我已经看到了javax.mail库的代码，您可以在其中向电子邮件添加附件：
MimeBodyPart attachmentPart = new MimeBodyPart();
FileDataSource fds = new FileDataSource("C:/text.txt");
attachmentPart.setDataHandler(new DataHandler(fds));
attachmentPart.setFileName("text.txt");
multipart.addBodyPart(attachmentPart);
但这要求文件驻留在此磁盘上的某个位置。
我想OutputStream从电子邮件库中获取一个权利，并将文件内容直接从我写入的另一个地方流式传输到其中OutputStream。
这可能吗？
尝试使用 ByteArrayDataSource，像这样
ByteArrayOutputStream baos = //Read the output stream
DataSource aAttachment = new ByteArrayDataSource(baos.toByteArray(),"application/octet-stream");
MimeBodyPart attachmentPart = new MimeBodyPart();
attachmentPart.setDataHandler(new DataHandler(aAttachment));
是的，这是可能的。使用 ByteArrayDataSource 的答案不能为大型附件提供令人满意的解决方案，因为它要求整个内容一次驻留在内存中。更好的解决方案是使用由 PipedInputStream 提供的 DataHandler，而 PipedInputStream 又由 PipedOutputStream 写入。当然，这需要第二个线程。下面的代码演示了这一点：
import com.sun.mail.smtp.*;
import java.io.InputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.util.Date;
import java.util.Properties;
import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.mail.*;
import javax.mail.internet.*;
public class javamail {
// Piped Data Source
private static class PipedDataSource implements DataSource {
InputStream in;
String type;
public PipedDataSource (InputStream in, String type) { this.in = in; this.type = type; }
public String getContentType() { return type; }
public InputStream getInputStream() { return in; }
public String getName() { return "DataSource"; }
public OutputStream getOutputStream() throws IOException { throw new IOException("No OutputStream"); }
}
// Main Method
public static void main(String [] args) throws Exception {
final int BUFFER_SIZE = 32768;
Properties properties = new Properties();
properties.put("mail.smtp.starttls.enable", System.getProperty("mail.smtp.starttls.enable","true"));
properties.put("mail.smtp.ssl.trust", System.getProperty("mail.smtp.ssl.trust","*"));
properties.put("mail.smtp.host", System.getProperty("mail.smtp.host","localhost"));
properties.put("mail.smtp.port", System.getProperty("mail.smtp.port","587"));
Session session = Session.getInstance(properties);
String host = properties.getProperty("mail.smtp.host");
int port = Integer.parseInt(properties.getProperty("mail.smtp.port"));
System.err.println("connect: smtp://"+host+":"+port); System.err.flush();
MimeMessage msg = new MimeMessage(session);
PipedInputStream in = new PipedInputStream(BUFFER_SIZE);
PipedOutputStream out = new PipedOutputStream(in);
// Set general headers
msg.setFrom(System.getProperty("mail.from","Unknown <unknown@example.com>"));
msg.setRecipients(Message.RecipientType.TO, System.getProperty("mail.to", "unknown@example.com"));
msg.setSentDate(new Date());
msg.setSubject("JavaMail Test");
msg.setHeader("X-Mailer", "JavaMail");
// Set main text - Part 1 - content provided here
MimeBodyPart part1 = new MimeBodyPart();
StringBuilder sb = new StringBuilder();
sb.append("This is the cover letter that describes the accompanying \n");
sb.append("attachment, which is a base64 encoded text document of \n");
sb.append("little more value than a demonstration.\n\n");
part1.setText(sb.toString()); // Writes a computed Content-Type Header
part1.setHeader("Content-Type","text/plain; charset=us-ascii; format=flowed; delsp=yes"); // Rewrite Header
// Set attachment - Part 2 - content provdied from another thread via a pipe
MimeBodyPart part2 = new MimeBodyPart();
part2.setDataHandler(new DataHandler(new PipedDataSource (in, "text/html"))); // Writes a Content-Type Header
part2.setHeader("Content-Type","text/plain; charset=\"utf-8\"; name=\"Lorem Ipsum.txt\""); // Rewrite Header
part2.setHeader("Content-Disposition", "attachment; filename=\"Lorem Ipsum.txt\"");
part2.setHeader("Content-Transfer-Encoding","base64");
// Join parts
MimeMultipart multipart = new MimeMultipart();
multipart.addBodyPart(part1);
multipart.addBodyPart(part2);
msg.setContent(multipart);
// Start thread to deliver content for Part 2 attachment via DataHandler
Thread t = new Thread() {
public void run() {
try {
PrintWriter w = new PrintWriter(new OutputStreamWriter(out,"UTF-8"));
w.print("Lorem ipsum dolor sit amet, ligula suspendisse nulla pretium");
w.print(", rhoncus tempor fermentum, enim integer ad vestibulum volut");
w.print("pat. Nisl rhoncus turpis est, vel elit, congue wisi enim nun");
w.print("c ultricies sit, magna tincidunt. Maecenas aliquam maecenas ");
w.print("ligula nostra, accumsan taciti. Sociis mauris in integer, a ");
w.print("dolor netus non dui aliquet, sagittis felis sodales, dolor s");
w.print("ociis mauris, vel eu libero cras. Faucibus at. Arcu habitass");
w.print("e elementum est, ipsum purus pede porttitor class, ut adipis");
w.print("cing, aliquet sed auctor, imperdiet arcu per diam dapibus li");
w.print("bero duis. Enim eros in vel, volutpat nec pellentesque leo, ");
w.print("temporibus scelerisque nec.");
w.println("");
w.println("");
w.flush(); // Ensure data completely flushed to buffer
w.close(); // closes the writer and PipedOutputStream
} catch(Exception e) { e.printStackTrace(); };
try { out.close(); } catch(Exception e) { e.printStackTrace(); }
}
};
t.start();
// Send the message on its way
SMTPTransport xp = (SMTPTransport) session.getTransport();
xp.connect();
xp.sendMessage(msg,msg.getAllRecipients());
System.err.println(xp.getLastServerResponse());
t.join();
return;
}
}
您可以使用在命令行中定义的以下属性（根据需要进行编辑）运行此代码：
-Dmail.from="sender@host.example.com"
-Dmail.to="receipient@host.example.com"
-Dmail.smtp.host=smtp.example.com
-Dmail.smtp.port=587 or 25
示例代码发送一封电子邮件，其中包含使用 us-ascii 编码的文本/纯文本求职信和使用 base64 传输编码的 utf-8 编码的文本/纯文本附件。如果 MX 支持，它还使用 STARTTLS（加密传输）。