessary to send files
through an SMTP server. This class takes care of all
low level details of interacting with an SMTP server and provides
a convenient higher level interface. As with all classes derived
from
SocketClient
,
you must first connect to the server with
connect
before doing anything, and finally
disconnect
after you're completely finished interacting with the server.
Then you need to check the SMTP reply code to see if the connection
was successful. For example:
try {
int reply;
client.connect("mail.foobar.com");
System.out.print(client.getReplyString());
// After connection attempt, you should check the reply code to verify
// success.
reply = client.getReplyCode();
if(!SMTPReply.isPositiveCompletion(reply)) {
client.disconnect();
System.err.println("SMTP server refused connection.");
System.exit(1);
}
// Do useful stuff here.
...
} catch(IOException e) {
if(client.isConnected()) {
try {
client.disconnect();
} catch(IOException f) {
// do nothing
}
}
System.err.println("Could not connect to server.");
e.printStackTrace();
System.exit(1);
}
Immediately after connecting is the only real time you need to check the
reply code (because connect is of type void). The convention for all the
SMTP command methods in SMTPClient is such that they either return a
boolean value or some other value.
The boolean methods return true on a successful completion reply from
the SMTP server and false on a reply resulting in an error condition or
failure. The methods returning a value other than boolean return a value
containing the higher level data produced by the SMTP command, or null if a
reply resulted in an error condition or failure. If you want to access
the exact SMTP reply code causing a success or failure, you must call
getReplyCode
after
a success or failure.
You should keep in mind that the SMTP server may choose to prematurely
close a connection for various reasons. The SMTPClient class will detect a
premature SMTP server connection closing when it receives a
SMTPReply.SERVICE_NOT_AVAILABLE
response to a command.
When that occurs, the method encountering that reply will throw
an
SMTPConnectionClosedException
.
SMTPConectionClosedException
is a subclass of
IOException
and therefore need not be
caught separately, but if you are going to catch it separately, its
catch block must appear before the more general
IOException
catch block. When you encounter an
SMTPConnectionClosedException
, you must disconnect the connection with
disconnect()
to properly clean up the
system resources used by SMTPClient. Before disconnecting, you may check
the last reply code and text with
getReplyCode
,
getReplyString
,
and
getReplyStrings
.
Rather than list it separately for each method, we mention here that
every method communicating with the server and throwing an IOException
can also throw a
MalformedServerReplyException
, which is a subclass
of IOException. A MalformedServerReplyException will be thrown when
the reply received from the server deviates enough from the protocol
specification that it cannot be interpreted in a useful manner despite
attempts to be as lenient as possible.
addRecipient
public boolean addRecipient(RelayPath path)
throws IOException
Add a recipient for a message using the SMTP RCPT command, specifying
a forward relay path. The sender must be set first before any
recipients may be specified, otherwise the mail server will reject
your commands.
path
- The forward relay path pointing to the recipient.
- True if successfully completed, false if not.
addRecipient
public boolean addRecipient(String address)
throws IOException
Add a recipient for a message using the SMTP RCPT command, the
recipient's email address. The sender must be set first before any
recipients may be specified, otherwise the mail server will reject
your commands.
address
- The recipient's email address.
- True if successfully completed, false if not.
completePendingCommand
public boolean completePendingCommand()
throws IOException
At least one SMTPClient method (
sendMessageData
)
does not complete the entire sequence of SMTP commands to complete a
transaction. These types of commands require some action by the
programmer after the reception of a positive intermediate command.
After the programmer's code completes its actions, it must call this
method to receive the completion reply from the server and verify the
success of the entire transaction.
For example,
writer = client.sendMessage();
if(writer == null) // failure
return false;
header =
new SimpleSMTPHeader("foobar@foo.com", "foo@foobar.com", "Re: Foo");
writer.write(header.toString());
writer.write("This is just a test");
writer.close();
if(!client.completePendingCommand()) // failure
return false;
- True if successfully completed, false if not.
listHelp
public String listHelp()
throws IOException
Fetches the system help information from the server and returns the
full string.
- The system help string obtained from the server. null if the
information could not be obtained.
listHelp
public String listHelp(String command)
throws IOException
Fetches the help information for a given command from the server and
returns the full string.
command
- The command on which to ask for help.
- The command help string obtained from the server. null if the
information could not be obtained.
login
public boolean login()
throws IOException
Login to the SMTP server by sending the HELO command with the
client hostname as an argument. Before performing any mail commands,
you must first login.
- True if successfully completed, false if not.
login
public boolean login(String hostname)
throws IOException
Login to the SMTP server by sending the HELO command with the
given hostname as an argument. Before performing any mail commands,
you must first login.
hostname
- The hostname with which to greet the SMTP server.
- True if successfully completed, false if not.
logout
public boolean logout()
throws IOException
Logout of the SMTP server by sending the QUIT command.
- True if successfully completed, false if not.
reset
public boolean reset()
throws IOException
Aborts the current mail transaction, resetting all server stored
sender, recipient, and mail data, cleaing all buffers and tables.
- True if successfully completed, false if not.
sendMessageData
public Writer sendMessageData()
throws IOException
Send the SMTP DATA command in preparation to send an email message.
This method returns a DotTerminatedMessageWriter instance to which
the message can be written. Null is returned if the DATA command
fails.
You must not issue any commands to the SMTP server (i.e., call any
(other methods) until you finish writing to the returned Writer
instance and close it. The SMTP protocol uses the same stream for
issuing commands as it does for returning results. Therefore the
returned Writer actually writes directly to the SMTP connection.
After you close the writer, you can execute new commands. If you
do not follow these requirements your program will not work properly.
You can use the provided
SimpleSMTPHeader
class to construct a bare minimum header.
To construct more complicated headers you should
refer to RFC 822. When the Java Mail API is finalized, you will be
able to use it to compose fully compliant Internet text messages.
The DotTerminatedMessageWriter takes care of doubling line-leading
dots and ending the message with a single dot upon closing, so all
you have to worry about is writing the header and the message.
Upon closing the returned Writer, you need to call
completePendingCommand()
to finalize the transaction and verify its success or failure from
the server reply.
- A DotTerminatedMessageWriter to which the message (including
header) can be written. Returns null if the command fails.
sendNoOp
public boolean sendNoOp()
throws IOException
Sends a NOOP command to the SMTP server. This is useful for preventing
server timeouts.
- True if successfully completed, false if not.
sendShortMessageData
public boolean sendShortMessageData(String message)
throws IOException
A convenience method for sending short messages. This method fetches
the Writer returned by
sendMessageData()
and writes the specified String to it. After writing the message,
this method calls
completePendingCommand()
to finalize the transaction and returns
its success or failure.
message
- The short email message to send.
- True if successfully completed, false if not.
sendSimpleMessage
public boolean sendSimpleMessage(String sender,
String recipient,
String message)
throws IOException
A convenience method for a sending short email without having to
explicitly set the sender and recipient(s). This method
sets the sender and recipient using
setSender
and
addRecipient
, and then sends the
message using
sendShortMessageData
.
sender
- The email address of the sender.recipient
- The email address of the recipient.message
- The short email message to send.
- True if successfully completed, false if not.
sendSimpleMessage
public boolean sendSimpleMessage(String sender,
String[] recipients,
String message)
throws IOException
A convenience method for a sending short email without having to
explicitly set the sender and recipient(s). This method
sets the sender and recipients using
setSender
and
addRecipient
, and then sends the
message using
sendShortMessageData
.
sender
- The email address of the sender.recipients
- An array of recipient email addresses.message
- The short email message to send.
- True if successfully completed, false if not.
setSender
public boolean setSender(RelayPath path)
throws IOException
Set the sender of a message using the SMTP MAIL command, specifying
a reverse relay path. The sender must be set first before any
recipients may be specified, otherwise the mail server will reject
your commands.
path
- The reverse relay path pointing back to the sender.
- True if successfully completed, false if not.
setSender
public boolean setSender(String address)
throws IOException
Set the sender of a message using the SMTP MAIL command, specifying
the sender's email address. The sender must be set first before any
recipients may be specified, otherwise the mail server will reject
your commands.
address
- The sender's email address.
- True if successfully completed, false if not.
verify
public boolean verify(String username)
throws IOException
Verify that a username or email address is valid, i.e., that mail
can be delivered to that mailbox on the server.
username
- The username or email address to validate.
- True if the username is valid, false if not.