将InputStream转换为DataHandler？

Question

我编写了实现DataSource的自定义类，将InputStream转换为DataHandler。我用它来发送邮件附件。但附件现在显示无效内容。

以下是自定义类实现：

public class InputStreamDataSource implements DataSource {
    private InputStream inputStream;

    public InputStreamDataSource(InputStream inputStream) {
        this.inputStream = inputStream;
    }

    @Override
    public InputStream getInputStream() throws IOException {
        return inputStream;
    }

    @Override
    public OutputStream getOutputStream() throws IOException {
        throw new UnsupportedOperationException("Not implemented");
    }

    @Override
    public String getContentType() {
        return "*/*";
    }

    @Override
    public String getName() {
        return "InputStreamDataSource";
    }
}

用于发送邮件功能的代码：

Multipart multipart = new MimeMultipart();

MimeBodyPart messageBodyPart = new MimeBodyPart();
messageBodyPart.setContent(message, "text/html");

// creates body part for the attachment
MimeBodyPart attachPart = new MimeBodyPart();
String attachFile = attachment.getName();       

InputStream ipStream=null;
ipStream = attachment.getInputStream();
DataHandler dataHandler = new DataHandler(new InputStreamDataSource(ipStream));
attachPart.setDataHandler(dataHandler);
attachPart.setFileName(attachFile); 

// adds parts to the multipart
multipart.addBodyPart(messageBodyPart);
multipart.addBodyPart(attachPart);

msg.setContent(multipart);
Transport.send(msg);