JAVA 邮件客户端错误

Question

我正在为 google 邮件服务器“smtp.gmail.com”在端口 25 上使用 JAVA 套接字连接构建一个简单的邮件客户端作为学校项目。与服务器的启动和连接都做得很好。但是在发出“STARTTLS”命令后进行身份验证时，我收到了一个奇怪的回复，有时服务器没有回复。以下是导致此错误的代码部分：

public class Client {

public static void main(String[] args) throws IOException {
    
    System.out.println("Connecting to server...");
    Socket cs = new Socket("smtp.gmail.com", 25);
    System.out.println("Connected to server! via port: " + cs.getLocalPort());
    
    OutputStreamWriter osw = new OutputStreamWriter(cs.getOutputStream());
    InputStreamReader isr = new InputStreamReader(cs.getInputStream());
    
    BufferedWriter bw = new BufferedWriter(osw);
    
    char[] inputBuffer = new char[1024];
    
    int len = isr.read(inputBuffer);
    String s = "";
    for(int i = 0; i < len; ++i){
        s += inputBuffer[i];
    }
    System.out.println("S: " + s);
    
    System.out.println("C: HELO localhost");
    bw.write("HELO localhost");
    bw.newLine();
    bw.flush();
    len = isr.read(inputBuffer);
    s = "";
    for(int i = 0; i < len; ++i){
        s += inputBuffer[i];
    }
    System.out.println("S: " + s);
    
    System.out.println("C: STARTTLS");
    bw.write("STARTTLS");
    bw.newLine();
    bw.flush();
    len = isr.read(inputBuffer);
    s = "";
    for(int i = 0; i < len; ++i){
        s += inputBuffer[i];
    }
    System.out.println("S: " + s);
    
    System.out.println("C: EHLO localhost");
    bw.write("EHLO localhost");
    bw.newLine();
    bw.flush();
    len = isr.read(inputBuffer);
    s = "";
    for(int i = 0; i < len; ++i){
        s += inputBuffer[i];
    }
    System.out.println("S: " + s);
    
    System.out.println("C: AUTH LOGIN");
    bw.write("AUTH LOGIN");
    bw.newLine();
    bw.flush();
    len = isr.read(inputBuffer);
    s = "";
    for(int i = 0; i < len; ++i){
        s += inputBuffer[i];
    }
    System.out.println("S: " + s);
    // extra code goes here, no need to show
    }
}

输出如下：

Connecting to server...

Connected to server! via port: 39167

S: 220 smtp.gmail.com ESMTP v52sm3768873wrc.53 - gsmtp

C: HELO localhost

S: 250 smtp.gmail.com at your service

C: STARTTLS

S: 220 2.0.0 Ready to start TLS

C: EHLO localhost

S: F

C: AUTH LOGIN

S:

如您所见，“STARTTLS”后的“EHLO localhost”回复不明确，之后“AUTH LOGIN”没有回复。我一开始以为应该是服务端发送的是Base64文本，所以我试着解码响应如下：

    System.out.println("C: EHLO localhost");
    bw.write("EHLO localhost");
    bw.newLine();
    bw.flush();
    len = isr.read(inputBuffer);
    s = "";
    for(int i = 0; i < len; ++i){
        s += inputBuffer[i];
    }
    System.out.println("S: " + new String(Base64.getDecoder().decode(s)));
    
    System.out.println("C: AUTH LOGIN");
    bw.write("AUTH LOGIN");
    bw.newLine();
    bw.flush();
    len = isr.read(inputBuffer);
    s = "";
    for(int i = 0; i < len; ++i){
        s += inputBuffer[i];
    }
    System.out.println("S: " + new String(Base64.getDecoder().decode(s)));

但是得到如下错误：

Connecting to server...

Connected to server! via port: 39199

S: 220 smtp.gmail.com ESMTP l27sm4475707wrb.65 - gsmtp

C: HELO localhost

S: 250 smtp.gmail.com at your service

C: STARTTLS

S: 220 2.0.0 Ready to start TLS

C: EHLO localhost

Exception in thread "main" java.lang.IllegalArgumentException: Illegal base64 character 15
      at java.util.Base64$Decoder.decode0(Unknown Source)

      at java.util.Base64$Decoder.decode(Unknown Source)

      at java.util.Base64$Decoder.decode(Unknown Source)

      at khaldoun.kassam.servertest.Client.main(Client.java:64)

我认为也许我应该使用 SSLSockets，但据我所知，有些人能够使用普通的套接字并且它对他们有效。我为这个问题搜索了很多但没有任何结果。我不知道发送到服务器的命令中是否缺少某些内容。我真的需要帮助。预先感谢您的宝贵时间。

Answer 1

你检查过打开 "Allow less secure Apps" 检查这里有什么遗漏吗 link 另外我猜你不能将端口 25 用于 SMTP

Google mail setup

JAVA 邮件客户端错误

JAVA mail client errors

java

sockets

smtp

base64

email-client