小编lry*_*lry的帖子

当我使用 JavaMailSender 发送带有附件的电子邮件时，它总是失败并抛出以下异常：

org.springframework.mail.MailSendException: Failed messages: javax.mail.MessagingException: IOException while sending message;
  nested exception is:
    java.io.IOException: Exception writing Multipart
; message exception details (1) are:
Failed message 1:
javax.mail.MessagingException: IOException while sending message;
  nested exception is:
    java.io.IOException: Exception writing Multipart
    at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1365)
    at org.springframework.mail.javamail.JavaMailSenderImpl.doSend(JavaMailSenderImpl.java:462)
    at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:359)
    at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:354)

这是我的代码

MimeMessage message = mailSender.createMimeMessage();
try {
    MimeMessageHelper helper = new MimeMessageHelper(message, true);
    helper.setFrom(userName);
    helper.setTo(toAddress);
    helper.setSubject(subject);
    FileSystemResource file = new FileSystemResource(filePath);
    helper.addAttachment(file.getFilename(), file);
} catch (Exception e) {
    log.error("oops..., ", e);
}
mailSender.send(message);

我很困惑可变引用如何在 for 循环中工作，而不可变引用则不然。它是一个迭代器吗？

我发现循环之后，引用chars引用了 value ""。

无参考

fn main() {
    let str_value: String = "abc".to_string();

    let chars = str_value.chars();
    for char_value in chars {
        println!("char: {}", char_value);
    }
}

char: a
char: b
char: c

不可变的引用

fn main() {
    let str_value: String = "abc".to_string();

    let chars = str_value.chars();
    for char_value in &chars {
        println!("char: {}", char_value);
    }
}

error[E0277]: `&std::str::Chars<'_>` is not an iterator
 --> src/main.rs:5:23
  |
5 |     for char_value in &chars {
  |                       -^^^^^
  | …