java的網絡功能非常強大，開發和使用也非常簡單，難怪microsoft極力要爭回程序語言的霸主地位。根據smtp協議使用java Socket寫了一個發送郵件的程序，
實現的原理非常簡單，首先建立和郵件服務器的Socket連接，然后進行和服務器握手，然后發送smtp指令，并封裝郵件體，然后發送即可。

import java.net.*;
import java.io.*;
import java.util.*;

public class SMTPSender{

Socket socket=null;
PRintWriter outData=null;
BufferedReader inData=null;

String smtpServer="";

String user="";
String pass="";
String from="";

String LINEFEED="/r/n";
boolean isNeedAuthLogin=false;
Vector to=new Vector();

public static void main(String[] args){
SMTPSender smtp=new SMTPSender();
smtp.setMailServer("mail.ehawa.com");
smtp.setMailFrom("root@ehawa.com","???","???");
smtp.addMailTo("root@ehawa.com");
if(smtp.send("hello","這是一個測試!")){
System.out.println("郵件發送成功！");
}else System.out.println("郵件發送失敗！");
}
public void setMailServer(String s){
smtpServer=s;
}
public void setMailFrom(String s,String uid,String pwd){
this.from=s;
this.user=uid;
this.pass=pwd;
this.isNeedAuthLogin=(this.user!=null&&this.pass!=null&&!this.user.equals("")&&!this.pass.equals(""));
}
public boolean addMailTo(String mailAddr){
to.addElement(mailAddr);
return true;
}
public boolean send(String subject,String content){
try{
if(smtpServer==nullsmtpServer.equals(""))return false;
if(from==nullfrom.equals(""))return false;
if(to.size()<1)return false;
socket=new Socket(smtpServer,25);
outData=new PrintWriter(socket.getOutputStream());
inData=new BufferedReader(new InputStreamReader(socket.getInputStream()));
//與郵件服務器連接成功
readResponse("220");
//HELO host
sendRequest("HELO "+smtpServer+LINEFEED);
readResponse("250");
if(isNeedAuthLogin){
//AUTH LOGIN
sendRequest("AUTH LOGIN"+LINEFEED);
readResponse("334");
//USERNAME:
sendRequest(new String(Base64.encodeString(user))+LINEFEED);
readResponse("334");
//PASSWord:
sendRequest(new String(Base64.encodeString(pass))+LINEFEED);
readResponse("235");
}
//MAIL FROM:<..>
sendRequest("MAIL FROM:<"+from+">"+LINEFEED);
readResponse("250");
//RCPT TO:<..>
for(Enumeration enu=to.elements();enu.hasMoreElements();){
String to1=(String)enu.nextElement();
sendRequest("RCPT To:<"+to1+">"+LINEFEED);
readResponse("250");
}
//DATA
sendRequest("DATA"+LINEFEED);
readResponse("354");
//郵件內容
StringBuffer s1=new StringBuffer("From: <"+from+">"+LINEFEED);
s1.append("To: <"+to+">"+LINEFEED);
s1.append("Subject: "+subject+LINEFEED);
s1.append("Date: "+new java.util.Date().toLocaleString()+LINEFEED);
s1.append("Content-Type: text/plain;charset=/"GB2312/""+LINEFEED);
s1.append(LINEFEED);
s1.append(content);
s1.append(LINEFEED+"."+LINEFEED);//發送
sendRequest(s1.toString());
readResponse("250");
//QUIT退出
sendRequest("QUIT"+LINEFEED);
readResponse("221");
try{
inData.close();
inData=null;
}catch(Exception ex){}
try{
outData.close();
outData=null;
}catch(Exception ex){}
try{
socket.close();
socket=null;
}catch(Exception ex){}
}catch(Exception e){
return false;
//e.printStackTrace();
}
return true;
}
private void readResponse(String cmd)throws Exception{
String tmp=inData.readLine();
if(tmp.startsWith(cmd));//System.out.println(" [S:]"+tmp);
else throw new Exception("##########郵件發送失敗!##########"+tmp);
while(tmp.startsWith(cmd+"-"))tmp=inData.readLine();
}
private void sendRequest(String msg){
//System.out.print("***[C:]"+msg);
outData.write(msg);
outData.flush();
}
public void close(){
try{
inData.close();
inData=null;
}catch(Exception ex){}
try{
outData.close();
outData=null;
}catch(Exception ex){}
try{
socket.close();
socket=null;
}catch(Exception ex){}
}
}