smtpexample.java

精通Java网络编程代码全部

//SmtpExample.java
//导入被使用的类
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.MalformedURLException;
import java.net.Socket;

public class SmtpExample {
	//默认的SMTP服务使用25端口
	public static final int SMTP_PORT = 25;
	//与SMTP服务器的连接相关的输出流
	public static BufferedWriter out;
	//与SMTP服务器的连接相关的输入流
	public static BufferedReader in;

	//方法printToOutputStream()向SMTP服务器发送命令
	private static void printToOutputStream(String words) throws IOException {
		out.write(words);
		out.flush();
		System.out.println("S : " + words);
	}

	//方法readFromInputStream()接收从SMTP服务器发回的响应信息
	private static String readFromInputStream() throws IOException {
		//读取服务器传回的响应信息
		String sentence = in.readLine();
		//响应信息开头为文本表示的状态码
		//2,3开头代表正确或目前正确，出现其它状态码则视为出现错误
		//如550代表无此用户，无法登陆
		if (!sentence.startsWith("2") && !sentence.startsWith("3")) {
			//打印错误信息
			System.err.print("Error :");
			System.err.println(sentence);
		}
		//日志输出
		System.out.println("R : " + sentence);
		return sentence;
	}

	//从邮件地址中取出主机名
	public static String getDestHost(String mail) throws MalformedURLException {
		int at = mail.indexOf("@");
		if (at < 0)
			throw new MalformedURLException("MailAddress : " + mail + " is not valid.");
		//邮件地址中@符号后的为主机名
		return mail.substring(at + 1);
	}

	//从邮件地址中取出用户名
	public static String getSenderName(String mail) throws MalformedURLException {

		int at = mail.indexOf("@");
		if (at < 0)
			throw new MalformedURLException("MailAddress : " + mail + " is not valid.");
		//邮件地址中@符号前面的为用户名
		return mail.substring(0, at);
	}

	public static void main(String[] args) {
		Socket s = null;
		try {
			//构着从终端读取键盘输入的读者对象，从终端读取邮件信息
			BufferedReader cin = new BufferedReader(new InputStreamReader(System.in));
			//从终端读取邮件发送者地址
			System.out.print("Mail From: ");
			String from = cin.readLine();
			//从终端读取邮件接受者地址
			System.out.print("Mail To: ");
			String to = cin.readLine();
			//从终端读取邮件主题
			System.out.print("SMTP Host: ");
			String smtphost = cin.readLine();
	
			System.out.println("Message body, end with Ctrl-D");
			String line, message = "";
			while (true) {
				line = cin.readLine();
				if (line.length() == 0)
					break;
				message = message + line + "\n";
			}
			//准备发送邮件
			System.out.println("Prepare to send.");
			//建立套接字连接到SMTP服务器
			s = new Socket(smtphost, SMTP_PORT);
			//获取相关的输入流
			in = new BufferedReader(new InputStreamReader(s.getInputStream()));
			//获取相关的输出流
			out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
			//读取欢迎信息
			String response = readFromInputStream();
			//发送HELLO命令
			printToOutputStream("HELLO" + "\n");
			//读取响应
			response = readFromInputStream();
			//发送邮件头
			printToOutputStream("MAIL FROM:" + from + "\n");
			response = readFromInputStream();
			printToOutputStream("RCPT TO:" + to + "\n");
			response = readFromInputStream();
			//发送邮件主体
			printToOutputStream("DATA\n");
			response = readFromInputStream();
			printToOutputStream(message + "\n.\n");
			//读取响应信息
			response = readFromInputStream();
			//发送完毕，QUIT命令退出
			printToOutputStream("QUIT\n");
			//关闭连接
			s.close();
			System.out.println("Message sent.");
			System.out.flush();
		} catch (Exception e) {
			//异常处理，异常信息输出到标准错误流中
			e.printStackTrace(System.err);
			System.out.println("Usage: java SmtpExample");
			if (null != s)
				try {
					//如果发送过程中产生异常，在退出前也好关闭连接
					s.close();
				} catch (IOException ioe) {
					ioe.printStackTrace(System.err);
				}
		}
	}
}