如何将MimeBodyPart ContentType设置为“text / html”？ [英] How to set MimeBodyPart ContentType to "text/html"?

问题描述

下面的程序显示了HTML multipart mime类型的意外返回值。为什么这个程序打印text / plain而不是text / html？

The program below shows an unexpected return value for HTML multipart mime type. Why does this program print "text/plain" and not "text/html"?

public class Main {
  public static void main(String[] args) throws javax.mail.MessagingException, java.io.IOException {
    javax.mail.internet.MimeBodyPart mime_body_part = new javax.mail.internet.MimeBodyPart();
    mime_body_part.setContent("<h1>foo</h1>", "text/html");
    System.out.println(mime_body_part.getContentType());
  }
}

我尝试过多种替代方法，包括设置包裹的ByteArrayDataSource在DataHandler中，但无济于事。当我用MimeMessage而不是MimeBodyPart尝试这个时，会发生同样的事情。

I have tried numerous alternative ways including setting a ByteArrayDataSource wrapped in a DataHandler, but to no avail. The same thing happens when I try this with a MimeMessage instead of a MimeBodyPart.

要在Linux上编译和运行：

To compile and run on Linux:

javac -classpath .:activation.jar:mail.jar Main.java
java -classpath .:activation.jar:mail.jar Main

推荐答案

致电 MimeMessage.saveChanges（） ，这将通过将MIME结构级联到您身体部位的 MimeBodyPart.updateHeaders（）的调用来更新标题。这是 updateHeaders 调用，它将内容类型从 DataHandler 传输到部件的MIME 内容 - 键入标题。

Call MimeMessage.saveChanges() on the enclosing message, which will update the headers by cascading down the MIME structure into a call to MimeBodyPart.updateHeaders() on your body part. It's this updateHeaders call that transfers the content type from the DataHandler to the part's MIME Content-Type header.

当您在内部设置 MimeBodyPart ，JavaMail的内容时（并且显然不会创建一个 DataHandler 对象包装您传入的对象。该部分的 Content-Type 标头是不立即更新。

When you set the content of a MimeBodyPart, JavaMail internally (and not obviously) creates a DataHandler object wrapping the object you passed in. The part's Content-Type header is not updated immediately.

在测试程序中没有直接的方法，因为你没有包含 MimeMessage 和 MimeBodyPart.updateHeaders（）不是 public 。

There's no straightforward way to do it in your test program, since you don't have a containing MimeMessage and MimeBodyPart.updateHeaders() isn't public.

这是一个充分说明预期和意外输出的工作示例：

Here's a working example that illuminates expected and unexpected outputs:

public class MailTest {

  public static void main( String[] args ) throws Exception {
    Session mailSession = Session.getInstance( new Properties() );
    Transport transport = mailSession.getTransport();

    String text = "Hello, World";
    String html = "<h1>" + text + "</h1>";

    MimeMessage message = new MimeMessage( mailSession );
    Multipart multipart = new MimeMultipart( "alternative" );

    MimeBodyPart textPart = new MimeBodyPart();
    textPart.setText( text, "utf-8" );

    MimeBodyPart htmlPart = new MimeBodyPart();
    htmlPart.setContent( html, "text/html; charset=utf-8" );

    multipart.addBodyPart( textPart );
    multipart.addBodyPart( htmlPart );
    message.setContent( multipart );

    // Unexpected output.
    System.out.println( "HTML = text/html : " + htmlPart.isMimeType( "text/html" ) );
    System.out.println( "HTML Content Type: " + htmlPart.getContentType() );

    // Required magic (violates principle of least astonishment).
    message.saveChanges();

    // Output now correct.    
    System.out.println( "TEXT = text/plain: " + textPart.isMimeType( "text/plain" ) );
    System.out.println( "HTML = text/html : " + htmlPart.isMimeType( "text/html" ) );
    System.out.println( "HTML Content Type: " + htmlPart.getContentType() );
    System.out.println( "HTML Data Handler: " + htmlPart.getDataHandler().getContentType() );
  }
}

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