java - 发送消息导致异常

Question

我尝试使用 Javamail API 发送消息，并使用 tomcat 作为网络服务器，但是每当我尝试发送没有文件和附件的消息时，以下代码都会导致一个大异常。尽管它可以将消息作为附件使用。

public static String send(String to,String body,Stringsubject,String file,String from)throws Exception{

                  if(file!=null||file!=" "){    

        File file1=new File(file);
        MimeBodyPart mb=new MimeBodyPart();
        FileDataSource f=new FileDataSource(file1.getCanonicalPath());
        mb.setDataHandler(new DataHandler(f));
        mb.setFileName(f.getName());
        mm.addBodyPart(mb);
        }

        mb1.setText(body);
        mm.addBodyPart(mb1);
                  message.setFrom(new InternetAddress(from));
        Address[] add={ new InternetAddress(to) };

              message.setRecipients(Message.RecipientType.TO,add);
              message.setSubject(subject);
              message.setContent(mm);
            //message.setText(body);
              Transport.send(message);
           return "Message sent";
}

异常(exception):

javax.mail.MessagingException: IOException while sending message;
  nested exception is:
    java.io.FileNotFoundException: C:\Program Files\Apache Software Foundation\Tomcat 6.0 (Access is denied)
    at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:779)
    at javax.mail.Transport.send0(Transport.java:191)
    at javax.mail.Transport.send(Transport.java:120)
    at foo.SendMessage.send(SendMessage.java:57)
    at foo.Mail.doPost(Mail.java:39)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
    at java.lang.Thread.run(Thread.java:619)
Caused by: java.io.FileNotFoundException: C:\Program Files\Apache Software Foundation\Tomcat 6.0 (Access is denied)
    at java.io.FileInputStream.open(Native Method)
    at java.io.FileInputStream.<init>(FileInputStream.java:106)
    at javax.activation.FileDataSource.getInputStream(FileDataSource.java:82)
    at javax.activation.DataHandler.writeTo(DataHandler.java:290)
    at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.java:1381)
    at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.java:852)
    at javax.mail.internet.MimeMultipart.writeTo(MimeMultipart.java:452)
    at com.sun.mail.handlers.multipart_mixed.writeTo(multipart_mixed.java:98)
    at javax.activation.ObjectDataContentHandler.writeTo(DataHandler.java:869)
    at javax.activation.DataHandler.writeTo(DataHandler.java:302)
    at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.java:1381)
    at javax.mail.internet.MimeMessage.writeTo(MimeMessage.java:1742)
    at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:737)
    ... 18 more

我的问题是，在将任何文件作为附件之前，我在上面的代码中使用了一个条件，那么为什么我会收到该异常？

Answer 1

if(file!=null||file!="") 不正确。我怀疑你想要的是 if (file != null && !file.trim().isEmpty()) 。

具体说 if (file != null || file != "") 与说 if (true) 相同，因为您使用了 OR 运算符并且由于 file 不能同时具有值​​“”和 null，这些条件之一将计算为 true，从而使整个表达式为 true。

顺便说一句，file != "" 是一种不好的形式。当通过尝试测试相等性时，您应该始终使用 equals() 方法，而不是 == 和 != 运算符。